Vol. 70, No. 15, April 11, 1989 EOS
cial for addressing m a j o r p r o b l e m s concerning t h e internal struc­
ture of t h e m a j o r planets. R e c e n t d e v e l o p m e n t s in spectroscopic
and
x - r a y diffraction techniques used w i t h t h e d i a m o n d - a n v i l cell
are b e g i n n i n g t o p r o v i d e this i n f o r m a t i o n . T h e pressure of the
i n s u l a t o r - m e t a l transition in solid h y d r o g e n is one of the m a j o r
p r o b l e m s in b o t h p l a n e t a r y and c o n d e n s e d - m a t t e r physics. In
recent e x p e r i m e n t s we h a v e contained hydrogen in a d i a m o n d anvil cell t o pressures in t h e 2 0 0 - 2 5 0 G P a range using new lowt e m p e r a t u r e , ultrahigh-pressure techniques. V i b r a t i o n a l R a m a n
s p e c t r a of t h e h y d r o g e n indicate t h e t h e solid remains in t h e
m o l e c u l a r s t a t e under at these pressures b u t undergoes an orie n t a t i o n a l ordering t r a n s f o r m a t i o n near 150 G P a ( a n d 77 K ) .
R e c e n t d e v e l o p m e n t s in single-crystal a n d polycrystalline x-ray
diffraction techniques h a v e p r o v i d e d essential information o n t h e
e q u a t i o n s of s t a t e of c o n d e n s e d p l a n e t a r y gases at high pressure.
X - r a y diffraction of m o l e c u l a r H a n d H e has been m e a s u r e d t o
2
26 G P a using single-crystal techniques, and diffraction of N e ,
A r , X e and H 0 has b e e n o b t a i n e d at pressures in t h e 100 G P a
2
range h a v e b e e n o b t a i n e d using p o l y c r y s t a l l i n e m e t h o d s . I n gen­
eral, t h e P- V relations d e t e r m i n e d f r o m t h e diffraction d a t a indi­
cate t h a t t h e materials are considerably m o r e compressible t h a n
T I R S c a n b e applied t o natural, p o l y m i n e r a l i c rock surfaces unlike
single-phase I R absorption. T I R S spectra can b e directly related t o
emission properties as measured with thermal emission spectrometers
such as theinstrument T E S w h i c h i s t o m a p Mars in the 1990's. In
this study, w e h a v e carried o u t a survey o f o v e r 7 0 varieties o f
s h o c k e d m a t e r i a l s f r o m terrestrial i m p a c t craters a n d r e g o l i t h b r e c c i a
meteorites, i n order t o e x p l o r e h o w T I R S spectra are distorted d u e t o
molecular disruptions caused b y shock processes; the results are
c o m p l e m e n t a r y t o the database o f IR absorption spectra for s h o c k e d
m i n e r a l s . O u r initial r e s u l t s s u g g e s t that there i s a m i n i m u m p e a k
s h o c k p r e s s u r e (Ps) t h r e s h o l d a t 2 5 0 - 3 0 0 k b a r i n c r y s t a l l i n e g r a n i t i c
or quartzose rocks at w h i c h point T I R S spectra are noticeably a n d
c o n s i s t e n t l y d e g r a d e d . T h i s c o n c u r s w i t h Stoffler's o b s e r v a t i o n s that
the refractive i n d e x o f quartz c h a n g e s at s h o c k l e v e l s a b o v e 2 6 0 kbar.
In a d d i t i o n , it a p p e a r s t o b e p o s s i b l e t o d i s t i n g u i s h h o m o g e n e o u s
rock melts from heterogeneous (impact glasses) types o n thebasis o f
T I R S spectra; t w o - p e a k e d T I R S spectra o fs h o c k - f u s e d rocks
from
t h e Ries i n d i c a t e t h a t q u a r t z a n d f e l d s p a r w e r e m e l t e d a n d q u e n c h e d
b e f o r e t h e y c o u l d c h e m i c a l l y equilibrate, a n e f f e c t that i s n o t p o s s i b l e
in e n d o g e n i c p r o c e s s e s s u c h a s v o l c a n i s m .
A progressive
degradation o f the quartz doublet in T I R S spectra has b e e n o b s e r v e d
a s a f u n c t i o n o f Ps f o r s a m p l e s f r o m t h e Ries a n d Barringer
Crater.
Analysis o f p o w d e r e d samples i s n o w underway to explore grainsize effects.
t h e predictions of s i m p l e pair-potential and statistical electron
m o d e l s used in p l a n e t a r y m o d e l s . T h e d e v e l o p m e n t of accurate
P-V-T
PZiA-03
e q u a t i o n s of state b a s e d o n static c o m p r e s s i o n d a t a a n d
U85uri
POSIER
theoretical calculations for t h e t h e r m a l contribution appropriate
THYROIDAL
for interiors of t h e large planets is e x a m i n e d , and comparisons
T E R R E S T R I A L
with recent c o m p o s i t i o n a l m o d e l s are presented.
T.
Planetary Mineralogy II (P21A)
Exhibit Hall E TUES A M
A V Murali, L.P.I.
Presiding
P21A-01
0830H
Quantitative
POSTER
Deconvolution
of Mineral
Absorption
Spectra
J M Sunshine and C M Pieters (Brown University, Department o f Geological
Sciences, Providence, RI 02912; 401-863-2417)
At visible and near-infrared wavelengths, spectra o f g e o l o g i c surfaces are
composed o f absorption bands from the minerals present in the target surface.
While such spectra contain diagnostic information, deconvolving these composite
signals to reveal the modal mineralogy is non-trivial. A successful approach,
described here, is to represent absorption bands as discrete mathematical
distributions and to then deconvolve the composite spectra into its fundamental
absorptions bands using a least-squares fitting procedure.
Gaussian distributions o f the form g ( x ) = s - e x p { - ( x - u ) 2 / 2 o 2 } , were first
assessed as an analytical model o f absorption bands. Although an efficient non­
linear least-squares fitting routine was developed, Gaussian distributions proved to
be inappropriate descriptions o f the absorption bands found in pyroxene spectra.
The Gaussian model required two distributions for each of the characteristic 1.0 and
2.0 urn pyroxene absorptions features, despite the fact that these absorptions are
each thought to b e dominated b y single electronic transitions. However, a
modified distribution model utilizing distributions o f the form g(x) = s e x p { - ( x - 1 | j . l ) 2 / 2 a 2 ) was developed which precisely describes each electronic transition
absorption band in pyroxene spectra with a single distribution, and as such
represents a significant improvement over the Gaussian analysis technique.
_
The extraction o f mineralogical information from a spectrum o f a mixture is
considerably simplified by modeling absorption spectra with these new modified
distributions. The two pyroxene components o f a pyroxene mixture spectrum
have, for example, been readily identifiable using this technique. Based on the
success o f the modified distribution model o f electronic transition ( F e + 2 )
absorption bands in pyroxene spectra, a similar approach was applied to the more
complex electronic transitions (Fe+2) ; olivine spectra. The systematic behavior
of olivine absorption bands, as described by R. G. Burns (Am. Min, 55, p . 1608,
1970) in single crystal transmission spectra, has been quantified for the first time
for particulate reflectance spectra. A s in Burns' transmission spectra, the modified
distribution model o f olivine reflectance spectra, shows a monotonic increase in the
band centers o f each o f the three olivine absorption bands as the composition
becomes increasingly fayalitic.
n
Since the band center and strength o f the absorption band are highly indicative
of the nature o f the absorption site, it is o f the utmost importance that the correct
deconvolution technique be used to describe absorptions in crystals. The ability o f
the modified distribution model to analytically describe the absorption bands in
both pyroxene and olivine spectra suggests that the modified distribution model
presented here b e the analytical method o f c h o i c e to characterize electronic
transition bands.
P21A-02
0830H
H 2 Q A N D T H E HYDRATION
POSTER
Thermal Infrared Reflectance Spectroscopy of Impact
Related R o c k s a n d Glasses
D. D'Aria (Geophysics Branch, N A S A / G S F C ,
Greenbelt, M D 2 0 7 7 1 and U M D Astronomy Dept.)
J. B . G a r v i n ( N A S A / G S F C , C o d e 6 2 2 , G r e e n b e l t , M D 2 0 7 7 1 ;
JGARVDSf/GSFCMAIL; 301-286-6565)
S h o c k m e t a m o r p h i s m o f r o c k s a n d m i n e r a l s i s a natural c o n s e q u e n c e
of exogenic processes such as hypervelocity impact. Indeed, impact
p r o c e s s e s h a v e d o m i n a t e d t h e g e o l o g i c history o f the solar s y s t e m .
W e seek t o characterize t h e effects o f shock m e t a m o r p h i s m o n solar
s y s t e m materials using thermal infrared reflectance spectroscopy
(TIRS), a sthis technique i s relevant t oremotely sensed thermal
emission observations o f planetary, asteroidal, a n d cometary
surfaces. T I R S differs f r o m traditional thermal I R transmission
s p e c t r o s c o p y i n that both refractive i n d e x a n d w a v e l e n g t h - d e p e n d e n t
absorption properties control t h e shape o f the spectra. In addition.
P L A N E T
RAW
S T A T E O F
M A T E R I A L * .
1
P21A-05
0830H
POSTER
Transmission Electron M i c r o s c o p y o f an A l l e n d e Refractory Inclusion
J . C . D o u k h a n a n d N . D o u k h a n ( B o t h at: L a b o r a t o i r e d e S t r u c t u r e e t
P r o p r i d t e s d e l'Etat S o l i d e , U n i v e r s i t y d e L i l l e , 5 9 6 5 5 V i l l e n e u v e
d'Ascq Cedex)
J.P.Poirier (Institut d e P h y s i q u e d u G l o b e d e Paris, 4 P l a c e Jussieu,
7 5 2 5 2 Paris C e d e x 0 5 )
W e h a v e studied b y transmission electron m i c r o s c o p y a crystal o f
c l i n o p y r o x e n e ( f a s s a i t e ) , from t h e c o a r s e - g r a i n e d r e f r a c t o r y i n c l u s i o n
E g g 6 o f the A l l e n d e m e t e o r i t e ( p r o v i d e d b y G.J. W a s s e r b u r g ) .
T h e p y r o x e n e contains euhedral inclusions o f pure spinel, d e v o i d o f
d i s l o c a t i o n s a n d w i t h o u t a n y topotactic relations w i t h their host. L o n g ,
clean dislocation walls, characteristic o f high-temperature anneal are
present in the p y r o x e n e c r y s t a l . S o m e dislocation w a l l s are d e c o r a t e d
with bubbles (or v o i d s ) , often in the shape o f tubes about 1 0 0 0 A in
diameter, along the dislocation lines .The dislocations constituting t h e
d e c o r a t e d w a l l s are i d e n t i c a l t o t h o s e o f the w a l l s that d o n o t e x h i b i t
b u b b l e s . W e b e l i e v e that t h e s e features are n o t h e a l e d fractures, b u t
are d u e t o the p r e c i p i t a t i o n o f a f l u i d m i g r a t i n g a l o n g the d i s l o c a t i o n s ,
as s o m e t i m e s o b s e r v e d i n o l i v i n e s f r o m peridotite x e n o l i t h s .
T h i s v i e w i s c o m f o r t e d b y the observation o f alteration products at t h e
interface spinel-pyroxene in regions o f high dislocation density,where
decorated w a l l s are present.
These observations provide g o o d evidence o f a metasomatic stage i n
the evolution o f the refractory inclusion supporting the c o n c l u s i o n s o f
Meeker etal.(1983).
1
J O N E S ,
L . L E B O F S K Y ,
A N D J . S . L E W I S
M U N I V E R S I T Y
O F A R I Z O N A ) .
3592
PLUM
DALE D R I V E ,
F A I R F A X ,
V A 22033.
THE
LOW-ALBEDO ASTEROIDS
I N T H E OUTER
BELT
( 2 . 5 - 5 A U ) A R E S P E C T R A L L Y
ANALAGOUS
TO
C H E M I C A L L Y
P R I M I T I V E ,
V O L A T I L E - R I C H
CARBONACEOUS
M E T E O R I T E S .
WHILE
INFRARED
OBSERVATIONS
SHOW
THAT,
ABOUT.
2 / 3 O F
T H E
" P R I M I T I V E "
C-class
ASTEROIDS
HAVE
T H E 3 4IM
ABSORPTION
TYPICAL
O F SURFACE
HYDRATED
S I L I C A T E S ,
T H E M O R E
D I S T A N T
P A N D
D
CLASSES APPEAR D I S T I N C T L Y
ANHYDROUS.
T H I S
C1ASS
DI S T I N C T I O N
I N D I CA T E S
THAT
O U T E R
BELT PLANETESIMALS
ACCRETED A S MIXTURES O F
A N H Y D R O U S
S I L I C A T E S ,
W A T E R
I C E ,
A N D
COMPLEX
O R G A N I C
K E R O G E N S .
A
B E L T - W I D E
HEATING
EVENT
(THAT
D E C L I N E D
I N
I N T E N S I T Y
WITH INCREASING
SOLAR DISTANCE)
MELTED I C E
ARID T R A N S F O R M E D
T H E S U R F A C E L A Y E R S O F MANY
C
AS T E R O I D S
T O T H E O BS ER VE D
C1Ay
MINERALOGY.
T H E UNSCATHED
P A N D D CLASSES
( 3 . 5 - 5 . 2
AU) D I D LOSE
S U R F A C E
ICES V I A
S U B L I M A T I O N ,
B U T R E T A I N E D
T H E O R I G I N A L
O R G A N I C / A N H Y D R O U S
S I L I C A T E
MINERALOGY.
O U R
O B S E R V A T I O N S
C O N F I R M
N E B U L A R
CONDENSATION
MODELS
R U L I N G
OUT. HYDRATED
S I L I C A T E S
A S MAJOR
WATER-BEARING
MINERALS
DURING
TERRESTRIAL
PLANET A C C R E T I O N . I C E
MUST HAVE BEEN T H E DOMINANT
FORM O F H
0 .
P21A-U6
U83UH
POSTER
Geochemical Studies o f Libyan Desert G l a s s
A . V . M u r a l i (Lunar
and Planetary
Institute,
Houston,
TX
77058
M . E . Z o l e n s k y (NASA/JSC,
Houston,
J. R . U n d e r w o o d (EL, NASA
Headquarters,
TX
77058)
Washington,
D. C,
20546)
R.
F . G i e g e n g a c k (Department
Pennsylvania,
Libyan
Philadelphia,
Desert
Glass
glass fragments
Egypt.
and
mass
over
the nature
sand
and formation
studies indicate
1) Although
study
of
-1.4 X10P g of
natural
km? of the Western Desert of
(employing
techniques)
associated
University
19104)
-6500
a systematic
spectrometry
and locally
PA
(LDG) represents
scattered
We made
of Geology,
INAA,
of several
and sandstone
varieties
to provide
of these enigmatic
microprobe
of LDG
insight
glass fragments.
into
These
that:
the LDG has restricted
(97-98
wt % S1O2; 1-2 wt% AI2O3)
(ppm)
(Fe=490-5200;
major
element
compositions
their trace element
contents
2
vary by as much
2)
P2IA-0H
UffiUri
abundances
steep
Paragenesis and Metastability of Mg-Carbonates on W e a t h e r e d
Equilibrated Ordinary Chondrites from Antarctica
M A Velbel (Dept. o f Geological Sciences, Michigan State
University, East Lansing, M I 48824-1115)
W h i t e efflorescences o f weathering origin occur superposed o n
fusion crusts, o r along fractures i n t h e interiors, o f
a p p r o x i m a t e l y 5 % o f all m e t e o r i t e s i n t h e U . S . A n t a r c t i c
collection . A l lefflorescences from equilibrated ordinary
chondrites studied t o date ( N = 4 ) consist o f the hydrous M g carbonates nesquehonite (+. hydromagnesite) . X-ray
diffraction and scanning electron microscope studies o f
efflorescences from L E W 85320 ( H 5 ) show abundant elongate
p r i s m a t i c c r y s t a l s o f n e s q u e h o n i t e ( i d i o m o r p h i c , not
p s e u d o m o r p h o u s after lansfordite), with m i n o r local
encrustations o f hydromagnesite. Previous studies s h o w e d that
terrestrial volatiles w e r e involved i n t h e rapid ( < 4 0 yr)
carbonate-forming reaction , and that m e t e o r i t e interior
temperatures occasionally permit liquid w a t e r . T h e M g
probably originated from weathering o f meteoritic olivine.
Superposition of hydromagnesite o n rounded terminations of
nesquehonite prisms from L E W 85320 suggests that lateparagenetic hydromagnesite probably formed by heating a n d / o r
desiccation of nesquehonite during sample handling.
1
1
2
LREE
HREE
enriched
(Eu/Eu
The gases
and
their
=
Our
studies
present
in the
and
^=3.8-4.2)
and flat
negative
europium
the terrestrial
element
a meteoritic
surftcial
into quartz-rich
sandstone,
eolion
in
H2O
proportions
atmosphere.
samples
of LDG
abundances
contain
(Ir=
-0.5
residue.
that LDG is the product
into quartz-rich
O2 , CO2,
are present
in some
siderophile
representing
suggest
([La/Sm]
products)
with derivation from
higher
of three variation
and distinct
streaks
possibly
a factor
of LDG ( A ^ , Ar,
4)
ppb),
Sc=0.46-2.5)
~0.5).
in the vesicles
dissociation
significantly
and
ppm). They all show parallel
patterns
consistent
Dark
Cr=1.2-29
of 5 to 30.
exhibit
(La= 5.4-15.3
([Tb/Lu]jy=1.1-1.2)
anomalies
3)
as a factor
The LDG fragments
REE
POSTER
Co=0.2-1.2;
of meteorite
and alluvial sand,
of the western Desert of
impact
and perhaps
also
Egypt.
2
3
Nesquehonite is unstable with respect to magnesite under
Earth-surface conditions. T h e r m o d y n a m i c analysis o f the
reaction forsterite+water+carbon dioxide = = >
nesquehonite+silica at Antarctic temperatures and p C 0
indicate a p o s i t i v e affinity for t h e w e a t h e r i n g r e a c t i o n f o r all
water activities greater than 0.3, c o m p a t i b l e with the p r e s e n c e o f
liquid water a s brines a n d / o r thin films. Thus, m e t a s t a b l e M g carbonate phases accurately record the physical-chemical
conditions (e.g., lower limits o f w a t e r activity) o f their
formation. Equilibrium assemblages w o u l d not; the forsteritem a g n e s i t e equilibrium d o e s n o t involve water, s o w a t e r activity
c o u l d n o t b e c o n s t r a i n e d if m e t a s t a b l e p r e c u r s o r p h a s e s later
converted to thermodynamicaUy stable phases. T h e possible
existance o f m e t a s t a b l e precursors (e.g., ikaite) s h o u l d b e
considered w h e n interpreting the significance o f Ca- and CaM g - c a r b o n a t e s a n d o t h e r "evaporite" m i n e r a l s i n c a r b o n a c e o u s
chondrites and S N C meteorites, and possible dehydration
products formed a s a consequence o f thermal excursions during
future planetary and asteroidal sample-return missions.
Neptune and Triton:
Pre-Voyager Analysis I (P21B)
323 TUES A M
K Baines,
Jet Propulsion Laboratory
Presiding
2
V e l b e l , 1988, Meteoritics, 2 3 , 1 5 1 - 1 5 9 .
Jull a n d others, 1988, S c i e n c e , 242, 4 1 7 - 4 1 9 .
Schultz, 1986, Meteoritics, 2 1 , 5 0 5 .
2
3
T h i s p a g e m a y b e freely c o p i e d .
P21B-01
G83GH
flWITED
Magnetosphere of Neptune
A F Cheng (The Johns Hopkins University Applied
Physics Laboratory, Laurel, MD 20707)
As even the existence of a magnetosphere at Neptune has
not
yet been
established.
any predictions
are
necessarily
hazardous.
Given
a
magnetic
moment
expressed in planetary units comparable to those of
Saturn and Uranus, the magnetosphere of Neptune should
have a magnetopause radius of ~30 planetary radii,
large enough to include Triton comfortably but not
Nereid. A key issue is whether Triton will prove to be
as strong a source of plasma and neutrals as is Titan
379
EOS Vol. 70, No. 15, April 11, 1989
at
Saturn;
b o t h moons a p p e a r g e n e r a l l y
comparable,
except that T r i t o n has a 2 1 ° o r b i t a l o b l i q u i t y to the
spin equator.
T r i t o n may m a i n t a i n a n i t r o g e n p l a s m a
torus
in
the magnetosphere.
Alternatively,
plasma
s o u r c e s a t N e p t u n e may b e d o m i n a t e d b y a p l a n e t a r y
non-thermal hydrogen exosphere
like
that a t Uranus.
The
V o y a g e r N e p t u n e e n c o u n t e r may a l s o
include
the
f i r s t low a l t i t u d e p a s s through t h e a u r o r a l z o n e o f a
planet
other
than
Earth.
Auroral
precipitating
p a r t i c l e s may b e d e t e c t e d a n d c o r r e l a t e d w i t h r e m o t e
sensing of
the p l a n e t a r y a u r o r a and measurements o f
field-aligned currents.
P21B-02
0850H
Deuterium o n Neptune:
Observational Constraints o n the
Origin a n d Evolution
B T- L u t z ( L o w e l l O b s e r v a t o r y , 1 4 0 0 W e s t M a r s H i l l
Flagstaff, A Z 86001; 6 0 2 - 7 7 4 - 3 3 5 8 ;
Road,
SPAN
PERCY::BLUTZ)
C d e B e r g h ( O b s e r v a Loire d e P a r i s , 5 P l a c e J u l e s J a n s s e n ;
92195 M e u d o n Cedex, France; 33-1-4507-7666;
SPAN
MESIOA::DEBERGH)
T O w e n (DESS, State University of N e w York, Stony
N Y
11794; 516-632-8188; BITNET
Brook,
TOWEN@SBCCMAIL)
P21b-M
fidtf-08
0920H
Cloud. S t r u c t u r e o n N e p t u n e :
from 1 9 8 6 - 1 9 8 8
SPAN
IAPOBS: :M A I L L A R D )
The
spectrum
observed
of spectral
form
of Neptune
in
the 1.6-micron
region
is
to contain spectral signatures of C H 3 D in a series
scans
made
Spectrometer
with
the Cassegrain
Fourier
Trans­
o n the 3 . 6 - m Canada-Francc-ITawaii
telescope o n M a u n a Kea. Analysis of the scans, recorded at
a spectral resolution of 4 c m
signal-to-noise
tification
-
1
ratio i n excess
of this
isotopically
Recent ground-based C C D images obtained with
the
University of Hawaii 2.24-m telescope (Mauna Kea Observatory)
have provided new information about cloud structure on
Neptune. Images were taken in 1986, 1987, and 1988, through
filters centered on three methane bands (6190, 7270, and 8 9 0 0 A )
and three continuum regions (6340, 7490, and 8260 A ) .
of 50, yields
t h e first
molecule
2
In all three years, a feature in the southern hemisphere
dominated the reflected sunlight at the strongest methane band
(8900 A ) ; no bright features have been detected in the northern
hemisphere.
T h e latitude of the 1988 bright feature (-30 ' ± 2 ' )
differs from the latitude of the brightest feature seen in earlier
years (-38° ± 3 ' ) . Furthermore, the rotation period of the 1988
feature ( 1 7 . 7 ± 0 . 5 hrs) is longer than the rotation period of
features observed in 1986 and 1987 ( 1 7 . 0 ± 0 . 0 5 hrs).
1
In 1988, the bright feature was also detected at a weaker
methane band (6190 A ) . These are the first reported images
showing discrete cloud structure at this wavelength, although
disk-integrated photometry at 6190 A has indicated structure in
the past. Also visible at this wavelength was an apparent polar
haze layer centered on the southern pole. T h e wide-angle camera
on the Voyager 2 spacecraft has a filter at this wavelength; the
resolution of the wide-angle camera will surpass that of groundbased telescopes in June 1989.
ratio for
observa­
tions
Neptune
The
T h e D / H ratio derived b y t h e m e t h a n e
implies
of about
observed
shown
a
global
enrichment
a factor
of 8 over
enhancement
to favor
accretion
of
of
deuterium
the protosolar
the C H 3 D / C H 4
models
o n
value.
ratio is
for the formation
of
Neptune over homogeneous
c o l l a p s e m o d e l s , a n d it i s u s e d
to c o n s t r a i n
that w a s present i n t h e primi­
the enrichment
The best images of Neptune have sufficient spatial resolution
to allow center-to-limb ( C T L ) profiles to be extracted. Models of
the observed C T L profiles indicate that the atmosphere of
Neptune has at least two distinct cloud layers: the 8 9 0 0 - A C T L
profile requires the presence of some material above the 5-mbar
level, but such a haze does not provide sufficient reflected flux at
the 6 3 4 0 - A continuum region, indicating another scattering layer
is present deeper than 1.5 bars. A bright optically-thick cloud at
2.6 bars provides a good fit to 6 3 4 0 - A reflectivity.
P21B-05
2
1
2
4
2
2
2
S i n c e t h e m i x i n g r a t i o p r o f i l e s of C H a n d
C H
a r e c o n t r o l l e d b y e d d y m i x i n g in t h e
l o w e r s t r a t o s p h e r e , t h e e f f e c t s of t h e
c o n d e n s a t i o n sink p r o p a g a t e s e v e r a l s c a l e
heights above the condensation level. This
reduces their mixing ratios below a mixing
ratio profile based upon a photochemical model
and s a t u r a t i o n a l o n e . H o w f a r a b o v e t h e
c o n d e n s a t i o n level t h i s r e d u c t i o n p r o p a g a t e s
is d e p e n d e n t u p o n t h e s t r e n g t h of eddy m i x i n g
in t h e l o w e r s t r a t o s p h e r e . T h i s f e e d b a c k o n
the photochemistry lowered t h e total haze
p r o d u c t i o n b y a b o u t h a l f from o u r p r e v i o u s
estimates.
2
2
0935H
6
2
N e p t u n e D u r i n g t h e Solar
Cycle
G W Lock w o o d . B L Lutz, a n d D T T h o m p s o n
P21B-09
(Lowell
103bH
Observatory, 1 4 0 0 W e s t M a r s Hill R o a d , Flagstaff, A Z
Ethane Abundance on Neptune
N A G W -
1505 a n d N G R - 3 3 0 1 5 1 4 1 .
The
brightness
of Neptune,
observed
at 4 7 2 a n d 551 n m
since 1972, continues basically to vary inversely with
activity,
increasing
solar m i n i m u m .
photochemical
varies
b y about
T h e effect
process
according
4% from
solar
solar
maximum
to
is thought
to b e caused
by a
Neptune's
atmosphere
that
in
to the Sun's
ultraviolet
output.
I n1 9 8 8 ,
Neptune w a sbrighter b y about 1% than a n y time during the
past
U905H
The Structure of the Atmosphere of Neptune Determined
from Groundbased and IUE Spectrophotometry: Con­
straints on Stratospheric and Tropospheric Aerosol
Properties, Methane Abundance, and the Ortho/Para
Hydrogen Distribution
17 years.
Discrete
"clouds," visible
only
K H Baines (Jet Propulsion Laboratory/California Insti­
tute of Technology, Pasadena, CA 91107; 818-354-0481)
(Sponsor: R A West)
images
bands,
have been reported a n d m a y account for the unusual
recent
visual
brightening.
W e p r e s e n t t h e p h o t o m e t r i c r e s u l t s , i n c l u d i n g if p o s s i b l e a n
updated
T Kostiuk, F Espenak, and M J Mumma (all at:
Planetary Systems Branch, Laboratory for
Extraterrestrial Physics, NASA Goddard Space
Flight Center, Greenbelt, MD 20706;
301-286-8431; SPAN LEPVAX::U32TK)
P Romani (SSAI, 7375 Executive Place, Suite 300,
Seabrook, MD 20706; 301-286-4859; SPAN
VIRIS::YS2PR)
D Zipoy (Astronomy Program, University of
Maryland, College Park, MD 20742;
301-454-7189)
Upper limits to the mole fraction of C H on
Neptune where determined from infrared heterodyne
spectroscopic measurements near 12/*m.
Observations were made at the NASA Infrared
Telescope Facility on Mauna Kea, Hawaii in June,
1988 with a resolving power X/AX-IO . This
resolution permitted the measurement of
individual emission line profiles of ethane
(RR[1,7]; 835.5217 c m " ) . Iterative fitting of
spectra calculated from existing atmospheric
models to the measured spectra permitted the
extraction of ethane mole fractions on Neptune.
Measured data did not show significant emission
profiles, but the signal-to-noise ratio was
sufficient to extract meaningful upper limits on
the C H mole fraction and to constrain existing
atmospheric and photochemical models of Neptune.
An upper limit to ethane mole fraction < 2 x 1 0 "
was derived. This value will be compared to
existing data and the implications on atmospheric
and photochemical models will be discussed.
2
1989measurement
to b e obtained
late April.
In
6
-6
addition,
w e will
present
an improved
geometric
albedo
resolution
annually since 1980.
1
This w o r k is s u p p o r t e d i n part b y N S Fgrant
Constraints on the global atmospheric structure of
Neptune are presented, derived from a broad range of
groundbased broadband (10-K spectral resolution) and
high-resolution (0.10-A resolution) spectra, as well as
IUE satellite spectra.
The analysis yields a narrow
family of models which characterizes a stratospheric
haze layer near the 1-mbar level presumably composed of
condensed hydrocarbons, an upper tropospheric methane
condensate haze near 1 bar, and a deep, opticallyinfinite
cloud
near
3.5 bars.
The global-mean
stratospheric haze column density is found from Miescattering theory to be 3.0 - 8.0 10
gm/cm^, in
agreement with recent calculations of hydrocarbon
production and sedimentation rates for sub-micron-sized
hydrocarbon condensates in the Neptunian stratosphere.
Neptunian stratospheric aerosols are relatively bright,
with the global mean imaginary index of refraction for
these particles being 0.002 - 0.007 in the uv, compared
to 0.005 - 0.020 found for Uranus by the Voyager
Science Team (J. B. Pollack et al. , 1987, JGR 9 2 ,
15037) in the mid-visible.
The methane haze optical
depth, 0.1 - 0.2 at 0.64 microns for isotropicallyscattering particles, is about half of that previously
found for Uranus (Baines and Bergstralh, 1986, Icarus
65, 406), and close to that found for stratospheric
particles.
Given the large methane molar fraction of
0.023 - 0.037 derived in this analysis, representing
some 18 - 30 percent of the mass of the troposphere,
the
low methane
cloud
opacity
indicates
that
significant vertical transport of methane crystals
occurs in the troposphere.
Finally, we find at least
85% of hydrogen is in the equilibrium state, in
agreement with theory.
in
r e c o r d e d t h r o u g h filters c e n t e r e d o n t h e r e d m e t h a n e
spectrum from 3 3 0 to 8 9 0 n m obtained at 0 . 8 - n m
and N A S A
grant N A G W -
ATM-8619590
1505.
Q
380
- 2
4
4
86001; 602-774-3358; S P A N PERCY: : W L O C K W O O D )
P2113-03
2
The Brightness a n d Geometric Albedo Variations o f
tive ices t r a p p e d i n t h e core o f t h e p l a n e t a s it f o r m e d .
This research is s u p p o r t e d i n part b y N A S A grants
5
2
2
iden­
Neptune.
6
2
in the
atmosphere a n d a measurement of the C H 3 D / C H 4
Photochemistry
M e t h a n e p h o t o l y s i s in t h e s t r a t o s p h e r e o f
Neptune produces C H , C H , and C H
in
abundances greater than those allowed by their
saturation mixing ratios over their respective
ices. W e have used a combined photochemicalc o n d e n s a t i o n m o d e l t o s t u d y t h i s and p r e d i c t a
total stratospheric haze production rate of
4.2 X 1 0
grams c m
sec
of these
h y d r o c a r b o n ices ( 7 5 % e t h a n e , 2 5 % a c e t y l e n e ,
trace diacetylene). This total production rate
is i n s e n s i t i v e t o w i t h i n a f a c t o r of t w o t o
o r d e r o f m a g n i t u d e c h a n g e s i n t h e eddy
diffusion coefficient and methane mixing
r a t i o , w h i c h i s w i t h i n o u r e s t i m a t e of
uncertainty for this number. W e have estimated
t h e o p t i c a l d e p t h s of t h e s e h a z e s b y b a l a n c i n g
the photochemical production rate by loss due
to sedimentation. For C H / C H
ice t o b e t h e
s o u r c e o f t h e h i g h a l t i t u d e h a z e layer t h e
lifetime for the haze particles must be longer
than the sedimentation time. Observed
v a r i a t i o n s in t h i s h a z e l a y e r a r e likely d u e
to d y n a m i c s , not photochemistry. Since C H
ice h a z e p r o d u c t i o n i s c o n f i n e d t o w i t h i n i t s
c o n d e n s a t i o n level a n d w h e r e C H
freezes o u t ,
it m a y f o r m a d e t a c h e d h a z e l a y e r .
a n d c o a d d e d t o obtain a total
substituted
4
P N R o m a n i ( S S A I , 7375 E x e c u t i v e P l a c e , S u i t e
300, Seabrook, MD 20706; 301-286-4859; SPAN
VIRIS::YS2PR)
S K A T R E Y A (Dept. o f A t m o s . , O c e a n i c , a n d
Space Sciences, Univ. of M i c h . , A n n A r b o r ,
M I 4 8 1 0 9 - 2 1 4 3 ; 3 1 3 - 7 6 4 - 3 3 3 5 ; SPAN
SPRLC::ATREYA)
H B Hammel
(Jet Propulsion Laboratory,
M . S . 169-237,
4 8 0 0 Oak Grove Drive, Pasadena, C A 91109; 818-354-2321)
(Sponsor: Bruce Jakosky)
J-P Maillard (Institute d ' A s t r o p h y s i q u e , 9 8 b i s B o u l e v a r d
Arago, 75104 Paris, France; 33-1-^1320-14-25;
1020H
Stratospheric Aerosols From C H
on Neptune
Ground-based Imaging
2
rVib-Ub
6
6
U950H
Neptune's Exospheric Temperature: Implications for
Electroglow
S A Curtis (Laboratory for Extraterrestrial Physics,
NASA/Goddard Space Flight Center, Greenbelt, MD
20771)
If the magnetic field of Neptune does not possess a
tilt and offset similar to that of the Uranus magnetic
field, then the Neptune magnetosphere will lack what
may be a major source of precipitation as compared to
Uranus. Limited to auroral energy inputs alone, the
Neptune exosphere may be much colder. Specifically,
we expect the exospheric temperature at Neptune to be
about 200° K as compared to nearly 800° K at Uranus.
It is also suggested that the high exospheric
temperatures, which also have been observed in
association with electroglow on Jupiter, Saturn and
Uranus, are a necessary condition for the occurrence
of electroglow on Neptune. Implications of this work
for the existence of Neptune electroglow are
discussed.
T h i s p a g e m a y b e freely c o p i e d .
Neptune's Arc Rings.
P D Nicholson (Astronomy Department, Cornell University, Ithaca N Y 14853;
607-255-8543; CUSPIF::NICHOLSON)
(Sponsor: B. Jakosky)
In July 1984 Neptune joined (he family of 'ringed' planets, with the
discovery during a stellar occultation of a narrow, azimuthally extended, par­
tially transparent structure orbiting the planet at a distance of ~ 67000 km,
or 2.68 Rn. The most puzzling aspect of this observation was lack of any
detectable feature in the data at the point where the star again crossed this
orbital radius, which led Hubbard et al. (Nature 8 1 9 636, (1986)) to dub
the feature an 'arc', rather than a ring. Since 1984, data from ~ 20 stellar
occupations by Neptune have been examined, at least 6 of which have yielded
additional evidence for incomplete rings, or arcs. In only 3 cases, however,
was the putative arc occultation observed at more than one telescope, and
for 2 of these the data are of relatively poor photometric quality. The sole
Vol. 70, No. 15, April 11, 1989 EOS
remaining unambiguous arc observation occurred on 20 August 1985. In no
experiment has a complete ring been observed.
The picture which emerges from these observations is fragmentary, and
almost certainly very incomplete. A major source of uncertainty is our cur­
rently poor knowledge of the orientation of Neptune's equatorial plane (linked
to the unknown mass of Triton), which translates into substantial uncertain­
ties in the calculated arc radii. Arcs exist at radii of ~ 2.3 and ~ 2.6 R , and
probably also near 2.15 Rn and perhaps also at 1.65 and 1.41 R^- Typical
widths are 1 0 - 2 0 km, with normal optical depths of 0.08 - 0.30. The arcs are
thus similar in width to the Uranian rings, but more similar in optical depth
to Saturn's C Ring. Information on arc lengths comes from a statistical com­
parison of occupation observations at widely-separated sites; typical lengths
of ~ 1000 km are indicated, but with an uncertainty of at least a factor of 3.
Combined with a fractional longitudinal coverage of 10 - 20%, this leads to
an estimate for the total arc population of 30 — 60.
N
2 4
of about 2 x 1 0
electron/sec with energies o f about 3 keV. If such
fluxes a r e present, they c o u l d p r o d u c e a detectable aurora. T h e
V o y a g e r v i e w i n g g e o m e t r y at Triton s e e m s w e l l - s u i t e d t o d i s c o v e r
s u c h a n aurora.
A recent stellar occultation has confirmed predic­
tions that Pluto has an atmosphere which is suffi­
ciently thick to globally envelope the planet and to
extend far above the surface. Because Pluto's atmo­
sphere consists of methane and perhaps other volatiles at temperatures below their freezing points,
the atmospheric bulk is a strong function of the
temperature of the surface ices. Pluto's volatile
atmosphere is sufficiently thick to regulate the sur­
face temperature of its volatile ices to a common
value. As Pluto approaches perihelion in its marked­
ly elliptic orbit, these ices will heat up and tend
to sublimate into the atmosphere.
This is expected
to cause a seasonal maximum in the atmospheric bulk
and a corresponding minimum in the exposed volatile
ices shortly after perihelion.
This lag will be
diagnostic of the thermal properties of the surface.
Because the atmosphere is also escaping, the ices
freshly deposited during the last winter should sub­
limate before this atmospheric maximum is achieved,
exposing darker material progressively more rapidly.
Observations of this effect may constrain Pluto's
total atmospheric bulk.
The Pluto-Charon System I
(P22A)
323 TUES PM
S A Stern, Univ of Colorado
Presiding
Several theoretical models of arc confinement have been proposed, each
of which invokes the presence of at least one rather large ( ~ 200 kin diameter)
P22A-U1
1330H INVITED
satellite orbiting near Neptune's Roche limit. It is possible that such a satellite
has already been detected in a chance occultation in May 1981 (Reitsema, et
Pluto-Charon Mutual Events:
al. Science 215 289 (1982)). Voyager imaging observations should identify
Overview a n d Preliminary Results
any satellites, and, with luck, provide us with a complete map of the spatial
distribution of arcs.
R P B i n z e l (Department o f Earth, A t m o s p h e r i c , a n d
Planetary Science, M I T , Cambridge, M A 0 2 1 3 9 )
(Sponsor: T. Jordan)
P21b-li
1110H INVITED
The Thermal Structure of Triton's Atmosphere: Pre-Voyager M o d e l s
CP.
M c K a y , J . B . Pollack, A . P . Zent, D . P . Cruikshank (Space Science
Division, N A S A A m e s Research Center, Moffett Field, C A 9 4 0 3 5 ) and
Regis Courtin (Observatoire de Paris-Meudon, M e u d o n , France)
W e have investigated the thermal s^ate of a N 2 - C H 4 atmosphere on
Triton.
W e have adapted a non-grey radiative-convective model de­
veloped for T i t a n . A s on T i t a n , we find that the organic haze that
would be produced by photochemical reactions is the most significant
factor affecting solar energy deposition. T h e production of haze m a ­
terial ( ~ 1 0
-
1
5
g cm
-
2
s
-
1
) is obtained by scaling from the T i t a n
value. Pressure induced absorption, primarily N 2 - N 2 , is the dominant
source of infrared opacity. In all model runs the tropospheric temper­
ature lapse rate is determined by the saturation of N 2 . B y varying the
O n c e e v e r y 1 2 4 years, Pluto's heliocentric m o t i o n c a u s e s the orbital
plane o f its satellite (Charon) t o s w e e p through t h einner solar
s y s t e m , t h e r e b y a l l o w i n g transits o f C h a r o n i n f r o n t o f P l u t o a n d
occultations
o f Charon behind Pluto t o b e observed. T h e current
s e r i e s o f m u t u a l e v e n t s b e g a n i n 1 9 8 5 ( B i n z e l e t a l . 1 9 8 5 , Science
2 2 8 , 1 1 9 3 ) w i t h partial transits and occultations. D u r i n g 1 9 8 7 a n d
1 9 8 8 , total transits a n d o c c u l t a t i o n s w e r e o b s e r v e d . T h e last partial
events will b e observable in 1990.
46 K , which corresponds t o surface albedo of 0 . 6 and emissivity of 0 . 6 ,
has negligible atmosphere ( ~ 2 m b ) with virtually no insulating or re­
flecting effects.
For higher albedo or emissivity the atmosphere has
even smaller effects.
=
In the other extreme (albedo = 0 . 0 5 , emissivity
0 . 3 ) we find a relatively w a r m surface temperature, ~ 5 9 K with
a corresponding pressure o f 5 4 m b . In all model runs there is a h o t
stratosphere (T ~ 1 2 0 K ) d u e t o absorption by tholin-like haze similar
to that on T i t a n .
T h e implications of these results for the Voyager
P22A-04
143UH
IIWITED
Dynamics of Pluto
A n t h o n y R D o b r o v o l s k i s (245-3 N A S A / A m e s R e s e a r c h C e n t e r ,
Photometric observations o f the times, durations and depths o f the
m u t u a l e v e n t s h a v e constrained Charon's orbital parameters a n d
have yielded n e westimates for thediameters a n d albedos o f Pluto
and Charon a swell a s estimates for the m a s s a n d density o f the
system.
T h u s mutual event observations are able t o constrain
physical a n ddynamical models.
Spectroscopic a n d spectrophotometric observations during periods (lasting about a n hour)
w h e n Charon i s totally occulted behind Pluto, have a l l o w e d t h e
c o m p o s i t i o n s o f their individual surfaces t o b e discerned.
surface albedo and emissivity we have considered a range of consistent
surface temperatures. For example a cold surface temperature of about
seasonal changes with emphasis on the impending
changes expected as a result of Pluto's imminent
perihelion passage.
D e c o n v o l u t i o n o f mutual event photometry will also allow surface
m a p s t ob e derived for o n e hemisphere o f e a c h body. (Charon i s i n
a s y n c h r o n o u s 6 . 4 d a y orbit.) T h e c h a n g i n g i m p a c t parameter o v e r
1 9 8 5 t h r o u g h 1 9 8 9 h a s c a u s e d C h a r o n t o p e r f o r m a "raster s c a n " i n
front o f Pluto's surface.
(Similar "scans" h a v e occurred f o r
Charon's surface.)
I naddition t o a discussion o f the n e w physical
parameteres gained from Pluto-Charon mutual event observations,
preliminary results f o rthe surface albedo distribution o f Pluto's
Charon-facing hemisphere, including evidence forpolar caps, will
be presented.
Moffett Field, C A ; 415-694-4194; S p a n
A historical perspective is given on Pluto's orbit, m a s s , density, and
rotation, tidal evolution of C h a r o n ' s orbit, origin of the system, and
prospects for future advances.
Because of its high eccentricity (e » 0 . 2 5 ) , Pluto's orbit crosses the
orbit of Neptune. Nevertheless, their orbits are separated by ~ 7 A U
by virtue of Pluto's high inclination ( I w 1 6 ° ) t o the invariable plane
of the Solar System. Furthermore, a 3:2 commensurability between
their orbital periods keeps P l u t o at least 1 7 A U away from Neptune.
Another resonance keeps Pluto's perihelion o u t of the plane of Nep­
tune's orbit.
Long-term numerical integrations have also revealed
additional cycles as well as chaotic behavior.
Before Charon w a s discovered, estimates of Pluto's mass from its
perturbations o n Neptune ranged from ~ 0 . 1 t o ~ 1 . 0 Earth masses.
An
flybys will be discussed.
upper limit of ~ 6 0 0 0 k m for Pluto's diameter then led t o un­
3
realistic densities of ~ 5 — 5 0 g / c m . T h e m o d e r n values of ~ 0 . 0 0 2
Earth masses, ~ 2 3 0 0 k m , and ~ 2 . 1 g / c m
P22A-02
1350H
IiWITED
T h e Interiors o f P l u t o
P21B-12
1130H
and
3
have been determined
from Charon's orbital radius and period.
a n dCharon:
Composition,
Structure,
Implications
Pluto's brightness varies by ~ 1 3 % over a 6.39-day cycle, identified as
the period of Pluto's rotation. T h i s equals Charon's orbital period t o
within the uncertainty of only a few minutes. Pluto's obliquity varies
Triton's Ionosphere
D a m o n P Simonelli a n d R T R e y n o l d s ( M S 245-3, N A S A / A m e s
Research
S K Atreya
(Atmospheric, Oceanic and Space Science
Department, University of Michigan, Ann Arbor,
MI
48109-2143; 313-764-3335)
Ground-based observations at 2.3 um and 0.89 microns
yield a C H 4 abundance of between 7 and 50 m-atm at the
surface of Triton (corresponding surface pressure of
0.1-1 mb). On the other hand, should a feature at
2.16 micron indeed be due to liquid N 2 , a surface
pressure of 130-300 mb of N would be expected. In
either case, the 'atmospheric' thermal structure
would determine the location of unit optical depth
for ionization (as the saturated vapor abundances of
C H 4 and N£ are expected to drop rapidly with height).
It is expected to be a few scale heights above the
surface. A peak electron concentration of a maximum
1000 electrons c m
is expected, with the solar EUV as
the ionization source.
Should Neptune possess a
magnetosphere similar to Uranus, the charged particle
ionization of N would dominate; the peak ion
concentration, however would be similar to that due to
the EUV. Unlike Titan, however, there is little
likelihood of the formation of the ions of H-C-N type,
as the vapor mixing ratio of C H 4 relative to N would
be small, < 1 0 ~
if N were present.
2
- 3
2
2
Span
Center, Moffett
Field,
C A94035;
415-694-3119;
2
between ~ 8 8 ° (prograde) and ~ 1 1 2 ° (retrograde) with a period of
~ 3 M y r . Like Uranus, P l u t o receives more heat at its poles than at
its equator (averaged over all seasons).
HAL::SIMONELLI)
Pluto is in a size class all its own, intermediate between the Galilean
The time required for tidal friction t o establish Charon's synchronous
satellites and the medium-sized satellites of Saturn and Uranus; and
orbit is on the order of 5 0 million years, while the time t o despin
it forms a unique "double planet" with its satellite Charon. Further,
Charon t o synchronous rotation is only a few million years.
Tides
the P l u t o / C h a r o n system m a y have had a more direct association
also d a m p Charon's orbital eccentricity over a timescale of ~ 5 0 M y r .
with the solar nebula than (for example) giant planet satellites that
A detectable eccentricity would b e evidence for recent impacts.
formed from circumplanetary disks. For all these reasons, the internal
structure and evolution of these two bodies is especially intriguing.
If the resonances between N e p t u n e and P l u t o ever broke down, close
Determination of the mean density of the P l u t o / C h a r o n system from
encounters with Neptune could not eject P l u t o from the Solar System.
ongoing "mutual events" has m a d e accurate internal modeling pos­
Conversely, Pluto is not likely t o b e a captured extrasolar wanderer,
sible for the first time—but it has also complicated the process, b y
but might have originated in the inner O o r t cloud. Chiron m a y have
way
split off from P l u t o , since the net angular m o m e n t u m of the system
of continuing changes in the best-fit density and the inability
to separate o u t the individual densities of the two bodies. T o these
is close t o the critical threshold for binary
complications must be added the usual modeling uncertainties—have
cannot be an escaped satellite of Neptune because tidal friction would
differentiation or solid-state convection occured, what is the density
have despun Pluto and fused it t o Chiron in under a million years.
fission.
However, Pluto
and hydration state of the rock component, are there contributions
from non-water ices, etc. Despite these difficulties, however, a co­
herent picture is emerging of two bodies that are significantly denser
and rockier than anticipated. T h e mean system density of roughly
2 g cm
-
3
severely limits the amount of light non-water ices that
6
}
24609::DOBRO)
can b e present in the Pluto and Charon interiors; and the density
translates into a rock/(rock -f- H 2 O ) m a s s ratio of at least w 0 . 7 ,
making P l u t o / C h a r o n rockier than any of the giant planet satellites
P 2 b - 1 3 1145H
with the exception of the inner Galileans.
Is There a Detectable Aurora o n Triton?
outer solar nebula—and m a y also bear witness t o volatile loss that
The Voyager 2 encounter w i t h N e p t u n e offers the best chance for clar­
ifying the history of the Neptunian s y s t e m and its relationship with
Pluto.
Analysis of the final P l u t o / C h a r o n mutual events will bet­
ter constrain the parameters of that system. T h e coming generation
of visible and infrared telescopes will provide still more information,
and m a y discover other satellites (or rings) of Pluto or Charon.
This unexpected rocki-
ness m a y be indicative of P l u t o / C h a r o n ' s formation from a CO-rich
occured during a Charon-forming impact event. W e look forward t o
A
J Dessler. F C Michel, a n dT W Hill (Space Physics and
Astronomy Department, Rice University, Houston, T X 77251;
713-527-4045)
With even a modest magnetic moment, Neptune will have a
magnetosphere o f impressive size. F o r example, i f the equatorial
magnetic field at cloud-top level is 0 . 3 Gauss, t h e nose o f t h e
magnetosphere will project nearly 8 x 1 0 k m ( 3 1 R ^ ) into the solar
wind. E v e n with a n improbably w e a k cloud-top field o f just 0.01 G ,
the n o s e m a g n e t o p a u s e d i s t a n c e i s still 2 . 5 x 1 0 k m ( 1 0 R ^ ) - T h e
m a g n e t o s p h e r e p r o m i s e s t o b erotationally d o m i n a t e d s o that t h e
p l a s m a p a u s e e x t e n d s t o t h em a g n e t o p a u s e . Neptune's satellite Triton,
w h i c h i s i n a n i n c l i n e d , retrograde orbit at 1 4 R ^ j , w i l l , e x c e p t u n d e r
the m o s t extraordinary o f circumstances, m o v e through this plasmasphere with a relative speed o f about 4 0 km/sec.
Triton h a s a n
atmosphere, a n d it ought t ohave a significant ionosphere. Plasma
f l o w past Triton should i n d u c e a potential o f the order o f 3 k V across
the ionosphere. W escale f r o m Saturn's satellite Titan and c o n c l u d e
that Triton's a t m o s p h e r e i s s u b j e c t t o sporadic b o m b a r d m e n t b y a flux
the approaching completion of the mutual event cycle, which should
P22A-05
1450H
finally stabilize the best-fit system density—and also anticipate fu­
ture improvements in astrometric techniques aimed at constraining
the relative masses of Pluto and its satellite.
The Mass Ratio of the P l u t o / C h a r o n System
R.L. Millis, L . H . Wasserman, O . G . Franz (Lowell Observatory,
Flagstaff, A Z 8 6 0 0 1 ; 6 0 2 - 7 7 4 - 3 3 5 8 )
C . C . Dahn ( U . S . Naval Observatory, Flagstaff, A Z 8 6 0 0 2 ;
5
602-779-5132)
P22A-U3
M 0 H iiWllElJ
5
A . R . Klemola (Lick Observatory, University of California,
Santa Cruz, C A 9 5 0 6 4 ; 4 0 8 - 4 2 9 - 4 0 4 9 )
Pluto's Atmosphere Near Perihelion
In an effort to predict the the ground track location of the June 9, 1988
L M Trafton (Astronomy Department, Univ. Texas at
Austin, Austin, TX 78712; 512-471-1476, INTERNET
lmt@astro.as.utexas.edu)
(Sponsor:
S A Stern)
I review the evidence for Pluto's extended atmosphere
and discuss model-dependent predictions for Pluto's
T h i s p a g e m a y b e freely c o p i e d .
occultation by Pluto, 5 5 plates containing Pluto and the target star
were taken with the 61-inch Astrometric Reflector at the U . S . Naval
Observatory's Flagstaff Station.
T h e resulting predictions provided
the basis for deployment of the Kuiper Airborne Observatory and a
portable groundbased station from Lowell Observatory, both of which
succeeded in observing the occultation. In this paper we discuss the
381
EOS Vol. 70, No. 15, April 11, 1989
use of these same astrometric observations to constrain the mass ratio
of the Pluto/Charon system.
PZZA-1U 1615H
A total of 73 exposures were obtained
on 14 nights between M a y 26 and June 1 1 , 1988.
All plates were
measured with respect to a common set of standard stars. T h e plates
were initially measured with the P D S microdensitometer at Lowell and
subsequently with the more sophisticated version of this machine at the
Yale University A s t r o n o m y Department. Both sets of measurements
Cosmochemical I n f e r e n c e s Concerning the I d e n t i t y
o f t h e H e a v i e r Gas i n P l u t o ' s A t m o s p h e r e
s
J.I.
L u n i n e and R . V . Y e l l e ( L u n a r and P l a n e t a r y
L a b o r a t o r y , U n i v e r s i t y o f A r i z o n a , T u c s o n , AZ
85721;
602-621-2789)
show a well-defined, cyclic variation in the position of the blended
Pluto/Charon image with respect to Pluto's ephemeris. T h e observed
motion of the center-of-light no doubt results from the motion of Pluto
and Charon about their common barycenter. However, the amplitude
and shape of the motion as a function of the satellite's orbital position
also depends on the relative brightness of the various faces of the two
bodies. T h e combined brightness of Pluto and Charon is accurately
known as a function of orbital phase, but the relative brightness of the
two objects has been measured at only one or two points in Charon's
orbit.
W e have attempted to model the variation in the position of
the center-of-light on the commonly adopted assumption that Charon
is constant in brightness. It is possible with this model to set useful
limits on the ratio of the masses of Pluto and Charon. However, we
are unable to match exactly the observed motion of the center-of-light
with our model. In our opinion, significant variation of albedo across
the surface of Charon is implied.
Pz4\-U/ 153UH
a
Recent a n a l y s i s o f the thermal s t r u c t u r e of P l u t o ' s
a t m o s p h e r e y i e l d s a mean m o l e c u l a r w e i g h t o f 2 2 t o 2 8
a . m . u . ( Y e l l e and L u n i n e , N a t u r e . s u b m i t t e d ) , w e l l a b o v e
t h a t of methane, the o n l y s p e c t r o s c o p i c a l l y
identified
gas i n P l u t o ' s atmosphere.
The d e r i v e d t h e r m a l
structure reproduces c e r t a i n f e a t u r e s of the s t e l l a r
o c c u l t a t i o n d a t a (Hubbard, t h i s s e s s i o n ) , so the
p r e s e n c e o f a g a s h e a v i e r t h a n methane a p p e a r s t o b e a
r o b u s t c o n c l u s i o n . Candidate g a s e s which are p l a u s i b l e
from t h e s t a n d p o i n t o f s o l a r n e b u l a m o d e l s a r e c a r b o n
monoxide, m o l e c u l a r n i t r o g e n and argon.
Cosmochemical
m o d e l s p r e d i c t a r g o n t o b e a t l e a s t two o r d e r s o f
magnitude l e s s abundant than t h e c a r b o n - b e a r i n g s p e c i e s ,
and r o u g h l y an o r d e r o f m a g n i t u d e l e s s a b u n d a n t t h a n
nitrogen.
Molecular nitrogen is a potentially
a t t r a c t i v e candidate as the h e a v i e r g a s , i n s o f a r as i t
d o m i n a t e s t h e a t m o s p h e r e o f T i t a n and may b e p r e s e n t on
Triton.
H o w e v e r , i t s p r e s e n c e on T i t a n i s m o s t r e a d i l y
e x p l a i n e d a s t h e p r o d u c t o f p h o t o l y s i s and s h o c k
c h e m i s t r y o f ammonia e a r l y i n t h a t s a t e l l i t e ' s h i s t o r y .
I f Pluto formed i n a gaseous nebula dominated by w a t e r ,
methane and ammonia ( a s p r e d i c t e d f o r T i t a n ) , i t w o u l d
have a b u l k d e n s i t y o f 1 . 5 t o 1 . 6 g / c m , w e l l below the
system v a l u e o f roughly 2 . 0 g / c m .
The m o s t l i k e l y
heavy gas f o r Pluto i s carbon monoxide, p r e d i c t e d t o
h a v e b e e n an a b u n d a n t c a r b o n - b e a r i n g g a s i n t h e o u t e r
solar nebula.
The b u l k d e n s i t y o f P l u t o i s
consistent
w i t h a s o l a r n e b u l a dominated b y c a r b o n monoxide as t h e
major c a r b o n - b e a r i n g m o l e c u l e .
S m a l l amounts o f m e t h a n e
i n the nebula would have been p r e f e r e n t i a l l y trapped i n
water i c e which a c c r e t e d t o form P l u t o , c o n s i s t e n t w i t h
a mixed methane-carbon monoxide atmosphere a t p r e s e n t
( a n d c o n s i s t e n t w i t h t h e m e t h a n e and c a r b o n m o n o x i d e
a b u n d a n c e s i n Comet H a l l y ) .
L e s s e r amounts o f n i t r o g e n
and a r g o n i n P l u t o ' s a t m o s p h e r e a r e p r e d i c t e d b y t h i s
model.
Origin of the Pluto-Charon Binary
W i l l i a m B M c K i n n o n (Dept. Earth and Planetary Sci. and M c D o n n e l l
Center for Space Sci., Washington Univ., Saint Louis, M O
63130;
3 1 4 - 8 8 9 - 5 6 0 4 ; Span WURST::MCKINNON)
normalized angular m o m e n t u m density H
of P l u t o - C h a r o n ,
assurriing equal densities for both components and that Pluto's mutual
occultation radius is close to correct, is 0 . 4 5 . This exceeds the critical
H,
0 . 3 9 , a b o v e which no stably rotating single object exists.
A
collisional origin for the binary is strongly implied. H exceeds 0 . 3 9 for
Charon densities p
3
c
exceeding 1 . 7 7 g c m - .
Even for p
= 2 . 3 g c m - , a tidally evolved Charon starting at the
3
a possible initial configuration, so 2.3 g cmr is
density.
the dynamical
upper
The dynamical lower limit (after Lin) is too
Pluto Occupations:
ture
Effect o f a L a r g e Near-Surface
Tempera­
Gradient
low to be meariingful, so a plausible cosmochemical lower limit of 1 . 0 g
cm~
3
is assumed. These density limits hint at but do not prove a Charon
less dense than Pluto; such would be consistent with a collisional origin
if one or both proto-objects were differentiated.
A density upper limit
closer to the system mean is possible if the rapidly rotating Pluto, as a
Jacobi ellipsoid, is not allowed to contact Charon at the Roche limit.
Viscosity will m o r e likely constrain Pluto to a more biaxial figure,
however. The angular momentum of the system requires that the protoobjects b e comparably (if not equally) sized, if off-center impact
velocities vary between escape ( - 1 . 3 km/s) and somewhat greater values
(-2.5
k m / s ) appropriate to the outer solar system.
T h e average
temperature increase, post-Charon formation, could be as great as 1 0 0 K
(for a 3 / 1 rock/ice mass ratio), triggering differentiation. This formation
scenario differs from that of the M o o n in that the comparable mass ratios
of the impactors allow non-Keplerian gravitation and viscous coupling to
m o v e Charon's mass to Roche altitude.
The impact velocities are too
low for vaporization of water ice except during jetting. Loss of material
during the jetting phase may be substantial, though, affecting the final
system ice/rock ratio in the case of differentiated proto-objects.
W . B . Hubbard. Lunar a n d Planetary Laboratory,
Exhibit Hall E WED AM
B Chao,
NASA/Goddard Space Flight Center
Presiding
PiiA-Ul 083UH PUSIER
Galileo: The Earth and Moon
Encounters
T h e o d o r e C. C l a r k e (Jet P r o p u l s i o n L a b o r a t o r y ,
California Institute of Technology, Pasadena,
CA 9 1 0 0 9 )
F r a s e r P. F a n a l e ( I n s t i t u t e o f G e o p h y s i c s ,
University of H a w a i i , Honolulu, HI 96822)
The voyage of t h e Galileo spacecraft, scheduled
t o b e l a u n c h e d O c t o b e r 1 2 , 1989 o n a V e n u s E a r t h - E a r t h - g r a v i t y - a s s i s t (VEEGA) t r a j e c t o r y t o
Jupiter, includes two encounters with the planet
E a r t h a n d t h e E a r t h - M o o n s y s t e m , t h e f i r s t in
D e c e m b e r 1 9 9 0 a n d t h e s e c o n d in D e c e m b e r 1 9 9 2 .
These fortuitous encounters provide unique Earth
and M o o n s c i e n t i f i c o b s e r v i n g o p p o r t u n i t i e s .
University
of A r i z o n a 8 5 7 2 1 ; ( 6 0 2 ) 6 2 1 - 6 9 4 2
Light curves from t h e J u n e 1988 occultation of a star b y P l u t o
show a s m o o t h behavior characteristic of a n isothermal
sphere, for normalized stellar
fluxes
336, p p . 4 5 2 - 4 5 4 , 1 9 8 8 ) .
Nature,
atmo­
<f> > 0 . 4 5 ( H u b b a r d , e t a l . ,
A t a b o u t <f> < 0 . 4 5 , o b s e r ­
vations show a n abrupt "knee" in t h e lightcurve, w i t h a rapid
b u t s m o o t h d e c l i n e t o <f> w 0 ( E l l i o t , e t a l . , Icarus,
press).
1989,in
T h e "knee" h a s b e e n interpreted a s t h e result of t h e
s u b m e r g e n c e of t h e stellar i m a g e i n a near-surface haze layer.
Y e l l e a n d L u n i n e (Nature,
1 9 8 9 ,i n press) point o u t that t h e
P l u t o a t m o s p h e r e is n o t likely t o b e isothermal, b u t should i n ­
stead undergo a rapid temperature change with a gradient o n
the order o f 5 K / k ma b o v e t h e planet's surface, such that t h e
High priority lunar science objectives include
composition and multispectral characterization
of M a r e O r i e n t a l e , t h e l u n a r f a r s i d e , t h e l u n a r
north pole, and unmapped portions of the
lunar south p o l a r region.
High priority Earth
science objectives include global mapping of
methane, other "greenhouse" gases, and
mesospheric water, and hydrogen geotail and
geocorona observations.
Calibrations and
measurements for comparison with observations at
Jupiter are an important objective for both the
Earth and t h e M o o n .
A 5 day Earth rotation
movie, as well a s searches for evidence of
postulated cometesimals raining down o n the
Earth and for evidence of an Earth shepherded
dust ring, are also planned.
h i g h a t m o s p h e r e ( c o r r e s p o n d i n g t o <f> « 1 ) i s a t a t e m p e r a t u r e
in excess of 1 0 0 K, while t h e near-surface temperature drops t o
about 5 0 K. In this paper, w e show that t h e calculated occulta­
tion lightcurve b y such a Pluto atmosphere h a s characteristics
P31A-02 083UH PUSIER
which agree w i t h those reported b y Elliot, et al. In particu­
lar, t h e stellar
PZ2A-U8
Planetary Physics (P31A)
This paper reviews the conditions and con­
s t r a i n t s o f t h e E a r t h a n d M o o n e n c o u n t e r s (ob­
serving geometry, lighting, temperature, teleme­
try, safety) w h i c h define t h e observing opportu­
nity and bound t h e science objectives, reviews
Galileo's Earth and Moon science objectives, and
reviews a preliminary timeline of events d e v e l ­
oped f o r t h e f i r s t E a r t h e n c o u n t e r .
P22A-11 1630H
appropriate Roche limit implies a Pluto with H > 0 . 3 9 alone. This is not
limit to Charon's
3
= 1.0 g cm- ,
3
c
2 2
3
c
H = 0 . 2 3 , significantly greater than that of the E a r t h - M o o n system.
Moreover, for p
n
3
3
The
f i n d s a ' c o n t a c t d i s t a n c e ' f o r P l u t o that i s l e s s t h a n t h e s i z e o f t h e
planet. T h u s it r e m a i n s an i s s u e w h e t h e r there is sufficient ionization
i n s i d e R t o p r o v i d e a n e l e c t r i c a l l y - c o n d u c t i n g barrier a r o u n d w h i c h
t h e m a g n e t i c f i e l d i s d r a p e d a n d d e f l e c t e d , t o f o r m a tail d o w n s t r e a m
(as is generally t h e c a s e f o r V e n u s and c o m e t s ) . If Pluto h a s a w e a k
i o n o s p h e r e t h e n t h e i n t e r p l a n e t a r y m a g n e t i c field w i l l p e n e t r a t e
P l u t o ' s a t m o s p h e r e , a n a l o g o u s t o t h e s i t u a t i o n at V e n u s f o r h i g h s o l a r
w i n d d y n a m i c p r e s s u r e s a n d l o w s o l a r a c t i v i t y . N o t e that t o stand o f f
the solar w i n d t o 6 Rpiuto w i t h
i n t e r n a l l y - g e n e r a t e d m a g n e t i c field
Pluto w o u l d require a d i p o l e m o m e n t o f > 1 . 3 x 1 0 G c m , greater
than 15 t i m e s that o f M e r c u r y .
196H IiWITt'D
4> i s r a p i d l y a n d s m o o t h l y q u e n c h e d t o a
flux
Numerical S i m u l a t i o n o f
Venus and E a r t h
value very close t o zero a s s o o n a s t h e stellar i m a g e enters t h e
Satellite
Capture f o r
Planets
part of t h e atmosphere where t h e strong temperature gradient
Effects
of
Irradiation
on t h e
Surface
of
Pluto
prevails. It s e e m s p o s s i b l e t h a t s u c h a m o d e l c o u l d e x p l a i n all
R J M a l c u i t ( D e p t . o f G e o l o g y and G e o g r a p h y , D e n i s o n
U n i v . , G r a n v i l l e , OH 4 3 0 2 3 )
D M M e h r i n g e r ( D e p t . o f A s t r o n o m y and A s t r o p h y s i c s ,
of t h e d a t a w i t h o u t t h e n e e d for a near- surface h a z e layer. If
R.E. Johnson (Department of Nuclear Engineering
Engineering Physics, University of V i r g i n i a ,
C h a r l o t t e s v i l l e , VA, 2 2 9 0 1 )
and
the model is correct, t h e temperature gradient should start at
a pressure o n t h e order of o n e microbar a n d t h e solid
Univ. o f Chicago, Chicago, IL 60637)
R R W i n t e r s ( D e p t . o f P h y s i c s and A s t r o n o m y ,
U n i v . , G r a n v i l l e , OH 4 3 0 2 3 )
surface
of t h e planet should lie s o m e 5 - 1 0 k m deeper.
A number o f
e x p e r i m e n t s on c h a r g e d p a r t i c l e and
photon
irradiations of
m e t h a n e i c e and
mixtures of
methane w i t h o t h e r
i c e s have been
carried
out over
the l a s t few y e a r s .
This data
w i l l be
used, along
with recent atmospheric
information to describe
the
e f f e c t s of solar i r r a d i a t i o n
on t h e s u r f a c e o f P l u t o
and i t s s a t e l l i t e C h a r o n .
P22A-12 1&45H
T h e solar w i n d interaction with Pluto's atmosphere
Fran B a g e n a l ( A P A S D e p t . , C a m p u s B o x 3 9 1 , U n i v . o f C o l o r a d o ,
Boulder, C O 8 0 3 0 9 - 0 3 9 1 )
R a l p h M c N u t t , Jr ( M I T C e n t e r f o r S p a c e R e s e a r c h , C a m b r i d g e , M A
02139)
P22A-09 1600H
s u g g e s t s that Pluto's a t m o s p h e r e s h o u l d stand o f f the solar w i n d at a
large distance from the planet. S i m p l e pressure balance calculations
R V Yelle and J I Lunine (Both at: Lunar and Planetary Laboratory,
University of Arizona, Tucson, A Z 85721; 6 0 2 - 5 2 1 - 4 6 5 2 )
are m e a n i n g l e s s , h o w e v e r , s i n c e t h e y w o u l d put t h e stand o f f
d i s t a n c e at > 2 3 a t m o s p h e r i c s c a l e h e i g h t s , w e l l a b o v e Pluto's
e x o b a s e a n d i n t o a h i g h l y - c o l l i s i o n l e s s r e g i m e . It t h e r e f o r e s e e m s
We propose that the dominant constituent in the atmosphere of Pluto
is a molecular species with a mass greater than or equal to 28, rather
than methane as customarily assumed. This conclusion is based on
the recently measured scale height of the atmosphere and on thermal
structure calculations.
Simple 1 - D models incorporating absorption
and emission of infrared radiation, thermal conduction, and N L T E
effects predict a temperature profile with a strong gradient near the
surface rising asymptotically to a temperature of 106 K at a few
microbars.
This temperature along with the measured scale height
constrains the mean mass of the atmosphere to 25 ± 3 . Candidates for
the heavier species are C O , N , and A r .
2
382
m o r e appropriate to apply the c o m e t a r y stand o f f distance R
Qmv/(47tV
e s c
p
wind density p
S
s w
w
V
s w
).
s
=
S i n c e b o t h t h e i o n i z a t i o n rate v a n d t h e s o l a r
scale with the square o f the heliocentric distance w e
o n l y n e e d t o k n o w t h e e x o s p h e r i c e s c a p e rate Q ~ 1 0
and thee s c a p e s p e e d V
e s c
.
2 8
m o l e c u l e s s"
1
T a k i n g t h e thermal speed appropriate for
C H 4 ( m = 1 6 ) at a temperature o f 6 0 K g i v e s an e s c a p e speed o f ~ 1
1
k m s" , (comparable to the cometary e x p a n s i o n speed) and w e obtain
a s t a n d o f f d i s t a n c e o f - 6 7 0 0 k m o r 6 Rpiuto- T h i s i s t h e c r i t i c a l
distance w h e r e t h e pick-up o f n e w l y - i o n i z e d material m a s s - l o a d s t h e
solar w i n d t o s t a g n a t i o n . If o n e c o n t i n u e s s c a l i n g f r o m c o m e t s o n e
T h i s p a g e m a y b e freely c o p i e d .
A three-body (sun, p l a n e t , planetoid) numerical i n t e ­
g r a t i o n c o d e w i t h an e n e r g y - d i s s i p a t i o n s u b r o u t i n e i s
used to a s s e s s the p o s s i b i l i t i e s of s a t e l l i t e capture
by way o f r a d i a l t i d a l e n e r g y d i s s i p a t i o n w i t h i n t h e
interacting bodies.
This study i s r e s t r i c t e d to venus­
l i k e and e a r t h - l i k e p l a n e t s i n a p p r o p r i a t e h e l i o c e n t r i c
o r b i t s i n t e r a c t i n g w i t h l u n a r - l i k e ( l u n a r mass and d e n ­
s i t y ) planetoids in coplanar o r b i t s with geometries
s i m i l a r to the r e s p e c t i v e p l a n e t a r y o r b i t s .
The m a j o r
v a r i a b l e s are: ( 1 ) the pericenter distance ( r ) of
c l o s e e n c o u n t e r s , ( 2 ) t h e d i s p l a c e m e n t Love number ( h )
f o r each body, ( 3 ) the e f f e c t i v e t i d a l
dissipation
f a c t o r (Q) f o r each b o d y , ( 4 ) the p l a n e t anomaly ( t h e
p o s i t i o n o f t h e p l a n e t r e l a t i v e t o t h e sun a t t h e b e ­
g i n n i n g o f t h e c a l c u l a t i o n ) , and ( 5 ) t h e p l a n e t o i d
anomaly ( t h e p o s i t i o n o f t h e p l a n e t o i d a t t h e b e g i n n i n g
of the c a l c u l a t i o n ) .
The r e s u l t s o f t h e s i m u l a t i o n s
can be p l a c e d i n t o f i v e c a t e g o r i e s : ( 1 ) c l o s e noncapture encounters i n which the p l a n e t o i d i s
deflected
i n t o a n e a r p a r a b o l i c c o u r s e b y t h e p l a n e t and t h e n
c o n t i n u e s on a h e l i o c e n t r i c o r b i t ; ( 2 ) n o n c a p t u r e s c e ­
n a r i o s i n which the p l a n e t goes i n t o a p l a n e t o c e n t r i c
o r b i t f o r a f e w o r b i t s and t h e n r e t u r n s t o a h e l i o c e n ­
t r i c o r b i t ; ( 3 ) s t a b l e c a p t u r e s c e n a r i o s ; and ( 4 ) c o l ­
l i s i o n s c e n a r i o s i n which the d i s t a n c e of c l o s e s t ap­
p r o a c h i s l e s s t h a n t h e sum o f t h e p l a n e t - p l a n e t o i d
radii.
From o u r l i m i t e d s e t o f c a l c u l a t i o n s we f i n d
t h a t s t a b l e p r o g r a d e c a p t u r e f o r an e a r t h - l i k e p l a n e t
p
T h e l o w d y n a m i c pressure o f the solar w i n d in t h e outer h e l i o s p h e r e
Composition and Thermal Structure of Pluto's Atmosphere
Denison
Vol. 70, No. 15, April 11, 1989 EOS
P31B-15
0830H
M.
POSTER
P i c k u p of N e w b o r n I o n s w i t h
Function
a n Initial
Ring
O . CHANDLER a n d H . SMNAGAHA ( B o t h a t : NASA/MSPC,
H u n t s v i l l e , AL 35812)
J . H . WATTE, J r . ( S o u t h w e s t R e s e a r c h I n s t i t u t e , S a n
A r r t o n i o , TX 7 8 2 8 4 )
Distribution
that nitrogen,
as w e l l as methane, i s p r e s e n t on t h e
basis
o f
accumulating
observational
evidence
(Cruikshank e t a l . , Icarus 74).
Radiative equilibrium
calculations
indicate
that
such
an atmosphere
will
probably be nearly isothermal.
Parameters i m p l i c i t i n
o u r T r i t o n m o d e l a r e Rj—1600 km, p - 2 g / c m , g - 9 0 c m / s ,
albedo-0.3,
cap albedo-0.6,
cap extent-35 degrees i n
colatitude.
3
The Neptune i o n o s p h e r e h a s b e e n s t u d i e d u s i n g a
one-dimensional i c o D s p h e r i c / t h e r m o s p h e r i c model
b a s e d o n t h e c u r r e n t b e s t e s t i m a t e s o f t h e Neptune
a t m o s p h e r e , a n d knowledge o b t a i n e d from t h e s t u d i e s
of t h e ionospheres o f t h e other outer planets
( J u p i t e r , Saturn, and Uranus).
Previous studies
suggested t h a t t h e r e must b e s i g n i f i c a n t i o n l o s s
mechanisms i n t h e i o n o s p h e r e s o f t h e o u t e r p l a n e t s
in order t o explain t h e observed electron d e n s i t i e s .
I f s i m i l a r i o n l o s s e s a r e p r e s e n t i n t h e Neptune
ionosphere, the peak_electron density.would b e on
the order o f 1 0 an" instead o f 6x10 c m
which i s e x p e c t e d from a "standard" i o n o s p h e r i c
theory.
I n t h e auroral region,ghcweger, t h e peak
e l e c t r o n d e n s i t y m i g h t r e a c h 1 0 cm" .
It is
l i k e l y t h a t m u l t i - l a y e r structure observed i n t h e
l o w e r i o n o s p h e r e s o f J u p i t e r , S a t u r n , and Uranus
w i l l a l s o b e o b s e r v e d i n t h e Neptune i o n o s p h e r e .
M E M a n d t a n d C S W u (Both at: Institute for Physical Science
a n d T e c h n o l o g y , U n i v e r s i t y o f M a r y l a n d . College Park, M D
20742)
The p i c k u p p r o c e s s e s of n e w b o r n ions b y the solar wind have b e e n
studied theoretically b y m a n y a u t h o r s . It is k n o w n that w h e n t h e
intrinsic t u r b u l e n c e i n t h e s o l a r w i n d i s m o d e r a t e t h e p i c k u p
p r o c e s s m a y b e described b y a quasilinear theory which s t r e s s e s
the r e s o n a n c e condition co ± Q i - k | | v | | = 0 a n d applies very well
to the c a s e i n which t h e distribution function of the newborn ions
exhibits a b e a m along t h e a m b i e n t magnetic field. However, w h e n
the s o l a r w i n d velocity V a n d t h e interplanetary m a g n e t i c field
are perpendicular, t h e initial n e w b o r n ion distribution function is
e x p e c t e d t o b e a ring i n v e l o c i t y s p a c e .
In t h i s c a s e t h e
aforementioned r e s o n a n c e condition i s n o t satisfied. However, a
mirror like instability c a n take place [ W u et al., 19881. A s a result,
the p i c k u p p r o c e s s n o longer follows t h e u s u a l quasilinear theory.
To investigate t h e p i c k u p of n e w b o r n i o n s w i t h a n initial ring
distribution w e have u s e d a h y b r i d c o d e t o perform n u m e r i c a l
simulations. In this paper we present the results of our study. It is
s h o w n that the pickup of ring ions c a n b e speedy a n d efficient. T h e
results are also c o m p a r e d with t h o s e obtained with a n initial ringb e a m distribution.
3
-
s
PMl-0^
0830H
Neptune
1 7
1 5
0830ri
POSTER
Progress
and P r e d i c t i o n s
M D Desch and M L Kaiser (both a t Laboratory f o r
E x t r a t e r r e s t r i a l P h y s i c s , NASA/Goddard S p a c e
F l i g h t C e n t e r , G r e e n b e l t , MD 2 0 7 7 1 )
The Stability of the Distribution of Continuously Cre­
ated Newborn Comet Ions*
J. D Gaffey, Jr and C S Wu (Both at: Institute for
Physical Science and Technology, University of Mary­
land, College Park, MD 20742)
In the literature numerous authors have discussed the
amplification of waves by newborn ions in the solar
wind.
However, all of the investigations in the past
have used model distribution functions, which primarily
describe newborn ions.
In the present discussion we
make use of a distribution function derived from a
quasilinear theory.
Particular attention is placed on
the long time asymptotic distribution, which describes
recently created newborn ions and pickup ions generated
throughout the entire process.
The results of the sta­
bility analysis based on this distribution function are
reported.
Emphasis
is placed on the low-frequency
hydromagnetic modes.
POSTER
S. A. Stern (LASP/University of Colorado, Boulder, CO
80309; 303-492-7669; SPAN ORION ::ASTERN
We
consider
the radiative
tlmescale
for Triton's
atmosphere. The radiative tlmescale t
Is the characteristic
time for the atmosphere to respond to radiative balance
changes:
m(T)Cp(T)
r
1
2
This approximation assumes the atmospheric temperature is
near the effective temperature, which is not unreasonable
in the absence of a strong greenhouse. Here m is the
atmospheric mass per unit area, a is the Stefan-Boltzmann
constant, and C
is the mole fraction weighted-average
constant-pressure specific heat of an atmospheric parcel.
We take m(T)=P(T)/g
where P(T) Is the strongly temperature
dependent saturation vapor pressure and g is the surface
gravity. Specific heat data for cryogenic N2 and CH4 gases
were taken from the International Critical Tables (1933);
vapor pressure relations for CH4 and N2 were taken from
Brown and Ziegler (1980). The model was run for two
bounding cases of the surface gravity: 60 and 135 c m / s e c .
p
7
Curtis
Desch,
U830H
Radiative Timescales on Triton and Their Implications
We w i l l p r e s e n t a p r o g r e s s r e p o r t o n t h e s e a r c h
for low-frequency Neptune radio emission using
the radio astronomy experiment onboard t h e
Voyager s p a c e c r a f t .
Detection of radio signals
from Neptune would p r o v i d e t h e f i r s t
direct
evidence o f a magnetosphere surrounding t h e
planet.
Based o nmagnetic dynamo and
radiometric s c a l i n g l a w s , we expect
first
detection o f Neptune approximately 4 5 - 9 0 days
b e f o r e e n c o u n t e r , o r l a t e May 1 9 8 9 a t t h e
earliest.
Voyager i s thus entering t h e d e t e c t i o n
w i n d o w n e a r t h e t i m e o f t h e S p r i n g AGU m e e t i n g .
Using an e q u a t o r i a l f i e l d s t r e n g t h o f 0 . 5 Gauss
and t y p i c a l s o l a r w i n d c o n d i t i o n s , w e e x p e c t t h e
r a d i o s o u r c e t o h a v e a s p e c t r a l p e a k n e a r 4 0 0kHz
and e m i t s l i g h t l y more t h a n 1 0 W t o t a l p o w e r .
a n d N e s s , JGR, 9 1 , 1 1 0 0 3 , 1 9 8 6 .
GRL, 1 5 , 1 1 4 , 1 9 8 8 .
2
2
2
F o r p l a u s i b l e p o l a r c a p t e m p e r a t u r e s o f 50K a n d 62K w e
obtain visible
o p t i c a l depths at T r i t o n ' s surface o f
0 . 0 3 a n d 0 . 3 r e s p e c t i v e l y , a s s u m i n g t h a t N£ i s p r e s e n t ,
a n d 0 . 0 0 1 a n d 0 . 0 1 a s s u m i n g t h e a t m o s p h e r e i s CH4 o n l y .
POSTER
Radio Emission:
The
photochemical production a l t i t u d e i s taken t o b e
the
l e v e l i n t h e m o d e l a t m o s p h e r e w h e r e t h e UV o p t i c a l
depth due t o methane p h o t o l y s i s i s u n i t y .
We u s e a n
average photolysis cross section o f 1 . 5 x l 0 "
c m , and
an a e r o s o l mass p r o d u c t i o n r a t e , s c a l e d f r o m T i t a n , o f
3xl0"
g/cm /s.
An a e r o s o l g r o w t h a n d t r a n s p o r t c o d e
incorporating coagulation, condensation,
sedimentation
and
eddy
diffusion
uses
these
inputs
and the T-P
structure
to calculate
the vertical
distribution o f
aerosol particles
i n the atmosphere as w e l l as t h e i r
size distribution.
The v e r t i c a l o p t i c a l depth t o t h e
surface due t o s c a t t e r i n g and absorption b y the haze
particles
i s c a l c u l a t e d from t h e s e d i s t r i b u t i o n s . The
i n i t i a l r e s u l t s presented here exclude condensation and
eddy d i f f u s i o n .
P31C-0S
P3irHb
2
*This research was supported by NASA.
2
P31B-17
0830H
P31C-03
POSTER
Electron Heating at the Comet - Solar Wind Interaction
Regions
U830H
POSIER
Solar W i n d Parameters Upstream o f Neptune
L o u i s A V i l l a n u e v a , J o h n T S t e i n b e r g , R a l p h L M c N u t t , Jr, A l a n J
A S Sharma and K Papadopoulos (Both at: Department of
Physics and Astronomy, University of Maryland,
College Park, MD 20742)
The
transition
regions
at
the comet-solar
wind
interactions at both the comets Halley and GiacobiniZinner have been found to be dominated by strong lowfrequency
hydromagnetic
turbulence.
These
large
amplitude waves can heat
the solar wind plasma by
different wave-particle interaction processes.
These
fluctuations can become kinetic Alfven waves in the
presence of gradients or shear.
The observed heating
of the solar wind protons may be attributed to the
Landau damping of these modes . Another mechanism for
heating by low-frequency waves is the transit time
damping
and this
accounts
for the observed
alpha
particle heating at comet Halley.
The electron heating
by
the low frequency
turbulence
through
different
processes is studied in this paper.
The heating rate
of the electrons by the kinetic Alfven wave is smaller
than that of the protons.
Similarly the transit time
damping is more efficient for ion heating than for
electron heating.
However the combined effect of these
processes
on the electron heating
is found
to be
significantly large.
The recent data
from the comet
Halley show that the ratio of the solar to the antisolar components of the electron heat flux vary over
the
interaction
region .
These
observations are
related to the above electron heating processes.
Lazarus,
2.
A.S. Sharma, P.J. Cargill and K. Papadopoulos,
Geophys Res. Lett., L5_, 740, 1988.
3 7
K.H. Glassmeier et al., J. Geophys. Res., 9_4,
1989.
W Belcher,
(Department
o f Physics a n d
Recent measurements o f the solar w i n d density a n d velocity
made
with the V o y a g e r 2 Plasma Science instrument (PLS) have
been
extrapolated
Neptune,
from
the location o f Voyager
i n order
t o determine
2 t o the location o f
t h e solar
wind
r a m pressure
upstream o f Neptune, a n d t opredict the location o f the Neptunian
m a g n e t o p a u s e . U s i n g m e a s u r e m e n t s m a d e during t h e period i n late
1988 from day 1 7 2 hour
1 9 U T t o d a y 3 0 8 hour
Voyager 2 w a s between 3.9 A U and 2.7 A U away
15U T , when
from
Neptune,
w e obtained a m e a n r a m pressure at Neptune o f 2.1xl0~
with with a standarad deviation o f 1.6xl0~
and
lowest
l.lxlO""
11
values
o f r a m pressure
Pascal and 2.6xl0~
moment o f~ 1 G 4
sure
balance,
disstance
largest
1 3
1 2
1 2
Pascal
Pascal. T h e highest
during
this
period
were
Pascal. A s s u m i n g a magnetic dipole
t o b e 46.9R ,
the mean
with
N
magnetopause
standoff
a s t a n d a r d d e v i a t i o n o f 5.&R .
The
N
values
o f the standoff
d u r i n g t h i s p e r i o d w e r e 62.%R
N
a n d 33.5R .
N
distance
determined
T h e typical solar w i n d
particle density at N e p t u n e i s o n t h e order o f 9 . 5 x l 0
- 3
cm
- 3
. We
will continue t o update this study using t h e m o s t recent V o y a g e r 2
m e a s u r e m e n t s f r o m n o w until t h e t i m e o f t h e V o y a g e r 2 N e p t u n e
encounter.
Imke
a n d Christoph
K. Goertz,
Synchrotron
from N e p t u n e : N e p t u n e ' s m a g n e t i c field a n d electron
G e o p h y s . R e s . Lett. 1 6 , 9 7 - 1 0 0 ,
radiation
population,
1989.
>
T h i s w o r k supported i n part b y N A S A contract 9 5 7 7 8 1 a n d N A S A
Grant N G L 2 2 - 0 0 9 - 0 1 5 .
Neptune, Triton; Pluto II
(P31C)
Exhibit Hall E WED AM
M D Desch,
NASA/Goddard Space Flight Center
Presiding
P31C-01
0830H
POSTER
The N e p t u n e I o n o s p h e r e ; Comparison w i t h t h e
I o n o s p h e r e s o f J u p i t e r . S a t u r n , and Uranus
P31C-04
083UH
POSTER
P h o t o c h e m i c a l Haze o n T r i t o n
J
P31C-06
U83UH
POSTER
Results From F i v e Years o f Pluto-Charon Mutual Event Observations
(dePater a n d Goertz, 1989*) a n d using pres­
w e determine
and smallest
•dePater,
1.
and John
Center for Space Research, M.I.T., Cambridge, M A 02139)
The following results were obtained. If Triton possesses
an N2
atmosphere
near
saturation
vapor
pressure
equilibrium,
then
diurnal
variations
should
be
Inconsequential for any surface temperature consistent with
the available albedo constraints (0.2<A<0.8). If the surface
temperature exceeds - 6 5 K , then the orbital/obliquity varia­
tions predicted to occur on 50-100 year timescales (Trafton
1984) will be highly damped. However, T>65K requires
greenhouse warming (Nolan and Lunine 1988). To prevent
this result from contradicting the apparent evidence for the
onset of a major summer towards the end of the century, it
would seem that no significant greenhouse is operating. If
CH4 is the only atmospheric constituent, the radiative
tlmescale will be substantially shorter, permitting diurnal
variations If T<60K (hence less than a few torr atmospheric
pressure). For a CH4-only atmosphere, seasonal variations
will be permitted unless T>90K, which cannot
obtain
without a substantial greenhouse.
A S t a n s b e r r v . M G Tomasko a n d J I Lunine (Department
of Planetary Sciences, University o f Arizona, Tucson,
AZ 8 5 7 2 1 ; 6 0 2 - 6 2 1 - 2 2 7 2 )
As
the
Voyager
flyby
o f
Neptune's
moon
Triton
approaches,
speculation
focuses
on the ability o f
Voyager's
cameras
t o image
the surface.
We m o d e l
photochemical hazes i n T r i t o n ' s atmosphere i n order t o
address this question.
Adapting Trafton's (Icarus 58)
model
o f an atmosphere
i n thermal equilibrium
with
v o l a t i l e i c e p o l a r c a p s , we c a l c u l a t e T r i t o n ' s
surface
pressure and temperature.
We i n c l u d e t h e p o s s i b i l i t y
T h i s p a g e m a y b e freely c o p i e d .
D J T h o l e n Constitute f o r A s t r o n o m y , 2 6 8 0 W o o d l a w n D r i v e , U n i v e r s i t y
of Hawaii, Honolulu, HI 96822)
(Sponsor: A . S t e m )
H i g h - p r e c i s i o n p h o t o m e t r i c o b s e r v a t i o n s o f o v e r fifty P l u t o - C h a r o n
mutual events have b e e n obtained at M a u n a K e a Observatory b e t w e e n
1985 and 1 9 8 9 . O n l y o n e year, 1 9 9 0 , remains i n the mutual event
s e a s o n , t h u s t h e five y e a r s o f o b s e r v a t i o n s r e p r e s e n t n e a r l y c o m p l e t e
sampling o f t h e entire range o f v i e w i n g geometries t h e s y s t e m c a n
p r o d u c e d u r i n g t h e s e a s o n . M o d e l fits t o t h e o b s e r v a t i o n s h a v e p r o d u c e d
a very reliable orbit f o r Charon around Pluto. T o this point, t h e orbital
eccentricity h a s remained undetectable, with a 2 o upper limit o f 0 . 0 0 0 9 ,
and t h e orbital period o f 6 . 3 8 7 2 3 0 ± 0 . 0 0 0 0 2 1 d a y s h a s b e e n s h o w n t o
b e indistinguishable from t h e rotational period o f P l u t o , b o t h results
s u g g e s t i n g that t h e s y s t e m h a s c o m p l e t e l y tidally e v o l v e d . T h e obliquity
is approximately
1 1 8 d e g r e e s , a n d c o u p l e d w i t h P l u t o ' s orbital
eccentricity o f 0 . 2 5 , demonstrates that Pluto a n d C h a r o n e x p e r i e n c e
rather e x t r e m e s e a s o n a l e f f e c t s .
The diameters o f both bodies have also b e e n determined t o high
accuracy, Pluto being 2 2 8 5 ± 4 0 k m and Charon being 1 1 9 0 ± 4 0 k m i n
diameter. K e p l e r ' s Third L a w c a n b e e m p l o y e d t o c o m p u t e a s y s t e m
m a s s o f o n l y 0 . 0 0 2 6 Earth m a s s e s . T h i s result, c o m b i n e d w i t h t h e
v o l u m e s o f Pluto a n d Charon c o m p u t e d from their diameters ( a s s u m i n g
spherical s h a p e s f o r both objects), y i e l d s a m e a n density f o r t h e s y s t e m
o f 2 . 0 6 5 ± 0 . 0 4 7 g m cm" , w h i c h indicates that Pluto i s substantially
rockier than t h e i c y satellites o f t h e other outer planets. T h e rock
c o m p o n e n t represents about 7 0 percent o f the s y s t e m b y m a s s , and about
5 0 percent b y volume.
3
A l b e d o m a p p i n g efforts h a v e s h o w n Charon t o b e noticeably l e s s
reflective a n d m o r e neutral i n c o l o r than P l u t o , w h i l e P l u t o s h o w s a h i g h
contrast surface w i t h bright, neutrally c o l o r e d polar c a p s a n d a m u c h
darker a n d r e d d e r e q u a t o r i a l r e g i o n . S u b s t a n t i a l v a r i e g a t i o n i n l o n g i t u d e
m u s t also b e present t o account f o r t h e rotational lightcurve variation o f
over 0.3 magnitude.
385
EOS Vol. 70, No. 15, April 11, 1989
P31C-07
0830H
Topographic
POSTER
Relaxation
on
Ice-Covered
Worlds:
Application to Pluto II.
R L Marcialis ( L u n a r & P l a n e t a r y L a b o r a t o r y , U n i v . of Arizona,
Tucson, A Z 85721; ( 6 0 2 ) 6 2 1 - 6 9 5 0
(Sponsor: Larry A . Lebofsky)
The
subject of t o p o g r a p h i c relaxation o n P l u t o was addressed
by M a r c i a l i s ( 1 9 8 5 ) .
R e c e n t l y , m o r e realistic m o d e l s o f P l u t o ' s
interior h a v e a p p e a r e d a s a result o f t h e m u t u a l event a n a l y s i s ,
allowing t h e q u e s t i o n t o b e r e a d d r e s s e d . S i n c e P l u t o ' s b u l k d e n ­
sity is a r o u n d 2 g m c m
- 3
, t h e m e t h a n e l i t h o s p h e r e p r o b a b l y is
m u c h t h i n n e r t h a n initially a s s u m e d . T h i s drastically alters t h e
conclusions o f o u r earlier s t u d y .
called the ion cushion by 0. Vaisberg and co-workers.
Venus
has a
magnetic
tail
formed
from
the
interplanetary magnetic
field
draped
around the
planet.
Mars too has a magnetic tail but there is
much debate as to whether the field is induced or
intrinsic to the planet.
The Phobos spacecraft
should be able to answer this question.
In its
initial 77 hour orbit on February 1, 1989 the
spacecraft came as close as 860 km to the surface of
Mars. As it crossed the subsolar region, it saw a 30
nT steady field but near periapsis (1713 UT) the
field was less than half this size and turbulent.
Above the nightside of the planet reversals of the
direction of the magnetic field are observed. While
these initial results alone are not sufficient to
settle the debate, we expect that the measurements
from the 4 more highly-elliptical-phase orbits and
those in the more nearly circular Phobos phase orbits
will be able to settle many of the controversies
surrounding the solar wind interaction with Mars.
A n e m p i r i c a l t e m p e r a t u r e - v i s c o s i t y l a w f o r w a t e r ice is r e s t a t e d
in t e r m s o f m e l t i n g t e m p e r a t u r e a n d h a s b e e n a s s u m e d t o h o l d for
m e t h a n e . Using the approach of Parmentier a n d H e a d ( 1 9 7 9 ) a n d
t h e interior m o d e l s o f M c K i n n o n & M u e l l e r ( 1 9 8 8 ) a n d S i m o n e l l i
et al. ( 1 9 8 9 ) , w e n o w find t h a t n o t o n l y c a n significant lateral
t o p o g r a p h y persist o n P l u t o , b u t t h e w a v e l e n g t h scale o f such fea­
P32A-02
1400H
First Results o f the Ion Composition in the Martian
Magnetosphere
tures is e x t r e m e l y sensitive t o t h e a c t u a l thickness o f t h e m e t h a n e
layer. T h i s result t h e r e f o r e l e a d s u s t o call for e x p e r i m e n t a l d a t a
o n t h e r h e o l o g y o f m e t h a n e ice in t h e relevant t e m p e r a t u r e r a n g e
of 5 0 - 6 0 ° K .
On
a g l o b a l scale, P l u t o ' s figure is still f o u n d t o b e essentially
R . Lundin. H . B o r g , B . Hultqvist (Swedish Institute o f S p a c e
Physics)
Zakharov, A . , N . Pissarenko, E . M . Dubinin (Space Research
Institute, U S S R A c a d e m y o f Sciences, M o s c o w , U S S R )
R . Pellinen, I. Liede, H . K o s k i n e n (Finnish Meteorological
Institute, Helsinki, Finland)
h y d r o s t a t i c , w h i c h i m p l i e s t h a t o n l y 2 m i l l i m a g o f its ( ~ 3 0 0 m i l limag) lightcurve m a y b e attributed t o shape.
T h i s result is
i n d e p e n d e n t o f r h e o l o g y a n d interior m o d e l a s s u m e d , for all b u t
t h e m o s t p a t h o l o g i c a l cases.
References:
M a r c i a l i s , R . L . ( 1 9 8 5 ) Bull.
Amer.
Astron.
Soc. 1 7 , 7 1 5 .
P a r m e n t i e r , E . M . a n d H e a d , J . W . ( 1 9 8 1 ) Icarus
Simonelli, D . P . , et al. ( 1 9 8 9 ) Icarus,
0830H
MHD Models of the Ionospheres of Venus and Mars
PUSitR
i4i5ri
Dayside Pickup Ion Precipitation at Venus and Mars:
Spatial Distributions and Energy Deposition
J G Luhmann (IGPP, University of California, Los
Angeles, CA 90024)
J U Kozyra
(Space
Physical
Research Laboratory,
University of Michigan, Ann Arbor, MI 48109)
78712; 5 1 2 - 4 7 1 - 3 4 6 6 )
Reflectance spectra of Pluto-Charon in the 0.5 to 1.0 jzm range
have been obtained spanning 1983 to 1988. T h e spectra cover the
full 6.4 day rotational period. M u t u a l event spectra were obtained in
1987 and 1988. Further observations are scheduled for 1989. There is
no evidence for significant variation of the CH4 band strengths with
rotational phase. This implies that the CH4 bands arise from Pluto's
Recent results on the surface
albedo distribution in the Pluto-Charon system derived from mutual
event observations are being used to model the contributions of frost
and gas to the observed spectra. Mutual event spectra are being used
to produce separate spectra of Charon and portions of the surface of
Pluto. In particular, polar region spectra m a y reveal the composition
If Pluto's atmospheric bulk is increasing as
the system approaches perihelion, changes in the CH4 band strengths
with time may b e measurable.
Mars-Venus Comparisons:
Atmospheres, Ionospheres, and
Solar-Wind Interactions I
(P32A)
323 WED PM
J A Slavin,
NASA/Goddard Space Flight Center
Presiding
IWIlED
The Solar Wind Interaction with Venus and Mars
C T Russell and J G Luhmann
(both at: Institute of
Geophysics and Planetary Physics, Los Angeles, CA
90024-1567)
W
Riedler and K Schwingenschuh
Institute, Graz, Austria)
(Space
Research
Both Venus and Mars deflect almost completely the
supersonic solar wind generating strong magnetosonic
bow shocks in front of these planets. In the case of
Venus, the magnetized solar wind plasma is convected
against the planetary ionosphere creating a magnetic
barrier which both puts a lid on the ionosphere and
shields the ionosphere from the solar wind flow. At
Mars an analogous region is found which has been
386
+
H. Shlnaaawa (NASA/MSFC, Huntsville, A L 35812)
(Sponsor: A l a n Stern)
1330H
T h e solar w i n d interacts almost directly with theupper atmospheres
and ionospheres o f planets such as V e n u s and Mars, which possess
only w e a k , o r nonexistent, intrinsic magnetic fields. T h e upper
a t m o s p h e r e s a n d i o n o s p h e r e s o f V e n u s a n d M a r s a r e k n o w n f r o m in
situ m e a s u r e m e n t s t o b e v e r y s i m i l a r i n t h e i r n e u t r a l a n d i o n
compositions.
F o r e x a m p l e , t h e m a j o r neutral s p e c i e s o n both
planets i s C O 2 and themajor i o n s p e c i e s is 0 2 . H o w e v e r , there are
also significant differences between the t w oplanets relevant tothe
solar w i n d interaction, such a s differences i n the gravitational
a c c e l e r a t i o n , i n t h e h e l i o c e n t r i c d i s t a n c e ( i . e . , s o l a r flux d i f f e r e n c e s ) ,
and p o s s i b l y i n t h epresence o f a n intrinsic magnetic field.
Observational data a n d theoretical m o d e l s will b e r e v i e w e d a n d
used to examine the behavior o f the ionospheric densities, i o n
v e l o c i t i e s , a n d m a g n e t i c fields at V e n u s and Mars a s they respond t o
varying solar w i n d conditions. F o r e x a m p l e , the ionosphere o f
Venus is k n o w n to b e permeated b y large-scale magnetic fields
w h e n t h e solar w i n d d y n a m i c pressure i s high, w h e r e a s itis free o f
such fields for conditions o fl o w solar w i n d dynamic pressure O n
the o t h e r h a n d , it i s l i k e l y that l a r g e - s c a l e m a g n e t i c fields are a l m o s t
always present in theionosphere o f Mars. T h e average ionospheric
plasma velocity i s d o w n w a r d o n both planets for magnetized
conditions, although it i s s o m e w h a t larger atV e n u s than at Mars.
T h e p l a s m a carries m a g n e t i c flux from the magnetosheath d o w n
into t h e i o n o s p h e r e . O h m i c dissipation o f the currents responsible
for t h e m a g n e t i c field takes p l a c e d e e p i n t h e i o n o s p h e r e s o f both
planets.
4 7 , 100-111.
S R Sawyer ( A s t r o n o m y Department, University of Texas, Austin, T X
P32A-01
and Mars
T. E. C r a v e n s ( D e p t . o f P h y s i c s a n d A s t r o n o m y , T h e U n i v e r s i t y o f
Kansas, Lawrence, K S 66045; 913-864-3610; S P A N
KUPHSX::CRAVENS)
P3ZA-U/
in press.
Pluto-Charon
of Pluto's polar caps.
IiWITED
Preliminary results o n the solar wind interaction with the Martian
m o o n Phobos will also b e discussed.
Reflectance Spectroscopy of the Surface and Atmosphere of
atmosphere and not a surface frost.
1515H
This report will review the first results in the Martian magnetosphere
from the three-dimensional ion composition experiment A S P E R A o n
the Soviet P h o b o s - 2 spacecraft. O f particular interest is the solar wind
interaction with the upper ionosphere at Mars and the subsequent
escape o f ionospheric plasma.
P32A-03
P31L-U8
P32A-06
C o m p a r i s o n o f the I o n o s p h e r i c R e s p o n s e t o the S o l a r W i n d at V e n u s
The
fluxes
and energy
spectra
of picked-up
planetary 0* ions incident on the dayside atmospheres
of Venus and Mars are calculated using the neutral
exosphere models of Nagy and Cravens (1988) and the
Spreiter and Stahara (1980) gasdynamic model of the
magnetosheath electric and magnetic field.
Cold
(-10 eV) 0* ions are launched from hemispherical grids
of starting points covering the daysides of the
planets and their trajectories are followed until
they either impact the dayside "obstacle" or cross
the
terminator
plane.
The
impacting,
or
precipitating, ion fluxes are weighted according to
the altitude of the hemispherical starting point grid
in a manner consistent with the exosphere density
models and the local photoion production rate.
"Maps" of precipitating ion number flux and energy
flux show the asymmetrical distribution of dayside
heating expected from this source which is unique to
the weakly magnetized planets.
P32A-04
1430rl
III/TIED
Solar W i n d Interaction w i t h Mars
F S Johnson a n d W B Hanson (University of Texas a t Dallas,
Richardson T X 75083-0688; 2 1 4 - ^ 9 0 - 2 8 2 0 )
Retarding P o t e n t i a l Analyzers carried o n t h e Viking Landers
have provided data that show that t h e ionospheric plasma
pressure a n d solar w i n d p l a s m a pressure above t h e ionopause are
insufficient t o b a l a n c e t h e i m p a c t pressure of t h e solar wind.
T h i s i n d i c a t e s t h e p r e s e n c e o f m a g n e t i c field, w h i c h
might be
either intrinsic o r induced.
T h e principal evidence that t h e
m a g n e t i c field i s i n t r i n s i c c o m e s f r o m t h e p o s i t i o n o f t h e s h o c k
front, w h i c h i m p l i e s t h e e x i s t e n c e o f a relatively larger obstacle
to t h e solar w i n d flow t h a n exists i n t h e case o f V e n u s . T h e
only altitude i n t h e Viking data o n electrons that
appears
suitable for identification a s a m a g n e t o p a u s e is t h e ionopause
near 3 0 0 k m , w h i c h is t o o l o w t o p r o v i d e t h e larger obstacle size
needed t o account for t h e observed location o f t h e shock front.
T h e observed l o c a t i o n o f t h e shock front should therefore b e
regarded a s equally anomalous fort h e t w o hypotheses for t h e
magnetic
field,
induced a n d intrinsic.
T h eViking 1 data
indicate t h a t t h e shock front w a s quasi parallel.
T h e r e is also
evidence i n t h e Viking 1 data that t h e extreme ultraviolet
airglow produced observable effects a n d corresponded t o a n
albedo o f t h e order o f 1%. B e l o w 10,000 k m , light from t h e
planet could enter t h e R P A a n d cause photo currents; sunlight
could n o t enter t h e instrument.
Part of t h e evidence for t h e
photocurrents is that t h ecollector current changed when t h e
potential o no n e o f t h e internal grids o f t h e R P A w a s changed
under conditions where this could only influence electrons o f
internal origin.
T h e remainder of t h e evidence comes in t h e
retarding potential scans w h e n t h e negative retarding potential
barrier fell b e l o w a b o u t 1 0 V ; t h e profile o f t h e o b s e r v e d c u r v e
indicates that electrons o finternal origin with energies u p t o 10
eV escaped during this part o f t h e sweep.
T h i s p a g e m a y b e freely
copied.
Trie ionospheres of Venus and Mars are discussed
based on ionospheric MHD models developed by
Shinagawa and Cravens (1988) for Venus, and by
Shinagawa and Cravens (1989) for Mars. The models
are currently being improved in order to study
various processes in more detail. Some new results
are presented and discussed.
P32AHJ8
The
15G0H
Transonic Nightward Flow in the Venus Ionosphere and
Implications for Mars
L Fu and K L Miller (Both at CASS, Utah State University, Logan, UT
84322-4405; 801-750-3437)
The nightward flow of ions in the Venus ionosphere has been shown
by measurements of the Pioneer Venus Retarding Potential Analyzer
(RPA) to be supersonic with respect to the neutral atmosphere in the
vicinity of the terminator. The axially-syrnrnetric flow of ions at high
velocities is possible on Venus, and presumably on other unmagnetized
planets. W e discuss characteristics of the ion flow in the Venus
ionosphere, as well as the possibility of similar ion velocities in the
Martian environment. Ion velocity at Venus has been modelled by
Elphic et al. (1984) using the momentum equation, giving results that
were consistent with measurements. If the continuity equation is
included in a one-dimensional calculation, it can be shown that
neglecting collisions and gradients in temperature results in a
maximum velocity equal to the thermal velocity. We have extended
the calculations of Elphic et al. to include continuity as well as
momentum. Either a gradient in temperature, collisions, or both are
required in our calculations for the ion velocity to accelerate through
the critical point to velocities greater than the thermal velocity.
Results of our calculation using Pioneer Venus measurements compare
favorably with measurements by the RPA. W e will discuss differences
between measured and modelled ion velocities in terms of the
limitations of a one-dimensional calculation. W e will also discuss
our calculations of ion velocities using current knowledge of the
Martian ionosphere.
Elphic, R. C , Mayr, H. G., Theis, R. F., Brace, L. H., Miller, K. L.,
Knudsen, W . C , Nightward ion flow in the Venus ionosphere:
implications of momentum balance. Geophys. Res. Lett. 11:1007-1010.
1984
P32A-09 1615H
R e s p o n s e o f t h e Venus I o n o t a i l t o Changes i n t h e S o l a r
EUV F l u x , S o l a r Wind P r e s s u r e and t h e IMF:
I m p l i c a t i o n s f o r Mars
L H B r a c e and R F T h e i s
Flight
(Both a t :
NASA/Goddard S p a c e
Center, Laboratory f o r Atmospheres, G r e e n b e l t ,
MD 2 0 7 7 1 ; 3 0 1 - 2 8 6 - 8 5 7 5 )
J G Luhmann (IGPP/UCLA, L o s A n g e l e s , CA 9 0 0 2 4 ; 2 1 3 825-1245)
J D M i h a l o v (NASA/Ames R e s e a r c h C e n t e r , M o f f e t t F i e l d ,
CA
94035; 415-694-5516)
I o n o s p h e r e i n s t r u m e n t s on t h e P i o n e e r Venus O r b i t e r
(PVO) h a v e shown t h a t t h e n i g h t s i d e i o n o s p h e r e o f Venus
e x t e n d s s e v e r a l t h o u s a n d km downstream from t h e p l a n e t ,
o f t e n e x h i b i t i n g c o m e t - l i k e t a i l r a y s , s t r e a m e r s , and
filaments.
T h i s r e g i o n , known a s t h e Venus i o n o t a i l ,
i s h i g h l y dynamic.
P r e v i o u s work h a s shown t h a t t h e
i o n o t a i l plasma o r i g i n a t e s i n t h e i o n o s p h e r e .
Most o f
t h e i o n o t a i l e l e c t r o n s a r e c o o l , b u t t h e i o n s have been
a c c e l e r a t e d t o v e l o c i t i e s somewhat g r e a t e r t h a n t h e
Vol. 70, No. 15, April 11, 1989 EOS
p l a n e t a r y e s c a p e v e l o c i t y by s o l a r wind i n t e r a c t i o n
processes not currently understood.
We h a v e i n v e s t i ­
gated the response o f the i o n o t a i l e l e c t r o n density t o
s o l a r v a r i a t i o n s t h a t might be expected t o i n f l u e n c e
i t ; s p e c i f i c a l l y t h e s o l a r wind d y n a m i c p r e s s u r e , s o l a r
e x t r e m e u l t r a v i o l e t ( e u v ) f l u x , and t h e a m p l i t u d e and
o r i e n t a t i o n o f the i n t e r p l a n e t a r y magnetic f i e l d a t
Venus.
A l l o f t h e s e p a r a m e t e r s a r e m e a s u r e d by PVO
instruments.
We f i n d t h a t t h e e u v ( p r i m a r i l y s o l a r
c y c l e v a r i a t i o n s ) e x e r t s primary c o n t r o l over t h e
i o n o t a i l causing i t s d e n s i t y t o be l a r g e r a t s o l a r
maximum.
T h e s o l a r wind d y n a m i c p r e s s u r e c a u s e s m a j o r
o r b i t t o o r b i t v a r i a t i o n s in the i o n o t a i l d e n s i t y , with
t h e t a i l n e a r l y d i s a p p e a r i n g a t h i g h p r e s s u r e s and
n e a r l y f i l l i n g up w i t h p l a s m a a t l o w e r p r e s s u r e s . T h e
i n t e r p l a n e t a r y m a g n e t i c f i e l d e x e r t s a much s m a l l e r
i n f l u e n c e on t h e i o n o t a i l , i f a n y . T h e i m p l i c a t i o n s o f
t h i s behavior for s o l a r wind-ionosphere interactions a t
Mars w i l l b e d i s c u s s e d .
P34WU
1630H
Plasma T e m p e r a t u r e s i n t h e D a y s i d e I o n o s p h e r e s
o f Mars a n d Venus a n d T h e i r R e s p o n s e t o t h e
Solar Cycle
A. J . K l i o r e , G. L i n d a l , L . F . M u l l e n , and D.
N.
Sweetnam
(Jet
Propulsion
Laboratory,
C a l i f o r n i a I n s t i t u t e o f Technology, Pasadena,
CA 9 1 1 0 9 )
Radio o c c u l t a t i o n measurements o f t h e e l e c t r o n
d e n s i t y v e r t i c a l p r o f i l e s on t h e d a y s i d e o f
Venus h a v e b e e n p e r f o r m e d w i t h t h e P i o n e e r
Venus o r b i t e r from 1 9 7 9 t o t h e p r e s e n t .
This
has a l l o w e d t h e e f f e c t s o f v a r y i n g s o l a r input
on t h e s t r u c t u r e o f t h e t o p s i d e i o n o s p h e r e t o
be o b s e r v e d from t h e maximum t o t h e minimum o f
S o l a r C y c l e 2 1 . I n 1 9 7 1 , n e a r s o l a r maximum,
a . substantial
number o f r a d i o
occultation
m e a s u r e m e n t s o f t h e d a y s i d e i o n o s p h e r e o f Mars
were o b t a i n e d w i t h t h e M a r i n e r 9 o r b i t e r , a n d
l a t e r , from 1 9 7 6 t o 1 9 7 8 , n e a r s o l a r minimum,
m e a s u r e m e n t s were a g a i n made w i t h t h e V i k i n g 1
and
2 orbiters.
From e a c h m e a s u r e m e n t , a
v e r t i c a l p r o f i l e o f t h e plasma s c a l e
height
can be o b t a i n e d ,
and b y assuming t h a t t h e
topside
ionosphere
is
in
diffusive
e q u i l i b r i u m , t h e i o n and e l e c t r o n t e m p e r a t u r e s
can be e s t i m a t e d .
I t i s f o u n d t h a t on Venus
the plasma s c a l e h e i g h t d e c r e a s e s by about a
f a c t o r o f 2 from s o l a r maximum t o minimum,
indicating
a
threefold
reduction
in
the
electron temperature.
On M a r s , a p p r o x i m a t e l y
t h e same p e r c e n t a g e
decrease
i n t h e plasma
s c a l e h e i g h t i s o b s e r v e d from s o l a r maximum t o
minimum.
Mars-Venus Comparisons:
Atmospheres, Ionospheres, and
Solar-Wind Interactions II
(P41A)
310 THURS AM
A Nagy, Univ of Michigan
Presiding
main m i s s i o n o r d i f f e r e n t s o l a r w i n d i n t e r a c t i o n s a r e
required
to
produce
the
distinctive
topside
c h a r a c t e r i s t i c s observed in the subsolar region.
(*
V i k i n g d a t a were p r o v i d e d
Sweetnam and G. L i n d a l , J P L . )
P41A-02
courtesy
o f D.
msH
Radio Scintillation M e a s u r e m e n t s o f the Solar W i n d
With theIonospheres o f V e n u s and Mars
Interaction
R. W o o . A . J . K l i o r e a n d L . M u l l e n ( A l l at: J e t P r o p u l s i o n
Laboratory, California Institute o f T e c h n o l o g y , Pasadena, C A
91109)
J. G . L u h m a n n ( I n s t i t u t e o f G e o p h y s i c s a n d P l a n e t a r y P h y s i c s ,
University o f California, L o s A n g e l e s , C A 9 0 0 2 4 )
In situ m e a s u r e m e n t s o f t h e i o n o s p h e r e o f V e n u s b y P i o n e e r
V e n u s Orbiter ( P V O ) h a v e revealed the presence o f large-scale
magnetic fields w h e n the solar w i n d d y n a m i c pressure e x c e e d s the
i o n o s p h e r i c p l a s m a p r e s s u r e . T h e s e fields o c c u r m o s t
frequendy
in t h e s u b s o l a r r e g i o n . It h a s r e c e n t l y b e e n f o u n d that t h e s e l a r g e scale magnetic fields are accompanied b y disturbed plasma
representing electron density irregularities i n t h e topside
ionosphere
Q G R . 9.4, 1 4 7 3 , 1989).
Furthermore,
these
irregularities cause radio scintillations w h i c h c a n b e remotely
detected during radio occultaion measurements. Like large-scale
magnetic fields, radio scintillations are, therefore, another
manifestation o f h i g h - d y n a m i c solar w i n d interaction with the
ionosphere.
W e have initiated a radio scintillation investigation o f the
ionosphere o f V e n u s based o n P V O radio
occultation
m e a s u r e m e n t s that h a v e b e e n c o n d u c t e d s i n c e 1 9 7 9 . R e s u l t s
pertaining to the variation o f h i g h - d y n a m i c solar w i n d interaction
with solar zenith angle and solar c y c l e will b e presented. T h e radio
o c c u l t a t i o n r e s u l t s c o m p l e m e n t t h e P V O in situ m e a s u r e m e n t s
b e c a u s e t h e latter a r e o n l y a v a i l a b l e f o r a p e r i o d o f t w o y e a r s
during solar m a x i m u m .
Measurements during solar cycle
m i n i m u m are especially interesting b e c a u s e conditions at V e n u s
during this t i m e are t h o u g h t t o b e similar t o those at M a r s .
P41A-05
The
1000H
T h e r m o s p h e r e s o f Venus and M a r s : A C o m p a r i s o n
S W BOUGHER ( L u n a r a n d P l a n e t a r y L a b . , U . o f A r i z o n a ,
T u c s o n , A Z 8 5 7 2 1 ) , a n d R G ROBLE ( N a t i o n a l C e n t e r f o r
A t m o s p h e r i c R e s e a r c h , B o u l d e r , CO 8 0 3 0 7 - 3 0 0 0 )
The NCAR t e r r e s t r i a l o n e - d i m e n s i o n a l NLTE r a d i a t i v e
transfer
model and the Thermospheric General
C i r c u l a t i o n M o d e l (TGCM) h a v e b e e n r e c e n t l y a d a p t e d t o
t h e t h e r m o s p h e r e s o f V e n u s a n d Mars
f o r s o l a r minimum
( F 1 0 . 7 - 6 7 ) a n d maximum ( F 1 0 . 7 - 2 0 0 ) c o n d i t i o n s .
The
former
global
mean
heat
balance
code
provides
inputs
and i n i t i a l i z a t i o n s
for i t s corresponding
circulation
model.
Self-consistently
c a l c u l a t e d TGCM
neutral composition,
t e m p e r a t u r e s , and winds
are
g i v e n f o r e a c h p l a n e t on 2 4 c o n s t a n t
pressure l e v e l s
a b o v e 1 0 0 km o n a 5 x 5 d e g r e e
latitude-longitude
grid. Inputs
include
internally
calculated solar
EUV,
UV,
and
IR h e a t i n g ,
a n d n e t CO
p h o t o d i s s o c i a t i o n over the
globe.
G l o b a l mean CO
cooling i s used to drive a
3-D p a r a m e t e r i z a t i o n f o r
total cooling.
We p r e s e n t c a l c u l a t i o n s u s i n g t h e a b o v e
standard fluxes
f o r both planets enabling a comparison
of
thermospheric structure
and c i r c u l a t i o n a t
Equinox.
Results
indicate
that planetary
rotation
significantly modifies
thermospheric
winds,
giving
strong
differences
between Venus
and
Mars.
Adiabatic heating
a n d c o o l i n g a r e a l s o more e f f e c t i v e
on M a r s
where
the planetary
radius i s smaller.
No
n i g h t s i d e "cryosphere", of
the type
observed
on
Venus, i s p r e d i c t e d
f o r Mars.
Model
and o b s e r v e d
a t o m i c - 0 a r e g r e a t l y d e p l e t e d on Mars compared t o
Venus.
The importance of fundamental p l a n e t a r y
parameters
( e . g . gravity,
sun-planet
distance,
r o t a t i o n , magnetic f i e l d , e t c . ) in affecting v e r t i c a l
structure
and d i u r n a l d e n s i t y ,
temperature
and w i n d
distributions
will
a l s o be discussed. F i n a l l y , the
TGCM
m o d e l h e a t b a l a n c e s m a i n t a i n a m o d e s t Mars s o l a r
activity variation
in exospheric
temperatures ( 3 1 0 190 K ) , w h i l e t h a t f o r Venus
is
a factor
of
two
s m a l l e r ( 3 0 0 - 2 3 5 K). T h i s
response
is
somewhat
different
than that predicted assuming r a d i a t i v e
equilibrium, y e t i t i s consistent with observations.
T h e results o f a similar investigation b a s e d o n radio occcultation
measurements o f Mars will b e presented and compared with those
of Venus.
r^tlA-U/
iU30ri
InViitU
Mars and V e n u s A t m o s p h e r i c E v o l u t i o n
P41A-U3
09UUH
itWIlHu
Mars and Venus Compared : The Neutral Thermospheres and Exospheres.
T Owen ( D e p a r t m e n t
o f E a r t h and S p a c e S c i e n c e s , S t a t e
U n i v e r s i t y o f New Y o r k , S t o n y
B r o o k , NY 1 1 7 9 4 - 2 1 0 0 ;
516-632-8188)
A I F Stewart (Laboratory for Atmospheric and Space Physics.University of
Colorado, Boulder, CO 80309-0392; (303)-492-8689)
I t i s not yet p o s s i b l e to present a
s i n g l e model
t h a t w i l l e x p l a i n t h e v o l a t i l e a b u n d a n c e s on t h e t h r e e
inner planets with
substantial
atmospheres.
Instead
we a r e f a c e d w i t h t h e u n e a s y
feeling
that
each body
has s u f f e r e d a unique f o r m a t i o n h i s t o r y
whose d e t a i l s
are s t i l l u n c l e a r .
It
remains
attractive to try to
account f o r the t o t a l
volatile
inventory
on
each
p l a n e t a s an
outcome
of
the l a t e
accretion
of
v o l a t i l e - r i c h m e t e o r i t e s and
comets,
in
different
p r o p o r t i o n s and s e q u e n c e s .
A l a r g e , low-temperature
i c y p l a n e t e s i m a l c o u l d be r e s p o n s i b l e f o r t h e p e c u l i a r
heavy n o b l e g a s abundance
pattern
on V e n u s ,
while
l a r g e impacts have a p p a r e n t l y d r a m a t i c a l l y reduced t h e
m a s s o f t h e M a r t i a n a t m o s p h e r e and p r o b a b l y e l i m i n a t e d
the i n i t i a l inventory
on t h e E a r t h .
V e n u s seems t o
show t h e e f f e c t o f an a d d i t i o n a l c o n t r i b u t i o n from t h e
s o l a r wind.
Subsequent e v o l u t i o n
h a s been dominated
by s o l a r d i s t a n c e and p l a n e t a r y m a s s , b u t w i t h i n t h e s e
The difference in the O and CO abundances does not greatly affect the
two m a j o r c o n s t r a i n t s , numerous p u z z l e s
remain
t o be
major ion composition, but it may have an important affect on the odd s o l v e d .
Among t h e s e
is
t h e q u e s t i o n o f how much CO
nitrogen chemistry. On Venus, N dominates NO because N( D) (which forms
r e m a i n s on M a r s ,
i n what
form,
deposited
b y what
NO upon reaction with CO2) is rapidly quenched by O and by CO. The p r o c e s s e s ?
An e s p e c i a l l y
intriguing
problem
for
detection of NO by Viking suggests that Mars is NO-dominated, implying that
exobiologists i s the quantity
and l i f e t i m e o f l i q u i d
the relative lack of O and CO critically reduces the quenching of N(2D). One
w a t e r on t h e e a r l y M a r t i a n
surface.
New s t u d i e s o f
consequence of this might be that on Mars the radiative recombination of NO
t h e a b u n d a n c e o f d e u t e r i u m on Mars p r o v i d e
additional
may not provide the admirable tracer of nightside thermospheric winds that it
support f o r geomorphological
evidence
suggesting
a
does on Venus.
warm, w e t e a r l y c l i m a t e t h a t
could
have
allowed the
The neutral exospheres of the two planets should differ greatly in
p r e s e n c e o f open b o d i e s o f w a t e r .
density. On Venus the dissociative recombination of 0 2 near the exobase
provides a substantial population of hot oxygen atoms extending up to about
4300 km, and lesser coronae of C and N also exist. The hot O atoms promote
the escape of H, although most of the escape flux of H originates on the night
P41A-08
1100H M I l t D
side where abundant cold-trapped H atoms charge exchange with hot
plasmaspheric protons. On Mars the source of hot atoms is weaker, and most
Atmosphere-surface interactions o n Venus a n d Mars
of them escape from Mars' weaker gravitational field, leaving a much reduced
The most striking difference between the thermospheres of Mars and
Venus is the much smaller abundance of O and CO relative to CO2 on Mars
(1-2% on Mars, 10-15% on Venus, near the ionospheric peak). Other major
properties such as the exospheric temperature and the theoretical wind
speeds are more remarkable for their similarities than their differences. Given
the comparable wind speeds, the depletion of the dissociation products of
CO2 on Mars appears to derive partly from the reduced solar fluxes and partly
from the increased flux divergences (estimated by the ratio of scale height to
planetary radius). Details of the circulation differ; on Venus the subsolar
upwelling is balanced by a downflow localized near 2 a.m. whereas on Mars
the upwelling is predicted to occur at 3 p.m., the downflow at 9 p.m., and a
peculiarly violent overturning is predicted just after sunrise. The case for
vigorous vertical eddy mixing on both planets to explain the scarcity of O and
CO is less compelling in light of the strong general circulations. On the other
hand, there is clear evidence of gravity-wave activity in the Viking entry
science data on Mars and in mass spectrometer data on Venus.
2
P41A-01
083UH
A P o s t - P i o n e e r Venus Reassessment o f t h e Dayside
I o n o s p h e r e o f Mars a s O b s e r v e d b y R a d i o O c c u l t a t i o n
Methods
+
M Hantsch ( U n i v e r s i t y o f G r a z , G r a z , A u s t r i a )
J G Luhmann (IGPP,
University
o f C a l i f o r n i a , Los
A n g e l e s , CA 9 0 0 2 4 )
A J K l i o r e ( J e t P r o p u l s i o n L a b o r a t o r y , P a s a d e n a , CA
90011)
The
dayside
altitude
profiles
of the electron
density in the Martian ionosphere obtained over a
decade ago w i t h t h e r a d i o o c c u l t a t i o n e x p e r i m e n t s on
t h e M a r i n e r 9 and V i k i n g 1 a n d 2 s p a c e c r a f t * a r e
collectively
reanalyzed
t o determine
the global
c h a r a c t e r i s t i c s o f t h e daytime ionosphere o f Mars.
The p r e s e n t s t u d y f o c u s e s on t h e c o m p a r i s o n w i t h
analogous p r o f i l e s o b t a i n e d a t Venus d u r i n g s o l a r
minimum c o n d i t i o n s when t h e s o l a r w i n d i n t e r a c t i o n
e f f e c t s on t h e i o n o s p h e r e s h o u l d b e m o s t l i k e t h o s e
at Mars.
C o n t r a s t s b e t w e e n t h e p r o f i l e s a t t h e two
p l a n e t s i n c l u d e an a l m o s t c o n s t a n t p e a k a l t i t u d e a t
Venus r e l a t i v e t o t h a t a t M a r s , w h i c h moves upward a s
the s o l a r z e n i t h a n g l e i n c r e a s e s , and a t o p s i d e s c a l e
h e i g h t a t Mars w h i c h i n c r e a s e s w i t h s o l a r
zenith
angle a t s o l a r z e n i t h angles near 4 5 ° while t h a t a t
Venus c o n s i s t e n t l y d e c r e a s e s w i t h i n c r e a s i n g s o l a r
zenith angle.
These d i f f e r e n c e s i n the ionospheres
r e f l e c t d i f f e r e n c e s i n the n e u t r a l atmospheres o f the
two p l a n e t s , b u t t h e y may a l s o r e f l e c t d i f f e r e n c e s i n
t h e i r s o l a r wind i n t e r a c t i o n s .
For example, t h e
r o t a t i o n o f Mars c o u l d p r o d u c e a more s u b s t a n t i a l
ionosphere near t h e t e r m i n a t o r and thus e x p l a i n t h e
peak a l t i t u d e b e h a v i o r , b u t e i t h e r t h e p r e s e n c e o f
dust i n the M a r t i a n atmosphere during the Mariner 9
corona. The reduced gravity on Mars also allows thermal Jeans escape of H
from the dayside; this is the dominant H escape mechanism.
R o n a l d P r i n n ( M I T 54-1824, C a m b r i d g e , M A )
B r u c e F e g l e y ( M I T 54-1822, C a m b r i d g e , M A )
Atmosphere-surface
PIlA-m
0930H
LWITtD
portant
interactions
o n Venus a n d Mars
determinants o f their atmospheric
are i m ­
composition.
These
interactions o n t h e present-day planets have s o m e obvious
The
Neutral
T h e r m o s p h e r e s o f Mars & Venus
ilarities a n d s o m e equally o b v i o u s differences.
O n both
sim­
planets
p h o t o c h e m i c a l r e a c t i o n s t e n d t o p r o d u c e s p e c i e s ( e . g . , SO2 a n d
J.
L . FOX ( I n s t i t u t e f o r A t m o s p h e r i c S c i e n c e s a n d
Department
of
Mechanical
Engineering,
SUNY-Stony
B r o o k , S t o n y B r o o k , NY 1 1 7 9 4 )
Similarities
and d i f f e r e n c e s
i n t h e c h e m i c a l and
thermal s t r u c t u r e s
of t h e t h e r m o s p h e r e o f Mars and
Venus a r e d i s c u s s e d .
B o t h a t m o s p h e r e s a r e composed
p r e d o m i n a n t l y o f CO^ w i t h a s m a l l a d m i x t u r e o f t h e
dissociation
p r o d u c t s CO, 0 and 0 _ .
The m o s t o u t ­
standing d i f f e r e n c e i s the greater d e n s i t y of atomicoxygen
in
the
thermosphere
of
Venus,
which h a s
important
implications
f o r the thermal
structure.
Both a t m o s p h e r e s c o n t a i n a s m a l l amount o f N^.
The
odd n i t r o g e n c h e m i s t r y on b o t h p l a n e t s i s compared and
potential
for contributions
to our understanding of
t e r r e s t r i a l odd-nitrogen chemistry i s discussed.
This page may be freely copied.
H2SO4
o nVenus, 0
3
and U 02
2
o nMars) which are distinctly
non-equilibrium w i t h respect t o surface minerals a n d c a n there­
fore p o t e n t i a l l y react w i t h a n d / o r b e i n c o r p o r a t e d into t h e r e golith.
T h e high pressures a n d temperatures
Venus allow purely thermochemical
faster
i n general
than
o n Mars.
a t t h e surface o f
reactions t o proceed
These
reactions
allow
much
near-
t h e r m o c h e m i c a l e q u i l i b r u m c o n c e n t r a t i o n s o f HCl a n d HF t o b e
attained in t h e atmosphere. T h e y also a c t as a n e t sink for p h o t o c h e m i c a l l y p r o d u c e d SO2 a n d a t m o s p h e r i c s u l f u r o n V e n u s
must
therefore b e replenished a t least episodically b yvolcanism. T h e
m u c h lower surface temperatures o n Mars m a k e
thermochemical
atmosphere-surface reactions improbable for all b u t very reactive
s p e c i e s ( O 3 , H2O2)
b u t t h e l o w temperatures d o facilitate simple
condensation-sublimation
processes with important
implications
387
EOS Vol. 70, No. 15, April 11, 1989
for atmospheric CO2 a n d H2O.
T h e rates of m a n y potentially
i m p o r t a n t gas-mineral reactions on Venus a n d M a r s are p o o r l y
quantified a n d l a b o r a t o r y studies of these reactions are needed so
crucial parameters such as atmospheric residence times (and thus
replenishment times) for trace gases c a n b e determined.
P41A-09
Water
1130H UNITED
P42li-UH
Mars (P42B)
303 THURS PM
B Bills,
Lunar and Planetary Institute
Presiding
Bruce G. Bills (Lunar and Planetary Institute, Houston TX 77058)
on Venus
P42b-Ul
T
M
_
Oceanic and Space Sciences, The University
o f M i c h i g a n , A n n A r b o r , M I 4 810 9;
313-763-2390)
Donahue
(Department
lbbH
A Revised Estimate of the Mean Moment of Inertia of Mars: Compositional and
Paleoclimatic Implications
153UH
of Atmospheric,
The mean moment of inertia of Mars is an important, but poorly known
parameter. In the absence of direct observations of the axial precession rate,
present estimates are based on an assumed partitioning of the observed second
degree gravity field into hydrostatic and nonhydrostatic components, and then
using the Darwin-Radau relation to estimate the mean moment from the
hydrostatic component. The only legitimate constraint on the decomposition is
that the hydrostatic component is an oblate spheroid. If the observed oblateness
were entirely hydrostatic, the resulting mean moment estimate would be 0.377
M R . The generally accepted value of 0.365 M R is obtained by assuming that
the nonhydrostatic component is a prolate spheroid with an equatorial axis of
symmetry. Both statistical arguments and a comparison with the Earth, Moon and
Venus suggest that a more plausible configuration for the nonhydrostatic
component is a maximally triaxial ellipsoid (intermediate principal moment
exactly midway between greatest and least). If that were the case for Mars, the
remaining hydrostatic component would be consistent with a mean moment of
0.345 M R . While a 5% change may not seem especially significant, a downward
revision in the moment of inertia by this amount would have major implications
for the composition and obliquity history of Mars.
2
The data concerning w a t e r vapor altitude and
latitudinal p r o f i l e s in the Venus a t m o s p h e r e
and the hydrogen budget will b e reviewed.
T h i s w i l l b e d i s c u s s e d in t h e c o n t e x t o f t h e
implications of t h e deuterium "enrichment"
for t h e h i s t o r y o f V e n u s w a t e r .
It w i l l b e
argued that Venus probably h a d a n early
ocean.
A s i m i l a r e x e r c i s e in t h e c a s e o f
M a r s leads to the c o n c l u s i o n that w h i l e Mars
h a s l o s t a s i g n i f i c a n t f r a c t i o n of i t s
o r i g i n a l e n d o w m e n t o f w a t e r , it h a s r e t a i n e d
a larger fraction than has Venus.
The CRAF/Cassini Initiative
(P42A)
303 THURS PM
T Owen, SUNY Stony Brook
Presiding
P^A-Ui
b3UH
M. Neugebauer)
T h e M a r i n e r M a r k II ( M M I I ) Project i s N A S A ' s n e w initiative f o r the
exploration o f the solar system's primitive bodies and outer planets.
T h e first t w o u s e s o f t h e n e w M M I I m u l t i m i s s i o n s p a c e c r a f t , w h i c h
will b e d e s c r i b e d in this talk, w i l l u s e d b e f o r the C o m e t R e n d e z v o u s
Asteroid Flyby ( C R A F ) a n d the Cassini missions. C R A F will flyb y
the asteroid H a m b u r g a , r e n d e z v o u s with (i.e., m a t c h t h e solar orbit
of) t h e short-period c o m e t Kopff, orbit its n u c l e u s , s e n d a n
instrumented penetrator/lander into thecomet's surface, and then
s t u d y t h e p r o p e r t i e s o f t h e c o m a a n d tail a s the c o m e t b e c o m e s a c t i v e .
T h e Federal R e p u b l i c o f G e r m a n y i s a partner i n theC R A F m i s s i o n .
C a s s i n i w i l l f l y b y t h e asteroid M a j a , f l y b y Jupiter, a n d then g o into
orbit about Saturn f o r a four-year study o f the planet, its satellites, its
magnetosphere and its ring system. Cassini will also deliver a probe,
provided b y the European S p a c e A g e n c y , into the atmosphere o f
Saturn's m o o n Titan.
140UH
B. M . Jakosky (Dept. of Geological Sciences a n d Laboratory
for A t m o s p h e r i c a n d S p a c e P h y s i c s , U . of C o l o r a d o ,
Boulder, C O 8 0 3 0 9 - 0 3 9 2 )
5
T h e M a r s orbital obliquity oscillates with periods of 1 0 a n d
1 0 years, with values reaching a s low a s about 1 5 ° . At such
values, t h e polar c a p s receive much less insolation, a n d a
y e a r - r o u n d covering of CO2 frost is e x p e c t e d . Contrary to
past predictions, however, it would be expected only on o n e
cap rather than both. T h e annual energy budget represents a
b a l a n c e b e t w e e n wintertime condensation a n d summertime
sublimation. It is extremely unlikely that both poles would in­
dependently
prefer t h e exact s a m e atmospheric pressure,
especially given differences in topography, surface physical
properties, a n d frost a l b e d o ; all of t h e a n n u a l frost would
eventually migrate to one polar cap.
With t h e other c a p los­
ing its C02-frost cover during s u m m e r , an underlying waterice c a p c a n heat up a n d sublimate water into the atmosphere.
B a s e d on p e a k s u m m e r t i m e t e m p e r a t u r e s a n d water-vapor
equilibrium, assuming a water-frost albedo like that of t h e
current northern residual c a p , t h e p e a k atmospheric column
water-vapor a b u n d a n c e would be about 3 pr | i m ; it may not
drop below 5 0 pr ^ m , depending on whether t h e perihelion or
a p h e l i o n s u m m e r c a p is e x p o s e d .
T h e s e v a l u e s imply
significant e x c h a n g e of water b e t w e e n poles e v e n at low
obliquity, a n d have implications for t h e atmospheric chemistry
at such times.
2
2
6
1545H
Virtually all of the models for the composition of Mars which have been
published in the last decade have used a moment value of 0.365 M R as a
constraint on the radial density profile. This, in conjunction with a mean density
of 3933 kg m"3 suggests (but does not demand) an STP mantle density of
3500-3600 kg m~3. This particular moment value has thus contributed to the
consensus view that the mantle of Mars is enriched in iron, relative to the Earth's
mantle. If the actual moment value is as low as 0.345 M R , a rather different
picture emerges. In that case, the mantle density must be quite close to 3200 kg
m~*. A density that low would require the mantle composition to be essentially
devoid of iron. Clearly, intermediate values of the moment would allow
intermediate compositions. The main point is that the range of plausible values
for the mean moment of inertia is large enough that no useful compositional
inferences may be drawn from it.
2
2
It has been suggested that, prior to formation of Tharsis, the obliquity of Mars
may have undergone very large periodic variations due to a resonance between
the axial and orbital precession rates. This mechanism has been invoked as a
major factor in the climatic evolution of Mars. The primary basis for this secular
spin-orbit resonance hypothesis consists of two simple observations. The first is
that an estimate of the present axial precession rate (7.47 arcsec/yr) lies between
two of the eigenfrequencies for orbital precession (6.77 and 7.75 arcsec/yr). The
second observation is that estimates of the contribution Tharsis makes to the
gravitational oblateness of Mars, taken at face value, suggest that prior to the
formation of Tharsis the axial precession rate might have been in exact resonance
with the slower of the two orbital terms. While such a resonance may have taken
place, direct observational support for it is lacking. The main point here is that
uncertainty in the present value of the axial precession rate (due to uncertainty in
the mean moment of inertia) is nearly as large as the putative effect of the
formation of Tharsis via a change in gravitational oblateness.
A Numerical Simulation o f Climate Changes During the Obliquity
Cycle o n Mars
R. F . D r a p e r (Jet P r o p u l s i o n L a b o r a t o r y , California Institute o f
Technology, Pasadena, C A 91109; 818-354-5684; N A S A M A E L
CRAF)
P42A-U2
Obliquity
P42b-U2
INVITED
T h e M a r i n e r M a r k II P r o j e c t
(Sponsor:
T h e Behavior of Volatiles on M a r s During Periods of Low
L M F r a n c o i s . J C G W a l k e r a n d W R K u h n ( A l l at: D e p a r t m e n t o f
Atmospheric, Oceanic and Space Sciences, University o f
Michigan, A n n Arbor, M I 4 8 1 0 9 )
A one-dimensional seasonal energy balance climate model has been
d e v e l o p e d for the Martian surface. T h i s m o d e l takes into account the
g r e e n h o u s e w a r m i n g o f c a r b o n d i o x i d e , t h e m e r i d i o n a l transport o f
heat, t h e C O 2 c o n d e n s a t i o n a n d s u b l i m a t i o n c y c l e , a n d its adsorption
i n t h e r e g o l i t h . It r e p r o d u c e s q u i t e w e l l t h e o b s e r v e d s e a s o n a l c h a n g e
of the atmospheric CO2pressure o n present-day Mars.
T h e y e a r l y - a v e r a g e d temperatures c a l c u l a t e d f r o m this climate m o d e l at
different obliquities are u s e d t o estimate t h e i m p o r t a n c e o f CO2 e x ­
changes b e t w e e n the regolith and atmosphere-cap systems during the
obliquity c y c l e . T h e role o f m e r i d i o n a l h e a t transport and g r e e n h o u s e
warming i s analyzed and s h o w n to b e important.
T h e m o d e l i s a l s o u s e d t o describe the c l i m a t i c effects o f the obliquity
c y c l e in t h e r e m o t e past o f the planet, w h e n the s o l a r l u m i n o s i t y w a s
lower and theatmospheric CO2pressure w a s higher, the possible
presence o f liquid water at s o m e point o n the planetary surface in the
Martian history i s discussed.
IWllED
The Comet Rendezvous Asteroid Flyby Mission
M . N e u g e b a u e r (Jet P r o p u l s i o n Laboratory, California Institute o f
Technology, Pasadena, C A 91109; 818-354-2005; S P A N
JPLSP::MNEUGEB)
P42B-G3
1600H
Vertical Distribution o f Martian A t m o s p h e r i c Water Vapor
H M Hart (Dept. o f Astrophysical, Planetary a n d Atmospheric
Sciences, U . of Colorado, Boulder, C O 80309-0391)
T h e science p a y l o a d tentatively selected for flight o n the C o m e t
Rendezvous Asteroid Flyby mission ( C R A F ) includes instruments for
r e m o t e s e n s i n g o f the asteroid a n d c o m e t target, a n i n s t r u m e n t e d
penetrator to b e fired into the surface o f the comet's nucleus,
instruments forthe collection and on-board analysis o f cometary
grains, a m a s s spectrometer forstudying g a sin thecomet's c o m a , and
an array o f p l a s m a i n s t r u m e n t s . T h e c a p a b i l i t i e s o f t h e s e i n s t r u m e n t s
and the strategy forusing t h e m to address fundamental questions
c o n c e r n i n g theorigin a n d e v o l u t i o n o f the solar s y s t e m , c h e m i c a l
evolution in space, and several poorly understood astrophysical
plasma processes will be described.
B M J a k o s k y ( D e p t . o f Geological Sciences a n d L a b o r a t o r y for
Atmospheric a n d Space Physics, U . of Colorado,
CO
The
Boulder,
80309-0392)
Viking
Orbiter
Mars
Atmospheric
Water
Detector
mea­
sured reflected solar radiance i n three absorption regions a n d
two c o n t i n u u m regions within t h e 1.4-/xm b a n d o f water vapor.
T h e three atmospheric transmittances obtained from t h e mea­
surements arecompared with t h e computation of transmittance
P42b-U5
ib30H
Tectonic Influences on the Development
Mangala Valles, Mars
J
R Zimbelman (CEPS, NASM,
Institution, Washington,
of
Smithsonian
DC 20560)
T h e orientation of channels and deposits
w i t h i n Mangala V a l l e s , M a r s , is strongly
controlled by tectonic modification of the
m a t e r i a l s over w h i c h t h e M a n g a l a flood events
moved.
Geologic m a p p i n g of the southern
r e a c h e s o f M a n g a l a V a l l e s (-7.5° t o - 2 2 . 5 ° ,
1 4 5 ° t o 150°W) a t a scale of 1:500,000 reveals
the close association between channel deposits
and several prominent scarps within the
ancient materials that separate the Mangala
V a l l e s deposits from t h e younger lava flows of
Daedalia Planum.
Between latitudes - 1 8 ° and
-10° the scarps have a dominant north-south
orientation and the Mangala Valles deposits
rest against the eastern margin of the
N o a c h i a n m a t e r i a l s in w h i c h t h e scarps a r e
located.
Between latitudes - 1 0 ° and - 8 ° some
scarps follow arcuate paths with an eastward
facing concavity while other scarps maintain
the dominant north-south trend.
Mangala
Valles makes a bend to the northwest near the
location where t h e arcuate scarps become
prevalent.
Both t h e north-south oriented
scarps and t h e arcuate scarps seem to b e
related to a proposed ancient impact basin
c e n t e r e d in D a e d a l i a P l a n u m ( C r a d d o c k e t a l . ,
LPS X I X , p p . 2 1 3 - 2 1 4 , 1 9 8 8 ) , an event that
established the major structural trends within
t h e o l d e s t m a t e r i a l s e x p o s e d in t h e r e g i o n .
The Mangala Valles flood events followed t h e
minimum topographic gradient around the
topography associated with the basin event.
for a m o d e l a t m o s p h e r e t o d e t e r m i n e w a t e r v a p o r c o l u m n a b u n ­
dance ( W ) , effective pressure ( P ) , a n d effective temperature ( T ) .
We have used a multi-layered single-scattering model t o demon­
strate that, forcases where t h e a t m o s p h e r e is relatively
P42A-03
1430H
Initiative
T h e m e a s u r e d 1.4-/xm a b s o r p t i o n s exhibit
1545H
only
a weak d e p e n d e n c e o n temperature; w ehave therefore used a n
a t m o s p h e r i c m o d e l consisting o f a single absorbing layer over a
T Owen (Department
of Earth and Space Sciences, State
University of New York, Stony
Brook, NY 11794-2100;
516-632-8188)
reflecting surface, a n d constrained t h e t e m p e r a t u r e t o t h e m o s t
likely value.
W e solve for t h e p a r a m e t e r s W a n d P , w h e r e P is
the average pressure o f t h e water vapor a n d thereby represents
In collaboration with the European Space Agency (ESA),
NASA is proposing
a joint mission to Saturn
with a
launch In 1996.
ESA would
build a probe to descend
through Titan's atmosphere to the satellite's surface,
while NASA would build the Saturn
orbiter,
to spend
four years
making
observations of the magnetosphere,
satellites, rings, and the planet itself.
Scientists
from Europe and the United
States
will
be able to
propose experiments on both
probe
and orbiter.
A
strawman payload for both components has been studied
and promises a
rich
yield
of
new
scientific
discoveries.
388
P42b-06
The Dust Environment of Mars
transmittance.
The CRAF-Cassini
clear
(fvisMe < 0 . 5 ) , s c a t t e r i n g p l a y s a m i n o r r o l e i n t h e a t m o s p h e r i c
a measure of t h e vertical distribution o f water vapor.
Obser­
vations were binned temporally t o obtain seasonal information,
and spatially t o decrease noise errors.
t e n d f r o m L =0°
s
t h r o u g h L =180°.
3
T h e temporal bins ex­
T h eresults indicate that i n
northern equatorial regions i nearly spring ( L , = 0 ° )
atmospheric
w a t e r is d i s t r i b u t e d n e a r l y u n i f o r m l y w i t h a l t i t u d e ; a s spring
p r o g r e s s e s (L =90°)
a
wards t h e surface.
the water vapor becomes concentrated to­
R e s u l t s for t h ez o n a l averages, a n d inter­
pretation o f t h e s e a s o n a l c h a n g e s i nvertical distribution will b e
presented.
This page may be freely copied.
M
Horanyi
(SCRI,
Florida
State
University,
Tallahassee, FL 32306)
J G Luhmann (IGPP, UCLA, Los Angeles, CA 90024)
M Tatrallyay
(Central Research Institute/Physics,
Budapest, Hungary)
A meteorite impact on any of the Martian satellites
can eject large amounts of micron and submicron sized
dust grains, which begin orbiting around Mars.
In
the present study, the lifetime of these particles
will be studied due to the solar radiation pressure.
However, we will point out that as the small grains
move in a radiative and plasma environment they will
collect surface charge and they will respond to the
polarized electric field generated by the solar wind
flow around Mars.
Using a simple plasma and field
environment model, we will determine the spatial and
charge distribution of the small dust grains.