Plasma measurements in Jupiter’s
magnetosphere
PlasmaMeasurementsin
Jupiter’sMagnetosphere
By:RobEbert
By: Rob Ebert
(and many thanks to Fran Bagenal and George Clark
for helping with this talk)
WorkshoponJupiter’sAurora,An>cipa>ngJuno’sArrival–March8
Workshop
on Jupiter’s Aurora, Anticipating Juno’s Arrival – March 8thth,2016
, 2016
Previous Missions to Jupiter
Flybys
Galileo
150
100
50
J
y (R )
50
Pioneer 10
Pioneer 11
Voyager 1
Voyager 2
Ulysses
Cassini
New Horizons
y (RJ)
100
150
0
0
-50
-100
Galileo
-150
30
15
0
-15
-30
-150
J
z (R )
30
15
0
-15
-30
-150
J
z (R )
-150
-100
-50
0
50
100
150
x (R )
-50
0
50
x (R )
J
10
Fig.
4 from Bagenal et al. 2014, SSRv
-100
J
10
100
150
Summary of Plasma Observations
Spacecraft
Instrument
Timeframe
Energy Range
Regions Explored at Jupiter
Pioneer 10
Plasma Analyzer (PA)
DOY 330 – 356, 1973
0.1 – 18 keV (protons)
0.001 – 0.5 keV (electrons)
foreshock, dawn magnetosheath,
inner/outer magnetosphere
Pioneer 11
Plasma Analyzer (PA)
DOY 330 – 344, 1974
0.1 – 18 keV (protons)
0.001 – 0.5 keV (electrons)
foreshock, dawn magnetosheath,
outer, inner and mid-latitude
magnetosphere
Voyager 1
Plasma Science (PLS)
DOY 59 – 81, 1979
0.01 – 6 keV/q (ions)
0.004 – 6 keV(electrons)
foreshock, dawn magnetosheath,
outer/inner magnetosphere,
magnetotail
Voyager 2
Plasma Science (PLS)
DOY 183 – 225, 1979
0.01 – 6 keV/q (ions)
0.004 – 6 keV(electrons)
foreshock, dawn magnetosheath,
outer/inner magnetosphere,
magnetotail
Ulysses
Solar Wind Observations
Over the Poles of the Sun
(SWOOPS)
DOY 33 – 47, 1992
0.255 – 34.4 keV/q (ions)
~0.001 – 0.814 keV (electrons)
foreshock, magnetosheath,
boundary layer and outer, inner
and mid-latitude magnetosphere
Galileo
Plasma Particle
Investigation (PLS)
DOY 341, 1995 –
DOY 264, 2003
0.9 – 52 keV/q (ions)
0.9 – 52 keV (electrons)
equatorial inner & outer
magnetosphere, satellite flybys
Cassini
Cassini Plasma
Spectrometers (CAPS)
October 2000 – April
2001
~0.001 – 50 keV (ions)
0.6 – 28 keV (electrons)
dusk bow shock, magnetosheath,
and boundary layer
New Horizons
Solar Wind Around Pluto
(SWAP)
DOY 56 – 173, 2007
0.02 – 7.5 keV/q (ions)
dusk magnetosphere, distant
magnetotail, boundary layer and
magnetosheath
Juno
Jovian Auroral
Distributions Experiment
(JADE)
JOI 7/4/2016
0.01 – 50 keV/q (ions)
0.1 – 100 keV (electrons)
!
Juno Approach
V
V!
Vb
-500
BIMF
!
e
-200
TA009782
!
-1000
Ion
Foreshock
Electron
Foreshock
0
200
X-JSO (RJ)
Solar
Wind
!
n
CushionRegio
ath
Magnetoshe
Tangent Field Lin
Y-JSO (RJ)
0
!
Bow S
hock
Magnetopau
se
400
Upstream Solar Wind
ICME dominated
CIR dominated
All solar wind types combined
Ebert et al. 2014
Numerous studies of SW upstream of Jupiter
(e.g. Slavin et al. 1985; Joy et al. 2002, Nichols et al. 2006,
Jackman and Arridge, 2011, McComas et al. 2014, Ebert et
al. 2014, among others)
-  Dynamic pressure distributions of ICMEs
and CIRs appear bimodal.
-  Less apparent when considering all SW
types.
-  SW obs. upstream of Jupiter are needed to
infer correlations between SW and remotely
observed auroral emissions.
McComas et al. 2014
Upstream SW + Remote Sensing
JADE-ISWobserva>ons
JovianAuroralEmissions
Nicholsetal.2009
-  Plenty of discussion regarding role of solar wind in driving variations in auroral
emission features.
-  Simultaneous observations of upstream solar wind/IMF and remotely sensed
auroral emissions are needed to accurately identify correlative relationships.
-  Understanding gained from these studies will help guide interpretation of the
auroral observations when Juno is inside the magnetosphere.
magnetopause
magnetopause
shape models
shapevary
models
withvary
solarwith
windsolar
dynamic
wind dynamic
developeddeveloped
models are
models
shaded
aretoshaded
show ato range
show of
a range
proba-of probapressure. pressure.
Table 2 Table
provides
2 provides
the pressure
the pressure
values ofvalues
the of
the inbilities
bilities
the boundary
in the boundary
location. location.
Open circles
Openindicate
circles indicate
surfaces with
surfaces
standoff
with distances
standoff distances
corresponding
corresponding
to different
to different
actual boundary
actual boundary
crossings crossings
observed.observed.
In places In
where
places
there
where there
probabilities
probabilities
of being inside
of being
theinside
magnetopause
the magnetopause
or inside the
or inside
are the
multiple
are multiple
closely spaced
closelycrossings,
spaced crossings,
the open the
circles
open circles
bow shock,
bowrespectively.
shock, respectively.
These probability
These probability
surfaces are
surfaces
are toappear
appear
be filled.
to be
There
filled.
is There
a substantial
is a substantial
spread inspread
the in the
defined bydefined
equation
by (2)
equation
with the
(2) coefficients
with the coefficients
corresponding
corresponding
dawn-dusk
dawn-dusk
dimensiondimension
of the observed
of the observed
dayside crossings
dayside crossings
to pressure
to values
pressurefrom
values
Table
from
2. Table
Because
2. the
Because
probability
the probability
suggestingsuggesting
that the upstream
that the upstream
boundary boundary
is rather blunt.
is rather
Theblunt. The
varies monotonically
varies monotonically
with distance
with from
distance
Jupiter,
fromthe
Jupiter,
bow theHuddleston
bow Huddleston
models ofmodels
the bowofshock
the bow
andshock
magnetopause
and magnetopause
for
for
shock location
shockislocation
usefullyisdescribed
usefully described
in terms of
inthe
terms
percentof the percenthigh solar
high
wind
solar
dynamic
wind dynamic
pressure pressure
conditionsconditions
are both are both
age of time
ageanofobserver
time an would
observer
be would
inside be
theinside
bow shock
the bow
at ashock
at a more
slightly
slightly
compressed
more compressed
at the nose
at the
but nose
are otherwise
but are otherwise
Magnetospheric Boundaries
Joyetal.2002
Figure 6.Figure
Comparison
6. Comparison
of the probabilistic
of the probabilistic
bow shock
bow
(a) shock
and magnetopause
(a) and magnetopause
(b) models(b)with
models
previous
with previous
models. The
models.
area between
The area the
between
25th and
the 25th
75th and
percentiles
75th percentiles
of the probability
of the probability
of being in
of the
being
solar
in wind
the solar
is wind is
shaded inshaded
panel (a).
in panel
In panel
(a). (b),
In panel
shading
(b),indicates
shading indicates
one sigmaone
bands
sigma
about
bands
the about
meansthe
of means
the bimodal
of the bimodal
distribution
distribution
in the probability
in the probability
of being of
inside
being
theinside
magnetosphere.
the magnetosphere.
Solid lines
Solid
show
lines
the show
high and
the high
low and low
pressure models
pressureofmodels
Huddleston
of Huddleston
et al. [1998].
et al.Dashed
[1998].lines
Dashed
show
lines
the show
Voyager
the models
Voyager[Lepping
models [Lepping
et al., et al.,
1981a]. 1981a].
Richardson1987
Estimated bow
shock distance
distribution
during Juno
-  Plasma observations provide a definitive signature
of magnetospheric boundaries.
-  Location of boundaries constrain the shape and
extent of the magnetosphere.
-  Aurora emissions may vary with boundary motion.
Ebertetal.2014
SW-Boundary Interactions
Where KH instabilities are probable
Where magnetic reconnection is probable
DESROCHE ET
AL.: CONDITIONS AT JUPITER’S
MAGNETOPAUSE
A07202
DESROCHE
ET AL.: CONDITIONS AT JUPITER’SA07202
MAGNETOPAUSE
β=1
Desrocheetal.2012
A07202
β=10
Huddlestonetal.1997
-  There are several theoretical models describing SW-magnetospheric interactions at
Jupiter but few observational constraints.
-  Additional observations of the plasma flow, density, temperature and composition
inside the magnetopause and in the outer magnetosphere are needed.
SW-Boundary Interactions
SW interaction mediated by KH instabilities
Delamereand
Bagenal,2010
SW interaction mediated by reconnection
Cowleyetal.2003
-  Understanding how the SW couples to the magnetosphere has important
implications for global magnetospheric dynamics.
Fig
show
mag
pane
regio
auro
for t
pane
visc
inter
pane
Dun
From
Bag
Cow
Juno: Capture Orbits and Prime Mission
Juno Orbit #1
30
Pj 1 2016 240 12:51:00
20
233
238
Z magnetic [RJ]
10
235
237
239
221
214
219
216
264
234
242
243
229
252
250
232
245
241
248
249
246
20
40
251
80
60
Rho [RJ]
259 267
266
218
217
255
225
227
254
222
260
261
220
265
253
215
256
258 263
100
120
247
244
−20
223
224 262
257
230
0
−30
0
226
236
240
−10
228
231
-  Juno will explore Jupiter’s:
-  Auroral regions
-  Polar magnetosphere
-  Plasma sheet
-  Outer magnetosphere/
cushion region
Juno Orbit #30
Juno Orbit #4
10
10
Pj 30 2017 318 18:31:00
Pj 4 2016 321 16:54:60
321
5
5
320
0
Z magnetic [RJ]
Z magnetic [RJ]
0
−5
322
−10
318
−5
317
319
−10
323
−15
−15
320
−20
0
5
10
15
Rho [R ]
20
25
−20
30 0
5
10
15
Rho [R ]
321
20
25
30
-  Little to no in situ plasma
observations in many of
these regions.
The Big Picture
Magnetospheric Science Objectives of the Juno Mission
Fig. 1 (A) The magnetosphere of Jupiter extends 63–92 Jovian radii in the direction towards the Sun, with a
tail that stretches beyond the orbit of Saturn >4 AU, and occupies a volume over a thousand times that of the
Plasma Sheet
Halflostasfastneutrals
->extendedneutralcloud
Halftransportedouttoplasmadisk
Delamere&Bagenal2003
-  Ions are picked up by Jupiter’s
magnetic field, spun up to the
planet’s rotation rate and transported
radially outward.
Plasma Sheet
19.8RJ
Vϕ=201km/s
O+/S++
T=29eV
S3+
-3
2+
ni=0.1–0.3cm
O
Vϕ=240km/s
T=89eV
ni=0.02–0.05cm-3
34.7RJ
H+
Bagenaletal.1981,reprocesseddatashownherebyBodischetal.2015;Doughertyetal.2015
•  When detectable signal in multiple cups we get determinations
of Vr,mass
Vphi
and dominated
Vz.!
-  Plasma
density
by heavy ions.
•  If there is only information in a single cup, assume zero Vr
+/S++ based on Cassini
-  Data
shown
here
reprocessed
to
include
estimates
for
O
and Vz and allow for variation from corotation in Vphi!
UVS observations + physical chemistry model (e.g. Delamere, Steffl, and Bagenal,
2005).
V
Jupiter
nsity in
eV, we
Radial
m equa4) and
an also
cles at
0 MeV
about a
t [e.g.,
e more
. Mod-
Saturn.
The model
for Jupiter
derived
from data
later found
could profile
be balanced
withwas
pressure
gradient
for- PLS observations one sees a wider range in temperatures,
shown
in
Figure
1.
The
densities
at
Saturn
are
derived
from
ces associated with the 20–200 keV plasma population. Not particularly in the outer plasma sheet. We only show the temCassini
CAPS
(<5 Rpressure
et al. [2008]
and (>5presR S)
only does
thedata
plasma
dominate
the magnetic
S) by Sittler
peratures around noon in Figure 3. The data around midnight
by
Thomsen
al. [2010].
sure,
but theetradial
profile of plasma pressure is also con- showed even greater scatter. Further work is needed to ascersiderably flatter than the 1/R6 variation in magnetic pressure tain whether this is a true variation between the Voyager
for a dipole field. It is the high plasma pressure in the plasma
A05209
BAGENAL
AND DELAMERE:
MASS AND ENERGY
A05209
disk that on
doubles
theorbit
scaleinofthe
Jupiter’s
magnetosphere
from
obtained
the G8
magnetotail
presented
by
the dipolar
distance
of ∼42 Rform
J to 65–90 RJ. The
Frank
et al. stand‐off
[2002] with
the functional
shallow gradient in plasma pressure accounts for the high The derived charge density does not depend on assumptions
"b2
compressibility ofnFrank02
the magnetosphere
with
the subsolar mag¼ a1 R"b1 þ a2 R
ð2Þ
of composition and agrees well with the sum of densities
netopause varying as solar wind ram pressure to the −1/∼4.5 for separate ion species derived by fitting resolved spectral
where
coefficients
given
Table 1.dipole
Our model
power,the
rather
than −1/6 are
power
for ainmagnetic
[Slavin peaks (see appendices A and B of McNutt et al. [1981] as
profile
somewhat
underestimates
theJoy
peak
densities
in the
et al., 1985;
Huddleston
et al., 1998;
et al.,
2002; Alexeev
well as simultaneous electron measurements [Scudder et al.,
outer
plasma sheet,
but we
show inand
section
3.1 that
this does
and Belenkaya,
2005].
Delamere
Bagenal
[2010]
argue 1981]. The semiregular factor of ∼5 variation in density is
not
significantly
affect
our
estimates
of
mass
and
energy
that the high‐beta plasma inside Jupiter’s magnetosphere due to the flapping of the plasma sheet over the spacecraft.
flows
system.
limits in
thethe
solar
wind interaction to a viscous boundary layer. Electron density has also been derived from measurements
[[1223]] In
we compare
the plasma
proAtFigure
Saturn2 the
plasma pressures
aresheet
lessdensity
than Jupiter
by the Voyager Plasma Wave (PWS) instrument, recently
file
in Figure
1 with
profile
of plasma
butfor
theJupiter
plasmadescribed
beta is still
greater
than aunity
beyond
8 RS cataloged by Barnhart et al. [2009] These PWS local meadensity
derivedetfrom
CAPS
data atofSaturn.
[e.g., Sergis
al., Cassini
2010] and
hasionvalues
2–5 inThe
the surements of charge density have been averaged over radial
profiles
represent
theand
peak
density,
n0, recently
in the center
the
plasma sheet.
Chou
Cheng
[2010]
built aofmodel
distances to give 9 points in the outer magnetodisk (>20 RJ)
plasma sheet. The Saturn values outside ∼5 RS are from
and agree well with the PLS measurements of total charge
Thomsen et al. [2010], who took statistical moments for data
density.
obtained October 2004 through March 2009. The profiles in
[10] The Galileo spacecraft orbited Jupiter for 7 years and
Figure 1.
2 (bottom)
derived from
measurements
taken1 Figure
Temperature
of the thermal
ions derived
at JupiFigure
Density are
measurements
derived
from Voyager
made 3.
extensive
measurements
of plasma
properties
in the
at
low
latitudes
and
when
the
corotational
flow
was
in
the
from
the
Galileo
PLS
data
obtained
±30°
around
noon
PLS (black line), Voyager 1 PWS (blue triangles), and ter
-
Juno
can
provide
new
insight
into
the
plasma sheet. We have taken estimates of plasma density
CAPS field
view
[Thomsen
et al.,
Figure
To (green
diamonds)
and moments
from Voyager
1 PLS data from
(blackthe
Galileo
PLSof(all
orbits)
obtained
±30°2010,
around
noon3c].
(green
derived
via statistical
of measurements
vertical
and
radial
profiles
of
the
push the profiles
inward
of midnight
5 RS we (red
tookcircles).
densityThe
values
al. [1981]).
model profile
used in in
diamonds)
and ±30°
around
pro- crosses,
Galileo McNutt
Plasma etScience
(PLS)The
instrument
and archived
fromfrom
an earlier
of CAPS
data
by curve,
Sittler etequation
al. [2008].
(black
curve)
is derived
beyond
∼10 RJcommufrom
file
Frankanalysis
et al. [2002]
(pale
blue
(2)) this
plasma
sheet,
including
measuring
the study
Planetary
Data
System
(W. Paterson,
private
Similar
densities
werefrom
found
PLS estimates
of2009).
the vertical
scale height
of density
in
the plasma
is
based plasma
on Galileo
PLS data
the by
G8 the
orbitVoyager
data obtained
nication,
We plotted
all Galileo
data
within
±30° of
the
conditions
within
days
of
the
instruments
when The
theymodel
flew through
the system
1980(thick
and sheet
(see
equations
(3)
and
(4)).
on
the nightside.
profile used
in thisinstudy
noon and ±30° of midnight. The densities derived from
gray curve, equation (1)) is a composite of three power law Galileo
perijove
passes
auroral
data beyond
aboutthrough
20 RJ are the
generally
lower than
profiles (blue, purple, and yellow lines).
3 of 17Voyager
1 values. This may be because of the assumption
region.
that the mass/charge is 16 in the Galileo analysis. If there are
[7] In section 2 we present a simple model of an axisymmetric significant numbers of protons in the outer magnetosphere,
plasma sheet based on in situ observations of the plasma fitting the Galileo data with both protons and heavy ions
density and temperature and derive basic descriptions of may yield higher densities. We point out that the depenBagenalandDelamere,2011;Bagenaletal.2014
is not a strong
how the latitudinal distribution and total plasma pressure dence of total charge density on composition
1/2
vary with distance from the planet. In section 3 we use this effect (depending as (charge/mass) ), and we estimate the
net uncertainty to be less than a factor or 2.
Plasma Sheet
L and the M mode, are shown by the crossesin Figure 6 for that the magnetosphericflow would deviate from rigid corotaVoyager 1 and in Figure 7 for Voyager 2. We emphasizethat tion as close to Jupiter as • 10 R•. We have been extremely
even though there is an intrinsic ambiguity in the species conservativein our selectionof spectrafor quantitativeanalyidentificationfor a givenA/Z* peak (i.e., is the 16peak S2+or sis, at least in part, to establishunequivocally this departure
O+?), the total mass and charge density determinationsare from corotation. Our best estimates of Vn are from fits to the
unaffectedby that ambiguity (see Appendix A). For corn- resolvedM mode spectrasuchas thosegiven in Figure 3. The
Plasma Sheet
DISTANCE (Rj)
/40
5OO
35
30
25
CA
20
15
IO
5
..... I ..... I ..... 1''1"'1.... I'"l"l'"l"l"'l"l .....I
-••..•_ •COROTATION
MMODE
400
•
u• 300
ANALYSIS
>,_2oo
IO0
0 .....
J .....
400
I .....
] .....
•
. = 200
+
I .....
+++•
'
$ ;
+
,oo
McNubetal.1981
I .....
[ .....
I .....
COROTATION
L-MODE
$oo
0 .....
J.....
+++
*...•.
ß
da•
ANALYSIS
+
I .....
62
I .....
I .....
I
SPACECRAFT
I .....
EVENT
I .....
63
TIME
I .....
VOYAGER
I .....
I
I .....
I
64
I
Fig 9. Valuesof the •mponent of velocity•to •e D sensorfor Voyager 1 as determ•ed from the M modeand the L
-  Plasma co-rotation
starts
to break
down
20 Rfor
McNutt
etsho•.
al. 1981).
mode analysis.The
component
of velocity
into the at
side~17
sensor-expected
•gid corotarion
is also
J (e.g.
-  Coupling currents and corresponding aurora are stronger in region where plasma
slips behind cororation (e.g. Hill 1979).
types
fieldThe
ns of
nitial
tered
into
sphere as reviewed by Hill et al. [1983].
[33] There are two other previous observations which
support the existence of a magnetic anomaly in the magnetosphere of Jupiter which are of significant global import.
The first is the magnetospheric ‘‘clock’’ which was detected
Plasma Sheet
m III
n the
s the
ed at
ongiwith
adial
adial
which
was
7 RJ
thors
e ion
f the
tudes
than
nized
ce of
he Io
1980;
995;
n the
to 25
adial
FrankandPaterson,2002
Figure
10. Examples of the three principal types of
electron pitch angle distributions. Directional differential
intensities
plotted
as functions
of pitch distributions
angle in each
Electronarepitch
angle
and energy
panel for all sensors. Date and time can be employed to
place these measurements in the context of Figures 5, 6, and
7. Shown in this figure are field-aligned beams in Figures
provide information about these currents.
Polar Magnetosphere
Little to no in situ plasma measurements, many fundamental questions:
-  What is the high latitude structure of the magnetosphere? Is it fundamentally
similar or different than Earth?
-  Where and how are the particles that excite the aurora generated?
-  How do the currents close between the plasma disk and the aurora region?
-  What causes the transient polar aurora?
-  How open is the magnetosphere to the IMF?
-  What is the size and the variability of Jupiter’s polar cap?
-  How is the main aurora related to magnetospheric dynamics and/or changes in the
solar wind?
-  Is there significant outflow from Jupiter’s ionosphere? How much does it
contribute to Jupiter’s plasma environment?
Acceleration Region
Magnetospheric Science Objectives of the
Juno Mission
UpwardCurrentRegionatEarth
SketchofAuroralAccelera>onRegionsatEarth
0
-250
-500
1000
500
0
-500
-1000
-1500
UT
ALT
ILAT
MLT
Fig. 24 The three types of
auroral zones based on
experience from Earth: upward
currents, downward currents and
Alfvénic regions. Adapted from
Carlson et al. (1998)
10
102
101
104
103
102
101
101
100
10-1
:06:35 :06:40 :06:45 :06:50 :06:55 :07:00
3953.1 3950.3 3947.4 3944.5 3941.6 3938.6
70.8
71.0
71.1
71.2
71.3
71.4
21.2
21.2
21.2
21.2
21.2
21.2
Minutes from 1997-02-09/06:06:35
9
6
7
Log eV/
cm2-s-sr-eV
0
4
10
103
Log eV/
cm2-s-sr-eV
5
4
-4
Log (V/m)2/Hz
Freq. (kHz)
Ions (eV)
Electrons (eV) Density (cm-3)
(mV/m)
(mV/m)
FAST ORBIT 1858
500
250
-12
-  Electron and ion observations are
needed to help discover the structure
and location of the auroral acceleration
regions at Jupiter.
-  What will this sketch look like for
Jupiter?
FromErguntalkat2015Juno/CassiniWorkshop
Mean en
Mean en
200
100
0
220
100
Precipitating Electrons
Wth = 2.5 keV
n = 619 m-3 (relativistic)
0
20
60
40
Energy flux (mW m-2)
J. Gustin et al. / Icarus 268 (2016) 215–241
80
0
100
250
60
40
Energy flux (mW m-2)
20
0
Wth = 2.5 keV
n = 521 m-3 (relativistic)
250
200
80
100
g
STIS ME 2 obs. #2
f
STIS ME 2 obs. #1
200
Mean energy (keV)
Mean energy (keV)
200
150
100
50
30
20
Energy flux (mW m-2)
10
40
100
50
Wth = 2.5 keV
n = 2276 m-3
0
0
150
50
0
0
Wth = 2.5 keV
n = 2505 m-3
40
20
Energy flux (mW m-2)
60
Fig. 4. (a) Energy–energy flux relationship for the main emissions (light blue and green stars) and flare emissions (black and yellow crosses) of the two STIS observations,
along with data points obtained by Gustin et al. (2004a) (dark blue stars and red diamonds). (b) and (c) STIS points from ME1 with the classic Knight relation. Curves are
shown for best fits (red) and electron source density n = 1000 m!3 (dashed) and n = 10,000 m!3 (dot-dashed), with electron source temperature fixed to 2.5 keV. (d) and (e)
Same as (b) and (c) with the relativistic Knight relation. (f) and (g) STIS points for ME2 with the classic Knight relation. (For interpretation of the references to color in this
Fig. 2. Map of the precipitating electron mean energy for the two STIS observations, both in a Earth-orbit view (a and c panels) and in a polar projected view (b and d panels).
figure legend, the reader is referred to the web version of this article.)
All the auroral regions, labels and grids are identical to those of Fig. 1. The ME1 and ME2 regions are the most energetic ('330 keV and '130 keV respectively), followed by
Gus>netal.2016
226
J. Gustin et al. / Icarus 268 (2016) 215–241
-  Remote sensing observations
used to estimate mean energy
and energy flux of precipitating
electrons; suggest spatial
variability.
the poleward flare emissions (70–90 keV). The IFP shows very weak absorption while the SSS and GFP show significant hydrocarbon absorption. The images are smoothed
over a 3 pixels boxcar500
for better legibility.
Mean energy (keV)
Main emission 1 obs #1 & #2
Main emission 2 obs #1 & #2
400
Flaresdetermine
1 obs #1 & #2
In order to empirically
the brightness and mean
Flares
2
obs #1 & #2
energy distribution
300associated with each auroral region, both the
vertical brightness and hEi histograms have been fitted with two
distributions often
200used in this field of study. First, a Maxwellian
distribution,
a
characteristics for both observations. The E0 and n parameters of
the best generalized Maxwellian are provided in Table 1.
As seen in Fig. 3a, b, o and p, the ME 1 region is very bright and
characterized by the most energetic primary electrons. The vertical
brightness distributions are relatively symmetric, around '260 kR.
The electronMain
mean
energies
hEi2004
determined from the CR method
emission
Gustin
100
E
are mostly between 100 and 700 keV, with several individual pixD ¼ C e"E=E0 ;
ð1Þ
High
latitudes
Gustin
2004
E0
els at higher or lower values. The average hEi value is quite high
0
('300 and '35560keV for observation 80
1 and 2, respectively). It
and a kappa distribution
40
20
0
Energy flux (mWshould
m-2) be noted that mean energies found in the literature are gen!
"
E
E0
D¼C
1 þ E 500eð"1"kÞ :
ð2Þ 500 erally determined from spectra obtained from the sum of numerE0
k
ous
pixels,
which averages the energies so obtained, while the
STIS ME 1 obs. #1
STIS ME
1 obs. #2
c
b
distributions shown here reflect the range of values reached by
A third distribution,
allowing
a
greater
flexibility
in
terms
of
shape,
400
400
the individual pixels of the auroral region, which expand the range
has also been used, namely the ‘generalized’ Maxwellian
of inferred values. Fig. 3o and p clearly show that several pixels
distribution
300 have hEi larger than 400 keV, well above values generally observed.
300
"ðnþ1Þ
As seen in Fig. 11a, for hEi larger than 400 keV, the CR is larger than
D ¼ CEn=2 E 2 e"E=E0 :
ð3Þ
energy (keV)
energy (keV)
-  Observations from Juno will
provide ground truth.
Conclusions
-  Plasma measurements from 8 previous missions have revealed a lot about the
structure of and dynamics within Jupiter’s magnetosphere.
-  There are still many open questions.
-  Juno’s orbit provides an opportunity to makes observations in several regions of
the magnetosphere that are either under-sampled or completely unexplored.
-  Key objective is to determine the structure of the region that accelerates the
particles that produce the aurora.
-  Many other high impact science opportunities during mission.