Next Generation Adaptive Optics
- Solar System Science Cases SSC meeting - June 21-22 2006, Hawaii, USA
F. Marchis (UC-Berkeley)
Members:
A. Bouchez (Caltech), J. Emery
(NASA-Ames), K. Noll (STSCI), M.
Adamkovics (UC-Berkeley)
General introduction
• AO expands the study of our solar system
– Good temporal monitoring to observe variable phenomena
(atmosphere and surface)
– Short time scale to respond to transit and unpredictable
events (impact of a comet on Jupiter)
• Keck Observatory and planetary science
significant contributions and dynamic sub-field.
Since 2000:
– 32% of Keck referee papers.
– 42% of all Keck press releases
– NASA (1/6 partner of Keck Obs) supports investigations
mostly in Planetary science
Science Cases
A few science cases were chosen to illustrate the
advanced capabilities of NGAO (with simulations)
• A. Binary Minor Planets
– Detection and orbits of asteroidal satellites
– Spectroscopy of moonlets
– Size and shape
• B. Satellites of Giant Planets
– Titan’s surface and its atmosphere
– Io’s volcanism
Minor Planets
• Building blocks of the Solar System linked to its formation
•~400,000 minor planets known
• Small apparent size (largest 1 Ceres, Dapp=0.7arcsec  “seeing” limit)
L5-Trojan
Main-Belt
L4-Trojan
Centaurs
TNOs
Diversity of shapes and sizes
25143 Itokawa
“Like archaeologists working to translate stone carvings left behind by ancient
civilizations, the collisional and dynamical clues left behind in or derived from the Main
Belt, once properly interpreted, can be used to read the history of the inner Solar System.
Bottke et al 2005
What are asteroids made of?
(a) Shape of NEA*
Toutatis observed with
radar
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Internal structure?
(b) Monolith
(c) Contact Binary
(d) Rubble Pile
From E. Asphaug, 1999, “Survival of the weakest”
* NEA= Near Earth Asteroid
Binary Asteroids
A Family Portrait
MB 87 Sylvia and its 2 moons
(VLT AO, 2005)
MB - Ida and Dactyl (Galileo 1993)
MB -45 Eugenia &
Petit-Prince
(CFHT AO, 1998)
TNOs 2003EL61
(Keck AO, 2005)
~85 multiple asteroidal systems known
Astronomical prize for astronomers and theorists
 Mass, density, constraints on formation of planets
Multiple asteroidal systems and NGAO
Considering 80 known multiple asteroidal systems:
Keck NGS
SR~40%,
mv<13.5
Keck LGS
SR<20%,
mv<17.5
Keck NGAO
SR>70%,
mv<17.5
Percent of observable
binary systems
<20%
~70%
~70%
Size ratio of smallest
satellite at 0.6”
1/40-1/50
~1/10-1/30
~1/70-1/90
• + better angular resolution in visible (~15 mas) -> close
doublet (sep. < 50 mas) can be also studied
• + a better sensitivity as well…
NGAO capabilities
Simulation context:
• 87 Sylvia was discovered in 2005: Rprimary = 143 km,
RRemus= 3.5 km, RRomulus=9 km
• Insert 2 more moonlets. One closer (6 km) at 480 km and
one smaller (1.75 km) at 1050 km
Triple system 87 Sylvia with VLT/NACO
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Pseudo-Sylvia simulated
Simulations
1.6”
•Better sensitivity
Detection of fainter
moonlet & closer moonlets
More multiple systems
•Better photometry
 Better estimate of the size
and shape of moonlet
•Better astrometry
 Reliable estimate of
orbital parameters, small
orders perturbations (e.g.,
precession, interactions
between moonlets, …)
Simulation of pseudo- Sylvia observed with various AO systems
Trans-Neptunian Object satellite systems
K band -2”
NGAO simulations
K band -2”
Hypothetical 3rd moon,
75 km diameter.
Keck 2 LGS-AO
2003 EL61: A Charon-sized (~1500 km) TNO with 2
satellites in non-coplanar orbits (Brown et al. 2006).
K band -1”
2003 EL61
at 51 AU
• Most large TNOs may have multi-satellite
systems, which record their formation and/or
collisional history.
• An NGAO survey of large TNOs would find all
satellites >100 km diameter out to 100 AU.
Identical system at 100
AU (mv=20), observed
using an off-axis V=16.5
NGS. & 50” separation
Low resolution spectroscopy
• Better AO correction  higher SN on spectra of moons
and primary (capture body, infant of primary, age, …)
• Visible wavelength range  characterize the surface
composition
Silicate absorption
bands centered at
1 and 2 m
Summary Science case A
• Keck NGAO will be the best tool for this
scientific subject (no space mission
scheduled, need for numerous
observations,…)
• Density & composition of minor planet is
the key to understanding the formation of
the solar system
Science Cases
A few science cases were chosen to illustrate the
advanced capabilities of NGAO (with simulations)
• A. Binary Minor Planets
– Detection and Orbits of asteroidal satellites
– Spectroscopy of moonlets
– Size and shape
• B. Satellites of Giant Planets
– Titan’s surface and its atmosphere
– Io’s Volcanism
Volcanism of Io
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• The most volcanically active place in the solar system
• Only 5 successful flybys with Galileo (spatial resolution of
global NIR observations 100-300 km)
• Outstanding questions:
- Internal composition linked to
the highest temperature of
magma
- Evolution in the orbital
resonance, constrained by the
heat flow measurement and
evolution
Io observed with NGAO in NIR
Keck NGAO - H Band
Keck NGS - H Band
0.9”
FWHM=33 mas
FWHM=44 mas
• Up to 0.9 m, thermal output of outburst can be detected (T>1450 K)
• Up to 0.7 m -> mafic absorption band (centered at 1 m)
• Thermal band imaging (3-5 m) capabilities are necessary
Comparison with HST
+ Better spatial resolution (~40 km) than Galileo spacecraft global NIR images
• Surface Changes
• Plumes
No future mission (with imaging capabilities) planned toward
Jupiter (brief flyby in 2007 by New Horizons)
 AO on Keck is an highly competitive instrument!
Why do we need NGAO?
• Best angular resolution provided in visible and NIR
Directly image planetary surface and atmosphere, characterized by
spectroscopy
• Excellent and stable Strehl ratio in NIR
Detect moonlets around asteroids & KBOs and determine their orbits
and spectra.
• A flexible AO system with service observing
Maximize the scientific return and efficiency of the observatory and
observe transient events or monitor regularly
The End
Other satellites
Satellite
name
Ang.
Size
(mas)
Max Ang.
Sep.
(arcsec)
Mv
comments
Mimas
60
30
13.0
Enceladus
80
39
11.6
Tethys
170
48
10.4
Dione
180
61
10.5
Rhea
250
85
9.8
Titan
830
198
8.3
Iapetus
230
576
11.2
Io
1200
95
5.2
Basaltic volcanic activity
Europa
1000
150
6.3
Young surface - ocean beneath?
Ganymede
1700
240
5.6
Ocean?
Callisto
1600
420
6.9
Himalia
60
3000
15.7
Volcanic activity (science, 2006)
Cryo-volcanoes?
Reminder: FWHM PSF(NGAO-R) = 14 mas
Other satellites
•Consider high resolution spectral analysis (R>1000) for
atmospheric features. Example geysers on Enceladus
•Problem due to giant planet halo contribution on the WFS?
80 mas
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Reminder: FWHM PSF(NGAO-R) = 12 mas
Other satellites
Insert here a figure showing which satellites can be observed
considering the glare of the planet
We should use Van Dam et al. measuremnts (sent to Mate)
Reminder: FWHM PSF(NGAO-R) = 12 mas
How many asteroids observable w/ NGAO?
Populations by brightness (numbered asteroids only)
Orbital type Total number
Near Earth
V < 15 15 < V < 16 16 < V < 17 17 < V < 18
424
346
50
25
3
118381
4074
9537
25330
45420
1010
13
44
108
262
31
0
1
2
2
TNO
108
0
0
0
2
Other
483
112
151
152
54
Main Belt
Trojan
Centaur
Mysterious Titan
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• Satellite of Saturn - D~5150 km
• Surface mostly hidden by an
opaque prebiotic atmosphere
• Studied with Cassini spacecraft (4
flyby already) and Huygens lander
(Jan. 2004)
• Spatial resolution of global
observations up to 9km in NIR
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Titan Surface and its Atmosphere
•
•
•
Goals: Observations of an extended object - imaging and spectroscopy
of its atmosphere. Comparison with previous NGS AO systems.
Illustration of the variability of solar system phenomena (volcanism,
clouds)
Inputs from TCIS: Simulated short exposureﾊ On-Axis PSFs (~2-4s)
(x10) at various wavelength (NOT YET DEFINED) in good seeing
conditions for a bright reference (mv=8.5). Should we expect a
degradation due to the angular size of Titan (D=0.8")ﾊ
Method:We will create a fake Titan observations considering also the
haze component in visible and NIR and using global map (with R=30200 km) of Cassini spacecraft.ﾊWe will focus on atmospheric windows
for which the surface canﾊ be seen (tools are ready MA & FM).
Wavelength not defined yet.- Deconvolution with AIDA may be included
(algorithm 95% ready FM)- Comparison with Keck NGS AO, VLT AO,
and Cassini will be included- Good temporal coverage from the ground
vs spacecraft will be discussed and illustrated by surface changes due
to a cryo-volcano (and/or clouds in the troposphere?)- Spectroscopy to
detect N2+ species in the atmosphere (high R) and measure winds in
Titan atmosphere at various altitudes (extremely high R).
Titan Surface and its Atmosphere
• First results - Comparison of H band observations
0.8”
FWHM= 44 mas
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FWHM= 34 mas
FWHM= 34 mas
About the fake image of Titan
based on Cassini map at 0.94 m, 600 pixels across,
spatial resolution of 9 km (1 mas) near disk center, Minnaert
function reflectivity, long=150W, lat=23S
Titan
Surface
and
its
Atmosphere
• Multi-wavelength observations
Prebiotic
atmosphere
Not completely
transparent in visibleNIR
cm
Atm.
window
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2.7
2.0
1.57
1.26
1.06
0.92
0.83
PSF used : NFAO - no blurring
0.75
Titan
Surface
and
its
Atmosphere
• Comparison HST-ACS/HRC & Keck NGAO
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Clear progress in angular resolution compared with HST
Surface Changes on Titan
HST/ACS R
KNGAO-R
Cryovolcanic-style surface change are detectable with KNGAO in J
band. In R band morphology is better estimated -> volcano caldera, lava
flow?