1. EPOXI @ Hartley 2
Overview
Mike A’Hearn
&
DIXI Science Team
&
Associated Remote Sensing Observers
EPSC-DPS Joint Meeting

2. 2

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5. Hartley 2 is Different
• Previously known and published
• Large changes in rotational state
• Activity driven by CO2
• Much water from icy grains
• Very high CO2/CO ~ 100
• Is Hartley 2 the prototype for
hyperactive comets aka comets with
large active fraction?
5

6. New Results - Grains
• Much of the water comes from grains
moving tailward - Knight
• Radiation pressure? Or sunward sublimation?
• Grains sublime slowly - Kelley/Protopapa
• Can now separate icy & refractory grains
- Protopapa
• New measurements of grain trajectories
- Hermalyn
6

7. New Results - Activity
• Two ends have very different CO2 abundance -
Feaga/Besse
• New results on low CO abundance & atomic species -
Weaver/Feldman
• OH spatially separate from other radicals - Knight
• nearly pure icy grains?
• Modeling CO2 Jets - Syal
• Light curves - Bodewits/Jehin/Combi/Meech/
Waniak
• IR spatial distribution - Mumma
7

8. New Results - Nucleus
• Ice on the surface - Sunshine
• Photometric Properties - Li
• Thermal properties - Groussin
• Rotational State & Models - Chesley/
Taylor/Drahus/Mueller/Bowling
(density)
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12. Motion of Chunks
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13. Absolute Abundances
• Data from E-55 h
• FOV large enough to avoid optical depth problems
• Same orientation as encounter (3 cycles earlier)
• CO2 ~20% of H2O at peaks; 10% at minima
• >2x higher than measured with ISO in 1997
• Q(H2O) down 5x from 1997
• Excited rotation illuminates all surface - ends are primordially
different
• CO ~0.2% in Hartley 2 at time of encounter using HST!
• Kawakita et al. with Akari find CO2/H2O 5-30% in many
comets, both Halley-type & Jupiter family, inside 2.5 AU
11

14. Implications
• Waist is probably redeposited
material, including H2O ice
• CO << CO : Not expected in
2
protoplanetary disk
• Tempel 1 CO ~ CO2; Halley CO >> CO2
(extended source? CO ~ CO2 from nucleus?)
• Is the abundance ratio primordial?
• CO2/H2O different in two lobes
• Argues against evolution
12

15. P-P Disk Abundances
• Dodson-Robinson et al. 2008 Icarus 200, 672
(as an example)
• r > 30 AU, disk is isothermal, 20K
• CO and CO2 both mostly ice
• CO/CO2 ~ 104 (in icy mantles)
• CO 40-50K, CO2 ~100K, H2O ~190K
• But see newer work on ice formation (surface
reactions)
• Garrod & Pauly 2011 ApJ 735, 15
13

16. Disk Temperatures
• Disk radial temperature
profiles for first 2 Myrs
• CO2 ice line inside present
Saturn, CO ice line inside
present Uranus
• How does planetary
migration alter this
picture?
• Did SP comets really form
near the giant planets?
Dodson-Robinson et al., 2009
14

17. Global Implications
• Suggest that most comets we see today formed at
10-30 AU
• Both JF and Oort cloud comets, or at least a significant
fraction of them
• Radial migration of giant planets mixed them up
• cf. Walsh et al. 2011 (Nature 475, 206) on migration
mixing up the asteroid belt
• Cometesimals were mixed during aggregation into
comets
• Comets were mixed with scattered disk & classical KB
15

18. Conclusions
• Every visit to a comet has surprised
us
• New phenomena, new physical processes
• Comets are more diverse than we thought
• We are slowly beginning to separate
evolutionary properties from
primordial properties
• Are comets as pristine as we claim?
16

19. Backup

20. P-P Disk Abundances
• Dodson-Robinson et al. 2008 Icarus
200, 672 (as an example)
• r > 30 AU, disk is isothermal, 20K
• CO and CO2 both mostly ice
• CO/CO2 ~ 10 (in icy mantles)
4
• CO 40-50K, CO2 ~100K, H2O ~190K
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21. Hartley 2 vs. Tempel 1
• Nuclear radius ~0.2x Tempel 1
• Activity in OH and CN: 10x Tempel
• Activity in dust: 2x Tempel 1
• Encounter closer to sun by ~1/√2
• All signals from coma stronger, gas 20x, dust 4x
• Activity estimate was pre-encounter, Earth-based
data show secular decrease (as seen in Tempel 1)
• Why is Hartley 2 proportionately so active?
• P ~ 18 h vs. ~40h
rot
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22. Carbon-Chain Depletion
• Still the only correlation
between chemistry and
dynamical history (A’Hearn
et al. 1995)
• Suggests a boundary in the
classical Kuiper belt at
which T passes a threshold
for certain reactions or
condensations
H B W2 T1 H2 CG
C2/CN +0.13 -0.36 -0.21 -0.09 +0.08 -0.31
TJ -0.61 2.56 2.88 2.97 2.64 2.74
T D D T T D
20

23. Carbon-Chain Depletion
• Still the only correlation
between chemistry and
dynamical history (A’Hearn
et al. 1995)
• Suggests a boundary in the
classical Kuiper belt at
which T passes a threshold
for certain reactions or
condensations
H B W2 T1 H2 CG
C2/CN +0.13 -0.36 -0.21 -0.09 +0.08 -0.31
TJ -0.61 2.56 2.88 2.97 2.64 2.74
T D D T T D
20

24. Carbon-Chain Depletion
• Still the only correlation
between chemistry and
dynamical history (A’Hearn
et al. 1995)
• Suggests a boundary in the
classical Kuiper belt at
which T passes a threshold
for certain reactions or
condensations
H B W2 T1 H2 CG
C2/CN +0.13 -0.36 -0.21 -0.09 +0.08 -0.31
TJ -0.61 2.56 2.88 2.97 2.64 2.74
T D D T T D
20

25. DI Flyby Spacecraft
Medium Res camera
(MRI)
•10 µrad/pixel
•8 filters
•High Res Camera (HRIV)
•2 µrad/pixel
•8 filters
•IR Spectrometer (HRII)
•10 µrad/pixel
•Slit 10 µrad x 5 mrad
•1.05 < λ < 4.8 µm
•230 < λ/δλ < 700
21

26. DI Flyby Spacecraft
Medium Res camera
(MRI)
•10 µrad/pixel
•8 filters
•High Res Camera (HRIV)
•2 µrad/pixel
•8 filters
•IR Spectrometer (HRII)
•10 µrad/pixel
•Slit 10 µrad x 5 mrad
•1.05 < λ < 4.8 µm
•230 < λ/δλ < 700
21

27. DI Flyby Spacecraft
Medium Res camera
(MRI)
•10 µrad/pixel
•8 filters
•High Res Camera (HRIV)
•2 µrad/pixel
•8 filters
•IR Spectrometer (HRII)
•10 µrad/pixel
•Slit 10 µrad x 5 mrad
•1.05 < λ < 4.8 µm
•230 < λ/δλ < 700
21

28. DI Flyby Spacecraft
Medium Res camera
(MRI)
•10 µrad/pixel
•8 filters
•High Res Camera (HRIV)
•2 µrad/pixel
•8 filters
•IR Spectrometer (HRII)
•10 µrad/pixel
•Slit 10 µrad x 5 mrad
•1.05 < λ < 4.8 µm
•230 < λ/δλ < 700
21

29. DI Flyby Spacecraft
Medium Res camera
(MRI)
•10 µrad/pixel
•8 filters
•High Res Camera (HRIV)
•2 µrad/pixel
•8 filters
•IR Spectrometer (HRII)
•10 µrad/pixel
•Slit 10 µrad x 5 mrad
•1.05 < λ < 4.8 µm
•230 < λ/δλ < 700
21

30. Deep Impact
• Main Goal: Compare volatiles inside
nucleus with ambient gases released
• Other Goals:Physical properties,
Cometary heterogeneity
• Launch 12 Jan ’05 Impact 4 Jul ’05
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31. DI Results
• No difference in volatiles down to ~20m
• Surface erodes as fast as thermal wave propagates inward?
• KOSI & theory both say there should be differences
• Dry ice and water ice sublime from different parts of
the nucleus
• Can’t exclude evolutionary process
• Nucleus is very porous (>75%)
• Both locally at impact site & bulk of nucleus
• Layers are ubiquitous
• TALPS model of formation
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32. CN Anomaly
• An early (Sept)
distraction
• ~800 tons of CN over
2 weeks
• No increase in H2O
• Little increase in
optically important
grains
• Not like most
cometary outbursts
• Instrumental effect?
TCM 19
TCM 20 TCM 21
19 Jul
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33. Movie Flying Under Comet
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34. Movie Flying Under Comet
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