1. The Deep Impact Mission Karen J. Meech, Astronomer Institute for Astronomy ESO, Feb 13, 2004

2. Photo: Olivier Hainaut (MKO, ESO)

3. Comets Inspire Terror Sudden appearance in sky Sudden appearance in sky Only a few bright naked-eye comets / century Only a few bright naked-eye comets / century Tail physically large  millions of km Tail physically large  millions of km Early composition: toxic chemicals Early composition: toxic chemicals

4. Historical Highlights 1066Halley Wm conqueror 1456 Halley Excommunicated 1531 HalleyObs by Kepler 1744 De Cheseaux6 tails 1858 DonatiMost beautiful 1811Flaugergeuscomet wine 1861TebbuttNaked eye, aurorae 1901Great SDaytime visibility

5. Historical Understanding Tycho Brahe 1577 Tycho Brahe 1577 Parallax – outside atm. Parallax – outside atm. Edmund Halley Edmund Halley 1531, 1607, 1681 1531, 1607, 1681 Orbit determination Orbit determination Newton – Principia Newton – Principia 1950’s – Models 1950’s – Models Whipple  ‘Dirty Snowball’ Whipple  ‘Dirty Snowball’ Lyttleton  ‘Sandbank’ Lyttleton  ‘Sandbank’

6. Physical Processes - Sublimation

7. Physical Processes Sublimation of gases Sublimation of gases Drags dust from nucleus Drags dust from nucleus Gravity low Gravity low Most dust escapes Most dust escapes Solar radiation pressure  coma  dust tail Solar radiation pressure  coma  dust tail photodissociation photodissociation Ionization  gas tail Ionization  gas tail Energy Balance Energy Balance Sunlight  Scattered light + Heating/Sublimation + Conduction Usually very small Energy needed depends on ice Inverse square law: 1/r 2

8. Comet Spectra Reflected sunlight from dust (blackbody radiation) Reflected sunlight from dust (blackbody radiation) Emitted “heat” Emitted “heat” Fluorescence Fluorescence 1P/Halley, 1910 A. Gomez

9. Archaeological Remnants Icy debris left from formation Icy debris left from formation Keys to chemistry & physics in nebula Keys to chemistry & physics in nebula Preservation of inter- stellar material? Preservation of inter- stellar material? Sources of organics  necessary for life Sources of organics  necessary for life

10. Comet Paradigms “Comets are the most pristine things in the Solar System” “Comets are the most pristine things in the Solar System” “Comets tell us about the formation of the Solar System “Comets tell us about the formation of the Solar System

11. Comet Formation

12. Ice Physics Ices condense T < 100K trap gasses Ices condense T < 100K trap gasses T < 30, trap @ solar abundance T < 30, trap @ solar abundance Fractionation @ higher T Fractionation @ higher T Annealing, 35K, 60K – gas release Annealing, 35K, 60K – gas release

13. Comet Formation Regions Oort: form in Jupiter-Neptune zone KBO: form in-situ hot population scattered out 1/3 scatter to Oort cloud Oort  LP comets, HF SP comets KBO  Centaurs  JF SP comets

14. Evolutionary Processes Pre-Solar Nebula Pre-Solar Nebula CR bombardment CR bombardment Accretion phase Accretion phase Sublimation/re-condense Sublimation/re-condense Storage in Oort Cloud Storage in Oort Cloud Radiation damage Radiation damage Volatile loss Volatile loss Chemical alteration Chemical alteration Heating from stars, SN Heating from stars, SN Radioactive Decay Radioactive Decay Gardening / erosion Gardening / erosion Active Phase Active Phase Loss of surface Loss of surface Crystallization of ice Crystallization of ice Build up of dust mantle Build up of dust mantle

15. Aging Processes Build up of surface dust Build up of surface dust Lower albedo Large grains cannot leave Uneven surface  jets Non gravitational acceleration

16. Observing Techniques Sun-warmed ices vaporize, drag dust Sun-warmed ices vaporize, drag dust Ground-based telescopes observe when bright Ground-based telescopes observe when bright Complex processes & chemistry Complex processes & chemistry Primordial composition? Primordial composition? Comet surface evolves over 4.5 Billion years Comet surface evolves over 4.5 Billion years

17. Comet Missions Giotto Halley 1986 Giotto Halley 1986 Flyby Flyby Deep Space 1 9/01 Flyby Deep Space 1 9/01 Flyby Stardust 1/04 Sample return Stardust 1/04 Sample return CONTOUR 3/12 Tour 3 comets CONTOUR 3/12 Tour 3 comets Deep Impact 4/05 Active Experiment Deep Impact 4/05 Active Experiment Rosetta(ESA) 2015 Orbit/Lander Rosetta(ESA) 2015 Orbit/Lander

18. ESA Giotto Mission 1P/Halley – March 1986 1P/Halley – March 1986 ESA – Giotto ESA – Giotto USSR – Vega USSR – Vega Size 15.3 x 7.2 x 7.22 km Size 15.3 x 7.2 x 7.22 km Sunward Jets (from “craters”) Sunward Jets (from “craters”) Mass spec: CHON particles Mass spec: CHON particles Plasma experiments Plasma experiments

19. Deep Space 1 Encounter with 19P/Borrelly 9/22/01 Encounter with 19P/Borrelly 9/22/01 Flyby distance 3417 km Flyby distance 3417 km 8 km long nucleus 8 km long nucleus Large albedo variations (0.009-0.03) Large albedo variations (0.009-0.03)

20. Stardust Results Entered coma 12/31/03 Entered coma 12/31/03 Dust collection 1/2/04 Dust collection 1/2/04 Close approach Close approach 236 km 236 km Comet diam 5 km Comet diam 5 km Pass through zero phase Pass through zero phase

22. The Deep Impact Mission Primary Goal Primary Goal Differences between interior and surface Pristine Solar System material Secondary Goal Secondary Goal Cratering physics Assess comet impact hazard Calibrate crater record Comet evolution

23. Simple but Challenging, 33 yrs ago It [an asteroid] was racing past them at almost thirty miles a second; they had only a few frantic minutes in which to observe it closely. The automatic cameras took dozens of photographs, the navigation radar's returning echoes were carefully recorded for future analysis - and there was just time for a single impact probe. The probe carried no instruments; none could survive a collision at such cosmic speeds. It was merely a small slug of metal, shot out from Discovery on a course which should intersect that of the asteroid. “ It [an asteroid] was racing past them at almost thirty miles a second; they had only a few frantic minutes in which to observe it closely. The automatic cameras took dozens of photographs, the navigation radar's returning echoes were carefully recorded for future analysis - and there was just time for a single impact probe. The probe carried no instruments; none could survive a collision at such cosmic speeds. It was merely a small slug of metal, shot out from Discovery on a course which should intersect that of the asteroid......They were aiming at a hundred-foot-diameter target, from a distance of thousands of miles... Against the darkened portion of the asteroid there was a sudden, dazzling explosion of light....” Arthur C. Clarke, 1968. In 2001: A Space Odyssey. Chapter 18

24. Mission Overview The Deep Impact mission will launch in 1/05 and arrive at comet 9P/Tempel 1 7/4/05; impacting the comet with a 370 kg impactor @10.2 km/sec. The goals are The Deep Impact mission will launch in 1/05 and arrive at comet 9P/Tempel 1 7/4/05; impacting the comet with a 370 kg impactor @10.2 km/sec. The goals are Uncover the primordial nature of the comet Uncover the primordial nature of the comet Learn about impact cratering Learn about impact cratering The pre-encounter observations are used to understand the nucleus properties (size, rotation, albedo, activity, dust environment) to plan for the encounter, and to establish a baseline for comparison post encounter The pre-encounter observations are used to understand the nucleus properties (size, rotation, albedo, activity, dust environment) to plan for the encounter, and to establish a baseline for comparison post encounter To date the observations include To date the observations include > 200 nights of data > 200 nights of data Participation by > 25 astronomers Participation by > 25 astronomers Participation from 17 telescopes, world-wide Participation from 17 telescopes, world-wide

25. Interplanetary Trajectory Launch Dec 2004 Encounter July 4, 2005 Geocentric Dist0.89 AU Heliocentric Dist1.49 AU (q) Approach phase63 o Solar Elong104 o

26. Approach & Encounter Tempel-1 Nucleus Shield Mode Attitude through Inner Coma Science and Autonav Imaging to Impact + 800 sec ITM-1 Start E-88 min ITM-2 E-48 min ITM-3 E-15 min Impactor Release E-24 hours TCA + TBD sec AutoNav Enabled E-2 hr Flyby S/C Deflection Maneuver E-23.5 hr 2-way S-band Crosslink 500 km Flyby S/C Science Data Playback at 175 kbps* to 70-meter DSS Flyby Science Realtime Data at 175 kbps* * data rates without Reed-Solomon encoding Flyby S/C Science And Impactor Data at 175 kbps* 64 kbps

27. Spacecraft Overview Instruments MRI, ITS, HRI

28. Imagers ParameterHRIMRIITS FOV [mrad] 2.0510.210.2 IFOV [  rad] 21010  [  m] 0.3-1.00.3-1.00.3-1.0 PSF FWHM [@0.7  m] <1.3<0.6<0.6 Full Frame Rate [s -1 ] 1/1.71/1.71/1.7 Radiometric Sensitivity Stars 0.1s m~11.3 Stars m~11.3 Boresight Alignment <1 mrad N/A

29. HRI Spectrograph Slit FOV 2.6Mrad IFOV 10  rad  1.05-4.8 mm PSF FWHM < 1 pix  744 @ 1.04  m 209 @ 2.6  m 385 @ 4.8  m

30. Cratering Physics Gravity control expected Gravity control expected Size & time sensitive to comet properties Size & time sensitive to comet properties Size ~ (impactor mass) 1/3 ; insensitive to other properties Size ~ (impactor mass) 1/3 ; insensitive to other properties Ejecta speed, jets – sensitive to other properties Ejecta speed, jets – sensitive to other properties Strength control possible Strength control possible Size (& ejecta speed) depends on impactor density Size (& ejecta speed) depends on impactor density Smaller crater than gravity control Smaller crater than gravity control Greater depth/diameter Greater depth/diameter Details sensitive to impactor shape Details sensitive to impactor shape Compression control possible Compression control possible Scaling relationships not known Scaling relationships not known Mechanism used to explain Mathilde’s craters Mechanism used to explain Mathilde’s craters Distinguish mode by ejecta morphology and crater size Distinguish mode by ejecta morphology and crater size

31. Formation Time Scaling T ~ m 1/6 T ~  c -2/3 T ~ R c -2/3 800-sec observing window provides large margin for extreme cometary properties, even down to bulk density 0.1 g/cc Most important thing is to know impactor properties Bulk Density = 0.3 g/cc Bulk Density = 0.8 g/cc

32. Baseline Predictions Gravity Controlled Gravity Controlled Crater Crater Diameter – 110m Diameter – 110m Depth – 27 m Depth – 27 m Formation Time 200s Formation Time 200s Ejecta Ejecta Max v = 2 km/s Max v = 2 km/s Negligible boulders Negligible boulders Ejecta clumping -> tracking (mass) Ejecta clumping -> tracking (mass) Long-term changes Long-term changes New active area (dys to months) New active area (dys to months) Increase ratio of CO and CO 2 to H 2 O Increase ratio of CO and CO 2 to H 2 O Simulations  Mass determination Simulations  Mass determination  v = 1.09 x 10 -3 mm/s  v = 1.09 x 10 -3 mm/s Below doppler limit Below doppler limit Need “sub-surface” flyby Need “sub-surface” flyby Ejecta plume can get mass Ejecta plume can get mass

33. HRI Spectroscopy Halley spectra @ 42000 km Halley spectra @ 42000 km

34. Ames Vertical Gun Facility Cu sphere @ 4.5 km/s Cu sphere @ 4.5 km/s Target: porous pumice (1 g/cc) Target: porous pumice (1 g/cc) 500 frames / sec 500 frames / sec 60 o impact angle 60 o impact angle Gravity control Gravity control Experiments: P. Schultz

35. Ejecta Plume Simulations Strength dominated Cone detaches Cone detaches Volatiles – drive ejecta, fill in cone Volatiles – drive ejecta, fill in cone Gravity dominated Expected scenario Expected scenario Simulations: J. Richardson

36. Modelling Mass / Density Viewing time 900 s Viewing time 900 s Use velocity to est M Use velocity to est M Simulations: J. Richardson

37. Ground-Based Support Characterize nucleus Characterize nucleus Size & Albedo Size & Albedo R N = 2.6 +/- 0.2, p v = 0.07 R N = 2.6 +/- 0.2, p v = 0.07 Rotation period & pole Rotation period & pole Periods 22.104, 42.091 hr Periods 22.104, 42.091 hr (  ) = 283+/-3, 18+/-3, (  ) = 62+/-3, 73+/-3 (  ) = 283+/-3, 18+/-3, (  ) = 62+/-3, 73+/-3 a:b = 3.3+/-0.2 a:b = 3.3+/-0.2 a = 5.4, b=c=1.6+/-0.2 a = 5.4, b=c=1.6+/-0.2 Phase Function Phase Function Baseline for activity Baseline for activity Dust Environment Dust Environment 10 microns R band

38. Dust Jun 15 2005 May 15 2005Apr 15 2005Feb 15 2005 May 1 2004 Mar 1 2004Jan 1 2004 Critical periods Mar-Apr 04 Mar-Apr 04 Onset Onset Feb-Jul 05 Feb-Jul 05 STSP STSP Dust models  velocity distn, size distn, Q dust Dust models  velocity distn, size distn, Q dust Evaluate motion of dust after leaving comet Evaluate motion of dust after leaving comet Add up the scattered light from grains Add up the scattered light from grains Fit to observations of surface brightness of coma versus time Fit to observations of surface brightness of coma versus time Want observations spread so observing geometry changes a lot Want observations spread so observing geometry changes a lot Small dust (fast) – many images/short time (mostly anti-solar) Small dust (fast) – many images/short time (mostly anti-solar) Large dust – equally spaced – long periods (monthly) (along orbit) Large dust – equally spaced – long periods (monthly) (along orbit)

39. Bohyunsan 1.8m (Korea) Bohyunsan 1.8m (Korea) Y-C. Choi Y-C. Choi D. Prialnik D. Prialnik Wise 1.1m (Israel) Wise 1.1m (Israel) Y-C. Choi Y-C. Choi D. Prialnik D. Prialnik KPNO: 4m, Wiyn3.5m, 2.1m KPNO: 4m, Wiyn3.5m, 2.1m M. Belton M. Belton N. Samarasinha N. Samarasinha B. Mueller B. Mueller P. Massey P. Massey R. Millis R. Millis Mauna Kea: Keck 10m, UH2.2m Mauna Kea: Keck 10m, UH2.2m K. Meech, M. F. A’Hearn K. Meech, M. F. A’Hearn M. Belton, C. Lisse M. Belton, C. Lisse Y. Fernandez, J. Pittichova Y. Fernandez, J. Pittichova H. Hsieh, G. Bauer H. Hsieh, G. Bauer S. Sheppard, P. Henry S. Sheppard, P. Henry Lowell 72” 42” Lowell 72” 42” M. Buie M. Buie ESO: VLT8.0m, NTT3.6m, Dan1.5m ESO: VLT8.0m, NTT3.6m, Dan1.5m H. Boehnhardt H. Boehnhardt O. Hainaut O. Hainaut K. Meech K. Meech CTIO: 4m, 1.5m CTIO: 4m, 1.5m M. Mateo M. Mateo N. Suntzeff N. Suntzeff K. Krisciunas K. Krisciunas TNG 3.6m TNG 3.6m G. P. Tozzi G. P. Tozzi J. Licandro J. Licandro McDonald: 2.7m 82” McDonald: 2.7m 82” T. Farnham T. Farnham Participating Observatories

40. Comet Paradigms “Comets are the most pristine things in the Solar System” “Comets are the most pristine things in the Solar System” “Comets tell us about the formation of the Solar System “Comets tell us about the formation of the Solar System

42. Stardust Mission Timeline Timeline Launch 2/7/99 – Delta II Dust 1: Feb-May 2000 Dust 2: Aug-Dec 2002 Enter coma: Dec 31, ’03 Earth Return 1/15/06 Science Goals Science Goals Comet imaging – 81P/Wild 2 ISM Dust collection Comet dust collection

43. Earth collection Arrival 1/15/06 Arrival 1/15/06 Final descent via parchute Final descent via parchute Curation and study – Johnson Space Center Curation and study – Johnson Space Center

44. Dust Collection Captured in aerogel Captured in aerogel 99.8% air 40x more insulation than fiberglass No heating at 6.1 km/s