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The Deep Impact Mission

The Deep Impact Mission. Karen J. Meech, Astronomer Institute for Astronomy ESO, Feb 13, 2004. Photo: Olivier Hainaut (MKO, ESO). Comets Inspire Terror. Sudden appearance in sky Only a few bright naked-eye comets / century Tail physically large  millions of km

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The Deep Impact Mission

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  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 • Only a few bright naked-eye comets / century • Tail physically large  millions of km • Early composition: toxic chemicals

  4. Historical Highlights 1066 Halley Wm conqueror 1456 Halley Excommunicated 1531 Halley Obs by Kepler 1744 De Cheseaux 6 tails 1858 Donati Most beautiful 1811 Flaugergeus comet wine 1861 Tebbutt Naked eye, aurorae 1901 Great S Daytime visibility

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

  6. Physical Processes - Sublimation

  7. Physical Processes • Sublimation of gases • Drags dust from nucleus • Gravity low • Most dust escapes • Solar radiation pressure  coma  dust tail • photodissociation • Ionization  gas tail • Energy Balance Sunlight  Scattered light + Heating/Sublimation + Conduction Usually very small Energy needed depends on ice Inverse square law: 1/r2

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

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

  10. Comet Paradigms • “Comets are the most pristine things in 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 • T < 30, trap @ solar abundance • Fractionation @ higher T • 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 • CR bombardment • Accretion phase • Sublimation/re-condense • Storage in Oort Cloud • Radiation damage • Volatile loss • Chemical alteration • Heating from stars, SN • Radioactive Decay • Gardening / erosion • Active Phase • Loss of surface • Crystallization of ice • Build up of dust mantle

  15. Aging Processes • 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 • Ground-based telescopes observe when bright • Complex processes & chemistry • Primordial composition? • Comet surface evolves over 4.5 Billion years

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

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

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

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

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

  22. 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. .....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

  23. 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 • Uncover the primordial nature of the comet • 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 • To date the observations include • > 200 nights of data • Participation by > 25 astronomers • Participation from 17 telescopes, world-wide

  24. Interplanetary Trajectory • Launch Dec 2004 • Encounter July 4, 2005 • Geocentric Dist 0.89 AU • Heliocentric Dist 1.49 AU (q) • Approach phase 63o • Solar Elong 104o

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

  26. Spacecraft Overview Instruments MRI, ITS, HRI

  27. Imagers

  28. HRI Spectrograph

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

  30. Formation Time Scaling T ~ m1/6 T ~ rc-2/3 T ~ Rc-2/3 Bulk Density = 0.3 g/cc 800-sec observing window provides large margin for extreme cometary properties, even down to bulk density 0.1 g/cc Bulk Density = 0.8 g/cc Most important thing is to know impactor properties

  31. Baseline Predictions • Gravity Controlled • Crater • Diameter – 110m • Depth – 27 m • Formation Time 200s • Ejecta • Max v = 2 km/s • Negligible boulders • Ejecta clumping -> tracking (mass) • Long-term changes • New active area (dys to months) • Increase ratio of CO and CO2 to H2O • Simulations  Mass determination • Dv = 1.09 x 10-3 mm/s • Below doppler limit • Need “sub-surface” flyby • Ejecta plume can get mass

  32. HRI Spectroscopy • Halley spectra @ 42000 km

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

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

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

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

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

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

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

  40. Stardust Mission • 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 • Comet imaging – 81P/Wild 2 • ISM Dust collection • Comet dust collection

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

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

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