The Deep Impact MissionThe Deep Impact Mission

Karen J. Meech, AstronomerKaren J. Meech, AstronomerInstitute for AstronomyInstitute for Astronomy

ESO, Feb 13, 2004ESO, Feb 13, 2004

Photo: Olivier Hainaut (MKO, ESO)Photo: Olivier Hainaut (MKO, ESO)

Comets Inspire TerrorComets Inspire Terror

Sudden appearance in skySudden appearance in sky Only a few bright naked-eye comets / centuryOnly a few bright naked-eye comets / century Tail physically large Tail physically large millions of km millions of km Early composition: toxic chemicalsEarly composition: toxic chemicals

Historical HighlightsHistorical Highlights10661066 Halley Halley Wm conquerorWm conqueror1456 1456 Halley Halley ExcommunicatedExcommunicated1531 1531 HalleyHalley Obs by KeplerObs by Kepler1744 1744 De CheseauxDe Cheseaux 6 tails6 tails1858 1858 DonatiDonati Most beautifulMost beautiful18111811 FlaugergeusFlaugergeus comet wine comet wine 18611861 TebbuttTebbutt Naked eye, Naked eye,

auroraeaurorae19011901 Great SGreat S Daytime visibilityDaytime visibility

Historical Historical UnderstandingUnderstanding

Tycho Brahe 1577Tycho Brahe 1577 Parallax – outside atm.Parallax – outside atm.

Edmund HalleyEdmund Halley 1531, 1607, 16811531, 1607, 1681 Orbit determinationOrbit determination Newton – Principia Newton – Principia

1950’s – Models1950’s – Models Whipple Whipple ‘Dirty Snowball’ ‘Dirty Snowball’ Lyttleton Lyttleton ‘Sandbank’ ‘Sandbank’

Physical Processes - SublimationPhysical Processes - Sublimation

Physical ProcessesPhysical Processes Sublimation of gasesSublimation of gases Drags dust from nucleusDrags dust from nucleus

Gravity lowGravity low Most dust escapesMost dust escapes Solar radiation pressure Solar radiation pressure

coma coma dust tail dust tail photodissociationphotodissociation

Ionization Ionization gas tail gas tail Energy BalanceEnergy Balance

Sunlight Sunlight Scattered light + Heating/Sublimation + Conduction Scattered light + Heating/Sublimation + Conduction

Usually very smallUsually very small

Energy needed depends on iceEnergy needed depends on ice

Inverse square law: 1/rInverse square law: 1/r22

Comet SpectraComet Spectra

Reflected sunlight from dust Reflected sunlight from dust (blackbody radiation)(blackbody radiation)

Emitted “heat”Emitted “heat” FluorescenceFluorescence

1P/Halley, 19101P/Halley, 1910

A. GomezA. Gomez

Archaeological Archaeological RemnantsRemnants

Icy debris left from Icy debris left from formationformation

Keys to chemistry & Keys to chemistry & physics in nebulaphysics in nebula

Preservation of inter- Preservation of inter- stellar material?stellar material?

Sources of organics Sources of organics necessary for life necessary for life

Comet ParadigmsComet Paradigms

““Comets are the most Comets are the most pristine things in the pristine things in the Solar System”Solar System”

““Comets tell us about Comets tell us about the formation of the the formation of the Solar SystemSolar System

Comet FormationComet Formation

Ice PhysicsIce Physics

Ices condense T < 100K trap gassesIces condense T < 100K trap gasses T < 30, trap @ solar abundanceT < 30, trap @ solar abundance Fractionation @ higher TFractionation @ higher T Annealing, 35K, 60K – gas releaseAnnealing, 35K, 60K – gas release

Comet Formation RegionsComet 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

Evolutionary ProcessesEvolutionary Processes Pre-Solar NebulaPre-Solar Nebula

CR bombardmentCR bombardment Accretion phaseAccretion phase

Sublimation/re-condenseSublimation/re-condense Storage in Oort CloudStorage in Oort Cloud

Radiation damageRadiation damage Volatile lossVolatile loss Chemical alterationChemical alteration Heating from stars, SNHeating from stars, SN Radioactive DecayRadioactive Decay Gardening / erosionGardening / erosion

Active PhaseActive Phase Loss of surfaceLoss of surface Crystallization of iceCrystallization of ice Build up of dust mantleBuild up of dust mantle

Aging ProcessesAging Processes Build up of surface dustBuild up of surface dust

Lower albedoLower albedo Large grains cannot Large grains cannot

leaveleave Uneven surface Uneven surface jets jets Non gravitational Non gravitational

accelerationacceleration

Observing TechniquesObserving Techniques Sun-warmed ices Sun-warmed ices

vaporize, drag dustvaporize, drag dust Ground-based telescopes Ground-based telescopes

observe when brightobserve when bright Complex processes & Complex processes &

chemistrychemistry Primordial composition?Primordial composition? Comet surface evolves Comet surface evolves

over 4.5 Billion yearsover 4.5 Billion years

Comet MissionsComet Missions

Giotto HalleyGiotto Halley 1986 1986 FlybyFlyby

Deep Space 1Deep Space 1 9/01 9/01FlybyFlyby

StardustStardust 1/04 1/04Sample returnSample return

CONTOURCONTOUR 3/12 3/12Tour 3 cometsTour 3 comets

Deep ImpactDeep Impact 4/05 4/05Active ExperimentActive Experiment

Rosetta(ESA)Rosetta(ESA) 2015 2015Orbit/LanderOrbit/Lander

ESA Giotto MissionESA Giotto Mission

1P/Halley – March 19861P/Halley – March 1986 ESA – GiottoESA – Giotto USSR – VegaUSSR – Vega

Size 15.3 x 7.2 x 7.22 kmSize 15.3 x 7.2 x 7.22 km Sunward Jets (from Sunward Jets (from

“craters”)“craters”) Mass spec: CHON Mass spec: CHON

particlesparticles Plasma experimentsPlasma experiments

Deep Space 1Deep Space 1

Encounter with 19P/Borrelly 9/22/01Encounter with 19P/Borrelly 9/22/01 Flyby distance 3417 kmFlyby distance 3417 km 8 km long nucleus8 km long nucleus Large albedo variations (0.009-0.03)Large albedo variations (0.009-0.03)

Stardust ResultsStardust Results

Entered coma 12/31/03Entered coma 12/31/03 Dust collection 1/2/04Dust collection 1/2/04 Close approachClose approach

236 km236 km Comet diam 5 kmComet diam 5 km Pass through zero Pass through zero

phasephase

The Deep Impact MissionThe Deep Impact Mission

Primary GoalPrimary Goal Differences between Differences between

interior and surfaceinterior and surface Pristine Solar System Pristine Solar System

materialmaterial Secondary GoalSecondary Goal

Cratering physicsCratering physics Assess comet impact Assess comet impact

hazardhazard Calibrate crater recordCalibrate crater record Comet evolutionComet evolution

Simple but Challenging, 33 yrs agoSimple but Challenging, 33 yrs ago

“ It [an asteroid] was racing past them at almost thirty miles It [an asteroid] was racing past them at almost thirty miles a second; they had only a few frantic minutes in which to a second; they had only a few frantic minutes in which to observe it closely. The automatic cameras took dozens of observe it closely. The automatic cameras took dozens of photographs, the navigation radar's returning echoes photographs, the navigation radar's returning echoes were carefully recorded for future analysis - and there was were carefully recorded for future analysis - and there was just time for a single impact probe. The probe carried no just time for a single impact probe. The probe carried no instruments; none could survive a collision at such instruments; none could survive a collision at such cosmic speeds. It was merely a small slug of metal, shot cosmic speeds. It was merely a small slug of metal, shot out from Discovery on a course which should intersect out from Discovery on a course which should intersect that of the asteroid.that of the asteroid.

.....They were aiming at a hundred-foot-diameter target, .....They were aiming at a hundred-foot-diameter target, from a distance of thousands of miles... Against the from a distance of thousands of miles... Against the darkened portion of the asteroid there was a sudden, darkened portion of the asteroid there was a sudden, dazzling explosion of light. ...”dazzling explosion of light. ...”

Arthur C. Clarke, 1968. In Arthur C. Clarke, 1968. In 2001: A Space Odyssey2001: A Space Odyssey. Chapter 18. Chapter 18

Mission OverviewMission Overview The Deep Impact mission will launch in 1/05 and arrive The Deep Impact mission will launch in 1/05 and arrive

at comet 9P/Tempel 1 7/4/05; impacting the comet with a at comet 9P/Tempel 1 7/4/05; impacting the comet with a 370 kg impactor @10.2 km/sec. The goals are370 kg impactor @10.2 km/sec. The goals are Uncover the primordial nature of the cometUncover the primordial nature of the comet Learn about impact crateringLearn about impact cratering

The pre-encounter observations are used to understand The pre-encounter observations are used to understand the nucleus properties (size, rotation, albedo, activity, the nucleus properties (size, rotation, albedo, activity, dust environment) to plan for the encounter, and to dust environment) to plan for the encounter, and to establish a baseline for comparison post encounterestablish a baseline for comparison post encounter

To date the observations includeTo date the observations include > 200 nights of data> 200 nights of data Participation by > 25 astronomersParticipation by > 25 astronomers Participation from 17 telescopes, world-wideParticipation from 17 telescopes, world-wide

Interplanetary TrajectoryInterplanetary 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

Approach & EncounterApproach & Encounter

Tempel-1Nucleus

Shield ModeAttitude through

Inner Coma

Science and Autonav Imaging to

Impact + 800 sec

ITM-1 StartE-88 min

ITM-2E-48 min

ITM-3E-15 min

Impactor ReleaseE-24 hours

TCA +TBD sec

AutoNav EnabledE-2 hr

Flyby S/CDeflection Maneuver

E-23.5 hr

2-wayS-band

Crosslink

500 km

Flyby S/C Science Data Playback at 175 kbps*

to 70-meter DSS

Flyby Science Realtime Dataat 175 kbps*

* data rates without Reed-Solomon encoding

Flyby S/C Science And Impactor Data

at 175 kbps*

64kbps

Spacecraft OverviewSpacecraft Overview

InstrumentsInstrumentsMRI, ITS, HRIMRI, ITS, HRI

ImagersImagers

ParameterParameter HRIHRI MRIMRI ITSITS

FOV [mrad]FOV [mrad] 2.052.05 10.210.2 10.210.2

IFOV [IFOV [rad]rad] 22 1010 1010

[[m]m] 0.3-1.00.3-1.0 0.3-1.00.3-1.0 0.3-1.00.3-1.0

PSF FWHM PSF FWHM [@0.7[@0.7m]m]

<1.3<1.3 <0.6<0.6 <0.6<0.6

Full Frame Full Frame Rate [sRate [s-1-1]]

1/1.71/1.7 1/1.71/1.7 1/1.71/1.7

Radiometric Radiometric SensitivitySensitivity

Stars 0.1s Stars 0.1s m~11.3 m~11.3

Stars 0.1 s Stars 0.1 s m~11.3m~11.3

Stars Stars m~11.3m~11.3

Boresight Boresight AlignmentAlignment

<1 mrad<1 mrad <1 mrad<1 mrad N/AN/A

HRI SpectrographHRI Spectrograph

Slit FOVSlit FOV 2.6Mrad2.6Mrad

IFOVIFOV 10 10 radrad

1.05-4.8 mm1.05-4.8 mm

PSF FWHMPSF FWHM < 1 pix< 1 pix

744 @ 1.04 744 @ 1.04 mm

209 @ 2.6 209 @ 2.6 mm

385 @ 4.8 385 @ 4.8 mm

Cratering PhysicsCratering Physics Gravity control expectedGravity control expected

Size & time sensitive to comet propertiesSize & time sensitive to comet properties Size ~ (impactor mass)Size ~ (impactor mass)1/31/3; insensitive to other properties; insensitive to other properties Ejecta speed, jets – sensitive to other propertiesEjecta speed, jets – sensitive to other properties

Strength control possibleStrength control possible Size (& ejecta speed) depends on impactor densitySize (& ejecta speed) depends on impactor density Smaller crater than gravity controlSmaller crater than gravity control Greater depth/diameterGreater depth/diameter Details sensitive to impactor shapeDetails sensitive to impactor shape

Compression control possibleCompression control possible Scaling relationships not knownScaling relationships not known Mechanism used to explain Mathilde’s cratersMechanism used to explain Mathilde’s craters

Distinguish mode by ejecta morphology and crater sizeDistinguish mode by ejecta morphology and crater size

Formation Time ScalingFormation Time Scaling

T ~ m1/6

T ~ c-2/3

T ~ Rc-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

Different Cometary Bulk Densities(Affects Gravitational Acceleration)

Impactor Mass (kg)

Cra

ter

Fo

rmati

on

Tim

e (

s)

Surface Density = 0.3 g/cc

150

200

250

300

350

400

450

50

550

100 200 400 600 1000

Bulk Density = 0.3 g/cc

Bulk Density = 0.8 g/cc

Baseline PredictionsBaseline Predictions

Gravity ControlledGravity Controlled CraterCrater

Diameter – 110mDiameter – 110m Depth – 27 mDepth – 27 m Formation Time 200sFormation Time 200s

EjectaEjecta Max v = 2 km/sMax v = 2 km/s Negligible bouldersNegligible boulders Ejecta clumping -> tracking Ejecta clumping -> tracking

(mass)(mass)

Long-term changesLong-term changes New active area (dys to New active area (dys to

months)months) Increase ratio of CO and Increase ratio of CO and

COCO22 to H to H22OO

Simulations Simulations Mass Mass determinationdetermination v = 1.09 x 10v = 1.09 x 10-3-3 mm/s mm/s Below doppler limitBelow doppler limit Need “sub-surface” flybyNeed “sub-surface” flyby Ejecta plume can get massEjecta plume can get mass

HRI SpectroscopyHRI Spectroscopy

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

2.5 3.0 3.5 4.0 4.5 5.0

Wavelength (microns)

Su

rfac

e B

rig

htn

ess

(kR

)

150 K145 K140 K135 KCO RequirementPre-Impact3.5 um Requirement

CO

CO2

H2CO

H2O

Halley spectra @ 42000 kmHalley spectra @ 42000 km

Ames Vertical Gun FacilityAmes Vertical Gun Facility

Cu sphere @ 4.5 km/sCu sphere @ 4.5 km/s Target: porous pumice Target: porous pumice

(1 g/cc)(1 g/cc) 500 frames / sec500 frames / sec 6060oo impact angle impact angle Gravity controlGravity control

Experiments: P. SchultzExperiments: P. Schultz

Ejecta Plume SimulationsEjecta Plume SimulationsStrength dominatedStrength dominated

Cone detachesCone detaches Volatiles – drive ejecta, fill in coneVolatiles – drive ejecta, fill in cone

Gravity dominatedGravity dominated Expected scenarioExpected scenario

Sim

ulat

ions

: J

. R

icha

rdso

nS

imul

atio

ns:

J.

Ric

hard

son

Modelling Mass / DensityModelling Mass / Density

Viewing time 900 sViewing time 900 s Use velocity to est MUse velocity to est M

Simulations: J. RichardsonSimulations: J. Richardson

Ground-Based SupportGround-Based Support

Characterize nucleusCharacterize nucleus Size & AlbedoSize & Albedo

RRNN = 2.6 +/- 0.2, p = 2.6 +/- 0.2, pvv = 0.07 = 0.07

Rotation period & poleRotation period & pole Periods 22.104, 42.091 hrPeriods 22.104, 42.091 hr (() = 283+/-3, 18+/-3, ) = 283+/-3, 18+/-3,

(() = 62+/-3, 73+/-3) = 62+/-3, 73+/-3 a:b = 3.3+/-0.2a:b = 3.3+/-0.2 a = 5.4, b=c=1.6+/-0.2a = 5.4, b=c=1.6+/-0.2

Phase FunctionPhase Function

Baseline for activityBaseline for activity Dust EnvironmentDust Environment

10 microns10 microns R bandR band

DustDust

Jun 15 2005

May 15 2005Apr 15 2005Feb 15 2005

May 1 2004Mar 1 2004Jan 1 2004

Critical periodsCritical periods Mar-Apr 04Mar-Apr 04

OnsetOnset Feb-Jul 05Feb-Jul 05

STSPSTSP

Dust models Dust models velocity distn, size distn, Q velocity distn, size distn, Qdustdust

Evaluate motion of dust after leaving cometEvaluate motion of dust after leaving comet Add up the scattered light from grainsAdd up the scattered light from grains Fit to observations of surface brightness of coma versus timeFit to observations of surface brightness of coma versus time Want observations spread so observing geometry changes a lotWant 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)

Bohyunsan 1.8m Bohyunsan 1.8m (Korea)(Korea)

Y-C. ChoiY-C. Choi D. PrialnikD. Prialnik

Wise 1.1m (Israel)Wise 1.1m (Israel) Y-C. ChoiY-C. Choi D. PrialnikD. Prialnik

KPNO: 4m, KPNO: 4m, Wiyn3.5m, 2.1mWiyn3.5m, 2.1m

M. BeltonM. Belton N. SamarasinhaN. Samarasinha B. MuellerB. Mueller P. MasseyP. Massey R. MillisR. Millis

Mauna Kea: Keck 10m, Mauna Kea: Keck 10m, UH2.2mUH2.2m

K. Meech, M. F. A’HearnK. Meech, M. F. A’Hearn M. Belton, C. LisseM. Belton, C. Lisse Y. Fernandez, J. PittichovaY. Fernandez, J. Pittichova H. Hsieh, G. BauerH. Hsieh, G. Bauer S. Sheppard, P. HenryS. Sheppard, P. Henry

Lowell 72” Lowell 72” 42”42”

M. BuieM. Buie

ESO: VLT8.0m, ESO: VLT8.0m, NTT3.6m, NTT3.6m, Dan1.5mDan1.5m

H. BoehnhardtH. Boehnhardt O. HainautO. Hainaut K. MeechK. Meech

CTIO: 4m, 1.5mCTIO: 4m, 1.5m M. MateoM. Mateo N. SuntzeffN. Suntzeff K. KrisciunasK. Krisciunas

TNG 3.6mTNG 3.6m G. P. TozziG. P. Tozzi J. LicandroJ. Licandro

McDonald: 2.7m McDonald: 2.7m 82”82”

T. FarnhamT. Farnham

Participating ObservatoriesParticipating Observatories

Comet ParadigmsComet Paradigms

““Comets are the most Comets are the most pristine things in the pristine things in the Solar System”Solar System”

““Comets tell us about Comets tell us about the formation of the the formation of the Solar SystemSolar System

Stardust MissionStardust Mission

TimelineTimeline Launch 2/7/99 – Delta IILaunch 2/7/99 – Delta II Dust 1: Feb-May 2000Dust 1: Feb-May 2000 Dust 2: Aug-Dec 2002Dust 2: Aug-Dec 2002 Enter coma: Dec 31, ’03Enter coma: Dec 31, ’03 Earth Return 1/15/06Earth Return 1/15/06

Science GoalsScience Goals Comet imaging – 81P/Wild 2Comet imaging – 81P/Wild 2 ISM Dust collectionISM Dust collection Comet dust collectionComet dust collection

Earth collectionEarth collection

Arrival 1/15/06Arrival 1/15/06 Final descent via parchuteFinal descent via parchute Curation and study – Johnson Space CenterCuration and study – Johnson Space Center

Dust CollectionDust Collection Captured in aerogelCaptured in aerogel

99.8% air99.8% air 40x more insulation 40x more insulation

than fiberglassthan fiberglass No heating at 6.1 km/sNo heating at 6.1 km/s