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rev. May 21, 2002 EMW

Deep Impact: First Look Inside a Comet
http://deepimpact.jpl.nasa.gov, http://deepimpact.umd.edu
M.F. A'Hearn, L.A. McFadden, C.M. Lisse, D.D.Wellnitz (U. MD.), M.J.S. Belton (BSEI), A. Delamere (BATC), K.P. Klaasen (JPL), J.Kissel (MPI), K.J. Meech (U. H.), H.J. Melosh (U. A.), P.H. Schultz (Brown), J.M. Sunshine (SAIC), J. Veverka (Cornell U.), D.K. Yeomans (JPL) and the Deep Impact Project Members
E. W. L. Tempel

1 2 3 4

. . . .

Wha How Wha How

t are the basic properties of a cometary nucleus and interior? do comets evolve? t is the composition of primordial ices in comets? would one mitigate a cometary impact on Earth?

Deep Impact's Scientific Questions:

Target: 9P/Tempel 1
Impa c to r R e l e a s e E -24 ho urs

Encounter Sequence
A utoN a v E na bl e d E -2 hr I T M - 1 S ta rt E -100 min I TM- 2 E -35 min I TM- 3 E -9 min T e mpe l 1 N uc le us

A Unique Experiment
F ly by S /C De fle c tion a n d De fle c tion M a n e u ve r R e le a s e + 12 min (101 m/s ) Fly by S/C Sc ienc e And Imp ac tor Data at 200 k bps *

64 kbps

2 -w ay S - ba nd C r os s link

5 0 0 km

Impa c t!

S c ie nc e a nd A utona v Ima ging to Impa c t + 800 s e c

TCA

Fly by Sc ienc e Realtime Data at 200 k bps *

S hie ld M od e A ttitude through Inn e r C oma TCA + 30 min Fly by S/C Sc ienc e Data Play bac k at 200 k bps * to 70-mete r DS N

Period Perihelion Rotation Radius Aspect Ratio

5.51 yrs. 1.51 AU 41 hrs 3.0 km 2:1 ?

* data rates with R eed -Solom on enc o ding
ITM = impactor targeting maneuver TCA = time of closest approach

(Not to scale)

Observing Sequence

L ook -b a c k Ima gi ng T C A +30 min

A 370 kg impactor will hit Tempel 1 at 10.2 km/s with a variety of possible outcomes:
· If impact energy goes into breaking the surface (strength dominated), then the crater will be small with a 3:1 diameter to depth ratio. The ejecta cone will detach. If impact energy goes into compressing porous material (compression dominated), then the crater will be small and deep with a weak ejecta cone. If impact energy excavates weak material (gravity dominated), then the crater will be large, ~60-240m in diameter, with a 4:1 diameter to depth ratio. The ejecta cone will remain attached. Since we know so little about comets, it is not clear which regime will dominate. The Deep Impact science team pre-launch expectation is that the newly formed crater will be gravity dominated.

Mission Trajectory
Launch Ja n 2, 200 4 Earth Flyby D ec 31, 2004 SUN S/C S/C Ea r th Orbit

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Tempel 1 Orbit (5.5 year Period) Impact July 4, 2005 dsun = 1.51 AU dearth = 0.895 AU

Earth at Encounter Perihelion July 5, 2005 dsun = 1.51 AU dearth = 0.900 AU

Approach: E-2 mo to E-24 hr (E = impact event) · Images and spectra of coma to study rotation Impactor release: E-24 hr to E · Color images of coma and nucleus · Spectra of coma and nucleus Impact: E to E+800 sec · High speed white light imaging of crater formation and ejecta cone · High speed IR spectra of ejecta vs. time · White light and color images of ejecta cone and crater formation · IR spectral map of nucleus and crater · Spectra of coma near limb · Color images of final crater · White light images with resolution < 2m/pixel of final crater Lookback: TCA+30 min to TCA+1 day (TCA = time of closest approach) · Images and spectra of evolving ejecta · Data playback up to 3 days after TCA From long before to long after impact · Continuous world-wide telescopic observations at multiple wavelengths

Expected Cratering Scenario

Tools of the Experiment
Star Trackers Debris Shielding

Scientific Measurements
· · · · · · · Map surface for shape and morphology Analyze albedo map in terms of surface and jetting processes Compare surface to interior, radially and laterally, to define mantle boundaries and interior heterogeneity
Inertial Reference Unit (IRU)

HRI Instrument

Impactor ITS=MRI-Vis w/ no filters 1024x1024 CCD
Instrument Platform MRI Instrument

Compare outgassing before and after for composition and evolution of gases Measure ejecta cone's half-angle for bulk density and porosity Determine process controlling shape of crater from debris cone structure Determine elemental, molecular, and mineralogical components of surface and interior from IR spectra
HRI-Vis 0.34 - 1.0 µm fov=2 mradians 1.4m/pixel @ 700 km range 9 filters 1 024 x 10 2 4 CCD

Flyby Spacecraft HRI-IR 1.1 - 4.8 µm fov=2.6 mradians 7m/superpixel @ 700 km range 2 prisms 512 x 256 HgCdTe MRI-Vis 0.3 - 1.0 µm fov=10 mradians 7m/pixel @ 700 km range 9 filters 1 024 x 10 2 4 CCD

3 4 2 2

7 7 4 9

Total Mass 0 kg % Cu % Al % other

Copper Deadmass 140 kg Density 3.0-5.5 g/cc Diameter 0.65 m Diam/Depth 4:1 99% Cu, 1% other