Deep Impact

Open Night

October 28, 2005

Terminology

! Albedo - % of sunlight reflected

! Volatiles - ices, material that is liquid or gas at

moderate temperatures but form solids/crystals at

low temperatures (e.g. water, carbon dioxide,

methane)

! Rock - objects such as silicates

! Organic materials - hydrocarbons (C-H-X)

Formation of Comet

Comets & the Early Solar System

! Formation far from Sun

- Not much processing

by solar radiation

! Small - not much

alteration of

composition by

compression

Connection to other planetary news

of the summer -

Kuiper Belt Object

UB313 - aka the “10th

planet”

The Kuiper Belt is

the reservoir from

which comets come

Anatomy of a Comet

! Nucleus - core of the

comet ~ 10 km in size

comprised of rock and

ices

! Coma - the

“atmosphere” of the

nucleus

! Dust & gas tail

The appearance cometary nuclei

from close flybly missions

Comet Halley

(Giotto -

March 1986)

Comet Borrelly

(Deepspace 1 -

September 2001)

Comet Wild 2

(Stardust -

January 2004)

" Observations of the Nucleus which is typical

obscured by coma

" Collection of samples of dust and volatiles

Deep Impact - July 3, 2005

! Comet consists ofunprocessed materialfrom theprotoplanetary disk

! Dig deep into cometnucleus to view materialunheated by the Sun

! And to determinephysical properties (e.g.material strength) ofnucleus

Comet Tempel 1

! Discovered in 1867 byWilhelm Tempel

! Orbital Period ~ 5.5 yr

! Perihelion ~ 1.6 AU

! Size ~ 11x4x4 km(9x2x2 miles)

! Albedo ~ 4%

! Spin period ~ 2 days

The Spacecraft! Impactor mass ~ 370 kg (~

820 lb on Earth) + 6.5 kg of

fuel (hydrazine ~ N2H4)

! Relative velocity ~ 10 km/s

(22,800 mph)

! Late stage self-navigation

! 4500 images returned

! Best resolution ~ 4 m (13 ft)

! Flyby closest approach ~

500km (300 miles)

Trajectory of Deep Impact

Simulation - close-up of encounter

Impact as Seen from Impactor

Impact Trajectory Maneuver

Impact as Seen from Flyby Spacecraft

Expansion rate ~ 5 km/s (3.1 miles per second)

Impact as Seen from Flyby Spacecraft

Brightening of Comet Tempel 1 as

seen from Earth

Mount Laguna Observatory - 1m telescope (San Diego St.)

R-band

Impact Ejecta Fan

-1 day impact +1 day

See for detailed reading of mission

& discoveries - Oct 14 ‘05

! Surface

! Ejecta & Shadow

! Spectra from Deep

Impact

! Spectra from Spitzer

Space Telescope

The Surface

! Outgassing observed during approach

! ~329 K (135O F) at “noon” & ~ 260 K (10O F) in shadow- Today’s high & low on L.I. ~ 35O F & 51O F

! Surface temperature, albedo, & spectra are indicativeof no ice on the surface

! Craters - prior impacts with solar system debris

Ejecta & Shadow

! Gas = steam + CO2! Fine Dust ~ 1-1000 µm

in size (human hair is ~70-180 µm in size)

! Lots of material inejecta even 13 minutesafter impact

! Surface is weak &powdery

DI Spectral Data

Green curve - 0.6

sec after impact -

water, carbon

dioxide &

hydrocarbons

Red Curve -

Before Impact

Blue curve - H20, CO2, & continuum model

Off-nuclear spectra - Hydrocarbons

below surface of Comet

Preimpact ~ -10 min Postimpact ~ +4 min

Recipe for a Comet - What the

Spitzer Space Telescope Observed

! Silicates of Olivine (found on Hawaii’s Green Sand Beach)

! Clay & Carbonates (thought to require liquid water to form)

! Iron compounds

! hydrocarbons (found in car exhaust & BBQ pits)

Summary - What have we learned

thus far?

! Craters observed on surface

! Surface is powdery

! No ice on surface, but there isice just below the surface

! Organic molecules, water ice,and silicate dust composition &abundances indicate that someof the comets originated closeto or within giant planet region

Acknowledgements

! Thanks to Dave Jewitt

! http://deepimpact.jpl.nasa.gov/home/index.html &

Science Magazine (Oct 14 ‘05)