Astrophysics of Life Conference Highlights

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Observing a Lunar Impact
Karen J. Meech, Astronomer Institute for
Astronomy University of Hawaii, NASA Astrobiology
Institute AAVSO Conference May 4-6, 2006
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Impact Physics
Stages

• Hypervelocity impacts
• Collision v 1-2 km/s where material behaves
  like a fluid
• Science uses
• Excavate hidden stuff
• Learn about impact processes?mitigation
• Scale depends on
• Target comp / porosity
• Impactor comp
• Angle of impact

Compression flash, hydrodynamic flow,
melting, vapor)
Penetration (downward growth, reverse plume)
Excavation (ballistic flow in response to
rarefaction)
Sand 60º (30 porosity)
P. Schultz, Lab
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Mission Science Goals

• Goals
• Chemical inventory of Moon
• Confirm origin models
• Look for water/ice on the moon

4.6 billion yr ISM dark cloud
Protoplanetary disk
Earth in the Hadean Oceans rocks form 4.4
billion yr ago
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Mission Profile

• Launch 9/27/03 Arianne 5
• Second use of Ion Engine
• Current flows across B field ? creates E field
• E field accelerates Xe ions
• Solar panels 1350 W power
• Thrust 0.07 Nt
• Acceleration 0.2 mm/s2
• Arrive 11/15/04
• 16 mo journey

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Trajectory

• Launch to an elliptical Earth orbit
• 2 dy / wk burn ? gives increasing elliptical
  spiral
• 200,000 km out, feel lunar gravity
• Pass through L1 (50,000-60,000 from Moon) ? lunar
  capture
• Lunar polar orbit
• Gradually reduce size of orbit

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Instruments
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Imaging Results

• DeGasparis tectonic rilles, range 1090 km
• Mayer-Bond craters
• Range 2685 km
• Hopmann crater
• Aitkin basin edge
• 88 km diam

• Humorum
• Highlands/mare
• 4.1 Gy basin

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End of Mission

• Exhaust Xe fuel ? lunar impact
• Impact far side on 8/17/06
• Science Rationale
• Effects of space weathering
• Physics and diagnostics of low velocity impacts
• Extended Mission
• 6/26/06 ? hydrazine thruster maneuvers
• Add 12 m/s velocity ? extend lifetime
• Impact 9/3/06 at 200 UT on near side
• The Impact
• Mass 290 kg (200 Al from body)
• Velocity 2 km/sec
• Where 36o S, 44o W

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Lunar Prospector

• Discovery (63M)
• Launch 1/6/98
• Lunar arrival 4 dys
• Science
• Water at the poles?
• 1st entire surface gravity map
• Local B field measured
• 1st global maps of lunar comp

• Aitkin basin
• 2500km diameter
• 12 km deep
• Permanently shadowed
• T

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Water at the Poles

• Clementine bistatic radar
• Lunar Prospector N spec
• High E interactions ? g rays, neutrons
• Ratio of high E and thermal n depends on amt of H

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LP Impact

• Controlled crash nr S pole
• Crater 4 km deep
• Impact angle 6.5o,
• 1.7 km/s, mass 161 kg
• Ejecta could rise 30 km
• Search for lunar water
• To produce 18 kg water
• Heated to 400 K, Vapor visible 4 sec later

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LP Impact Results
OH Image from McDonald Obsty
HST UV spectra search for OH

• LP hit the expected crater
• No detection of water or OH (Keck, HST, McDonald)
• Not enough E to liberate H2O from hydrated
  minerals
• No enhanced Na, HCN or C2
• No dust observed

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SMART 1 Predictions

• Timing Uncertainty
• /- 1 orbit
• Previous perilune alt 400m
• Impact regime
• Strength dominated
• Si should not melt
• 80 cold ejecta
• Crater size
• 5-10 m
• 30-100 tons of dust
• Brightness of flash
• 50 E in thermal ? mag 7.4
• More likely ? 16
• Duration 20 millisec

• Spectra
• Emission from s/c volatiles N2, H4 ? NH3
• Near IR ? mineral properties
• Dust Plume
• Visible from Earthshine
• Dust 15 mm
• 1 reaches sunlight ? mag 11.5

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SMART 1 vs. LP
Timelines

• Better than Lunar Prospector
• Direct view of impact site, dark part
• Illumination by Earthshine
• More Energy (

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Will we see it?

• Lunar meteorite impacts are seen
• Ogawamura Obsty
• Aug 11, 2004, 182827
• Perseids
• 9th mag, 1/30 s duration
• Confirmed by 2 others

• Discovery
• 0.6m newtonian TV camera
• Confirmations
• 0.6 m TV
• 0.16m TV

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World Plans