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Observing a Lunar Impact

Observing a Lunar Impact. Karen J. Meech, Astronomer Institute for Astronomy University of Hawaii, NASA Astrobiology Institute AAVSO Conference May 4-6, 2006. Impact Physics. Stages:. Hypervelocity impacts Collision v > 1-2 km/s where material behaves like a fluid Science uses

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Observing a Lunar Impact

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

  2. 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

  3. 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

  4. 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

  5. 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

  6. Instruments

  7. 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

  8. 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 2:00 UT on near side • The Impact • Mass: 290 kg (200 Al from body) • Velocity: 2 km/sec • Where: 36o S, 44o W

  9. 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 < 100K

  10. 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

  11. 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

  12. LP Impact Results OH Image from McDonald Obsty • 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 HST UV spectra – search for OH

  13. SMART 1 Predictions • 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 • 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

  14. Timelines SMART 1 vs. LP • Better than Lunar Prospector • Direct view of impact site, dark part • Illumination by Earthshine • More Energy (< 1 kg meteorite @ 40 km/s)

  15. Will we see it? • Lunar meteorite impacts are seen • Ogawamura Obsty • Aug 11, 2004, 18:28:27 • 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

  16. World Plans

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