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Observing a Lunar Impact

Delve into the scientific pursuit of observing a lunar impact, exploring the stages of impact physics and the details of mission profiles. Discover the goals, instruments used, imaging results, and impact outcomes that shed light on the mysteries of the Moon.

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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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