The lunar regolith presented by Alexa Halford and Brian Morsony Out line Observations of the regolith Alexa Regolith formation Brian Space Weathering Brian Detailed outline What is the Lunar Regolith Quick History Observations of the regolith Apollo and luna missions Meteorites Remote sensing with Radar What is the Lunar Regolith Fragmented and unconsolidated rock material The entire lunar surface consists of regolith The average thickness 5 m for maria 12 m for the highlands All of the samples collected by Apollo and Luna Missions are from the regolith Boundary between the solid Moon and the Interplanetary medium The product of more than 4 billion years of impacts and SW interaction Quick history Lucey et al 2006 Apollo Luna Meteorite Observations Rocks 1cm diameter 1500 rocks collected by Apollo most less then a gram largest 11 7 kg Scoops 10 cm at surface 30 cm in trenches Drive tubes and Rotary drill cores 10 cm 3 m 24 cores and drive tubes on 6 Apollo missions and 1 on each of the three luna missions Composition of Lunar samples Most common minerals Silicates Plagioclase Feldspar Pyroxene Olivine Oxide minerals Ilmenite Spinel Armalcolite Apollo Landing sites http www floridastars org apollosites html http documents wolfram com applications astronomer GraphicsGallery ApolloLandingSites html Grain size Mean diameter increases with depth Quick story Laul et al1981 Laul et al1980 Chemical Comparisons between different sites Apollo 11 Apollo 12 Laul et al1980 Apollo 14 Apollo 15 Apollo 16 Variations due to depth Lucey et al 2006 meteorites 34 lunar meteorites found as of October 2005 Highlands 3 5 ejection events Maria 5 6 ejection events Meteorites as ground truth Lucey et al 2006 Meteorites as ground truth Lucey et al 2006 Thickness of regolith Average thicknesses Maria 4 5 m Highlands 10 15 m Lower limits found by drilling and cores Seismic experiments at Apollo 11 12 and 14 17 Electromagnetic multi frequency probing at Apollo 17 landing sites http spaceflight nasa gov gallery images apollo apollo16 html as16 113 18347 html Radar measurements of lunar regolith Used radar data at 70 cm wavelength Rocks 10 cm too small to scatter Boulders 10 m regarded as regolith substrate Shkuratov et al 2001 Comparison of Apollo seismic data to model regolith thickness Shkuratov et al 2001 Average thickness v Age Shkuratov et al 2001 Outline Origin Volcanism Impacts Mixing Small impacts Weathering Micro impacts Solar wind sputtering Solar wind Implantation Solar wind history Origin Volcanism Impacts Volcanism Ancient volcanism releases molten rock into atmosphere Small particles solidify before falling back to surface Creates spherical glass particles found in regolith Volcanic ash creates small grains 40nm in size Impacts Break down rocks Fuse regolith into new rocks Break Down Impacts grind down existing rocks into smaller particles Creates fine grains that make up regolith Typical particle size of 40 m 800 m Fusion Impact shock compacts and melts lunar rock Material solidifies into new rocks Breccias Can be in the form of fractured breccia crystallized impact melt or glassy impact melt Breccias Fragmented breccia formed by compression Can be made of regolith material Glassy melt breccia formed when material melted and then solidifies Can glue larger particles together glassy melt breccia or be mostly glass impact glasses Crystalline melt breccias form in larger impacts where melted material pools and cools more slowly than in small impacts Similar to rocks formed from magma crystalization Formation locations of Breccias Mixing of Regolith Impacts eject material at surface exposing material at deeper layer in crater and covering surrounding area with ejecta Over time many layers end up overlapping creating a regolith with material compositions and ages mixed together impact gardening Weathering Material at the surface of the moon exposed to Micrometeor impacts Solar wind Cosmic Rays Micrometeorite Impacts Reduce grain sizes over time Produce small amounts of melt Fuses nearby particles together with glass creating agglutinates Voids due to release of gases Micrometeorite Impacts Produce iron vapor Iron condenses as nanophase spheres 3nm 7nm diameter Incorporated into agglutinates or deposited on surface of grains Forms rim of material 60nm 200nm thick rich in iron nanoparticles This makes grains appear darker and redder over time Soil Grain Rim Sputtering Solar wind and cosmic rays causes sputtering Preferentially removes lighter elements from grain surfaces Contributes to rim formation Also produces some iron vapor Solar Wind Implantation Solar wind particles impact Moon penetrate into grains and are trapped This is the dominant source of some elements in the regolith e g H noble gases N Solar Wind History Regolith contains record of solar wind particles This can be used to determine solar wind composition and flux with time Infer solar luminosity and variability with time Solar Wind History Results Xe measurements indicate solar wind flux has been at at least the current level or higher for past several billion years A change in 3He 4He ratio would indicate mixing of 3He from core of sun into convective zone which would effect D H ratios inferred from present solar wind data 3He 4He Initailly appeared to be significant evolution However same evolution seen in 20Ne 22Ne ratio which is not explained by mixing in sun Correcting for this 3He 4He ratio constant for 4 Gyr Ratio Solar Energetic Particles Regolith shows two components to solar wind with different penetration depths High energy component appears to have same composition as solar wind but current flux at these energies is 2 orders of magnitude to low to produce observed implanted particles Solar 3He 3He and Deuterium fuse into 4He at around 10 100 KeV Easier than D T fusion Most Helium on Earth is 4He from radioactive decay Helium on moon from solar wind so lots of 3He 1 000 000 tons on Moon vs 1 ton on Earth Powering the US for 1 year requires 25 tons of 3He References www asi org Wieler R and Heber V S 2003 Space Science Reviews 106 197 Marty B Hashizume K Chaussidon M and Wieler R 2003 Space Science Reviews 106 175 http en wikipedia org wiki Space weathering Lucey P et al 2006 Reviews in Mineralogy and Geology 60 83 Starukhina L V 2003 Solar System Research 37 1 36 http www psrd hawaii edu July04 PSRD newMineral pdf Thompson T W 1987 High resolution lunar radar at 70 cm wavelength Earth Moon Planets 37 59 60 Shkuratov Y G and