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Thermal2+ Dissociation 0 Forfeo Fe Reduction Tosio Fe2 TODAY’S SESSIONS INTERACTIONS BETWEEN SPACE AND PLANETARY SURFACES METEOR MICRO-METEOR IMPACTS LUNAR SWIRLS Magnetic Fields + Solar Wind INTERACTIONS BETWEEN SPACE AND PLANETARY SURFACES. Amanda Hendrix: LRO/CRATER discoveries of the lunar radiaon environment and lunar regolith alteraon by radiaon. Anton KulChitskiy: Regional Variaons in UV Lunar Signatures. Solar wind access to lunar regolith DEM modeling. Jan Deca: Electromagne9c PIC simulaons of the solar wind interac9ons with lunar mag- nec anomalies: Ion and electron dynamics. Shahab Fatemi: (virtual) Plasma interac9ons with lunar magne9c anomales. Andrew Poppe: Plasma modeling of solar wind interac9on with Reiner Gamma and Airy magne9c anomalies. Timothy Glotch: Diviner lunar radiometer observaons of lunar swirls. David BleweN: Nature and origin of lunar swirls. PM ---------------------------------------------------------------------- Kathrine Burgess: EELS measurement of Fe oxidaon state in space-weathered lunar soils. Joshua Cahill: The Maturely, Immature Orientale Impact Basin. Benjamin Greenhagen: Simulang lunar eclipse in the lab. Key to understanding the epiregolith. Joshua Bandfield: Geng the temperature right-Accurately deter-mining thermophysical and spectral proper9es planetary surfaces. Andrew Jordan: Possible dielectric breakdown weathering effects on the comminu9on of lunar regolith. Leos Pohl: Asteroid material shielding poten9al against high energy par9cles. SPACE WEATHERING PROCESSES: A MISSING FACTOR Larry Taylor Planetary Geosciences Institute University of Tennessee Knoxville, TN, 37996 <[email protected]> OUR MOON PROVIDES PARADIGMS for: PLANETARY EVOLUTION of the TERRESTRIAL PLANETS; SPACE WEATHERING on ALL AIRLESS BODIES Space weathering includes all those physical and chemical factors that affect an airless body in space, ?? Space Weathering Lunar ROCK Versus SOIL 6 AGENTS OF SPACE WEATHERING Micro-Meteorites Solar-Wind Particles OSIRIS-REx Galactic/Cosmic/Solar Rays Bennu Temperature (diurnal) Gravity Space Weathering on the Moon 95% H+ (Protons) 4% He+ (Alpha Particles) 30,000 - 70,000 km/hr 1-10 KeV Mach 20 - 60 Phys/Chem Sputtering Diurnal Temperature Ion Implantation Change Micrometeorite Impacts on a Lunar Glass Bead Projectile Φ 1 = Crater Φ 10 Micrometeorite size = ~0.5 µm 5 µm Impact Craters Cintala (1992) Impact Velocities for Micro-Meteorites Mercury = ~20 km/sec; Hi Flux Moon = ~12-13 km/sec Main Asteroid Belt = 4-5 km/sec Vesta = 3.8-4 km/sec Vapor-Deposited Nanophase Feo on Plagioclase Keller & McKay (1993, 1997) TEM: (all black spots = np-Fe) SiO2-rich glass Courtesy of Sarah Noble Plagioclase 10 nm Wentworth et al. (1999) 100 Å Airless-Body Regolith Cycle Taylor (2000) Micrometeorites Micrometeorites + + S-W Ions S-W Ions + + Temp. Agglutination Temp. Melting Vaporization 0 0 Fe SiO2 Si Vapor-Deposited 0 SiO2 + npFe Selective Comminution (especially glass) Course (100 µm) Grain size Fine (<10µm) MATURITY University of Tennessee, Planetary Geosciences Institute Larry Taylor, [email protected] FeSi Hapkeite FeSi2 Fe Si Feo 2 Feo Fe2Si Sio SiO+ o = Fe O = = = Solar Wind=O is bit of a RedO HerringO O O= SW Hydrogen is NOT Required Thermal2+ Dissociation 0 ForFeO Fe Reduction toSiO Fe2 Micro- Vaporization Micro- Meteorites Meteorites Lunar Soil Anand and Taylor (2004) ____ 2 m ________ 2 meters 433 EROS NEAR Shoemaker (2000) 433 Eros _____ 50 m _____ 50 m the asteroid Itokawa. Yano et al. (2006) NEA Itokawa 50 nm Hayabusa Mission Noguchi et al. (2013) TEM Bright-Field Pyroxene Kapoeta Meteorite (Howardite) Noble et al. (2010) Short-Pulse Laser Experiments to Simulate Micro-Meteorite Impacts Micrometeorite bombardment has been simulated in laser oblation experi- ments (Moroz et al. 1996, Yamada et al. 1999, Sasaki et al. 2001, 2002, Sasaki and Hiroi 2003, Brunetto et al. 2006) Ion bombardment has been simulated in radiation experiments (Brunetto and Strazzulla 2005, Marchi et al. 2005, Strazzulla et al. 2005, Brunetto et al. 2006) Np-Fe has been produced in these laboratory simulations, supporting the Sasaki et al. (2001) role of these particles in producing the effects attributed to space weather- ing. BUT no duplication of vapor-deposited rims on lunar grains. Temperature Variations Delbo et al. (2014) Bennett et al. (2013) Space-weathering of Solar System bodies: A laboratory perspective. Chem Rev., Spec. Issue Astrochemistry, 9086-9150 (beaucoup refs.) Delbo et al. (2014) Thermal fatigue as the origin of regolith on small asteroids. Nature Res. Lett. 508, 233-236. Molaro et al. (2015) Grain-scale thermoelastic stresses and spatio-temporal temperature gradients on airless bodies, implications for rock breakdown. Jour. Geophys Res.: Planet., 1-23. 10 cm rock = 3,000 yrs. Delbo et al. (2014) cm 1 AU Micrometeorites Diurnal Thermal Diurnal Thermal Avg.Rotation Period: ~8 hrs. Time Required to Break Down 90 % of Rocks on Asteroids Delbo et al. (2014) Thermal Cycling RoCk experienCes thermal shoCk and stress! Thermal-MeChaniCal ProCesses: More effiCient in weathering of asteroid surfaCes than micro-meteorite impacts! ??? STRESS DEVELOPED 100 % Pyroxene dT/dt 25 % Plagioclase Hypothesis: 75 % Pyroxene ASSUMPTION: MiCrometeorite ImpaCt + Low Gravity = Loss of Larger Grains. Asteroid surfaCes experienCe beauCoup thermal cycles (e.g., fast rotaon) Should have smaller-grained regolith Molaro et al. (2015) dT/dt Molaro and Byrne (2012) THERMAL-STRESS PROCESSES PHYSICAL PROPERTIES ☼ Density ☼ Heat Capacity ☼ Thermal Conductivity ☼ Young’s modulus ☼ Poisson’s ratio ☼ Coefficient of Linear Expansion Scale of observation of a process ≠ EROS Scale of operation of that process ____ 2 m MAJOR FACTORS FOR SPACE WEATHERING: MERCURY to ASTEROIDS UnderstandingL DISTANCE Space from SUNWeathering is the L SOLAR- WIND PARTICLES LKey MICRO-METEORITE to Remote Sensing IMPACTS of AirlessL TEMPERATURE Bodies in our CHANGES Solar System MERCURY 0.4 AU MOON ASTEROIDS (Main Belt) SW = Major++ 4xM 1.0 AU 2-2.5 AU M-M = Major++ 30xM SW = Major SW = Minor M-M = Minor T = Major ?? M-M = Major T = Moderate T = Major NP-Fe = Major ++ 4xM NP-Fe = lots NP-Fe = Minor Soil = Major++ + Agglut 50 % glass Soil = Eh! + Fine .
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