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  1. “Rummaging through Earth’s Attic for Remains of Ancient Life” John C. Armstrong, Llyd E. Wells, Guillermo Gonzalez Icarus 2002, vol. 160 December 9, 2004 Ashley Zauderer

  2. What was the Ancient-Earth like? Images courtesy of NASA

  3. When did the moon form? Images courtesy of NASA

  4. When did life develop? Images courtesy of NASA

  5. Could early remains from the Earth be buried in the Moon’s regolith in high enough concentrations to motivate a search mission? Images courtesy of NASA

  6. Background Earliest geologic information we have about the Earth dates back to 3.476 Gyr Goal: How and when did life develop on the Earth?

  7. Preservation on the Moon? • No atmosphere • No widespread, long-lived volcanism • Lacks hydrologic & tectonic cycles Images courtesy of NASA

  8. Procedure • Calculate mass of material incident on Earth during period of interest • Determine velocity distribution of material ejected from Earth during impacts • Apply transfer efficiencies to estimate the mass reaching the moon • Determine the fractional volume of terran material in lunar regolith compared • to total material accreted from other sources

  9. Lunar Timeline

  10. Large Craters in North America Earth Impact Database – Planetary and Space Science Center

  11. Procedure • Calculate mass of material incident on Earth during period of interest • Determine velocity distribution of material ejected from Earth during impacts • Apply transfer efficiencies to estimate the mass reaching the moon • Determine the fractional volume of terran material in lunar regolith compared • to total material accreted from other sources

  12. Period of Heavy Bombardment - Frequent impacts

  13. Period of Heavy Bombardment • - material ejected over • range of velocities

  14. Procedure • Calculate mass of material incident on Earth during period of interest • Determine velocity distribution of material ejected from Earth during impacts • Apply transfer efficiencies to estimate the mass reaching the moon • Determine the fractional volume of terran material in lunar regolith compared • to total material accreted from other sources

  15. Ejecta Transfer Processes • Direct Transfer • v ~ escape velocity • Orbital Transfer • v = escape velocity • Lucky • v >> escape velocity

  16. Direct Transfer • Low relative velocity with respect to the moon • “gravitational focusing” • Maximum velocity ~ escape (11.2 km/s) Minimum velocity ~ 10.94 km/s • Zharkov (2000) estimates at 3.9 Gyr • Moon was ~ 21.6 earth radii away • Period ~ 5.9 days

  17. Orbital Transfer • Velocity ranges: 11.2 – 11.7 km/s • Numerical simulations by Stadel (2001) using the pkdgrav code with variable timesteps, N = 252 ejecta particles and planets • Conservative estimate since they only determined material transferred in 5000 years or less

  18. Las Vegas Transfer • For particle velocities > escape velocity • Depends on cross-sectional area of the moon at given time

  19. Procedure • Calculate mass of material incident on Earth during period of interest • Determine velocity distribution of material ejected from Earth during impacts • Apply transfer efficiencies to estimate the mass reaching the moon • Determine the fractional volume of terran material in lunar regolith compared • to total material accreted from other sources

  20. Procedure • Calculate mass of material incident on Earth during period of interest • Determine velocity distribution of material ejected from Earth during impacts • Apply transfer efficiencies to estimate the mass reaching the moon • Determine the fractional volume of terran material in lunar regolith compared • to total material accreted from other sources • Finally, estimate the likelihood of survival of the • biological and geochemical tracers.

  21. Survivability of tracersas a function of velocity Armstrong et al., Icarus 2002

  22. Conclusions • -surface abundance of terran material • on the moon estimated to be 7 ppm • (20,000 kg over a 10 km x10 km region) • 1-30 kg transferred from Venus • >180 kg tranferred from Mars Images courtesy of NASA

  23. Earth Earth

  24. References -Armstrong, John C., Wells, Llyd E. and Gonzalez, Guillermo. Icarus 160, 183-196 (2002). -Melosh,H. 1985. Ejection of rock fragments from planetary bodies. Geology 13, 144-148. -Zharkov, V.N. 2000. On the history of the lunar orbit. Solar System Res. 34, 1-11. Images courtesy of NASA