“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

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

When did the moon form? Images courtesy of NASA

When did life develop? Images courtesy of NASA

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

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

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

Procedure 1.Calculate mass of material incident on Earth during period of interest 2.Determine velocity distribution of material ejected from Earth during impacts 3.Apply transfer efficiencies to estimate the mass reaching the moon 4.Determine the fractional volume of terran material in lunar regolith compared to total material accreted from other sources

Lunar Timeline EventBillions of Years Ago Lunar Formation4.6 Crust Formation4.4 Start of Heavy Bombardment 3.9 Maria Formation Slow constant bombardment 3.8 Today0

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

Procedure 1.Calculate mass of material incident on Earth during period of interest 2.Determine velocity distribution of material ejected from Earth during impacts 3.Apply transfer efficiencies to estimate the mass reaching the moon 4.Determine the fractional volume of terran material in lunar regolith compared to total material accreted from other sources

Period of Heavy Bombardment - Frequent impacts

Period of Heavy Bombardment - material ejected over range of velocities

Procedure 1.Calculate mass of material incident on Earth during period of interest 2.Determine velocity distribution of material ejected from Earth during impacts 3.Apply transfer efficiencies to estimate the mass reaching the moon 4.Determine the fractional volume of terran material in lunar regolith compared to total material accreted from other sources

Ejecta Transfer Processes Direct Transfer –v ~ escape velocity Orbital Transfer –v = escape velocity Lucky –v >> escape velocity

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

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

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

Procedure 1.Calculate mass of material incident on Earth during period of interest 2.Determine velocity distribution of material ejected from Earth during impacts 3.Apply transfer efficiencies to estimate the mass reaching the moon 4.Determine the fractional volume of terran material in lunar regolith compared to total material accreted from other sources

Procedure 1.Calculate mass of material incident on Earth during period of interest 2.Determine velocity distribution of material ejected from Earth during impacts 3.Apply transfer efficiencies to estimate the mass reaching the moon 4.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.

Survivability of tracers as a function of velocity Armstrong et al., Icarus 2002

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

Earth

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