““Rummaging through Earth’s Attic Rummaging through Earth’s Attic for Remains of Ancient Life”for Remains of Ancient Life”

John C. Armstrong, Llyd E. Wells, Guillermo GonzalezJohn C. Armstrong, Llyd E. Wells, Guillermo GonzalezIcarusIcarus 2002, vol. 160 2002, vol. 160

December 9, 2004December 9, 2004Ashley ZaudererAshley 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

BackgroundBackground

Earliest geologic information we have about the Earth dates back to 3.476 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

ProcedureProcedure

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 TimelineLunar Timeline

Event Billions of Years Ago

Lunar Formation 4.6

Crust Formation 4.4

Start of Heavy Bombardment

3.9

Maria Formation 3.9 - 3.2

Slow constant bombardment

3.8

Today 0

Large Craters in North AmericaLarge Craters in North AmericaEarth Impact Database – Planetary and Space Science Center

ProcedureProcedure

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 BombardmentPeriod of Heavy Bombardment

- Frequent impacts

Period of Heavy BombardmentPeriod of Heavy Bombardment

- material ejected over range of velocities

ProcedureProcedure

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 ProcessesEjecta Transfer Processes

• Direct Transfer– v ~ escape velocity

• Orbital Transfer– v = escape velocity

• Lucky– v >> escape velocity

Direct TransferDirect 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

Orbital TransferOrbital 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 TransferLas Vegas Transfer

• For particle velocities > escape velocity

• Depends on cross-sectional area of the moon at given time

ProcedureProcedure

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

ProcedureProcedure

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 tracersSurvivability of tracersas a function of velocityas a function of velocity

0

5

10

15

20

25

30

biomarkers organics volatiles isotopes

Mass Fraction

14 km/s

22.5 km/s

25 km/s

30 km/s

40 km/s

50 km/s

65 km/s

Armstrong et al., Icarus 2002

ConclusionsConclusions

-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 Earth

ReferencesReferences

-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