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

“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?
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When did the moon form?
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When did life develop?
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Could early remains from the Earth
be buried in the Moon’s regolith
in high enough concentrations
to motivate a search mission?
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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?
Preservation on the Moon?
-No atmosphere
-No widespread, long-lived volcanism
-Lacks hydrologic & tectonic cycles
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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
Event
Billions of Years Ago
Lunar Formation
4.6
Crust Formation
4.4
Start of Heavy
Bombardment
Maria Formation
3.9
Slow constant
bombardment
Today
3.8
3.9 - 3.2
0
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 ~ 10.94 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
Mass Fraction
30
25
14 km/s
22.5 km/s
25 km/s
30 km/s
40 km/s
50 km/s
65 km/s
20
15
10
5
0
biomarkers
organics
volatiles
isotopes
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
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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.
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