Transcript Other planets?

How can we study quakes on
other planets?
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Cannot do it entirely from earth
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Need to send people or landers to the planet
On the Moon:
Apollo Mission sent
astronauts to the
moon 1969-1972
where they installed 6
seismometers (4 were
operational) on the
near side.
Stations returned data
through 1977 (8 yrs)
Recorded between 6003000 “moonquakes”
per year
Buzz Aldrin setting up one station, by Alan Bean (another lunar astronaut) 1984
Lunar Seismic Events
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More than 12,000 quakes recorded (between M 0.5-1.5)
Three types of events were recorded
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meteor impacts (pea size
impacts up to 1000 km away)
Astronaut noise (landings and
rocket boosts, and even foot
steps)
moonquakes
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some shallow events < 60 km
deep
mostly deep focus
deep events form a partial
spherical shell between 6001,000 km depth
Near
side
Moonquakes
With no active tectonics or volcanism, what is causing the
moonquakes, and why are they so deep?
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Something must be
causing applied stresses
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Possibly thermal stress
from cooling
more likely tidal stresses
from the Earth (6x greater
than on earth)
Why are the quakes only on
the near side?
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Similar tidal stresses exist
on back side
quakes probably exist on
backside too but not easily
detected (size, distance)
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Shallow lunar structure from
seismology
Both P and S velocities
increase regularly with
depth.
Inferred density shows that
a material with r~3
exists to 60 km
consistent with basalt
and gabbro (crust)
Deeper than 60 km
assumed density is
consistent with
pyroxenes (mantle)
crust
mantle
Seismicity on other planetoids
Mars:
1970’s Viking I & II landers were equipped with seismometers.
Though there are no active tectonics, Mars is expected to have considerable
thermal stress (actively cooling) and is thought to be more active than the moon.
Seismometer on Viking:
I: did not work
II: worked for ~2years but only recorded
1 “marsquake”
– poorly coupled to surface
– significant wind noise
– considerable temperature
variations
Seismometers have not been deployed to any other planetary object
What planetoids would be good
candidates for future seismic studies?
What planetoids would be good
candidates for future seismic studies?
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body should be composed of brittle elastic solids
for quakes (no gas giants: Jupiter, Saturn,
Uranus, Neptune)
must be accessible with a lander and return data
(stay within the solar system)
Must have induced stresses (tidal, thermal,
cratering)
What planetoids would be good
candidates for future seismic studies?
Great candidates include:
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Venus
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possible volcanism (quakes associated)
thick atmosphere tough to penetrate!
What planetoids would be good
candidates for future seismic studies?
Great candidates include:
•
Venus
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–
•
possible volcanism (quakes associated)
thick atmosphere tough to penetrate!
Galilean Moons
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Io: most active body in solar system
What planetoids would be good
candidates for future seismic studies?
Great candidates include:
•
Venus
–
–
•
possible volcanism (quakes associated)
thick atmosphere tough to penetrate!
Galilean Moons
–
–
Io: most active body in solar system
Europa: Ice tectonics
What planetoids would be good
candidates for future seismic studies?
Great candidates include:
•
Venus
–
–
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Galilean Moons
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possible volcanism (quakes associated)
thick atmosphere tough to penetrate!
Io: most active body in solar system
Europa: Ice tectonics
Callisto: Cratering
Almost any large rocky
body would work