How can we study quakes on other planets?

• Cannot do it entirely from earth• Need to send people or landers to the planet

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 600-3000 “moonquakes” per year

Buzz Aldrin setting up one station, by Alan Bean (another lunar astronaut) 1984

On the Moon:

Lunar Seismic Events• More than 12,000 quakes recorded (between M 0.5-1.5)• Three types of events were recorded

– meteor impacts (pea size impacts up to 1000 km away)

– Astronaut noise (landings and rocket boosts, and even foot

steps)– moonquakes

• some shallow events < 60 km deep

• mostly deep focus • deep events form a partial

spherical shell between 600-1,000 km depth

Nearside

MoonquakesWith no active tectonics or volcanism, what is causing the

moonquakes, and why are they so deep?

• Something must be causing applied stresses

– 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?

– Similar tidal stresses exist on back side

– quakes probably exist on backside too but not easily detected (size, distance)

?

Shallow lunar structure from seismology

Both P and S velocities increase regularly with depth.

Inferred density shows that a material with ~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 planetoidsMars: 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 workII: 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 goodcandidates for future seismic studies?

What planetoids would be goodcandidates for future seismic studies?

• 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 goodcandidates for future seismic studies?Great candidates include:• Venus

– possible volcanism (quakes associated)– thick atmosphere tough to penetrate!

What planetoids would be goodcandidates 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

What planetoids would be goodcandidates 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 goodcandidates 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– Callisto: Cratering

• Almost any large rocky body would work