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 where they installed 6 seismometers (4 were operational) on the near side. Stations returned data through 1977 (8 yrs) Recorded between “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 ) 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 ,000 km depth Near side

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

Moonquakes With 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) ?

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

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

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 –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