Earthquake

Seismic events similar to earthquakes also occur on other planets and on their satellites. Scientific missions to Earth’s moon and to Mars have provided some information related to extraterrestrial quakes. The current Galileo mission to Jupiter’s moons may provide evidence of quakes on the moons of Jupiter.

Between 1969 and 1977, scientists conducted the Passive Seismic Experiment as part of the United States Apollo Program. Astronauts set up seismograph stations at five lunar sites. Each lunar seismograph detected between 600 and 3,000 moonquakes every year, a surprising result because the Moon has no tectonic plates, active volcanoes, or ocean trench systems. Most moonquakes had magnitudes less than about 2.0 on the Richter scale. Scientists used this information to determine the interior structure of the Moon and to examine the frequency of moonquakes.

Besides the Moon and the Earth, Mars is the only other planetary body on which seismographs have been placed. The Viking 1 and 2 spacecraft carried two seismographs to Mars in 1976. Unfortunately, the instrument on Viking 1 failed to return signals to Earth. The instrument on Viking 2 operated, but in one year, only one wave motion was detected. Scientists were unable to determine the interior structure of Mars with only this single event.