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SciShow Space explores the origins of Earthquakes that aren't on Earth. Moonquakes and Marsquakes can happen, too!
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Over at SciShow we've talked about the science of earthquakes' how the shifting, sliding, pushing, and pulling of Earth's tectonic plates causes the seismic activity that we all know and love and kind of fear... But what about our celestial neighbors? Are there earthquakes on worlds that aren't Earth?

Well, in the 1970's Apollo astronauts placed seismometers on the moon to see what it was up to and until the last of them was switched off in 1977, these instruments recorded more than 12,000 seismic events of varying degrees including one quake with a magnitude of 5.5! And Mars meanwhile has been found to have a system of faults or fissures in the crust, and possibly volcanic activity.

But moonquakes and Marsquakes are different than earthquakes. What makes moonquakes so interesting isn't so much their magnitude, but their persistence. Most quakes on Earth tend to dissipate after a minute or so because water interacting with the rock below the surface acts like a kind of sponge to tamp down the vibrations.

But not so on the moon which is cooler, drier, and more rigid. Its surface isn't pieced together from tectonic plates like Earth's is. Instead, it's been described as being like a tuning fork. Those old Apollo instruments have recorded shallow moonquakes lasting more than 10 minutes! Some of these are likely vibrations caused by meteorite impacts. Others are probably thermal quakes caused by the difference in temperature between the lunar day and night, each of which lasts about two weeks. When sunlight first strikes the moon's surface, the expansion of that frozen crust can cause seismic activity. But the most common moonquakes appear to be related to the tidal stresses between the Earth and the moon.

The mechanisms behind them aren't really well understood, but these quakes happen pretty regularly and seem to be the result of internal stress caused by the moon's gravitational interaction with Earth. These quakes are low magnitude but occur at great depths, as much as 700 kilometers below the lunar surface. Then, there's a whole category of shallow moonquakes that originate between 20 and 30 kilometers below the surface that still have scientists baffled. Yep, we're still analyzing data from 1977, trying to figure out the origin of all the moon's quakes!

Scientists know even less about Marsquakes, in large part because we don't have the trove of data that we do from the moon. In fact, only the Viking landers which touched down on Mars in the mid-1970s had seismometers on board. And the only quakes they detected came from vibrations as the spacecraft landed. But recent photographs by NASA's Mars Reconnaissance Orbiter have revealed intriguing new evidence of Marsquakes and volcanic activity. The orbiter revealed a pair of long gashes in the Martian surface that appear to have formed following eruptions of a giant volcano known as Elysium Mons.

The mountain probably hasn't blown its top in millions or maybe even billions of years, but photographs suggest that there's still movement beneath the surface. The key evidence is fresh boulder tracks, traces left in the Martian soil by the movement of huge boulders which scientists believe could only have been caused by seismic activity. A 2012 analysis of the tracks from boulders ranging in size from 2 to 20 meters found that the number and size of the tracks decreased over a radius of 100 kilometers from the faults around Elysium Mons. Scientists estimate that a relatively recent Marsquake with at least a 7.0 magnitude was responsible for jarring these boulders loose. So hey, Los Angeles, and Tokyo, and Mexico City - I guess it's good to know we're not along, uh, right?


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