This spectrogram shows the largest quake ever detected on another planet. The marsquake struck the Red Planet on May 4 , 2022 and measured magnitude 5 . Courtesy NASA/JPL-Caltech/ETH/Zurich.
May 4th is unofficially known in sci-fi circles as Star Wars Day (“May the Fourth Be With You”) here on Earth. But, on another planet, far, far away, the date is now infamous to one of its robotic inhabitants. That’s the day the Mars InSight lander felt one of the strongest marsquakes ever to hit that world. It registered magnitude 5 and was the latest 1,313 quakes the lander detected since it arrived on Mars in 2018. InSight scientists are still analyzing the data to figure out exactly where on Mars the quake struck, and what may have caused it.
Here on Earth, we get quakes all the time because our planet is geologically quite active. Just as an example of one spot that shakes a lot, the Big Island of Hawai’i can experience upwards of 300 quakes a day, particularly if one of its volcanoes is getting ready to erupt. Countries along the so-called “Ring of Fire” in the Pacific also experience a lot of quakes due to tectonic plate motions and volcanic eruptions. Many happen when geological faults snap, or there’s a sudden movement of one or more tectonic plates. Earth’s continents and oceans ride along on top of these pieces of crust. There are 15 major plates and several smaller ones. They jostle each other and often that motion translates to shaking at the surface.
All this activity provides evidence about how active our planet really is. In addition to quakes, we have mountain-building processes, volcanic activity, plate motions, and activity even deeper in the center of our planet. Studies of seismic waves from earthquakes provide a way to “peek inside” Earth to get an idea of its structure.
Mars “Geology” and a “Big One” Marsquake
On Mars, however, things are quite a bit different. For a long time, planetary scientists suspected that the Red Planet was geologically dead (or dormant). Yet, the surface shows evidence of volcanism, as well as what’s called a hemispheric dichotomy, which simply means that the northern and southern hemispheres are very different from each other in terms of cratering and average altitudes. In addition, the crust varies in thickness between the two halves of the planet. So, clearly, the planet isn’t completely dead. It’s more like planetary scientists just don’t know enough about the Martian interior yet.
InSight’s domed Wind and Thermal Shield, which covers its seismometer, called Seismic Experiment for Interior Structure, or SEIS. This instrument detected the May 4, 2022 marsquake. Credit: NASA/JPL-Caltech
It’s not clear why this dichotomy exists, and it’s even less clear about what’s happening inside Mars. It may have had some version of plate
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