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Hey Mars, what's shakin'?
NASA's Mars InSight lander just detected two more relatively large quakes on the Red Planet, and they came from the direction of a very interesting region that is known to be tectonically active. This highlights one of the bigger questions we have about Mars: Is it volcanically active today? Like, now?
InSight touched down on in a volcanic plain called Elysium Planitia on November 26, 2018. Its main mission is to study the interior of Mars using seismographs, a heat probe, and radio signals to determine the structure of the planet. It also has a weather station to measure the temperature, wind, and pressure (you can get a daily report, too).
The heat probe, unfortunately, never really got a chance to work; it was designed to dig its way down about 5 meters into the surface, but, despite some pretty heroic efforts, it never got very far, and that part of the mission was ended.
The seismic package, however, has worked wonderfully, and more than 500 quakes have been detected. When something shakes, rattles, and rolls on Mars, it creates sound waves called seismic waves that move through the planet's insides. Different types of waves move differently, so that helps scientists understand the interior of Mars. Most of the waves InSight has detected are shallow, high-frequency waves that come from some event in the crust of Mars, but several dozen are lower frequency, and can propagate through Mars' mantle (which, like Earth's, is solid, but not as hot and likely doesn't move like ours does).
During the first year on Mars (which is two Earth years long) it detected two quakes of decent size, magnitude 3.5 and 3.6. Then, for a while, InSight didn't detect many big ones. That's likely because in Martian winter the air is too unsteady and the wind noise masks seismic activity. SEIS, the seismic detector, sits under a small dome deployed by InSight to protect it from wind, but that can only go so far.
Now, with Martian spring in the northern hemisphere, things have calmed down atmosphere-wise, and in March SEIS detected two more relatively large quakes, magnitude 3.1 and 3.3. I've been in a few earthquakes when I lived in California, and that's definitely big enough to feel, though not really big enough to do any damage.
All of these quakes came from the direction of Cerberus Fossae, a series of troughs and cracks in the Martian crust about 1,600 km east of InSight. This region is very cool: The cracks likely formed long ago when the huge Tharsis volcanoes formed, creating an enormous bulge in the crust. This extension of the crust caused the surface to crack at Cerberus Fossae, like a balloon covered in dry mud cracking and separating if you inflate it.
What makes that area so very interesting is that the surface around it is young, and I do mean young: Crater counts indicate it's less than 10 million years old, and some parts may be closer to 2 million. A huge volume of liquid erupted from the ground back then — possibly water, though it may have been lava — and plowed its way across the region.
A few million years is a tiny fraction of the 4.5 billion year age of Mars, so that means the planet was volcanically active very recently. Is it still today? That's a question we'd love to know the answer to, and InSight may help. These biggish quakes indicate something is going on over there.
InSight recently got a mission extension through at least December 2022, which is great news. Scientists hope to detect more quakes over time, of course, and they're also hoping to lower the noise SEIS feels so they can detect weaker quakes (it can even feel the change in the ground as it cools during brief solar eclipses caused by the Martian moon Phobos!). In recordings made where the seismic waves are converted to sound, you can hear some short, sharp pops (collectively called, seriously, dinks and donks). You can here one near the beginning of this recording from Sol 173*:
At first it wasn't clear what they were, but now engineers think they come from thermal movement in the cable attaching SEIS to the lander, when large temperature swings cause it to expand and contract. They plan on using a scoop on the lander to dig up some of the surface and drop it on the cable, insulating it a bit. Hopefully that will mask some of the noise and improve the quality of the detections. You can see their efforts in this short video made up of a series of images taken by a camera on the lander:
It's amazing what you can learn about a planet by sitting very still on it and feeling very carefully for movement. It's cool that we're finding out about the structure of Mars beneath its crust, but I'm particularly interested in knowing if Mars is still active volcanically. No one knew if Mars had any activity on it until relatively recently, and for most of my life it was thought to be a dead world. Now, though it may only be mostly dead, with still a little kick left in it.
*Mars spins once every 24 hours 37 minutes, so that's the length of its day. To avoid confusion with Earth days we call those sols, and they're numbered from the time a given mission lands starting at 0, so in this case Sol 173 was the 174th Martian day after InSight landed.