NASA’s Mars InSight lander has just detected two more relatively large earthquakes on the Red Planet, and they came from a very interesting area known to be tectonically active. This highlights one of the bigger questions we have about Mars: Is it volcanically active today? Like it, now?
InSight landed 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 temperature, wind and pressure (you can also get a daily report).
Unfortunately, the heat probe never really got a chance to work; it was designed to burrow about 5 meters into the surface, but despite some pretty heroic efforts, it never got very far, and that part of the mission was over.
However, the seismic package has worked extremely well and more than 500 earthquakes have been detected. When something on Mars vibrates, rattles and rolls, sound waves are created seismic waves that move through the inside of the planet. Different types of waves move differently, so that helps scientists understand the interior of Mars. Most of the waves detected by InSight are shallow, high-frequency waves from an event in the crust of Mars, but a few dozen have a lower frequency and can propagate through the mantle of Mars (which, like Earth’s , is solid, but not as hot and probably not moving like ours).
During its first year on Mars (which is two Earth years long), it detected two earthquakes of considerable magnitude, magnitude 3.5 and 3.6. Then InSight didn’t discover much big for a while. That’s probably because in the Martian winter the air is too unstable 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 it can only go so far.
Now, with Mars Spring in the Northern Hemisphere, things have calmed down in terms of atmosphere, and in March SEIS discovered two more relatively large earthquakes, magnitude 3.1 and 3.3. I’ve experienced a few earthquakes while living in California, and that’s certainly big enough to feel, but not really big enough to cause any damage.
All of these earthquakes came from the direction of Cerberus Fossae, a series of troughs and cracks in the Martian crust about 1,000 miles east of InSight. This region is very Cool: The cracks probably formed a long time ago when the huge Tharsis volcanoes formed, creating a huge bulge in the crust. This expansion of the crust caused the surface at Cerberus Fossae to burst, like a balloon covered in dry mud that bursts and comes off when you inflate it.
What makes that area so interesting is that the surface around it is young, and I mean young: crater counts indicate it is less than 10 million years old, and some parts may be closer to 2 million. A huge amount of liquid then erupted from the ground – possibly water, although it may have been lava – and plowed its way through the region.
A few million years is a fraction of Mars’ 4.5 billion years old, so that means the planet was very recently volcanically active. Is it still today? That’s a question we’d like to know the answer to, and InSight can help. These great earthquakes indicate it something is going on there.
InSight recently got a mission extension to at least December 2022, which is great news. Scientists of course hope to detect more earthquakes over time, and they also hope to reduce the noise that SEIS feels so they can detect weaker earthquakes (it can even sense the change in the ground as it cools during short solar eclipses caused by the Martian Phobos!). In recordings made where the seismic waves are converted into sound, you can hear short, sharp bangs (collectively called, seriously, dinks and darkYou can find one at the beginning of this recording of Sol 173
At first it wasn’t clear what they were, but now engineers think they come from thermal movement in the cable that attaches SEIS to the lander, when large temperature changes cause it to expand and contract. They plan to use a shovel 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 consisting of a series of photos taken by a camera on the lander:
It is 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 find out about the structure of Mars beneath its crust, but I’m particularly interested in knowing if Mars is still volcanically active. No one knew if Mars had any activity on it until recently, and for most of my life it was thought to be a dead world. Now, although it may be alone mostly dead, with another small staircase in it.
Mars rotates every 24 hours and 37 minutes, so that’s the length of its day. To avoid confusion with Earth days, we call them sols, and they are numbered from the moment a particular mission lands, starting at 0, so in this case Sol 173 was the 174th Martian day after InSight landed.