NASA’s Mars InSight landing has just detected two relatively large earthquakes on the red planet and came from the direction of a very interesting region that is known to be tectonically active. This highlights one of the biggest questions we have about Mars: is it volcanically active today? I like, now?
InSight touched down on 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 had a chance to work; it was designed to dig about 5 meters to the surface, but despite some rather heroic efforts, it never got very far and this part of the mission was over.
The seismic package, however, has worked wonderfully and more than 500 earthquakes have been detected. When something shakes, breaks and rolls over Mars, it creates so-called sound waves seismic waves moving through the interior of the planet. Different types of waves move differently, so it helps scientists understand the interior of Mars. Most of the waves detected by InSight are high-frequency, shallow waves that come from some events in the crust of Mars, but several dozen are less frequent and can propagate through the mantle of Mars (which, like the of the Earth, is solid, but not as hot and likely not to move as ours does).
During the first year on Mars (which is two years from Earth), it detected two earthquakes of decent size, magnitudes 3.5 and 3.6. Then, for a while, InSight didn’t detect many large ones. This is likely because in Martian winter the air is too unstable and wind noise masks seismic activity. SEIS, the seismic detector, is under a small dome deployed by InSight to protect it from the wind, but it can only get this far.
Now, with the Martian spring in the northern hemisphere, things have calmed down in terms of the atmosphere, and in March SEIS detected two relatively large earthquakes, of magnitude 3.1 and 3.3. I experienced a few earthquakes when I lived in California, and it’s certainly big enough to feel, though not 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 1,600 km east of InSight. This region is a lot cool: cracks probably formed a long time ago when huge Tharsis volcanoes formed, creating a huge bulge in the crust. This extension of the crust caused the surface to crack at Cerberus Fossae, like a balloon covered in dry mud that cracks and separates if we inflate it.
What makes this area so interesting is that the area around it is young, and I mean young: craters indicate that it is less than 10 million years old and some parts may be closer to 2 million. Then a huge volume of liquid erupted from the ground (possibly water, although it could have been lava) and made its way across the region.
A few million years is a small fraction of the age of 4.5 billion years of Mars, so the planet was volcanically active recently. Is it still today? This is a question we would love to know the answer to and InSight can help. These gross earthquakes indicate it something is going through there.
InSight has recently received a mission extension at least until December 2022, which is great news. Scientists hope to detect more tremors over time, of course, and also hope to reduce the noise the SEIS hears to be able to detect weaker earthquakes (you can even feel the change in the ground as it cools during brief solar eclipses caused by the Martian Moon Phobos!). In the recordings made where the seismic waves become sound, you can hear some short, sharp pops (collectively called, really, dinks i donks). You can find one near the beginning of this recording of the Sun 173*:
At first it was not clear what they were, but now engineers think they come from the thermal movement of the cable that secures SIX to the lander, when large temperature fluctuations cause it to expand and contract. They plan to use a spoon in the lander to dig up part of the surface and drop it on the cable, insulating it a bit. Hopefully this masks some of the noise and improves the quality of the detections. You can see his efforts in this short video consisting of a series of images taken by a camera in the lander:
It’s amazing what you can learn about a planet sitting very still and feeling very carefully about the movement. It’s great that we find out about the structure of Mars under its crust, but I’m mostly interested to know if Mars is still volcanically active. No one knew if Mars had any activity there until relatively recently, and for most of my life it was thought to be a dead world. Now, it can only be above all dead, he still has a small stitch left.
*Mars rotates once every 24 hours 37 minutes, so that is the length of its day. To avoid confusion with Earth days, we call them alone and they are numbered since a given mission lands from 0, so that in this case, Sol 173 was the 174th Martian day after InSight landed.