NASA’s Mars InSight launcher has just detected two relatively large earthquakes on the Red Planet and are coming 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? That, now?
InSight touched 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 get a daily report).
Unfortunately, the heat probe never had a chance to work; it was designed to dig down about 5 meters above the surface, but despite some rather heroic efforts, it never got very far and that part of the mission was over.
However, the seismic package worked wonderfully and over 500 earthquakes were detected. When something shakes, shakes and rolls on Mars, sound waves called where seismic moving through the interior of the planet. Different types of waves move differently, so help scientists understand the interior of Mars. Most of the waves detected by InSight are low-frequency, high-frequency waves that come from an event in the crust of Mars, but a few dozen are of lower frequency and can propagate through the mantle of Mars (which, like Earth, it is solid, but not as hot and probably does not move like ours).
In the first year on Mars (which is two years long on Earth), it detected two earthquakes of decent size, magnitude 3.5 and 3.6. Then, for a while, InSight didn’t detect many large ones. This is probably 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 that can only go so far.
Now, with the Martian spring in the northern hemisphere, things have calmed down in terms of atmosphere, and in March SEIS detected two more relatively large earthquakes, magnitude 3.1 and 3.3. I was in a few earthquakes when I lived in California, and it’s certainly big enough to feel, though not big enough to do any damage.
All of these earthquakes came from the direction of Cerberus Fossae, a series of gutters and cracks in the Martian crust about 1,600 km east of InSight. This region is very cold: cracks probably formed a long time ago when huge Tharsis volcanoes formed, creating a huge swelling in the crust. This expansion of the crust caused the surface to crack at Cerberus Fossae, like a balloon covered in dry mud that breaks and separates if you inflate it.
What makes this area so interesting is that the area around it is young and I mean young: the number of craters indicates that it is less than 10 million years old, and some parts may be closer to 2 million. A huge volume of liquid erupted from the ground then – possibly water, although it could have been lava – and made its way into the region.
A few million years is a small part of Mars’ 4.5 billion-year-old age, so that means the planet has been active volcanically very recently. Is it still today? This is a question we would like to know the answer to, and InSight can help. These large earthquakes indicate something it happens there.
InSight recently received an extension of the mission until at least December 2022, which is great news. Scientists hope to detect more earthquakes over time, of course, and also hope to reduce the noise SEIS feels so they can detect weaker earthquakes (they may even feel the change in the ground as it cools. during short solar eclipses caused by the Martian Moon Phobos!). In recordings made where seismic waves are converted into sound, you can hear some short, sharp pops (collectively called, seriously, dinks and donkey). You can find one here near the beginning of this record from Sol 173*:
At first it was not clear what they were, but now engineers believe they come from the thermal movement of the cable that attaches the SEIS to the landing gear, when large temperature fluctuations cause it to expand and contract. They intend to use a spoon on the lander to dig up part of the surface and leave it on the cable, insulating it a little. We hope that this 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 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 attentive to movement. It is extraordinary to find the structure of Mars under its shell, but I am particularly interested to know if Mars is still volcanically active. 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 just be Especially dead, there was still a small blow left.
*Mars spins once every 24 hours and 37 minutes, so this is the length of its day. To avoid confusion with Earth days, we call those soils and are numbered from the moment a particular mission lands from 0, so in this case Sol 173 was the 174th Martian day after InSight landed.