NASA’s Mars InSight lander has just detected two more relatively large earthquakes on the Red Planet, coming from a very interesting region known to be tectonically active. This highlights one of the bigger questions we have about Mars: is it volcanically active today? As, now?
InSight hit a volcanic plain called Elysium Planitia on November 26, 2018. Its main mission is to study the inside 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 also get a daily report).
The heat sin unfortunately never really got a chance to work; it was designed to dig about 5 feet into the surface, but despite some heroic efforts, it never got very far, and part of the mission ended.
However, the seismic package worked wonderfully and more than 500 quakes were detected. When something on Mars shakes, rattles and rolls, it creates sound waves called seismic waves moving through the inside of the planet. Different waves move differently, and this helps scientists understand the inside of Mars. Most waves that InSight has noticed are shallow, high-frequency waves coming from an event in the crust of Mars, but a few dozen are lower frequency and can propagate through the mantle of Mars (which, like Earth, is solid is, but not as hot and probably does not move like ours).
During the first year on Mars (which is two Earth years long) he detected two earthquakes of decent size, size 3.5 and 3.6. Back then, InSight did not detect many large ones for a while. This is probably because the air is too unstable in the Martian winter and the wind noise covers the seismic activity. SEIS, the seismic detector, sits under a small dome deployed by InSight to protect it from wind, but it can only go that far.
Now, with the Mars spring in the northern hemisphere, things have calmed down atmospherically, and in March SEIS detected two more relatively large tremors, strength 3.1 and 3.3. I’ve had a few earthquakes before when I lived in California, and it’s definitely big enough to feel, though not really big enough to cause damage.
All of these earthquakes come from the direction of Cerberus Fossae, a series of craters and cracks in the Mars crust about 1,600 km east of InSight. This region is very cool: the cracks probably originated long ago when the large Tharsis volcanoes formed, causing a huge bump in the crust. This expansion of the crust caused the surface at Cerberus Fossae to burst, like a balloon covered with dry mud that tears and separates when you inflate it.
What makes the area so interesting is that the area around it is young, and I mean young: crater counts indicate that it is less than 10 million years old, and some parts may be closer to 2 million. A large amount of liquid erupted from the ground at the time – possibly water, although it was lava – and plowed over the region.
A few million years is a small fraction of the age of 4.5 billion years of Mars, so it means that the planet was very recently volcanically active. Is it still today? This is a question we would like to know the answer to, and InSight can help. These large earthquakes claim something go on there.
InSight recently got a mission expansion until at least December 2022, which is good news. Of course, scientists hope to detect more tremors over time, and they also hope to reduce the noise felt by SEIS so that they can detect weaker tremors (it can even feel the change in the soil as it cools during short solar eclipses caused by the Mars Moon Phobos!). In recordings made where the seismic waves are converted into sound, you can hear some short, sharp bangs (collectively called, serious, eateries and donkeys). You can find one here near the beginning of this recording of Sol 173*:
At first it was not clear what it was, but now engineers think they are coming from a thermal motion in the cable that SEIS attaches to the lander, when large temperature fluctuations cause it to expand and contract. They plan to use a spoon on the lander to dig up a portion of the surface and drop it on the cable and insulate it a bit. Hopefully this will mask the noise and improve the quality of the detection. You can see their efforts in this short video which consists of a series of images taken by a camera on the lander:
It’s amazing what you can learn from a planet by sitting very still on it and feeling very careful for movement. It’s cool that we’re finding out about the structure of Mars under its crust, but I’m particularly interested to know if Mars is still volcanically active. No one knew if Mars had relatively any activity on it until relatively recently, and for most of my life it was a dead world. Well, even if it might just be mostly dead, with another small kick left.
*Mars rotates 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 are numbered from the time a given mission lands at 0, so in this case Sol 173 was the 174th March day after InSight landed.