Quakes on Mars
We’re shooting off to Mars, because there’s news out this week that the red planet is seismically active and it experiences marsquakes. Katie Haylor has this report...
Katie - NASA's insight mission is tasked with finding out what's going on inside the red planet. In November 2018 the static lander arrived on the surface, and got to work. Now, the publication of several papers worth of data are revealing its findings so far, and the Open University's planetary geoscientist David Rothery gave me the lowdown.
David - Well, in 10 months there have been not far short of 200 separate Marsquakes, and most of them are small events and they appear to be vibrations that travel just through the crust, that's the outermost rocky layer of the planet. And they're not very well understood. But there have been 24 recorded that measure magnitude 3 to magnitude 4 on the Richter scale, which have caused vibrations, which had been strong enough to travel through the crust into the mantle and then back out of the surface where the detector is.
Katie - These Marsquakes are detected by Insights' seismometer sitting on Mars' surface: it is essentially a very sensitive microphone that records the planet's vibrations.
David - They can pinpoint the source of some of these earthquakes. At least two of these appear to be in a region about a thousand kilometres from the Lambda Kerberos fault side. This is where the surface is quite badly fractured, some quite deep chasms there, where people had previously suggested there were earthquakes. So you can see where boulders have tumbled down slopes and bounced through recent sand dunes. So something recently disturbing the ground. Could that be earthquakes? Well now it seems that inference was right because Marsquakes have been pinpointed back to that very region.
Katie - So what's actually causing these Marsquakes?
David - Well, these Marsquakes are not like the big earthquakes we get on the earth, which are at the boundaries between moving plates. Mars's crust and upper mantle is not divided into rigid plates sliding around on a plastic interior like we have on the earth. The quakes on Mars are like what happens inside Earth's continents where stresses just cause some fracturing or some buckling or something like that. So they're relatively small. They're like the biggest quakes that we occasionally get in the UK. But Mars's crust, a rigid outer layer, is under stress, and now and then the stress overcomes the strength of the rock and the rock fractures. And that's a Marsquake.
Katie - Now that we know for sure that Mars is indeed quaking. How does this help us better understand the geology of our planetary neighbour?
David - We'd like a few more quakes before we extrapolate too wildly. But we do know, number one: Mars is active today. Quakes are definitely happening. Previously we inferred them, now we've seen them. It's likely that part of the mantle is mushy because the shaking wave, so-called S waves, do not travel very well at all through part of a mantle. Whereas the compressional waves do travel quite well. So we're beginning to understand the mechanics of inside Mars.
Katie - Looking ahead, could these findings have any impact on, perhaps one day, a base on Mars?
David - What we're learning about the properties of the shallow crust will help because we want to know what we're building on. But some people have been saying on social media: "Oh there are Marsquakes, it's too dangerous to go and put bases there". That's completely untrue. You wouldn't refuse to build a base in the UK because there's occasionally a magnitude 3 earthquake here, or in the middle of Siberia because there's a magnitude 3 earthquake every so often. Mars is perfectly safe seismically. You wouldn't build a base in the bottom of one of the chasms on Kerberos Fossi, because you've got a great big cliff above you and a boulder could fall off if dislodged by a Marsquake. That's common sense. We're not learning from this that we shouldn't go to Mars because Marsquakes occur. We're understanding about the interior of the planet from what Marsquakes can tell us.