Mamata Bruce, Paul Mars, Kansas discussed on NASACast Audio
Mm-hmm because even the little bit of perturbation of the tether shaking in the wind or just even expanding temperature-wise dislike nanometer creates a huge huge annoy source on our seismometers so you create this whole system to make the tether so that wouldn't be pushing against the size monitor. We have a little loop in there. That's basically annoy shunt. Dont instead of pushing directly on the seismometers any little vibrations or thermal noise or whatever it is pushing against a spring and so one of the things we had to do is actually pull all the tether away from the size modern towards the lander which was not particularly easy took us a bunch of tries to get just pulled back enough because the problem that we had is if we pulled it too much. There's no way to push it back. We kind of had to sneak up on pulling it a little bit in fact the very first time we try to pull it. We didn't move at all second any time. We try to pull it. We moved at like barely and then the third time we moved at just about enough in the end that ended up taking us about two weeks all told it took about two months to stat up. All the elements of the size Mamata Bruce says it took another month to make sure it was working correctly. We were busy that whole time there's a handful of things you have to do but each thing takes preparation and then you have to check it out afterwards and we're always trying to make sure everything is safe. We don't WanNa be swinging a robotic arm around run into the antenna or punch a hole in the thermal protection of the seismometers so we checked everything in the test faciliate. JPL each one of those was round the clock preparation and work by the team to get it done and so that was an exhausting three months to get the seismometers working. It was worth every minute because the seismometers seismometers has been performing amazingly well. I mean we're getting seismic data at a precision that is in some parts of their frequency bands thousand thousand times better than anything has been done on the earth because of the background noise on the earth no matter where you go on the earth you have a certain amount of vibration just from the storms and the ocean and the waves beating against the shoreline you can go to the center of Kansas and you're still getting a pretty big signal from ocean turbulence but we don't have any oceans on March so we're actually seeing vibrations that have never been seen on the earth because you can never get that quiet on the earth and so this is new territory for seismology in a technical sense as well as in a geographical sense as has noted in episode two. Apollo astronauts had put seismometers on the moon which also doesn't have oceans the moon seismometers were very similar but that was using sixties and seventies technology so they actually got some noise that was as low as ours but over much more narrow frequency band seismic signals have information at all different frequencies and all the different frequency bands have different kinds of information higher frequencies tend to die out with distance. Just like certain sounds you hear from long distance like if you hear thunder from a long distance away is just a rumble. If you hear thunder up close you hear the crack you hear the high frequencies as well so the high frequencies in seismology pity tell you about things that are close in but for more distant quakes several hundred miles to several thousand miles away you're seeing lower and lower lower frequencies as the dominant contributor and so you want size momber that measures all the different frequencies all the way down to some frequencies that may be takes almost listen our for an oscillation to finish which is the frequencies that which the whole planet vibrates or rings in episode two. Bruce had explained how quakes cause earth to ring like a clear clear bell but the moon to crash like a Gong guests that Mars would have more of a bell ring like Earth. There's the ring but there's still some of that scattered Kinda hissy stuff going on the signals that we're looking at are kind of halfway in between so on the earth. If you get a fault fault or get a crack and then just leave it alone for a few hundred million years there's water that seeps through at minerals crystallize in the cracks and you get a kneeling healing of these cracks and so after some amount of time another wave goes through there. It doesn't even see that crack anymore. Just passes passes through on the moon. It's very dry and so those cracks maintain sells for hundreds of millions or even billions of years there's and so there's lots of things that reflect and scatter the seismic waves and so when you scatter a wave instead of going straight from point. A. To point it be it bounces around takes drunken walk and finally you know maybe ends up back at point B but instead of going one hundred miles in a direct route it may have taken to three hundred miles to get to where you are and so it comes in really late so we've got moon quake signals that last four an hour or more whereas the same size quake on the earth with last four maybe fifteen or twenty seconds and so we're seeing some of the same type of scattering processes we think on Mars as we saw the moon and especially for the close events so we think that the outer portions of the Martian crust maybe the upper ten or twenty miles might be more fractured and less a kneeled than the earth which tells us that possibly the Martian crust is drier than the Earth's crust. Although that's still speculative at this point the few events we've had from farther away. Don't seem to be quite so scattered a few events from a over a thousand kilometers away those waves are dipping down into the upper mantle so we think that deeper into the crust or into the mantle things don't seem to be so fractured up Marzieh's between the earth and the moon a lot of different ways and it looks like this is just one more way see that it really lies on that line. Even the picture of Mars is just starting to emerge bruce's happy to be seeing even small Mars quakes again we we didn't start measuring at a level that we could detect them until about saul one hundred and then we went for another month with seeing nothing which was it's a little concerning so we started watching and we're waiting for our first. Mars quake and we're waiting. We're waiting after after about a month was kind of looking are watching sing and when you're going for weeks without seeing anything you start to get a little bit fearful earful that well do. We really know what we're doing here or really gonna see something so first. Mars quake that we saw was on Sol one twenty eight and it turns out. It's very unusual Joie. We haven't seen another one quite like that. Since most of the energy was at high frequencies and since then most of our quakes have been much lower frequency since then we've been getting about one or two seismic events per week most of very small earth they would probably be magnitude wonder `and to were actually only able to see very small. Mars quake signals for part of the day. There's a lot of wind activity and so the small quakes get drowned out by that north. We've found out very early on bet. The pattern of atmospheric noise is very repeatable every day. Eh so about six o'clock at night. It gets very quiet and then around midnight. The wind comes up in from midnight to about six or seven in the morning. The wind's blowing very steadily then the sun comes up and you start getting turbulence and the noise just goes up quite a bit and then it just keeps on going until about sundown again and we can see that each and every day so now we know the window to spend our time watching. Paul Mars quakes one of the Nice things about Earth's seismology. Is You get dozens of Nice earthquakes every day. We get all excited when an earthquake happens but most of the earth is unpopulated. There's oceans there's wilderness and when earthquakes occur out there nobody but seismologists knows about and so- seismologists can spend a few months collecting being data and you'll have a few hundred signals to work from in lots of information there on Mars. The activity is probably something like a factor of thousand and less so instead of having several hundred quakes over the course of a month. We have a handful of maybe a half a dozen and so so we have to wait a lot longer for the number of quakes you have this giant thousand piece jigsaw puzzle and every week we get one piece so we have after you've really really patient and we have all these pieces that don't fit together yet and just have to assume that as we get more pieces will be able to start making the connection. It's funny. I start thinking about what it must have been like to be a seismologist back in the early nineteen hundreds when people were first starting to piece together you know what was going on the Earth but for those first ten or twenty years of the twentieth century you look at Seismic Graham and just scratch your head what's going on underneath there and we sort of take take it for granted. You Open up a textbook. There's a cross there's a mantle. There's a core and they show you nice clean seismic grand with all these wiggles and this corresponds to this path but somebody had to figure that out from scratch and we're having to do that on Mars now in it's not as easy as it looks. The weather station on insight helps rule out how a breeze or an air pressure event shakes the seismometers by amplifying the vibration of insight shaking in the wind. You can get a sense of the weather on Mars plus. As kind of a bonus were actually able to see dust devils in the weather the data we have the pressure data and steering slowly during the day and suddenly it'll drop about several Pascal and interpret that as a dust devil passing very close to us and it's like a hurricane when you have super low pressures in the eye of a hurricane you have very low pressures in the center of industrial because it's essentially little vacuum cleaner where the air from the surface of being sucked up higher into the atmosphere and we can actually see that in the seismic data as well because as the dust devil is sucking up the air is actually like a vacuum cleaner pulling on the ground as well and so we can actually see the tilt of the ground as a double goes by and so we've seen hundreds of those things now and by doing that we actually get some information about the surface of Mars because the amount that a tilts is related to how steph off the surfaces that this very stiff. It doesn't tilt very much if it's relatively bendable it tilts a lot and so we're actually starting to measure the elastic nick properties of the upper few meters of the Martian surface by looking at these dust devil signals. If.