Conversation with Mars Geologist Matt Smith — Part 1 of 4
Upon hearing of Spirit’s untimely passing last week, I met up with Matt Smith, a Seattle-based Mars geologist and grad student at the University of Washington. The following is the first part of our hour-long conversation over lunch (at the Saigon Deli in the U District, very tasty), where I played the part of a know-nothing kind of person — because nobody could possibly be that ignorant, right?
TOAD: So, NASA said that Spirit died yesterday officially, after not communicating for over a year. But before that, instead of lasting 3 months as planned, it became this six year long mission. Hundreds of thousands of images. What other things did it send? Did it just send images?
MATT SMITH: It sent all kinds of data. It had a pan cam, which is the big panoramic camera that takes the really cool pictures of the landscape, and then it also had a microscopic imager, which is a microscope on an arm so you can look at the rocks up close. It had a spectrometer. So it could look at thermal wavelengths and figure out mineral compositions.
TOAD: Is it the thermal spectrometry that lets you figure out which minerals you’re looking at?
MATT SMITH: Uh-huh. Individual minerals have diagnostic absorptions in the way they interact with radiation. So they found silica on the surface. And silica has this unique spectrum to it — it absorbs certain wavelengths better than others — so based on that you can tell: that’s silica and not pyroxene or some other mineral. So it is thermal spectroscopy that is used to identify all these cool minerals. Spirit also had something called a Moessbaur spectrometer. It uses the absorption of high-energy gamma rays to determine elemental composition, but only with certain elements. But it identifies iron-bearing minerals really well. And iron is the most common element that is both found in rocks and detectable by Moessbaur. So if something has iron in it at all, it will use that for identification. Another thing Spirit had was an alpha proton spectrometer which shot alpha particles at the surface, and it excited the elements that it encountered and emitted X-rays. And you could use the frequency of the X-rays to figure out what elements were in there. So you could figure out elemental abundances of your samples.
TOAD: So basically, it was super-rich data.
MATT SMITH: Yeah. You got a lot of information. And that’s why it was so useful and kind of revolutionary, the data it sent back, because it was so specific to a location and it was so much data they couldn’t get from orbit. For example, the rover had this thing called a RAT tool, the Rock Abrasion Tool, and so it would —
TOAD: Scratch the surface?
MATT SMITH: Yeah. It was kind of a bit of sandpaper and it would rub the surface, so it could figure out not only surface compositions, but it could dig down to figure out subsurface compositions and see how different the surface was from the subsurface. The satellites can only see the surface, so the question is: are we seeing what’s actually happening at depth, or are we only seeing a coating over the surface, or is it just dust?
TOAD: Right. And it also had a brush tool so it could dust off the samples before photographing them and using all that spectrometry.
MATT SMITH: Yeah. There’s a dust coating on everything on Mars, because there’s dust everywhere. So the rovers could brush that dust off. Or, they could take a spectrum of what it looks like, as is, and then brush off and take another spectrum and then RAT into it and take another spectrum to see what these different levels tell you and how that relates to what you think.
TOAD: Very cool. So did it do any independent analysis of this data?
MATT SMITH: No.
TOAD: Was it just sampling and sending back?
MATT SMITH: That was it. It had an arm that would put those sensors right up against the rock and sense, and then send that data back, and all the analysis was done on Earth.
TOAD: What about directing it to go specific places or looking at specific rocks?
MATT SMITH: That was all communicated from here.
Actually, the scientists in mission control chose points and goals for the rovers, but the rovers were both under autonomous navigation control. See How Mars Exploration Rovers Work and The Rover Manual.
MATT SMITH: I’ve never actually been in mission control so I don’t really know how they actually communicate. But I know it sounds like an interesting dance because it takes so long to communicate. Travel time is 8 minutes, I think, between Earth and Mars and so you send a signal for it to do something, it sends back the picture it takes, …
TOAD: And you look at it and scratch your head and say: “I think we want to go here, what do you think?”
MATT SMITH: Exactly. And 8 minutes after you tell it to do something, it will get that. And in early mission they also have to do it on Mars time, so they have to be up in the middle of the night, you know, directing the mission. I imagine it doesn’t jibe a lot with our nine-to-five view of science that we do here.
TOAD: I thought scientists worked twenty-four hours a day. And you don’t need food or sleep. So is this why or part of the reason why Spirit only traveled less than five miles in its entire six years of operations?
MATT SMITH: Yeah. It also got stuck a lot more than Opportunity, it got a lot more wheel problems. It broke a wheel in the middle and was dragging it, and wasn’t able to travel as fast. I think it was a lot more susceptible to power problems too. Dust storms reduce the power and a lot of dust got deposited on Spirit and so its capability to move was less, which is ultimately what killed it in the end. I think it was mostly power issues and mobility issues, because it got stuck a couple of times.
TOAD: And then finally got stuck completely for about a year, before it lost communications.
MATT SMITH: It got stuck in an unfavorable geometry relative to the sun. In winter it would drive to the top of a hill and then park facing the sun because in winter it can’t do a lot of science. So it would just sit there and stay alive, and then it would do all of its good science in the summer. But when it finally got stuck it was kind of facing away from the sun and it got a bit shaded too, so it didn’t have the greatest conditions when it got finally down.
TOAD: So in terms of field geology, five miles is not awesome coverage, right?
MATT SMITH: It’s not super-great, especially on Mars. Mars, at least in my mind, you expect it to be this big homogeneous planet where there’s a lot of basalt, impact craters, not a lot happening on small scales. But what the rovers were able to identify is that even in spots like where Spirit was which is Gusev crater, in a fairly homogeneous area, there was a lot happening spatially and it discovered a lot of those things as it moved. And so it added a lot as far as complexity to what we know of the surface. So there’s a lot of small-scale heterogeneity that we didn’t know about.
TOAD: So, a silly question. In the New Scientist, they did an obit for Spirit, which said things like “Spirit, first robot geologist, died today.” And I wrote in similar style, “It is survived by its twin, Opportunity” and so on. So, it’s a bit cutesy, but do you think that it’s fair? Is it fair to call Spirit and Opportunity “robot geologists”?
MATT SMITH: Yeah, I think so.
TOAD: Even though they’re only measuring and collecting data…
MATT SMITH: And not interpreting?
TOAD: And not interpreting.
MATT SMITH: So from a philosophical point of view, are they actually doing geology?
TOAD: Are they? Are they doing field geology? Or not really?
MATT SMITH: As much as they can. They can’t go very far. They can’t walk up steep slopes very well.
TOAD: But they went up 30 degree slopes, right?
MATT SMITH: Did they?
TOAD: I think Spirit in particular climbed Husband Hill in Gusev crater. I mean, 30 degrees is not too steep, but it’s nothing to scoff at. I know many people who can’t do that.
MATT SMITH: Well, I guess. It’s hard to really equate them. Because, what’s in a toolkit for a field geologist on Earth? There’s you know, a compass, and a magnet, and acid, and …
TOAD: A hammer.
MATT SMITH: Right, a hammer. And this guy’s got spectrometers and a microscope. So maybe if we were all robots and we could have all the tools we wanted and we could do all we wanted in the field… Maybe the rover, it’s better than a field geologist! It’s not much for interpretation, but its description — top-notch!
Parts 2 through 4 to be posted soon.