Interview with Matt Golombek

Now that Spirit has landed safely on Mars, the mission science team has begun to think about where they’d like to send the rover and what scientific experiments they’d like to do. Astrobiology Magazine’s managing editor Henry Bortman caught up with geologist Matt Golombek on the second day of the mission to get his initial impressions of the Spirit landing site and the possibilities for scientific discovery. Golombek was the chief scientist for the Pathfinder mission and is a landing site scientist for the MER missions.

Astrobiology Magazine (AM): There have been a couple of comments indicating that from the images that Spirit has sent so far, the science team can already tell that Gusev Crater is, as predicted, a dried-up lakebed. I look at these pictures and just see a bunch of rocks. What makes it a lakebed?

Matt Golombek (MG): Well, you can’t tell at this point. We don’t know. But in the [site] selection [process], we evaluated every piece of data that was available to be evaluated, and we made a series of predictions [about the site].

At the largest scale, we said it would be safe for landing, it’d be safe for driving, and we said it would have less rocks than the VL Viking Lander 1 and 2 sites. And that’s exactly what we see.

Now, you can actually tell an awful lot just by looking at the geomorphology [landforms, rocks and dust] of the site. What you see is a reasonably flat surface. You see very shallow craters – what I would interpret as craters – we don’t know that for sure, but I’m pretty sure that’s what they are.

What you don’t see are a lot of drift or dunes. You see some dune material. In some ways those dunes look like Mermaid Dune at the Pathfinder site. It looks to me – preliminary impressions, not just mine, but many of the other geomorphologists on the team – is that this is a site that’s had aeolian [wind-blown] activity, that dunes have marched across the site and taken most of the fine-grained stuff with it.

So you don’t see a lot of dune material. We didn’t see any dunes, really, just a few small ones, like [at the] Pathfinder [site]. We saw what looks like a lag deposit, like you’ve taken away all the fines and what you’re left with are the rocks that are too big [for the wind] to move. And a duricrust surface, which is a more heavily cemented surface, particularly in the center of a bowl-shaped crater [visible in some images].

So in a lot of ways, [the site is] pretty much similar to what we expected and predicted.

AM: Okay, but people have said, “It looks just like a lakebed.” What is it about the terrain that makes people say that?

MG: Just the flatness.

AM: But you can find a lot of flat places that aren’t lakebeds.

MG: That’s right. There’s nothing unique at this point. I think we really need to go out and start looking at the mineralogy and start looking at the deposits, and that’s really what’s going to tell us. But it looks like [just what] you’d expect [a lakebed to look like]: a flat surface like that. Part of that is its location inside a crater. But we could be totally wrong about that, and we won’t know till we get out and start looking around.

AM: So would it be accurate to say that you haven’t found anything that’s inconsistent with the theory that Gusev is an ancient lake bed, rather than that you have seen clear evidence that it is?

MG: Yeah, that’s right. There’s nothing that we have yet that would compellingly indicate that we’re on the bottom of a lakebed, certainly the primary surface of a lakebed.

AM: And will you be able to tell that from the images that will be coming back from Mars in the next few days?

MG: We’ll get clues. If we see certain deposits [in the images from] the Mini-TES, the thermal emission spectrometer, that indicate standing-body-of-water deposits – anhydrites, carbonates, things like that – that would be fairly compelling to suggest that we’re sitting in a place where water was.

In the absence of that, we’re probably going to need to go and look at some of those rocks up close, in detail, with the Mössbauer [spectrometer] and the APXS Alpha Proton X-ray Spectrometer.

AM: Steve Squyres mentioned that in some of the images you can see the lip of what might be a crater.

MG: Yeah. My interpretation is that that is a shallow crater. And it looks like it’s been filled in. And that lip looks like it would be a piece of the crater rim. It looks like there’s a series of boulders along that rim. So that’s one of our first targets, to traverse across that shallow crater and get to that rock on that rim.

And then at a broader scale, we’re looking at where we’ve actually come to rest. We have the DIMES images – [a series of 3 images taken during the lander’s descent] – now, so we know roughly where we are. We don’t know precisely. We’re still lining up the azimuths. But there is an exposure, that etched terrain, just to the southeast. Those are those irregular cliffs or mountains in the distance. They look to be 1 to 2 kilometers away. And given how flat this surface is, that might be a place that we decide is important enough that that’s where we want to be heading towards.

But all of this is just the very initial ideas that we have.

AM: Are they actually close enough to get to?

MG: The estimates for the [total] drive distance that we set for the mission depended upon what the rock abundance was and how flat the terrain was. Well, we have a very smooth site that is just about ideal for long-range driving. And if we don’t see a lot of variability in the [nearby] rocks, it’s very likely that [after checking] a couple of those out, maybe at the edge of that crater lip, [we’d] start heading off to look at something different as well. And this etched terrain really looks like it’s a different [geological] unit. It’s been mapped by everyone as a different unit than the stuff that we landed on.

AM: Is it different mineralogically as well?

GM: We have no indications of any mineralogy at this site that are unique, so we can’t say from that yet. But there’s a gazillion reasons why you wouldn’t pick that up from orbital data. We have a much better chance, now that we’re on the surface, of starting to see those distinctions. And that’s really what we’ll be looking for.

So in the next week, we’re going to try to pinpoint where the spacecraft is, and we’ll come up with fairly specific plans for the near-long-term, maybe the first couple of weeks: getting to the rim of that small crater, perhaps. And I think we’ll try to [also develop] a long-long-range goal for the mission that would include a target that we’d like to get to by the end of the 90 sols.

AM: How far could Spirit go, if everything went well?

GM: The tests that were done were done in Viking 1 and 2 terrain, which has 20 percent rock abundance, and a much more variegated surface. And this surface has, it looks like, 5 to 10 percent rocks. That’s pretty much exactly what the remote sensing [orbital] data said.

I can’t tell you how thrilled I am that this site is just what we said it was going to be.

You saw how flat it is. So avoiding the rocks is going to be a piece of cake. There just aren’t very many big ones that you need to worry about. And you could easily provide X-Y waypoints [interim destinations] along the way. I don’t see what the problem would be; you could easily go 50 meters a sol if you wanted to. And you’ve got 90 sols, so you could go quite a distance.

AM: And there’s nothing that restricts the total distance the rover can go other than its energy budget. As long as its batteries get recharged every day, it can just keep going?

MG: Just the energy budget, that’s right. And typically you’d be trading driving for remote sensing or other [science] activities. You want some mix of those, obviously.

It really depends upon the variability of the materials at the site. If we look with the Mini-TES and we see a dozen different kinds of materials, well chances are there’s going to be a lot of interest in figuring out what those are first, before you start trundling across [the terrain].

But if it looks like one or two rock types, and we figure out what those are, and we look at the sediments and those are all consistent, then there’s every indication that we should try to get to something that, mapped out, looks like a different thing; and this etched terrain looks completely different – from the geomorphology, anyway. It’s had a different geologic history [than the nearby material]. So that would be a great place to go.