RAY SUAREZ: Twin rovers named Spirit and Opportunity continue to explore opposite locations on Mars. To update us on their travels, and what we've learned so far about the red planet, I'm joined by Steven Squyres. He's a professor of astronomy at Cornell University, and the principal investigator for the Mars Exploration Rover Project.
Professor Squyres, you've got two vehicles that are ranging now pretty widely away from their landing area. What have you been able to find out so far?
STEVEN SQUYRES: Well, there's been a lot going on at both landing sites. At the Gusev Crater landing site, where Spirit landed, we're in the process of doing our first really long drive. We landed about 250 yards from a big impact crater, something that's about 200 yards in diameter. And so we're in the process now of making our way towards it, typically going 20, 30 yards a day. And over the next couple of weeks, we're going to climb up to the crater rim and peer in and see what we see.
The other landing site, which is at a place called Meridiani Planum, and that's where Opportunity touched down, we actually landed inside an impact crater. And exposed within the wall of that impact crater is a fantastic outcrop of finely layered rock that we think may have a very interesting story to tell about what happened long ago on mars. So we're focused very much on trying to understand that outcrop, but also some of the soil around it.
RAY SUAREZ: Well, now that you have a chance to have the tools on the landers dig into the Martian soil and get, you know, beyond just the outer layer that you can see with your cameras, what are you turning up?
STEVEN SQUYRES: Well, we just did that yesterday, so we're sort of still in the process of getting the data off of the spacecraft. What we did, we did what we call a trenching activity. And it's similar to what might happen to you if you take your four-wheel-drive vehicle to the beach and you kind of spin your wheels a little bit. You can dig your way into the sand a little bit. And so what we did with our six-wheel-drive vehicle is position one our wheels so that we could spin it and sort of move sand and soil out of the way and dig a trench that's, oh, four-, five-, six-inches deep, back out of it, and then use our instruments to look into the hole.
And what it does is it provides us with a way to see below the surface of Mars. And what we've gotten down from the spacecraft so far are the first pictures from deep down inside the hole. We have a microscope on the end of an arm, and we can reach the arm down below the surface into the hole that we dug, and look at the things that we see in the soil there.
When we look at the soil at the surface at Meridiani Planum, what we see is sand grains, and then sprinkles on top of that lots and lots of sort of gravel-sized objects -- we call them granules. They come in all different shapes -- some of them are very angular, some of them are perfect spheres, which is very strange.
And what we wanted to know is, are there any of these things down below the surface? Is it just a surface coating, or are there any down below? So we dug a trench with the wheels, stuck the microscope in there, looked at the wall of the trench, and what we found were lots of very, very fine grain soil, much finer than what we had seen at the surface, plus some granules that are stuck into the wall of the trench, and they're perfectly circular and they're also shiny, much shinier than anything we've seen at the surface. And we don't understand that yet.
RAY SUAREZ: Well, what are some of the forces on Mars that could have created that distribution of fine and less-fine granules, the natural sources that could have created something like a spherical piece of rock?
STEVEN SQUYRES: Well, there's a couple of different questions here. Regarding the spherical objects -- we call them spherals, which is short for spherical granuals -- we've sort of got three theories for how those formed.
One possibility is that there ... it's something called le pili, I think it's an Italian word meaning "little rocks," or something like that. But anyway, when you have a volcanic eruption and you toss a lot of volcanic ash up into the air, as it settles out, what can happen is pieces of this very fine ash will kind of glom together and make little round balls. Pompeii is actually buried in a lot of this stuff. And then these little round balls will sort of fall out. So, that's one possibility -- that we're seeing the results of a volcanic eruption.
Another thing that we've looked at is the possibility that if you have a different kind of volcanism, where you spray lava into the air, or you have an impact in which a meteorite from space hits the surface with an enormous amount of energy, and again sprays molten rock into the air because it melts rock when it hits, those little droplets of molten rock can then fall down to the surface and make effectively make little glass beads that we would then be seeing in the soil.
A third possibility, which we're sort of intrigued by, is that these might be what we're called concretions. And in fact, when we look in that outcrop that I mentioned, we see these things embedded in the rock. And what can happen is if you have an outcrop of rock that has water percolating through it, and the water has materials dissolved in it, those materials can solidify or precipitate around little nucleation sites and then grow little spherical objects. If they're actually concretions, then that would be an indicator that water was involved in their formation.
So when we drive up to this rock outcrop where we know there are some of these spherical objects, we're going to be studying them in intense detail to try to find out which one of those three ideas is correct.
RAY SUAREZ: What tools have you got onboard to take a look at those rock outcroppings and get a better idea of how they were formed and how they make up the bedrock of Mars?
STEVEN SQUYRES: Well, we've got, we got a lot of tools. This rover is sort of like a Swiss-Army knife, it's got a lot of things on it. The rover has a mast that sticks up in front and that mast supports two instruments, one is some a very high-resolution color cameras. The other is an infrared spectrometer that we can use to look off in the distance, and from a distance tell us something about what the rocks are made of.
Once we then decide where we're going to go, we can drive over to the target. And then the rover has an arm. The arm is almost exactly the same dimensions as my arm with a shoulder and an elbow and a wrist and a hand. And on the hand there are four fingers: There's a microscope for looking at the rocks up close; there are two spectrometers to tell us a lot more detail about what the rocks are made of; and then we have this device called the RAT, R-A-T, that's short for Rock Abrasion Tool. And that's a tool for grinding away the outer layer of a rock that's sort of opening a window in the interior of the rock that the other instruments can then look in.
RAY SUAREZ: Now, I've heard you refer to the warranty expiring dates on these two rovers. The way things are going, and now that you've been able to clear up some of the earlier glitches, could Spirit and Opportunity be rolling around and telling you new things for a lot longer than the 90-day window?
STEVEN SQUYRES: I think they really could. We always said that this was intended from the outset as a 90-day mission, but what that means is, as you said, it's 90 sols, 90 Martian days, which are called sols, is when the warranty expires. It doesn't mean that when the sun comes up on the 91st sol that the wheels are going to fall off, it just means that that's what we designed them for.
But vehicles like this are designed with a lot of conservatism, a lot of margin. You build them to be tougher than you think they need to be. And the good side of that is that once the warranty expires, you've still got a pretty healthy vehicle on your hands. And what we're finding is that the vehicles are performing extremely well. They're in excellent health. And they're showing every sign of lasting considerably beyond that 90-Martian day target that we had initially set. So I think they're going to be tooling around Gusev and Meridiani for a good long time.
RAY SUAREZ: Well, that means we'll get another chance to talk to you. Steven Squyres, thanks a lot.
STEVEN SQUYRES: Nice to talk to you.