After a hair-raising ride through the atmosphere, NASA's Mars Science Laboratory (MSL) has landed safely on Martian soil with cheers all around. Now engineers are busy checking out the rover Curiosity's condition while the mission's science team takes a first look around the surface locale. In the months ahead (the prime mission is slated to last a few months shy of two years) scientists plan to drive Curiosity around its touchdown site in Gale Crater and then up the slope of Mount Sharp, which rises six kilometers from the basin floor. Along the way they will look for geologic evidence that water once flowed across the landscape as well as signs of ancient microbial life.

Scientific American talked Monday with John Grotzinger, MSL project scientist, to get an insider's perspective on the landing and upcoming plans. Grotzinger has been on the MSL team since 2007, working from his office at the nearby California Institute of Technology, where he specializes in sedimentology, stratigraphy, geo-biology and ancient surface processes on Earth and Mars.

[An edited transcript of the interview follows.]

Does the landing site remind you of any place on Earth?
The landing site itself is quite different—Mount Sharp, with this five-kilometer stack of flat-lying layers—there's nothing quite like it on Earth. There are places where you see even thicker stratigraphic sections [on Earth], but because of plate tectonics they're usually very deformed, and faulted and folded…or if they're flat-lying, they're thin, on the order of hundreds of meters rather than kilometers.

Where we've landed in the ellipse, at a large scale from orbit, looks fairly familiar—it's a feature we call an alluvial fan. It's a feature that forms out in arid climates like Death Valley where it rains only occasionally and builds these deposits. We think we've landed very near the base of one of those.

How will decide now where exactly you want to go?
We have lots of data from orbit, and as the instruments check out we going to be getting more data from our own rover. We put it all together and we look at the patterns that we see from orbit—and we make decisions based on what looks interesting, what looks significant and, most importantly, what hypothesis can we test by analyzing this rock versus that rock. We look at all these options and then string them together like a chain of pearls and go after them one after another.

It's a big decision-making processing. The whole team is involved, everyone gets to have their say, and we talk about it enough that people eventually feel comfortable making the decisions.

Any chance of finding contemporary water in the vicinity of where you've landed and where you want to go?
I think it's going to be pretty dry. We had to provide some evidence to the agency [NASA] that we were not going to land on a place that had ice or water near the surface—and if we ever did find either one of them, we wouldn't be able to go there until a NASA commission has approved us to do that, because we don't want to contaminate an existing water source.

We've had several rovers on Mars now. Why another rover, and why this rover in particular?
I think the way to think about a rover is the same way that a geologist uses an off-road vehicle here on Earth. You have to go to many different places—you can't just say you've done one rover mission or two rover missions and say you're done. Because really what you're trying to do is analyze the past, the deep geologic past, in terms of major events that influence the evolution of the planet, including those kinds of events that may have created environments that were habitable to microorganisms. The trick always is that you need to find the best places to go to, because you're really not sure when it is you might discover something you're actually looking for.

How far up Mount Sharp will you be able to go, and at what angle of incline?
The whole thing is potentially drivable. It's shaped like Hawaii—it's quite high in elevation, but that elevation is all dissipated over some pretty general slopes. We will probably go up to the first kilometer where we see a significant change from a time in the planet's history when it formed clays and sulfates to a time when you see anhydrous [water-free] minerals there. We'll cross that boundary and afterwards look at our data and decide whether it's worth continuing to go up, or whether we should go back down and sample a different area on the way down.

Is there a maximum angle of inclination the rover can handle?
We have a flight limit of about 20 degrees, but we're pretty sure we can handle things up to 25 degrees.

When do you see science kicking into high gear?
I think after the commissioning, the second half of commissioning, I think we'll be ready to go—that will probably be two, three months out. Once that happens we'll get the keys to the car…. We're pretty confident we're going to find a lot of good stuff right where we are.

How does today compare to what you might have expected yesterday or a week or month ago?
The way that many of us feel today is a great sense of relief and also great sense of accomplishment. It's just been something we've been after for many, many years now—it just all came home.