ROBERT SIEGEL, HOST:
A geological question about Mars may have been solved. It involves how a three-mile-high mountain formed in the middle of a 96-mile-wide crater. That's the crater NASA's Curiosity rover has been exploring for the past two years. Joining us now is Doctor John Grotzinger with NASA's Jet Propulsion Lab in Pasadena. He is a project scientist on the rover's team. Welcome to the program.
JOHN GROTZINGER: Thank you very much for having me.
SIEGEL: And the mountain that's been named Mount Sharp - tell us what does it look like and what were the theories about how it came to be?
GROTZINGER: Mount Sharp is about five kilometers high, roughly three miles. That's taller than anything in the lower 48 of the U.S., but it's shaped more like Mount Fuji. It's a broad dome that ultimately has a high point, and it sits in the middle of the crater. It's called Gale crater. And there's been a lot of ideas over the years as to how it might form, but it's been mostly interesting to us as a science team because the lower part of the mountain seems to have involved water in its formation, but we never knew exactly how.
SIEGEL: Well, what did the rover discover once it got up close to Mount Sharp?
GROTZINGER: What Curiosity discovered was that there were rivers that once flowed from the edge of the crater down into a broad bowl, and there the waters accumulated as a lake that came and went. And the deposition of sediment in that lake is what created the lower part of the mountain.
SIEGEL: That's a lot of sediment.
GROTZINGER: It is a lot of sediment because the crater is about as big as the Los Angeles basin, and all that material has to come from somewhere. So it implies that there was a large amount of erosion in the presence of water that transported the sediment towards the middle of this big bowl.
SIEGEL: So does this change our sense of how much water there was on Mars at one time?
GROTZINGER: You know, it does. It's an idea that's been around for a while - that water was involved on Mars. But we're never quite sure exactly how that was manifested. Was it a flash in the pan and a great flood that emerged and swept things away, or did the water accumulate in a more earthlike way?
And what we're seeing is really consistent with the latter where there was probably snowfall or maybe even rain up in the mountains adjacent to the crater, and that may be seasonally it became warm enough that ice might melt and supply water down into the lake. And so what we're beginning to get a sense now is for a hydrological cycle on Mars - one that involves the circulation of water in a more earthlike way than we had dared to admit before.
SIEGEL: What's the next question on Curiosity's agenda?
GROTZINGER: Well, what we're going to do now is - the mountain is basically a stack of more or less flat-lying layers. And those layers are like the pages in a long novel. And as we drive up the mountain, we go through the layers, and we read them like the chapters in a book. And we hope they're going to tell us about the environmental history of Mars - how the climate behaved, how it changed, and at what times might the planet have been most habitable for life if life ever did evolve on Mars.
SIEGEL: Doctor Grotzinger, thank you very much for talking with us.
GROTZINGER: Thanks for having me.
SIEGEL: That's John Grotzinger who is at NASA's Jet Propulsion Laboratory in Pasadena. He's a project scientist on the Curiosity rover team. Transcript provided by NPR, Copyright NPR.