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This Sunday night a one ton, six-wheeled rover called Curiosity will land on Mars. The purpose of NASA's mission is not to find life there; scientists aren't far enough along to do that. Instead, they're looking for the building blocks of life - water and organic compounds. NPR's Joe Palca has this preview of Curiosity's two-year mission.
JOE PALCA, BYLINE: Curiosity is landing near the Martian equator, at a place called Gale Crater. It's a crater 96 miles across with a mountain, three miles high, in the middle. Since water and life typically go together, finding signs that Mars might once have had lakes and rivers would give a strong indication that life could have existed there. The floor of Gale Crater is one of the lowest spots on Mars. And since water flows downhill, if there ever were lakes and streams on Mars, at some point the water should have wound up there.
To carry out this search for water, Curiosity is loaded with instruments. A lot of them are for studying rocks. And why would you want to study rocks when you're interested in water? Geologist David Blake, from NASA's Ames Research Center, says it's because certain minerals only form in certain circumstances.
DAVID BLAKE: If we identify all the minerals that are present in, say, a 4-billion-year-old sample in Gale Crater, we can tell you what the conditions of the environment were, whether it was a lake, whether it was a stream bed; just what the surrounding conditions were.
PALCA: Blake's in charge of an instrument on the rover - called CheMin - that can identify the minerals in a rock sample. He says in an odd way, Mars can teach us a lot about Earth's geologic history.
BLAKE: If you look for a 4-billion-year-old rock on the Earth, you won't find it.
PALCA: That's because Earth is a geologically active planet, and ancient rocks have been buried by the movement of tectonic plates.
BLAKE: But on Mars, these rocks are sitting at the surface. So we can go to Mars and look at rocks that are probably very similar to those on the early Earth, and tell a story about both planets.
PALCA: Another nifty instrument on the rover is called ChemCam. Roger Wiens, of Los Alamos National Lab, is the scientist in charge of that instrument. It shoots a pulse of laser light at nearby rocks, from the rover's arm.
ROGER WIENS: It's for only 5-billionths of a second but during that time, ChemCam directs, basically, the energy of a million light bulbs into the area the size of a pinhead.
PALCA: All that energy makes the rocks glow. And by analyzing the spectrum of colors in that glowing light, scientists can say what chemical elements are present - like hydrogen and oxygen, as in H2O.
The most complex scientific instrument on the rover is called SAM, for Sample Analysis at Mars. It's the instrument designed to look for organic compounds, the kind of compounds that are necessary for life. Finding these would give another sign that there might once have been life on Mars.
While SAM was on its nine-month trip to Mars aboard Curiosity, scientists figured out there could be a problem with the instrument. Paul Mahaffy, of NASA's Goddard Space Flight Center, is in charge of SAM. He says in running simulations on Earth, scientists realized that there was a chance that samples poured into SAM could become contaminated from contact with Teflon that's part of the instrument.
PAUL MAHAFFY: So we're taking a careful look at that, and how that might impact our ability to measure trace organic compounds; and how we would work around that problem, if we were to encounter it.
PALCA: But before any of these instruments gets to do its thing, Curiosity has to land safely on Mars - and that's no simple thing. Adam Steltzner is the engineer in charge of the landing. He says the landing sequence starts at about 80 miles above the Martian surface.
ADAM STELTZNER: We start at about 13,000 miles an hour.
PALCA: A heat shield slows things down to about 800 miles an hour. Then, a parachute comes out.
STELTZNER: It's the world's largest supersonic parachute.
PALCA: At this point, the rover is nearly directly above the landing site.
STELTZNER: About a mile above the surface, we let go of our parachute.
PALCA: And the rover, with a kind of jet backpack strapped to its back, uses the jet pack's rockets to slow it to practically a crawl.
STELTZNER: And then finally, 20 meters above the surface, we detach the rover from this jet backpack, and the rover is lowered below the jet backpack. And for the last 10 meters or so, the two bodies just continue down at a very slow pace, until the rover touches down.
PALCA: During the landing, no one on Earth is able to help the rover. It either works, or it doesn't.
STELTZNER: We've taken our best understanding of the spacecraft and the challenges it will face at Mars, and we've put it into software; and put that on the spacecraft, and wish it well.
PALCA: And we'll know on Sunday night whether those wishes come true. Joe Palca, NPR News. Transcript provided by NPR, Copyright NPR.