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Later today, a space probe from Earth will hurdle through the Martian atmosphere. And if all goes well, it'll come to a gentle landing near the red planet's north pole. The mission is called Phoenix. It's not designed to look for life on Mars, but it will say whether conditions for life once existed there.
NPR's Joe Palca has this preview of today's events.
JOE PALCA: The Phoenix spacecraft lifted off from Cape Canaveral in Florida last August and set a course for Mars.
Mr. BARRY GOLDSTEIN (Project Manager, Mars Phoenix Mission): We have had a very peaceful cruise.
PALCA: Barry Goldstein of NASA's Jet Propulsion Laboratory in Pasadena is project manager for the Mars Phoenix mission. Peaceful is good; peaceful is what project managers like. But the peaceful part of the mission is about to end. Terrifying is how people describe the phase of the mission known as EDL - entry, descent and landing. Goldstein describes what's supposed to happen.
Mr. GOLDSTEIN: Approximately 14 minutes before we land, we go through what we call cruise-stage separation.
PALCA: The cruise stage supplied the power and communications for Phoenix during its trip from Earth. But it's no use on the surface of Mars, so it's cast away before EDL starts. About seven minutes before landing, the spacecraft hits the top of the Martian atmosphere, traveling more than 12,000 miles an hour.
Even though the atmosphere is thin, it's substantial enough to slow the spacecraft down to 750 miles an hour. Three minutes before landing comes the parachute.
Mr. GOLDSTEIN: The parachute will open up, and that will decelerate us yet again quite a bit from there - will take is down to about 125 miles an hour.
PALCA: Then, Phoenix cuts loose from the parachute and starts firing its landing engines.
Mr. GOLDSTEIN: And the next 34 seconds, which is what we call terminal descent, go from approximately 125 miles and hour down to five miles an hour.
PALCA: The last 100 feet or so will be at that gentle 5 miles an hour.
Mr. GOLDSTEIN: And then we detect surface and we cut off our engines and let the dust settle, and we're on the ground. Everything will work fine.
PALCA: If it sounds like there's a nervous catch in Goldstein's voice, it's understandable. Going from 12,000 miles an hour to a full stop in seven minutes means a lot of equipment has to work perfectly.
Mr. GOLDSTEIN: A lot of people ask me what is going to give me the most terror, what am I most worried about the night of landing.
PALCA: What Goldstein is most anxious about is something that happens just before the landing sequence starts. It's a command to turn on Phoenix's radio transmitter.
Mr. GOLDSTEIN: And the reason is not because it's the most difficult. It's frankly one of the more simpler aspects of EDL. But once we have communication going, at least that part of my brain will know that at the very least, we are going to learn something from this mission.
PALCA: The radio will transmit information about how the landing is going. And if something does go wrong, the signal should provide clues about what happened. A failure would be bad, but a failure with no data at all is totally frustrating.
Assuming EDL is a success, Phoenix will be the first lander to explore the polar regions on Mars. Previous missions have all been closer to the equator.
Mr. MICHAEL HECHT (Member, Phoenix Science Team, NASA Jet Propulsion Laboratory): The Mars of the equatorial regions of low latitude is a very ancient Mars. You see features there that were essentially unchanged for billions of years.
PALCA: Michael Hecht is a member of the Phoenix Science Team. He's with NASA's Jet Propulsion Laboratory. Hecht says there is water in the form of ice at the higher latitude near the poles, and there is clear evidence that the ice is changing the landscape.
Mr. HECHT: So, what we're looking at at these latitudes are relatively recent processes. Now, that might mean they're millions of years old, but what makes them fundamentally different is that they're ongoing.
PALCA: Hecht says Phoenix has instruments on board that can reveal some of the processes by measuring the minerals and elements that are in the soil and ice where the lander touches down. JPL's Deborah Bass is another member of the Phoenix Science Team. She says one thing the mission was not designed to do is look for life on Mars.
Ms. DEBORAH BASS (Member, Phoenix Science Team, NASA Jet Propulsion Laboratory): Phoenix is looking for habitability - so, the likelihood of a location that's capable of supporting life rather than looking for life itself. Phoenix will not be looking for DNA, unfortunately.
PALCA: That will have to wait for a future mission to Mars.
Joe Palca, NPR News.
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