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#1 David



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Inviato 07 agosto 2007 - 11:28

Phoenix to taste Mars water

Baking samples allows analysis




Phoenix launch
Spacecraft: Phoenix Mars Lander
Rocket: Delta 2
Pad: 17A at Cape Canaveral Air Force Station
When: Launch opportunities Friday at 5:35 and 6:11 a.m. EDT; more opportunities through Aug. 24 

CAPE CANAVERAL - After its launch, cruise through space and suspenseful descent, NASA's Phoenix Mars Lander will do what no other spacecraft has done: drink Martian water.

"We're going to be able to go and, if we're successful at doing it, actually be able to taste the water on another planet," said project manager Barry Goldstein of the Jet Propulsion Laboratory in California.

The lander, due to launch Friday from Cape Canaveral, is expected to touch down as early as May 25 in the far northern reaches of Mars.

There, it will have an estimated three months to dig into the frozen soil, bake samples in tiny ovens and analyze their chemistry in hopes of finding the building blocks of life.

Based in part on the Mars Polar Lander lost in 1999, Phoenix won't move around like the rovers that have been exploring the planet since 2004.

"We don't have wheels or ice skates up in the northern area . . . we like to call it vertical mobility," Goldstein said.

The craft's robotic arm gives it that vertical mobility. Nearly eight feet long, it can dig about 20 inches into the permafrost to scoop up samples.

"We put material in an oven and heat it, and it's not all that dissimilar from putting food in your oven at home," said principal investigator Peter Smith of the University of Arizona. "At a certain temperature, it starts to smoke, and if you turn it up to 500, it really starts to smoke."

That's how the instrument detects organic material.

"We have a mass spectrometer that can sense those smoke signals, so to speak, and tell us just what that smoke is made out of," Smith said.

Scientists think the ice may hold these building blocks of life because it's possible the whole area was once flush with water.

Mars' orbit and its tilt vary over hundreds of thousands of years, causing huge climate fluctuations. In warmer periods, the ice may melt into water, which would be more conducive to life. Microbes may survive even into the frozen periods.

The Phoenix Lander won't detect life, but it should be able to tell whether life is possible there.

"The polar region, this permafrost region, is 25 percent of Mars, and we're digging one trench. I mean, it's not exactly an exhaustive search," Smith said with a laugh.

"So we don't expect to be so lucky as to land in some biological swamp land there and just have all kinds of organisms crawling around. We think it's much more likely that we can determine if this is a place where an organism could live."

Though the lander can't move, it is exploring an area that appears fairly uniform from orbit, so the landing site should be representative of the region.

NASA's Mars Odyssey identified large areas where water ice appears to be frozen just under the surface near the north and south poles.

While the rovers, Spirit and Opportunity, have been able to learn about the water on Mars billions of years ago through geology, Phoenix should be able to find water today, in frozen form.

Phoenix isn't only looking down. In addition to measuring temperature, pressure, wind and humidity, it will shoot a laser into the sky to detect dust and ice particles in the lower part of the atmosphere.

"This is what's called the planetary boundary layer, which is where the weather takes place on Mars," Smith said.

Of course, the $420 million mission has obstacles to overcome first.

The craft will launch on a Delta 2 rocket, in a window that extends through Aug. 24. Next spring, it will enter Mars' atmosphere at 12,750 mph. A parachute and thrusters, leaner versions of those used on the 1970s Viking landers, will help it slow to 5.4 mph for its landing.

Its touchdown site, which is still being refined, will be crucial for success. The lander's solar arrays would benefit from a southward tilt that would let Phoenix soak up extra sun and power.

Rocks could threaten the craft or the arrays, so the landing site has been chosen partly for its safety.

"We are tolerant of rocks around a third of a meter to a little bit more than that, depending on exactly where it would possibly contact the lander," said Ed Sedivy, Phoenix program manager with craft builder Lockheed Martin Space Systems.

"We'd rather not see a half-meter rock . . . but that's something that's probably survivable for us," he said. "Larger than half-meter, and we have a problem."

Mission managers say they have worked hard to eliminate as much risk as they can, working through issues with the landing radar and the descent imaging camera. The latter will take one photo on the way down instead of many, to eliminate a possible conflict with receipt of crucial engineering data.

"We feel ready," Smith said. "We're not going to sit on our laurels here and just launch and take vacation for the next 10 months. We're going to be pursuing all the failure modes that we can, especially for landing."

If necessary, they will alter software or the timing of events to ensure their success.

And unlike Polar Lander, Phoenix will be in communication throughout its descent.

"We have been discussing at rather a gauntlet of reviews just how much residual risk we have on this mission, and that's been a rather kind of volatile topic where people get quite concerned," Smith said.

"Obviously, if there's too much risk, you don't launch the mission. Even though we think we know all the failure modes and have fixed them, you can't ever be sure you've found them all."

After working on instruments for the Polar Lander and for another mission that never flew, Smith is ready for Phoenix to rise from the ashes.

"While it's more dangerous than orbiter missions," Smith said, "the payoff can be very large, and we're very hopeful for that."

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