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   Science & Technology

15 May 2008

NASA Phoenix Spacecraft Descends to Red Planet May 25, May 15, 2008

(Fewer than 50 percent of all Mars landing missions have touched down safely)

By Cheryl Pellerin
Staff Writer

Washington -- On May 25, if all goes well, NASA’s Mars Phoenix lander will join the Mars rovers on the ground and three spacecraft in orbit around the Red Planet to find out if conditions on Vastitas Borealis -- the arctic plains of Mars -- ever have been favorable for microbial life.

After a nine-month, 195-million-kilometer journey, Phoenix will enter the top of the Martian atmosphere at a speed of nearly 5.7 kilometers per second. Within 6.5 minutes, it will use heat-generating atmospheric friction, then a parachute, then firings of descent thrusters to reduce its velocity to about 2.4 meters per second just before its three legs touch the Martian surface.

"This is not a trip to grandma's house,” Ed Weiler, associate administrator for NASA's Science Mission Directorate, said during a May 13 briefing. “Putting a spacecraft safely on Mars is hard and risky. Internationally, fewer than half of all attempts to land on Mars have succeeded."

International contributions to the mission came from the Canadian Space Agency (CSA), the University of Neuchatel in Switzerland, the universities of Copenhagen and Aarhus in Denmark, the Max Planck Institute in Germany and the Finnish Meteorological Institute. And data from the NASA-European Space Agency Mars Express mission helped scientists decide where Phoenix should land.

The mission includes a U.S. investment of $420 million -- including development, science instruments, launch and operations -- and a $37 million CSA investment for the spacecraft’s meteorological station.


Phoenix, named for a mythical bird that dies in fire and is reborn from its ashes, is an appropriate name for a mission that arose from two Mars mission failures in 1999 -- the Mars Climate Orbiter, which was lost in September after it fired its main engine to go into orbit around the planet, and the Mars Polar Lander, which was lost in December during an attempted landing on the planet.

After those losses, some missions were cancelled and the Mars program was restructured “to attempt a mission launch every 26 months to focus the science to follow the water,” Weiler said. “One of the major goals is to answer the question of whether life now exists or ever existed on Mars, and we know that without water there is no life.”

In 2002, NASA's Mars Odyssey orbiter discovered that plentiful water ice lies just beneath the surface throughout much of high-latitude Mars. Peter Smith at the University of Arizona-Tucson proposed to take a spacecraft identical to and built in the same era as the failed Mars Polar Lander, fix its problems and launch it to the north polar regions of the fourth planet from the sun.

NASA chose the Phoenix proposal over 24 other proposals to become the first endeavor in the Mars Scout program of competitively selected missions.

“The team has done everything possible to ensure a successful landing,” Weiler said, “but remember, although we’ve fixed all the known issues from the Mars Polar Lander, there are always the unknown unknowns.”

“It may not be a trip to grandma’s house but I think we might be using grandma’s car,” said Doug McCuistion, director of the Mars Exploration Program at NASA. “This is 1960-1970s technology and this team has done an outstanding job in working through this system to make sure we knew as much as we could know about it.”

Phoenix will be the first spacecraft to land in the Martian arctic and it is the first Scout mission -- small, competitively selected missions that complement NASA’s strategic flow of missions -- and, McCuistion said, “ it’s the first mission that’s actually going to touch the water” on Mars.


The solar-powered robotic lander will manipulate a 2.3-meter arm to scoop up samples of soil and underground ice. Onboard laboratory instruments will analyze the samples. Cameras and a Canadian-supplied weather station will supply other information about the site's environment.

Other Mars landers – Viking I and Viking 2 in 1976, the Mars Pathfinder in 1997, and the twin Mars rovers Spirit and Opportunity in 2004 -- landed in the dry regions of Mars’s equatorial zone.

“These dry regions are where we can expect to discover the ancient history of Mars as written into the rocks,” said Peter Smith, Phoenix principal investigator.

Phoenix is doing something quite different,” he added. “By landing in the ice in the northern plains, we’re looking at active processes that are taking place today. These processes have to do with the expansion and contraction of that ice throughout the seasonal changes.”

Climate change will be written into the Martian soils because during summer in the Martian northern hemisphere, the tilt of the planet’s spin axis points the North Pole almost directly at the sun. When that happens, Smith said, “we can expect an opportunity where the ice might actually melt to liquid water and change the properties of the soil, change the chemistry of the soil and change the microscopic properties of the soil, all of which we’ll be able to detect.”

The composition and texture of soil above the ice could give clues about whether the ice ever melts in response to long-term climate cycles. Another important question is whether the scooped-up samples contain carbon-based chemicals that are potential building blocks and food for life itself.

A miniature DVD attached to the deck of the Phoenix lander contains the names of about 250,000 people from more than 70 nations, plus selections of Mars-related literature, arts and music.

The “Visions of Mars” mini-DVD features works by Percival Lowell, H.G. Wells, Isaac Asimov, Ray Bradbury and many others. The California-based Planetary Society provided the disc and invited the public to submit names for it over the Internet.

More information about Phoenix is online at NASA and at the University of Arizona-Tucson Web sites.

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