Washington University student playing role in Mars landing

ST. LOUIS (AP) -- As the spacecraft Phoenix heads for Mars, the success of the mission rests in part on the work of a 21-year-old St. Louis college student.

Weather permitting, NASA on Saturday will launch its Phoenix Mission, the first project of the space agency's Scout program, a lower-cost complement to more expensive Mars missions. Phoenix will launch from Cape Canaveral, Fla., aboard a Delta II rocket on the 423-million-mile trip to the Red planet's northern plains. It is expected to land in May.

A team at Washington University in St. Louis led by Raymond Arvidson, chairman of the earth and planetary sciences department, played a key role in determining the landing spot -- no easy task on a planet known for its rocky terrain.

For senior Tabatha Heet of Jefferson City, the work wasn't as glamorous as it sounds. Her contribution largely involved counting rocks, a pivotal but painstaking duty.

"It was tedious," Heet said. "It involved staring at a computer screen for a really long time."

A rocky landing could cause the Phoenix to tilt or tip over. Also, large rocks could prevent the unfurling of the craft's solar panels. The instruments are solar-powered, so if the panels can't open, the mission can't succeed.

Starting last fall, Heet worked 20 hours a week for four months staring at grainy pictures and counting one rock after another. She began with large images of Mars from an instrument called HIRISE, a sophisticated imager that permits the viewing of rocks as small as about 1 yard wide. A software package called ENVI helped make the measurements.

Heet would then divide the large image into subsets and begin counting rocks.

"My end product was a color-coded map," Heet said. "Red was really bad -- you can't land there. Green was good -- go for it."

Heet's work was vital to the project, Arvidson said, allowing his team to "zero in on the safe havens."

Previously, experts thought the most promising landing area was one deemed Region B. But HIRISE, a more sophisticated imager than was previously available, showed that landing at Region B would be a mistake.

"It wasn't that there were so many rocks," Arvidson said. "It's just that they were clustered in rock fields and as big or bigger than the lander."

So the team turned its attention to the other side of the planet's northern plains. Heet's counts helped lead the team to find a potential landing spot in an area called Region D with at least 10 times fewer rocks than Region B.

She is confident the landing will be a smooth one.

"I can't wait," she said. "I'm pretty confident because NASA agrees with me, but there's also this part in the back of my mind that thinks, 'what if it crashes on a boulder and it will be my fault?"'

Unlike the twin rovers Spirit and Opportunity launched in 2003, Phoenix will sit in one place in the northern arctic area of Mars. It will extend its long arm to dig trenches in the permafrost and scoop up soil for analysis. The goal: Determine if the underground ice may have melted, creating a wetter environment.

Phoenix lacks the tools to detect past or current life, but scientists hope it sheds light on whether the northern arctic possesses the signature ingredients for microbes to exist.

After its three-month mission, it will turn into a weather station and collect data on the atmosphere.

Arvidson has been involved in Mars missions for three decades. In addition to leading the effort to find a landing spot, he will oversee the gathering of soil and water-ice samples and the function of the robotic arm camera, which will take images of soil, water-ice and trench walls.

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On the Net:

Phoenix Mars mission: http://www.nasa.gov/mission--pages/phoenix/main/index.html.

Washington University: http://news-info.wustl.edu.