27 May 2008Kenneth Chang
The first pictures sent back by NASA's Phoenix Mars lander from the northern arctic plains of Mars show a flat terrain marked by a polygonal pattern of shallow troughs and a few pebbles scattered about.
"I know it looks a little like a parking lot," said Peter H. Smith of the University of Arizona, the mission's principal investigator, at a news conference four hours after Phoenix's landing on Sunday, "but it's a safe place to land."
But the monotonous landscape is not why Phoenix went to Mars. "I guarantee it. There's ice under this surface," Dr. Smith said. "It doesn't look like it. You don't see ice, but it's down there."
"Follow the water" has been NASA's mantra for its Mars exploration for more than a decade. Phoenix will be the first space probe to directly touch Martian water when its robotic arm digs down to the ice layer, expected a few inches beneath the surface, and scoops up some for examination.
Phoenix reached its destination after a 422-million-mile journey that lasted almost 10 months.
During the final, tense minutes of the descent, long stretches of quiet in the mission control room at the Jet Propulsion Laboratory were punctuated by cheers and clapping as confirmation of crucial events like the deployment of the parachute were confirmed.
Then, at 7:53 p.m. Eastern time, Richard Kornfeld, the lead communications officer for entry, descent and landing, announced: "Touchdown signal detected."
The mission controllers, wearing identical blue polo shirts made for the occasion, erupted in cheers and began hugging one another in congratulations.
"It was better than we could have possibly wished for," said Barry Goldstein, the project manager for the mission. "We rehearsed over and over again. We rehearsed all of the problems, and none of them occurred. It was perfect, just the way we designed it."
At 9:53 p.m., there were more cheers as confirmation came that one more critical event, the unfolding of the solar arrays, had occurred without problem. And then the first pictures arrived: black-and-white images of the solar panels, of one of the lander's footpads and of surrounding terrain, showing the polygonal fractures caused by repeated expansion and contraction of the underground ice.
The next few days will be spent checking the condition of the spacecraft. Then it will begin the first up-close investigation of Mars's northern polar region. Instruments on the spacecraft include a small oven that will heat the scooped-up dirt and ice to 1,800 degrees Fahrenheit. Analyzing the vapors will provide information on the minerals, and that will, in turn, provide clues about whether the ice ever melted and whether this region was habitable. The mission is to last three months, with the possibility of a two-month extension.
"We see Phoenix as a stepping stone to future investigations of Mars," Dr. Smith said.
But Phoenix had to get to the surface first. Mission managers sent their last instructions to Phoenix around noon Eastern time on Sunday. From there, the spacecraft operated on autopilot all the way to the surface.
During the day Sunday, the pull of Mars's gravity accelerated the spacecraft from 6,300 miles per hour to 12,700 m.p.h. when it entered the Martian atmosphere. The friction of the atmosphere slowed the craft down by 90 percent, then a parachute provided further drag. For the last kilometer down to the surface, 12 thrusters slowed Phoenix to a velocity of 5.4 m.p.h. before it bumped onto the surface.
Phoenix set down in a very flat spot, sitting at a tilt of about three-tenths of a degree.
The landing held an extra dose of anxiety, because Phoenix has the same basic design as NASA's Mars Polar Lander, which crashed while landing near the south pole in 1999. The Phoenix spacecraft was originally going to go to Mars's equatorial region as Mars Surveyor 2001, but after investigations of the Polar Lander failure turned up major flaws in the design, that mission was canceled and the almost complete Surveyor spacecraft was put into storage.
Dr. Smith proposed resurrecting the Surveyor spacecraft as Phoenix for a new mission. Testing identified more than a dozen flaws in the lander design, and mission managers believed they had fixed the problems.
NASA's budget for Phoenix is $420 million, which includes testing and retrofitting the spacecraft, outfitting it with new instruments, launching and operating the mission. The Canadian Space Agency contributed $37 million for one of the instruments, a weather station. In addition, the development and construction of the original Surveyor 2001 spacecraft cost $100 million.
http://www.nytimes.com/2008/05/27/science/space/27mars.html?_r=2&hp=&oref=slogin&pagewanted=print
