On Mars, the Phoenix has landed

Updated 6:31 PM PDT with initial information from the arrival of Phoenix on Mars and then again at 7:20 PM PDT with one of the first images from the lander. That follows an earlier update to reflect the Phoenix lander's acceleration as it approached Mars and to clarify its speed and course in traveling through space.

NASA said Sunday evening that radio signals have been received from the Phoenix spacecraft on the surface of Mars.

The Phoenix Mars Lander is the latest embodiment of humankind's quest to learn whether life might once have been sustainable on the Red Planet and to prepare for eventual human exploration there.

But before it can dig into the surface, Phoenix first had to traverse the Martian atmosphere. Those seven minutes of descent, the very last leg of the months-long journey, are what could have been the killer: the lander, its developers say, faced "seven minutes of terror" before touching down. Of 11 total previous attempts by several nations to put a spacecraft on Mars, according to NASA, only five had been successful.

In entering the thin Martian atmosphere and heading to the surface, Phoenix faced these tribulations: "aeroshell braking" via friction with the atmosphere that would heat it to thousands of degrees, a parachute opening that would give the lander a hard jerk to slow it further, and pulsing retrorockets tasked with making a soft touchdown.

Because it takes 15 minutes for signals to travel between Mars and Earth, Phoenix was designed to land autonomously. The confirming signal came shortly before 5:00 p.m. PDT Sunday.

"We've passed the hardest part and we're breathing again, but we still need to see that Phoenix has opened its solar arrays and begun generating power," Barry Goldstein, Phoenix project manager at NASA's Jet Propulsion Laboratory, said in a statement Sunday. Batteries are providing power at the moment.

NASA said that it expects to learn the status of the solar arrays later Sunday night, along with information on whether the stereo camera and weather station have been moved into their deployed positions, as Phoenix relays signals via the Mars Odyssey orbiter. The first attempt to use the 7.7-foot robotic arm will come in a couple of days.

In the final day or two before landing, all was well.

"The spacecraft is in good health," Brent Shockley, Phoenix configuration and information management engineer at NASA, wrote in the Phoenix Mars Lander blog on Saturday. On Sunday, NASA reported that it had decided not to make any final adjustment to the spacecraft's trajectory.

In its approach to Mars, the vehicle had been traveling at an incredibly high rate of speed--though exactly how fast depends on the point of reference. Shockley wrote Friday: "Phoenix is currently traveling 75,400 miles per hour with respect to Earth. With respect to the sun, however, Phoenix is traveling 44,300 miles per hour. With respect to Mars, Phoenix is traveling a modest 6,090 miles per hour."

At midday Sunday, NASA said things were accelerating: "The spacecraft's speed relative to Mars increased from 6,300 miles per hour at 8:30 a.m. Pacific Time to 8,500 mph at 12:30 p.m., headed for a speed higher than 12,000 mph before reaching the top of the Martian atmosphere."

Shockley joked in his blog about the spacecraft's energy efficiency. "At a time when gas prices are soaring," he wrote, "Phoenix is getting good fuel economy at about 2 million miles per gallon."

The lander is now about 170 million miles from Earth--after having traveled 422 million miles through space after liftoff from Earth in August.

Using its robotic arm, Phoenix will dig into the surface to bring up both soil and ice. In its platform structure, the lander will then analyze those samples to help scientist on Earth create models of Mars' historic climate and to predict future atmospheric conditions.

Water on Mars exists only in solid and gaseous form, though previous missions to and around the planet have suggested that it once flowed in liquid form--as recently, NASA says, as about 100,000 years ago.

Scientists are also hoping that Phoenix can help determine "habitability" properties of the soil such as pH and saltiness.

The Stereo Surface Imager atop the lander, meanwhile, will produce panoramic images of the surface with a resolution of 1,024 x 1,024 pixels.

Even with a successful landing and initial operation, the Phoenix machinery isn't likely to have more than a short-term mission. Besides simply operating in the extreme cold of the Martian arctic and facing a potential onslaught of dust storms, it is not expected to get back into operation after the Martian winter when its solar panels will be rendered ineffective by complete darkness.

That said, no one expected the Mars rovers Spirit and Opportunity to last more than a few months, and they ended up sending back data for a number of years.