In memoriam: The Mars lander's legacy

By Andrea Thompson

Senior writer

updated 7:10 p.m. ET Nov. 11, 2008

Now that NASA's Phoenix Mars Lander is likely dead, mission scientists have time to fully examine the treasure trove of data generated in its five months in the red planet's arctic region, in order to shed more light on the mysteries of Mars.

Phoenix's confirmation of water ice below the Martian arctic surface and its surprising characterization of the Martian dirt are among the findings researchers will be busy investigating further in the next few months.

The Phoenix mission will also help inform future missions to Mars, including the upcoming MAVEN orbiter mission and the planned Mars Science Laboratory rover.

Beginning to end
Phoenix landed in the Vastitas Borealis plains of Mars on May 25 to the jubilant cheers of mission controllers. (Phoenix was in part a replacement for the failed Mars Polar Lander, so tensions to have a successful landing were running high.)

In the five-plus months it spent alive at its landing site, the spacecraft dug up samples of Martian dirt and subsurface water ice and analyzed them for signs of the planet's past potential habitability.

Yesterday NASA announced that the mission, whose final cost was about $475 million, was effectively over. Dwindling sunlight (caused by the transition from summer to fall at Phoenix's location, which is roughly equivalent to northern Alaska on Earth) and light-obscuring dust in the atmosphere finally pushed Phoenix below its power threshold on Nov. 2.

"It's rather tough living up north above the (Martian) arctic circle, so we always knew that the end would be coming near for us," said Phoenix project manager Barry Goldstein of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Phoenix's demise, while expected to come with diminishing light and plummeting temperatures, occurred a few weeks sooner than engineers had hoped, largely due to the poor weather at its landing site. But even with its early death, Phoenix went above and beyond its primary mission goals, which were achieved by the end of its original three-month mission in August.

"The vehicle ... has achieved all of its science goals and then some, and I've think we have had a huge success," Goldstein said.

Slide show   Red Planet touchdown Revisit the first pictures from NASA’s Phoenix Mars Lander – and the celebration back on Earth. more photos

Phoenix's findings
The biggest success of the mission was to confirm the presence of water ice under the surface of the Martian arctic — which had first been detected by the Mars Odyssey orbiter in 2002 — though that discovery didn't come right away.

"When we landed, we looked around, we saw a field of dirt and rocks that was spread out to the horizon, and we didn't see ice right away, it wasn't until we looked under the spacecraft that we found out we were standing on it, and this was quite a thrill for everybody," said Phoenix principal investigator Peter Smith of the University of Arizona in Tucson.

Over the course of the mission, Smith and his team used Phoenix's robotic arm and analysis instruments to scrape, poke, prod and characterize this rock-hard ice layer.

"We've excavated to the ice, we know its depth, we know how it changes over the surface, we've seen different types of ice," Smith said, adding that the analysis of the ice isn't over.

In digging down to the subsurface ice layer, Phoenix also scooped up samples of the overlying dirt and analyzed them in its microscopes, wet chemistry lab (which dissolved the samples in water to look for soluble chemicals) and Thermal and Evolved-Gas Analyzer (TEGA) (which baked the samples and analyzed the vapors given off). These analyses led to some surprising findings.

Unlike other landers and rovers that have detected acidic dirt with plenty of sulfates — indicative of volcanic activity — Phoenix found the dirt at its landing site was alkaline with lots of carbonates and clay minerals, the later of which typically form when liquid water is around.

"On the Earth, we would conclude immediately that there was liquid water in this soil — for Mars we have to be a little more careful, and we're going to develop this story as we can, as we interpret our data," Smith said. "But definitely liquid water has been a part of this soil" in the past.

The dirt samples also showed evidence of salts and perchlorate. Perchlorate was "totally unexpected," Smith said, and "has profound implications for Mars," because it can act as a potential energy source for microbes.

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