The scientists behind NASA’s Phoenix Mars Lander mission now know that they had their first close-up look at Martian ice — because it has vanished from the picture.
Days ago, streaks and bits of whitish material were spotted at the bottom of a trench dug by the lander's robotic scoop, leading scientists to speculate that the stuff was either ice or salt. An initial chemical analysis was inconclusive, but scientists said they could tell by seeing if the material disappeared after exposure to the thin Martian atmosphere.
Under such conditions, water ice would turn directly into vapor rather than melting into liquid, in a process known as sublimation. When scientists compared Sunday's pictures with imagery captured early Thursday, dice-sized crumbs of the white material were clearly missing.
"It must be ice," the University of Arizona's Peter Smith, principal investigator for the Phoenix mission, said Thursday in a NASA status report. "These little clumps completely disappearing over the course of a few days, that is perfect evidence that it's ice. There had been some question whether the bright material was salt. Salt can't do that."
A larger vein of white material is still visible in the trench, which scientists have dubbed "Dodo-Goldilocks."
The Phoenix team reported that the lander's robotic scoop hit a hard surface while it was digging in a different trench early Thursday, and they speculated that the surface could represent a layer of ice. The new trench is nicknamed "Snow White 2," and lies right next to the Snow White 1 trench in an area that has been set aside for scientific study.
"We have dug a trench and uncovered a hard layer at the same depth as the ice layer in our other trench," Ray Arvidson of Washington University in St. Louis, co-investigator for the robotic arm, was quoted as saying in the status report.
After three attempts to dig further into the surface, the arm went into a holding position. Such an action is expected when the robotic arm comes upon a hard surface, NASA said.
One of the primary aims of Phoenix's mission is to determine whether the layers of soil and ice in Mars' north polar region contain the chemical building blocks of life. The lander can cook soil samples in its ovens and analyze the composition of the gases given off. The probe is not designed to detect life itself, however.
A fix for the glitch
Also on Thursday, NASA said that Phoenix team members at Lockheed Martin Space Systems in Denver were working on a software patch to fix a glitch that cropped up this week.
The lander lost a day's worth of pictures on Tuesday when it generated a large amount of duplicative engineering data. As a precaution, the spacecraft was given instructions to transmit its data to Earth at the end of each day rather than storing it overnight in its flash memory. That procedure will be followed until the glitch is corrected, managers said.
"We now understand what happened, and we can fix it with a software patch," Barry Goldstein, project manager for the $420 million Phoenix mission at NASA's Jet Propulsion Laboratory, said in Thursday's update.
Mission managers expect to transmit the patch to Phoenix in a few days so that scientific data can once again be saved onboard overnight when needed.
Goldstein noted that the three-month schedule for Phoenix's primary mission has 30 days of extra time built in for dealing with unanticipated problems. Only one day has been used so far, he said.
"The mission is well ahead of schedule. We are making excellent progress toward full mission success," Goldstein said.