Scientists are now confident that NASA's Phoenix lander, which touched down on Mars last month, is standing on a vast plane of ice, making this the first mission to actually come into contact with frozen water.
Researchers had been watching some chunks of white material that the lander had dug up with its robotic arm. A photo taken four days later showed the chunks had entirely vanished, the way snow can on a sunny, dry day.
"It is with great pride and a lot of joy today I announce we have found the proof that we've been seeking that this hard, bright material is water ice and not some other substance," said Peter Smith, the team's lead investigator. Some researchers had speculated the white material might be salt of some kind.
Satellite measurements had indicated that something containing hydrogen lay below the surface, possibly H20 — water ice. That's why this landing site was picked. The first photos taken after Phoenix touched down last month showed a dusty dry landscape. Scientists were relieved to find out ice lay beneath.
"It's just amazing," Smith said. "If you were to get a broom and sweep this off, we're on an ice sheet."
He said this means a full quarter of the planet's surface — near the planet's poles — may be covered with ice.
In the near future, scientists want to have the Phoenix lander scoop up some of the ice and load it into a small oven. By heating it and analyzing the vapors, they should be able to tell what's mixed in with it.
"I think the big story is that we can reach out and touch it," said Mark Lemmon, a researcher on the project from Texas A&M University. "We can use instruments to taste and smell it."
The big question is whether Mars has the basic ingredients for life. That includes not just water, Smith said, but also "food" in the form of organic molecules.
"We don't eat rocks," he said. "We have to have carbon ... chain materials that we ingest into our bodies. ... That's what has to be there if we're going to have a habitable zone on Mars."
The team hopes to have an answer this summer. A future mission could go and actually look for life.
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