These images from the Phoenix Mars Lander show sublimation of ice in the trench informally called "Dodo-Goldilocks" between Sols 20 and 24 (June 15 and 18, 2008.
Credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University
Scientists said today they have "found proof" of water ice on Mars away from the polar ice caps, a discovery made by NASA's Phoenix Mars Lander.
The finding is a crucial first step toward learning whether the ground on Mars is hospitable, because all life as we know it requires water. Now scientists can get on with the business of studying the chemistry of Mars dirt in more detail.
When the probe took photos of a ditch it had dug four days before, scientists noticed that about eight small crumbs of a bright material had disappeared. They concluded those crumbs had been water ice buried under a thin layer of dirt that vaporized when Phoenix exposed them to the air.
"It's with great pride and a lot of joy I announce today we have found proof that this hard material really is water ice and not some other substance," Phoenix principal investigator Peter Smith of the University of Arizona, Tucson said at a briefing Friday.
The finding had been discussed tentatively yesterday, but in a press conference today, researchers left no doubts.
Phoenix's robotic arm first revealed the crumbs about 5 cm deep in the trench called "Dodo-Goldilocks" on June 15. By June 19, they had vanished. If the crumbs had been salt, they wouldn't have disappeared, scientists said, and if the ice had been made of carbon dioxide, they wouldn't have vaporized.
"What this tells us is we found what we're looking for," said Mark Lemmon, a Phoenix co-investigator from Texas A&M University. "This tells us that we've got water ice within reach of the [robotic] arms, which means that we can continue the investigation."
The $420 million mission landed on the arctic plains of Mars May 25, embarking on a quest of at least four months to search for signs that the environment was once habitable to life.
A "significant result"
Finding ice on Mars isn't completely shocking, since observations from past satellites sent to orbit the planet, such as the 2001 Mars Odyssey spacecraft, have indicated that ice is likely to lie beneath the planet's surface. Still, if confirmed, this would be the first direct finding of that ice by a probe on the ground.
??We certainly expected to find ice there," said Bruce Jakosky, a geologist at the University of Colorado who has been involved with past missions to the red planet. "It was the [previous] evidence for ice that sent us to that location. But there?s a difference between expecting it and finding.?
Jakosky called the discovery a ?significant result? that allows the Phoenix mission to go forward with its wet chemistry experiments, analyzing the soil for the history and composition of the ice.
?If they had found no ice, which was a real possibility, that would make this much harder,? he told SPACE.com. ?I?m anxious to see the results of the chemical analysis.?
And although the 2001 Mars Odyssey satellite could measure the average water ice content in roughly the top meter of ground over areas of several hundred kilometers, these data didn't reveal how that ice was spread out, said Maria Zuber, a geophysicist at MIT who worked on past Mars missions, including the Spirit rover.
"We don't know the form of the water, beyond the fact that there is too much there to be explained solely by water bound in minerals," Zuber said. "So chunks, a layer, etc. are all possibilities. The [Phoenix] observation is an important advance in our understanding of water on Mars, and continued sampling will undoubtedly add to the story."
The next questions to answer are what chemicals, minerals and organic compounds might be mixed in with the water.
"Just the fact that there's ice there doesn't tell you if it's habitable," Smith said. "With ice and no food it's not a habitable zone. We don?t eat rocks ? we have to have carbon chain materials that we ingest into our bodies to create new cells and give us energy. That?s what we eat and that's what has to be there if you're going to have a habitable zone on Mars."
To find this out, mission scientists plan to eventually put samples of ice into Phoenix's oven instrument, the Thermal and Evolved-Gas Analyzer (TEGA), which is designed to bake Martian dirt and analyze the vapors it emits to detect its composition. They also plan to use the onboard Microscopy, Electrochemistry and Conductivity Analyzer (MECA) instrument, a wet chemistry lab that measures levels of acidity, minerals, and conductivity in dirt samples.
"Now we know for sure that we are on an icy surface and we can really meet the science goals of our mission at the highest level," Lemmon said. "I am just sitting at the edge of my chair waiting to find out what the TEGA and MECA can tell us about these soils."
Expect the unexpected
Although the ice finding was expected, until Phoenix actually found it, many scientists were still holding their breath.
"As for the ice, we were expecting to find it, but science is full of the unexpected, so until they actually found the ice and can begin to study it there are real questions about whether or not the hypothesis was correct," said Phil Christensen, a geophysicist at Arizona State University who worked on 2001 Mars Odyssey, Mars Global Surveyor, and the Mars Exploration Rover missions. "The real excitement will come when they start to study the ice in detail and attempt to learn how it formed and how old it is."
Additional reporting for this article was contributed by Jeremy Hsu, SPACE.com staff writer.
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