DENVER, COLORADO -- Ankle-deep water covering all of Mars. That's how much is thought to be lurking subsurface on the red planet.
Data gathered by NASA's Mars Odyssey spacecraft has given the first global look at the total amount of water stored near the Martian surface.
However, expert taking part in the annual meeting of the American Association for the Advancement of Science (AAAS) continue to be baffled by what they see following years of spacecraft observations of the planet. Increasingly, Mars appears to be a water-rich world capable of supporting future human explorers and, perhaps, home for present-day life.
Reservoirs of water
The first global map of hydrogen distribution on Mars was released Saturday, yielded by sensors aboard NASA's Mars Odyssey.
For nearly a year, a neutron spectrometer has been busily mapping the hydrogen content of the planet's surface. By measuring changes in neutrons given off by Mars' surface material, that hydrogen is most likely in the form of water-ice, said William Feldman, a Principal Investigator on the Mars Odyssey mission at the Los Alamos National Laboratory in New Mexico.
Feldman said several "reservoirs" of water have been found to dot Mars. Along with the polar caps, as well as small traces of water held in the Martian atmosphere, there are lower concentrations of hydrogen found closer to Mars' equator, ranging from two- to 10-percent water by mass.
Mars geology appears to be rich in minerals that retain significant amounts of water. The neutron spectrometer data shows water ice close to the surface in many locations, and buried elsewhere beneath several inches of dry soils.
"We don't see anything with less than two percent water equivalent hydrogen," Feldman said.
Missing-in-action
Surprisingly, Feldman said, two large areas on Mars show indications of relatively large concentrations of sub-surface hydrogen. One of those locales is within Arabia Terra - a stretch of Martian desert that's some 1,900-miles (3,057-kilometers) wide. The other is on the opposite side of the planet, also showing a mega-amount of sub-surface hydrogen.
Feldman said that the neutron spectrometer measures down a few feet (1 meter). Still to be determined is the true depth of the water-ice deposits. Speculation ranges from several feet to a half-mile or more below the surface. If those deposits are present, the true answer to where huge amounts of missing-in-action water went on Mars can be found underground, he said.
How did Mars attain a global water table?
"The answer iswe've got work to do. We don't know," Feldman told the AAAS audience.
Funny ejecta blankets
Other Mars scientists continue to evaluate years of data collected by both the Mars Odyssey and the venerable Mars Global Surveyor.
Maria Zuber, a professor of planetary sciences at the Massachusetts Institute of Technology (MIT), assessed data gleaned by the Mars Orbiter Laser Altimeter (MOLA) instrument on the Mars Global Surveyor spacecraft.
Zuber said that MOLA and other sensors suggest that a fair amount of water did pool in the northern hemisphere of Mars long ago. A rapid cooling of the world in its past could have coughed up carbon dioxide into the atmosphere. That, in turn, spurred greenhouse warming and rising atmospheric pressures, so much so, that liquid water could have been stable on the surface for some period of time.
Still, where the water went is a head scratcher.
A bit of evidence may be found around craters in the northern plains that have "funny ejecta blankets," Zuber said. Called ramparts, essentially every crater in that area looks like a rock thrown into a mud puddle. These features could be tied to water-rich or icy materials still residing below the surface, she said.
Climate change on Mars
Mars is a planet showing "contemporary climate change," said Michael Malin of Malin Space Science Systems of San Diego, California. He reviewed imagery collected by the Mars Global Surveyor showing shifting features on the planet.
From landslides and whirlwinds of dust to gullies seemingly formed by a seeping fluid like water - Mars is alive with change.
"There are features that cannot be explained by the present environmentthat I believe require a different environment in the not too recent past," Malin said.
For example, there are huge areas of denuded, barren terrain. "I'm at a loss to explain it, but I see it all over the planet. There is something that we don't know that could shape most of Mars it's unknown," Malin said.
Non-earthcentric strategy
Finding out if Mars is a habitat for life is on a discovery-driven pathway, said Raymond Arvidson, Chair of the Department of Earth and Planetary Sciences in Arts and Sciences at Washington University in St. Louis, Missouri. A step along that pathway is coming this year, he said, with many steps to follow.
NASA is launching two Mars Exploration Rovers in just a few months. The robots may well touch down at two sites, one spot thought rich in hematite, the other on an ancient lakebed. "They both should be sopping wet, if Feldman is correct," Arvidson said.
Whether Mars has been, or is now, an abode for life continues to intrigue scientists. Deciding what life is, and how to measure it a key challenge, said Kenneth Nealson, a biologist at the University of Southern California.
Nealson advises that the first rule must be: "Keep an open mind - life might be different from what we know." That quest he labeled as "non-earthcentric" life detection.
"What you would like to do is have a strategy that focused on physics, chemistry, and geology. That strategy would be to take measurements that are so definitive that, if life was there, you wouldn't miss it," Nealson told SPACE.com. "Let's develop non-earthcentric methods until they are so good that they never fail on Earth. Then we'll have a package that we can send anywhere to look for life," he said.
Nealson said he is pleased to see more attention paid to novel search-for-life strategies. "The notion that you could do non-earth-centric life detection is now almost popular. When we started this, you could have been burned at the stake," he said.
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