odyssey_why_011127 Now that the Mars Odyssey spacecraft has returned its
first pictures, showing that its cameras work, it officially joins a long list of spacecraft that have studied whether or not water does or ever did exist at or near the surface of the Red Planet.But what will Odyssey do that hasn't already been done? And why do we need yet another robotic probe orbiting Mars? Shouldn't we be sending geologists by now? And hey, isn't the real question, is there life on Mars?
The answers, from NASA's point of view, are elementary:
- We still don't know if there is water anywhere close to the surface of Mars, except for the frozen variety at the poles.
- We don't know how harsh the radiation environment is, and thus what it would take to protect human explorers.
- If there is life on Mars, it needs water.
Odyssey is part of a years-long program of Mars missions -- orbiters and landers -- that aims to learn enough about the still-mysterious planet to properly plan a crewed mission, one that many researchers figure will be needed to find any conclusive evidence for life.
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 | This picture shows both a visible and a thermal infrared image taken by the thermal emission imaging system on NASAs 2001 Mars Odyssey spacecraft on November 2, 2001.
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| Schematic breakdown of Mars Odyssey
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Though NASA has not committed to such a mission, agency officials make it clear that they are not sending robots merely for the fun of operating a toy by joystick from several million miles away.
"I feel that we are now taking the steps to go to Mars with people," said departing NASA administrator Dan Goldin shortly after Odyssey arrived at Mars Oct. 23.
Well of optimism
A human trip to Mars is not yet top priority, however. For now, the entire Mars program is built around one simple directive: Follow the water.
Why? Because wherever there is water on Earth, scientists have found life. Under the seafloor. In Arctic ice. In scorching hydrothermal pools.
So wherever there are signs of water on Mars -- canyons that look as though they were carved by rivers, layered sediments that might once have been a lake bottom, fans of material that could indicate recent hydrothermal activity -- there could be life. Or at least fossils, the signatures of past life.
So the search for water on Mars is really a search for life.
But with all the years of photographic water witching, the only thing so far discovered with any certainty is a well of optimism. Photographic evidence and infrared data clearly point to a planet scarred by massive floods sometime in the past. Few doubt that Mars was once warmer and possibly wet, perhaps more than a billion years ago, however. But there is no solid proof of this, and even less evidence for any recent hydrological activity.
Some scientists believe we'll never know how deep any remaining Martian water is until we go there and drill a well, a project that would likely require human engineers in space suits.
Water on Mars? Maybe not
Odyssey, meanwhile, has a set of eyes that can virtually drill into the surface, perhaps as far down as 100 meters. Recent
studies have suggested there may be water at that depth. But the scientist responsible for the newest search is not expecting to spot a drop."Mars has been a very cold, dry planet for a long time," says Philip Christensen, an Arizona State University geologist who is in charge of the cameras on Odyssey. "The chance of finding near-surface liquid water is, I think, very remote."
Christensen has been studying Mars since 1976. He worked on the Viking program. By now, you would expect him to at least hope to find water on Mars, as it would be one of the most important scientific discoveries of our time. But hope is not in Christensen's science vocabulary.
"As a scientist, you shouldn't hope to find anything," Christensen said in an interview a few days before Odyssey arrived at Mars. "Mars is what it is, and we're just trying to unravel it. You should go and see what's there and then say, 'This is what I found.'"
That's not to say that Christensen has entirely given up.
"We know water was there, so it's not a pipe dream to think there is water near the surface and accessible." And he certainly has adequate tools to advance the search.
Odyssey is equipped with two cameras that operate through a single observing lens. Incoming light or heat radiation from Mars is split to the appropriate camera. The setup is called a Thermal Emission Imaging System, or THEMIS.
Next page: Shadows on Mars
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