PASADENA, Calif. -- NASA's Mars Odyssey spacecraft has confirmed suspicions that the radiation on Mars is so intense that it could endanger astronauts sent to explore the Red Planet, scientists said last week.
The high radiation levels measured by the unmanned probe also suggest that any extraterrestrial life that might call Mars home would have little chance of surviving unless it were shielded beneath the planet's dusty, cold surface, said Cary Zeitlin of the National Space Biomedical Research Institute in Houston.
"It would have to be pretty robust against all kinds of environmental horrors," said Zeitlin, one of the scientists working on the project.
The conclusions stemmed from new data released by scientists at NASA's Jet Propulsion Laboratory from the first year of scientific results from the $300 million mission.
Scientists also presented information on the minerals and elements that make up the planet's surface, including measurements that show its northern hemisphere is richer in water than its southern half. Near the planet's north pole, frozen water makes up as much as 75 percent, by volume, of the top 3 feet or so of soil, said William Boynton, one of the mission's scientists.
"We're talking ice with a little bit of dirt mixed in it and not the other way around," Boynton said.
NASA talks vaguely of future manned missions to Mars, where astronauts could use that ice for drinking water, fuel and oxygen to breathe. The new radiation findings suggest such a mission would be risky.
Even so, possible accidents involving the spacecraft that would take astronauts to and from Mars pose a far greater risk, Robert Zubrin, president of the pro-exploration Mars Society, said in a telephone interview.
"The idea (radiation) represents this incredible, forbidding obstacle to Mars exploration just isn't so," Zubrin said.
Mars is continuously bombarded by radiation from the galaxy at large, as well as by periodic bursts from the sun. The radiation would expose astronauts in orbit to an effective dose 2.5 times greater than that received by humans in low Earth orbit aboard the international space station, Zeitlin said.
A three-year mission would expose astronauts to the radiation limit considered safe by NASA over the career of an astronaut, he added.
The radiation environment on the surface of Mars is unknown but probably poses a similar risk, even though the planet's tenuous atmosphere would provide some shielding.
"It still remains to be seen what the hazards are on the surface," Odyssey project scientist Jeffrey Plaut said.
The main worry for astronauts on Mars would be the periodic bursts of charged particles that stream outward from the sun. On Earth, a global magnetic field and a substantial atmosphere protect against that radiation.
Observations made last year show bombardments of solar radiation can last more than a week. Presumably, astronauts on Mars would have to remain confined in some sort of shelter during such blasts of radiation, Zeitlin said.
"They're manageable, as long as the spacecraft has these refuge areas," Zeitlin said.
Mars Odyssey's science mission is expected to last 1 1/2 more years but probably will e extended. The spacecraft has been thrifty enough with its fuel to enable it to stay in orbit 20 more years, Plaut said.
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