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updated 4/28/2010 10:25:13 PM ET 2010-04-29T02:25:13

Scientists haven't found E.T. just yet, but they may be pinning down the best places and ways to look for alien life during future space missions, NASA researchers said Wednesday.

Experts on the search for extraterrestrial life spoke to reporters from the Astrobiology Science Conference near Houston to celebrate 50 years of astrobiology research.

Scientists there said they are still eager to find life elsewhere in the universe despite the firestorm this week kicked off by famed cosmologist Stephen Hawking, who suggested that perhaps humans shouldn't be so eager to find aliens since there's a chance they would want to colonize Earth or strip it for resources.

"We're interested and prepared to discover any form of life," said Mary Voytek, astrobiology senior scientist at NASA Headquarters, during the teleconference.

The lure of new missions
Cornell University planetary scientist Steve Squyres, principal investigator of the Mars Exploration Rover project, said NASA scientists were currently considering a list of 28 future science missions that could help discover signs of extraterrestrial life.

"Astrobiology and the search for life is really central to what we should be doing next in the exploration of the solar system," Squyres said.

Slideshow: Month in Space: January 2014 He mentioned a host of possible robotic missions, including visits to Mercury, Mars, the moons of Jupiter and Saturn, and even distant outer solar system flybys. In particular, the Saturnian moons Titan — with its lakes of methane and ethane — and Enceladus, with its plumes of water vapor, seem like possibly habitable sites.

Squyres also said NASA is considering an ambitious three-part mission to Mars that would return samples of rock back to Earth for scientists here to study in person.

This mission "might reveal a great deal about whether Mars once harbored life," he said.

Mars samples
Other scientists on the panel agreed that a Mars sample return mission would be invaluable.

"I personally think if we're ever going to be able to show that there was past life on Mars — if there was past life on Mars — I think we're going to need to study the samples here on Earth rather than robotically," said Bill Schopf, a researcher at the University of California, Los Angeles. "I think if we had the rocks back tomorrow and I had them in my lab, I think we could solve this problem."

Schopf and another researcher, Jack Farmer of Arizona State University, announced the results of a recent study in which they found that a type of mineral deposit called sulfate can harbor fossils of ancient organisms.

Although the scientists studied samples of sulfate from Earth, this material is also present in large quantities on Mars. The fact that they found fossilized life in Earth's sulfate means that Mars' sulfate would be capable of storing a record of life, too, if that life existed. Thus, collecting samples of sulfate on Mars would be a good place to look for Martian life, they said.

Another possible place to look for life in the solar system is asteroids. Researchers announced for the first time Wednesday that they'd found direct proof of frozen water and organic compounds — which could include the ingredients for life — on a space rock in the main asteroid belt between Mars and Jupiter. Both water and organic materials are considered necessary to make a place habitable.

"Any time you have materials like that present you have a candidate that is worthy of study," Squyres said. "We should go where the data lead us."

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