Think life on Earth is weird? It might be even weirder on distant planets and moons, according to a new report. Instead of thriving on water, extraterrestrial organisms might live in a sea of liquid methane. Or instead of getting energy from the sun, they might thrive on hydrochloric acid.
These possibilities could revolutionize future space missions in search of life elsewhere in the solar system, says the report, issued today by the National Academy of Sciences (NAS).
The report concludes that scientists need to consider an expanded list of characteristics that define life, including so-called "weird" life-forms that may thrive where Earth organisms couldn't.
Instead of dispatching spacecraft to dig into the subsurface of Mars, considered a prime candidate for primitive life because of its watery past, the report says the probes may have better luck on Saturn's moon Titan, which has seas of liquid methane and ethane.
In fact, the report concluded that Titan is the most likely candidate in the solar system for weird life.
"It's a carbon world, so there's plenty of different kinds of carbon compounds there, and the possibility is that there may be the carbon compounds that make up life," said John Baross, an oceanographer at Seattle's University of Washington, who lead the report team.
Different Life
Baross chaired the committee that prepared the report released by the National Research Council, an arm of the NAS.
The report probes the question: How might life on distant worlds be different than life on Earth?
"We don't want to not recognize a life form because it doesn't exactly resemble Earth life," Baross said.
All life on Earth studied to date has certain characteristics and needs: water, carbon-based metabolism, a chemical- or light-based energy source, and the ability to evolve.
Since these characteristics make life on Earth possible, scientists have long assumed they are required for life elsewhere in the universe. But advances in biology and biochemistry in the last decade show that the basic requirements for life may not be so concrete, according to Baross.
Seth Shostak is a senior astronomer at the SETI Institute in Mountain View, California, which is dedicated to the search for alien life. He was not part of the report but said the premise is "very justified."
For example, he said, the Viking lander missions to Mars in the 1970s were controversial, because although they did not find life, they only looked for Earthlike life.
(Read related story: "Viking Mission May Have Missed Mars Life, Study Finds" [October 23, 2006].)
"Let's be a little more broad-minded. Let's not just look for life as we know it," Shostak said.
"The only problem," he added, "is it's very difficult to look for life as you don't know it, because you don't know how to look for it. I think that's what motivates this study."
Weird Life
According to the report, the search for life elsewhere in the solar system and beyond should include efforts to detect "weird" forms of life.
For example, laboratory experiments have recently demonstrated that scientists can change the DNA of Earth organisms, which then continue to encode the new genetic information.
The findings suggest that "a different life-form doesn't necessarily have to have exactly the same chemistry that Earth life has," Baross said.
Even weirder life, he said, may tap into different sources of energy than the sun, which most Earth organisms depend upon.
Perhaps most intriguing, Baross continued, is the possibility that extraterrestrial life could thrive on a solvent other than water, such as the liquid methane and ethane on Titan.
(Read related story: "Saturn Moon Has Lakes, "Water" Cycle Like Earth's, Scientists Say" [January 5, 2007].)
"Could a carbon-based life-form survive and live in that?" Baross said.
"That's pretty much an unknown to Earth life."
(See a picture gallery of what extraterrestrial life might look like.)
Finding Weird Life
The hunt for weird life on other planets and moons begins with studying life on Earth, Baross explained. For example, one of the biggest unanswered questions about Earth life is how it originated.
"What comes out of this report is that there's so much about Earth life that we don't understand," Baross said.
This is especially true about life forms that exist in extreme environments like arid deserts, high-altitude lakes, and snuggled up against boiling deep-sea vents.
"The possibility exists that there are still organisms that can tell us something about early life and even possibly the origin of life that we haven't really tapped into," Baross said.
The lessons learned from Earth's weird life can then guide the search for even weirder life elsewhere in the universe, the researchers noted.
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