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WASHINGTON (Reuters) - Extraterrestrial life may well be so weird we would not immediately recognize it, and scientists looking for alien life should be seeking the unfamiliar as well as the familiar, experts advised on Friday.
They said NASA'S current approach to "follow the water" works well if the assumption is that life everywhere is just like life is on Earth -- based on water, carbon and DNA.
But the "life as we know it" approach could easily miss something exotic, the National Academy of Sciences panel advised.
"The purpose of this whole report was to be able to look for life on other planets and moons with an open mind ... and not maybe miss some other life form because we looking for some obvious life form," said John Baross, professor of oceanography at the University of Washington in Seattle, who chaired the committee.
The U.S. space agency commissioned the report from the National Research Council, one of the independent National Academies set up to advise the federal government on scientific issues.
The panel of biochemists, planetary scientists, geneticists and other experts considered all the possible ways that life can arise and exist.
Recent discoveries of extremophiles -- organisms living in conditions of heat, cold and dark and using chemicals once thought incompatible with life -- have changed ideas of where life can survive.
As a biochemist, Baross said lab experiments also show water does not necessarily have to be the basis for life. It might be possible for a living organism to use methane, ethane, ammonia or even more bizarre chemicals, he said.
"We had some discussion about how weird to make this because there are so many concepts out here. There are so many theories about what life is and what could be a living system," Baross said in a telephone interview.
NASA and other groups are looking hard for extraterrestrial life. Telescopes search for spectral signatures from other planets that might suggest water is on the surface. Robots on Mars are seeking evidence of water, past or present.
"We wanted to actually think outside of that box a little bit and at least try to articulate some of the other possibilities besides water-carbon life," Baross said.
All life on Earth uses some form of DNA or RNA to encode the basic information for replicating and changing, but perhaps other life forms exist that use a different method to do this, the report suggests.
NASA might also think about returning to some of the more promising places in our own solar system to look for evidence of life, the committee said. They include Saturn's moons Titan and Enceladus and even steamy Venus.
"If you are a biochemist, Titan is of enormous interest, because it's a carbon moon. It does have clearly some liquid methane or liquid ethane lakes or pools. There could be chemical reactions going on that could be favorable for producing complex biochemicals," Baross said.
"The exploration that could lead to a novel life form ... would be the most profound discovery ever made," Baross said.
Stumbling past it or worse, destroying it because it did not look like life, would be an equally profound tragedy, he said.