If we ever find aliens on other planets, they might look like Romulans or Wookies, though it's far more likely that extraterrestrial creatures will eat acid and breathe methane. They may have genetic codes containing six, eight, or twelve nucleotides instead of the four we have here on Earth--or they may operate with systems entirely different than DNA.

Life may be so bizarre beyond our world that we may not even recognize it, says a new report from the National Academy's National Research Council. The authors found that life as it commonly exists on Earth--based on being biosolvent in liquid water, requiring a carbon-based metabolism, and having a molecular system that evolves and the ability to exchange energy with the environment--is not the only basis for life elsewhere in the universe.

The report, commissioned by NASA as part of its mission to search for life in outer space, suggests that astrobiologists turn their eyes toward Earth to study creatures found in its extreme environments.

"It is critical to know what to look for in the search for life in the solar system," said committee chair John Baross, a professor of oceanography at the University of Washington, Seattle, in a press release about the report. "The search so far has focused on Earth-like life because that's all we know, but life that may have originated elsewhere could be unrecognizable compared with life here. Advances throughout the last decade in biology and biochemistry show that the basic requirements for life might not be as concrete as we thought."

While some of this may seem obvious--that life might be different in outer space--this report adds yet another reason to explore life in extreme places on Earth, such as volcanic vents and deserts that resemble conditions on Mars and other planets. In metagenomics, there are scientists putting their efforts toward finding bacteria that employ novel methods to store and use energy that might be mimicked by humans.

The report suggests that space missions and exploration should be aimed at more than just planets where conditions seem most favorable to Terran life. Likewise, probes should be built to look for exotic evidence of life-forms. For instance, Titan, one of Saturn's moons, seems to have liquid mixtures of water and ammonia that might contain life, according to the committee.

Perhaps most interesting is the report's suggestion that humans who most often think geocentrically might gain a better understanding of fundamental philosophical questions about the nature of life. This kind of thinking may also hasten the discovery of life beyond our small planet. These life-forms may not speak to us in a low growl like Chewbacca, but they will most likely reveal a great deal about the nature of life, including our own.