Life as we don't know it

Posted by Daniel Pendick
on Monday, July 09, 2007

Could NASA's current approach to exobiology — the study of alien life forms — end up with astronauts stumbling across extraterrestrial life and not even realizing it? A report by the National Research Council (NRC) released Friday raises this provocative question. (The NRC is part of the National Academies, nonprofit institutions that provide independent, expert advice to the nation on science, engineering, and medicine.) You can read the report online, or buy it for $24.95.

For me, this is one of those I-hate-it-when-I'm-right moments. In an earlier blog about the media hoo-hah surrounding discovery of an "earthlike" exoplanet around the star Gliese 581, I pointed out that exobiology seems inordinately focused on finding life forms similar to those on Earth.  On the other hand, this "terracentric" stance increases the chance of failing to recognize unearthlike life. As the NRC report notes:

"No discovery that we can make in our exploration of the solar system would have greater impact on our view of our position in the cosmos, or be more inspiring, than the discovery of an alien life form, even a primitive one. At the same time, it is clear that nothing would be more tragic in the American exploration of space than to encounter alien life without recognizing it."

But there is also an important advantage of focusing on earthlike alien life: As we stumble around in the darkness of the solar system, at least we have a clear picture of what it is we are looking for. And if we find it, we might actually notice.

The NRC calls for more research so we will be fully prepared to find life, even weird forms of it. The report states four basic properties a life form would likely have:

  • "A thermodynamic disequilibrium of some sort, from which energy can be harvested." (In Earth life, for example, organisms that can harvest energy from hot, mineral-rich water flowing out of volcanic vents on the seafloor.)
  • "A chemical environment that allows the persistence of covalent bonds." (Like Earth's relatively mild climate, in which living things produce stable organic compounds by joining atoms of carbon with other types of atoms.)
  • "A liquid environment." (Lakes, streams, groundwater, oceans, and atmospheric moisture, from which plants, animals, and microorganisms draw water to fill their cells.)
  • "A molecular inheritance system that can support Darwinian evolution." (On Earth, DNA and genes.)

Taking these four conditions as the minimum, said NRC committee chair John Baross, professor of oceanography at the University of Washington, Seattle, "Our investigation made clear that life is possible in forms different than those on Earth,"

Broadening exobiology to include the search for "weird" life is not just an academic question. We are spending hundreds of millions of dollars to fling probes at Mars and other solar system bodies, partly in the hope of discovering extraterrestrial life. We ought to be clear in our minds what we are looking for — and make sure we will have a chance of finding life even if we don't really know exactly what it would look like if we found it. This will be especially important if the long-awaited Mars sample-return mission ever gets off the ground.

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