In the search for extraterrestrial life, some scientists say we're focusing too much on finding signs of existence as we know it, and in the process, we may be missing more strange forms of life that don't rely on water or carbon metabolism.

Now researchers from Austria have started a systematic study of solvents other than water that might be able to support life outside our planet. They're hoping their research will lead to a shift in what they call the "geocentric mindset" of our attempts to detect extraterrestrial life.

"With our current measurement strategy for life on other planets, we will only be able to detect life which shares most of its parameters with terrestrial life," astrobiologist Johannes Leitner of the University of Vienna, who presented his research Friday at the European Planetary Science Congress in Germany, wrote in an e-mail. "Presently we will not be able to detect exotic life, because we have no idea of its potential properties and by this, our probes to planetary surfaces do not carry instruments which can look for something exotic."

For instance, Leitner said, we can send rovers to Mars carrying antibodies that detect traces of chemicals and bacteria that would indicate life. But because we can only make antibodies to known substances, this method will be limited to finding Earth-like life.

"When we try to find a definition for life, in most cases, such a definition is more a summary of the specific properties of terrestrial life," Leitner said. Because life on Earth requires water, most of the search for extraterrestrial life thus far has focused on the "habitable zone," or the relatively narrow region around a star where liquid water could exist.

But while water is liquid only between zero and 100 degrees Celsius, other solvents are liquid over a much larger temperature range. For instance, because ammonia stays liquid at a lower temperature, an ocean of ammonia could exist on a planet much further from its host star. By exploring the properties of more potential solvents, such as sulfuric acid and formamide, the researchers hope to expand the potential life-supporting zone.

The Austrian researchers are certainly not the first to consider the possibility of exotic life supported by a solvent other than water. According to Ariel Anbar, head of the astrobiology program at Arizona State University, the idea dates back to at least 1954, when J.B.S. Haldane speculated that ammonia might be able to sustain life at a symposium on the origin of life.

"The notion of alternative solvents is certainly plausible, though entirely unproven," Anbar wrote in an e-mail. But because life as we don't know it is so hard to study, he said the topic has received less attention than it deserves.

Leitner's team is starting its search for exotic life by investigating the thermal and biochemical properties of potential solvents, especially focusing on each substance's ability to support a non-carbon-based metabolism. "We know, for instance, that a carbon-oxygen-based metabolism simply won't work in an ammonia or sulfuric acid solvent," Leitner said in a press release. "If life exists in the Venusian atmosphere, it probably won't work in the same way as life on Earth."

For now, Anbar says our search for extraterrestrial life is limited more by our access to extraterrestrial environments than by our conception of what life might look like. "However, as we plan future missions to Mars and elsewhere, especially Titan," he said, "and as we begin to consider the prospects for life in the solar systems other than our own that are being discovered at a rapid pace, it's important to begin thinking about 'weird life' so that we don't miss something under our noses."

*Image 1: Artist's rendering of exoplanets orbiting a distant star. ESA/AOES Medialab.

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