Water, water, water—whether on Mars or on Jupiter’s moons Europa and Ganymede and Callisto, scientists looking for signs of life beyond Earth have long assumed that life needs water. The only requirement that gets equal billing is the presence of organic molecules, which is why the atmosphere of Saturn’s moon Titan, which is loaded with organics, is so intriguing to astrobiologists. But while astronomers (and sci-fi fans) have said for decades that discovering extraterrestrial life would be the most revolutionary finding in the history of science, they have not faced the flip side of this contention: that “nothing would be more tragic in the American exploration of space than to encounter alien life without recognizing it.”
So concludes a new report from the National Research Council, part of the National Academies, released this afternoon. “The Limits of Organic Life in Planetary Systems”—or, as it’s become known, the “weird life” report—was requested by NASA, and the space agency comes across as having about as much imagination as an amoeba. By assuming that ET would run on the same biochemistry as life on Earth—an attitude the panel calls “terracentricity”—NASA has foolishly limited its search for life beyond Earth, the 11-person panel of scientists concludes.
In particular, NASA is “focused on locations where liquid water is possible, and it emphasizes searches for structures that resemble cells of terran organisms . . . and tests for amino acids and nucleotides similar to those found in terrestrial proteins and DNA,” says the report. But “if life originated independently, even within our own solar system, it might have nonterran characteristics and, thus, not be detectable by NASA’s” missions, which are “designed explicitly to detect terran biomolecules or their products. Further, if life is possible in solvents other than liquid water, it might exist in planetary environments other than the few that are currently targeted.”
The unwarranted assumption that life requires water has led astronomers studying Mars for signs of past or present life to rule out anyplace without liquid water. But ammonia or formamide could also serve as biosolvents. As it happens, mixtures of liquid water and ammonia may lurk within Titan, leading the panel to recommend that NASA give a higher priority to missions to that Saturnian moon.
Weird life might also use hereditary material different from terran life, where DNA is made of four molecules called nucleotides. The new field of synthetic biology—creating life or its building blocks in the lab—has created hereditary molecules using six or more nucleotides. And rather than relying on a carbon-based metabolism, as terran life does, weird life could get energy from a reaction of sodium hydroxide and hydrochloric acid, breaking free of the carbon assumption. “Life is possible in forms different than those on Earth,” said oceanographer John Baross of the University of Washington, who chaired the committee. But we won't find it with the blinkers NASA's been wearing.