An article in the current issue of Air & Space suggests that life forms on other planets may be so incredibly weird that we'd have a hard time spotting them. In fact, ET microbes may not contain water or carbon-based molecules, chemicals associated with life, on this planet anyway. The article was spurred in part by news in January that the Viking space probe may have killed Martian microbes, if any existed, with the very tests it was using to search for them.
From Air & Space:
Thanks to the discovery of unusual creatures on Earth, such as “extremophile” bacteria adapted to the extreme heat of underwater thermal vents, most astrobiologists accept the possibility that life-forms on other planets could have unfamiliar appearances or adaptations. However, most still envision microbes filled with water and carbon-based, or organic, molecules. It’s not unreasonable, says David Grinspoon, astrobiology curator of the Denver Museum of Nature and Science and formerly NASA’s principal investigator for exobiology research. He points out that such compounds have been detected in practically every corner of the universe that has been examined.
However, he and other researchers now suggest that an element other than carbon may serve as the backbone for molecules essential to life-forms on other planets. One proposed substitute is silicon, which occupies a place on the periodic table directly under carbon. Vertical rows on the table represent an element’s most basic behavior, so carbon and silicon’s close positions suggest that one can be swapped for another to form molecules with similar characteristics, says Grinspoon…
The probes that search for life on other planets use technology that can detect a range of chemicals beyond water and organic molecules. The trick is to devise experimental protocols that do not destroy or miss signs of possible life…
