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Exobiology (Greek, ‘study of life out there’), a term coined by the US geneticist Joshua Lederberg, is the study of, or search for, extraterrestrial life. Biologists assume that, as life has evolved on Earth, it will also have evolved, though possibly very differently, on any number of other planets. No compelling evidence for the existence of extraterrestrial life has so far been recognized and there are many critics of the field and its theories, not least because of its perceived associations with sf.
The prime aim of the exobiologist is to devise a means of detecting alien life, however radically different it may be from terrestrial life. The great distances involved mean that such investigations have largely been limited to scanning for unusual thermodynamic patterns at the surface of other planets.
Theoretical predictions suggest that there are a great number of inhabited planets, most home to civilizations far more advanced in time than those of humans. Attempts have been made to communicate by placing unambiguous pictorial messages on satellites and sending coded radio messages. Radio telescopes can detect signals from over 1,000 light years distant and have been used, notably by Soviet scientists, to listen for messages from distant stars. The SETI (Search For Extraterrestrial Intelligence) programme represents a concentrated effort to scour the radio waves for patterns which might have originated from a sentient source. Such signals would not necessarily have been sent as deliberate attempts at communication from other planets, but would nevertheless be recognizable as evidence of extraterrestrial life. Radio waves have been emitted unintentionally from Earth for some 100 years and may ultimately be received by a similar SETI programme on a distant planet.
The detection of life by chemical means is also a highly developed science, but is limited by the space probe technology available for collecting samples. Although the presence of organic molecules may be taken as circumstantial evidence for the existence of life, it has been shown experimentally that certain physical conditions can promote the abiotic formation of organic molecules. RB
See also biogenesis; biopoiesis; panspermia.Further reading Henry Cooper, The Search for Life on Mars; , Francis Crick, Life Itself. |
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