Astrobiology hunts for alien life by studying the toughest life on Earth
No one has found life beyond Earth, yet a whole science is built on the premise that it may exist. Astrobiologists search Mars and icy moons for chemical traces while studying microbes in scalding deep-sea vents and bone-dry deserts, to learn how far life can be pushed.
Astrobiology, also called exobiology or xenology, asks where life comes from, how it first develops, where in the cosmos it might be found and what lies ahead for it. The Russian astronomer Gavriil Tikhov coined the term in 1953 from Greek words for star, life and study; the molecular biologist Joshua Lederberg's exobiology is narrower, limited to searching for life beyond Earth. The planetary scientist David Grinspoon calls the field a form of natural philosophy, anchoring speculation about the unknown in established theory, since the existence of alien life is a testable hypothesis.
Research runs along three lines. One maps habitable environments, such as Mars, Europa and exoplanets, using geobiology. Another hunts biosignatures, including organic compounds, isotope ratios or microfossils, through remote sensing and landers. The third probes how life arose from non-living matter on Earth, borrowing from paleobiology, to judge what other planets would need.
The modern field took off with the Space Age. Sputnik 1, launched in 1957, pushed scientists to take life on other worlds seriously, and NASA's Viking programme became the first US mission to land on Mars and look for life. In the 1980s and 1990s, the discovery of microbes thriving at deep-sea hydrothermal vents showed life could endure harsh conditions, and stable isotope techniques sharpened the search. This century brought ESA's Beagle 2, lost minutes after landing on Mars, NASA's Phoenix lander studying Martian water history, and the Curiosity rover.
The work rests on working assumptions. Carbon, fourth most abundant element in the universe, bonds readily with itself into long, stable yet reactive molecules, so most life is presumed carbon-based. Liquid water is treated as essential, though some suggest water-ammonia mixtures. Life probably needs a steady environment, since huge stars burn out too fast, and some energy source, which need not be sunlight: extremophiles at vents live on chemical energy in total darkness. Researchers stress these assumptions could shift as knowledge grows.
Source: Astrobiology
