Two of the most fundamental questions asked by people, and as yet still unanswered by science, are how life emerged on the Earth, and whether we are alone in the cosmos: does life exist in extraterrestrial locations as well? These deeply important questions form the core of a new kind of science, one that recently has been rapidly gathering momentum. Astrobiology is supported by a flood of new information from studies on the origins of terrestrial life, and our deep-space probes and telescopes exploring the Universe around us. The science incorporates everything from understanding the survival of life in the most extreme environments on Earth and looking for the earliest evidence of cells in the ancient rocks of our planet, to exploring the alien worlds of our solar system to determine if they have ever provided an environment suitable for life of their own.
Within our own solar system, astrobiologists consider several possible habitats for extraterrestrial life. These include our next-door neighbour planet Mars (if not now, then at least earlier in its history), as well as Jupiter’s moon Europa which is known to have a global ocean of water beneath its icy surface, and perhaps the giant hydrocarbon-soaked moon of Saturn, Titan. Only one of these locations, the surface of Mars, has ever been tested for life. This was back in the 1970s with the twin Viking robots, but the results of their biological detection instruments were ambiguous to say the least.
Another recent development in astrobiology has been the ability to detect planets in other solar systems: new worlds orbiting distant stars in the night sky. Over 340 of these so-called extrasolar planets, or exoplanets, have been discovered so far (as of May 2009), and we are now on the brink of being able to detect a terrestrial planet orbiting a sun-like star: a second Earth.
In this article, we’ll look at two aspects of the astrobiology of extrasolar planets: how to spot them, and how to check for signs of life across the gulf of deep space.