We are almost certainly not alone in the Universe. This is one exciting implication behind research into a ‘murky’ exoplanet orbiting a red dwarf star just 20 light years away from our solar system, which, it is generally agreed, could conceivably host life.
Gilese 581d was first discovered in 2007 and is a planet right at the edge of the Gilese system’s ‘Goldilocks’ zone – so called because it represents the region around any star which is not too hot, but not too cold to sustain liquid water. According to climate models run in a study published in Astrophysical Journal Letters, it could well be that the exoplanet’s atmosphere keeps conditions warm enough to sustain a hydrological cycle.
This is the second planet to be detected in the Gilese system which has excited astronomers. In 2010 Gilese 581g was announced, also within the Goldilocks zone – but other scientists have since questioned whether that planet even exists. Detecting exoplanets is still a painstaking business consisting of measuring the infinitesimal reduction in light reaching Earth from a distant star when a planet moves between that star and us, and there have been many false alarms regarding planets beyond our solar system.
If Gilese 581g does turn out to exist, however, there would be two planets in the same system which could potentially host life. Originally Gilese 581c, which was discovered around the same time as 581d, was also a contender, but astrophysicists have since ruled out the possibility of that planet being suitable for life on the grounds that its surface is an estimated 1,000C.
According to the BBC, however, French researchers at Paris’s Institut Pierre Simon Laplace have been running computer simulations of Gilese 581d’s atmosphere and are now confident that it contains high levels of carbon dioxide, which could make it able to sustain liquid oceans, clouds and rainfall.
None of this means, however, that humans could one day colonise Gilese 581d – it’s important to note that the dim light reaching the planet from its red dwarf sun and its dense atmosphere would make it completely toxic to us. Also, 20 light years makes the Gilese system a close neighbour in galactic terms, but it is still an impossibly long way away.
Robin Wordsworth of the French team is particularly pleased with the results of these climate models, however, as it demonstrates that there is a far greater variety of environments and planets than we have been able to observe in our own solar system. And the relative proximity of the Gilese system means that: “with future generations of telescopes, we’ll be able to search for life on Gliese 581d directly.”
The chances are that Gilese 581d does not host life. What is exciting is not just that it could be habitable, but that we are able to make educated guesses with such confidence about such a distant world. With the existence of the first rocky exoplanet to be discovered, Kepler 10b, being confirmed in early 2011, the search for life on other worlds is gathering pace.
