Top five places to look for extraterrestrial life
It’s a mighty big universe, but ET hunters are zeroing in on these prime candidates, reports Andrew Masterson.
For all the hope and expectation, it is sobering to recall that, despite the best efforts of scientists and engineers, there is still no evidence that life exists anywhere beyond our own planet. There are, however, some planetary prime suspects. Here are the five places astronomers and astrobiologists think are the best chances for harbouring ET.
News of this planet, a “rocky super-earth”, was announced in the journal Nature in April. Orbiting a red dwarf 39 light-years from Earth, the planet sits in its star’s habitable zone and has an estimated mass almost seven times that of our own planet, leading to the assumption that it comprises rock encasing a solid iron core. According to Jason Dittmann of the Harvard Smithsonian Centre for Astrophysics in Massachusetts, US, LHS 1140b’s density means it might have survived the runaway global warming thought to denude many red dwarf planets. If so, it might now boast a stable atmosphere and liquid water. “This is the most exciting exoplanet I’ve seen in the past decade,” he said. “We could hardly hope for a better target to perform one of the biggest quests in science – searching for evidence of life beyond Earth.”
Thanks to data from NASA’s Cassini spacecraft, Saturn’s moon Enceladus has emerged as every ET-hunter’s favourite target – mainly due to the strong likelihood that it features a subterranean ocean. In April this year, a team of scientists from the South West Research Institute (SWRI) in Texas, US, revealed a plume of hydrogen erupting from the moon’s surface. The plume may well be evidence of hydrothermal vents in the subsurface ocean – the same type of vents that support extremophile life on earth. “The discovery of hydrogen gas and the evidence for ongoing hydrothermal activity offer a tantalising suggestion that habitable conditions could exist beneath the moon’s icy crust,” says principal investigator Hunter Waite.
Another of Saturn’s 53 moons, Titan is known to have permanent hydrocarbon lakes, a nitrogen-heavy atmosphere, and possibly a subsurface ocean beneath a salty crust. It is a possible host for either water-dependent or methane-dependent life.
This planet, discovered in August 2016, orbits the star Proxima Centauri, 4.2 light-years away from our sun, and is the nearest candidate beyond the solar system for hosting ET. Research in May’s Astronomy & Astrophysics journal found the chances of life existing on the planet may hinge on its orbital speed. Astrophysicists at the University of Exeter calculated that if Proxima-b rotates on its axis three times for every two times it orbits its sun, then the chances of it being habitable are substantially improved.
The announcement of the Trappist-1 system in February, with seven rocky planets orbiting an ultracool dwarf star, sent ripples of excitement through astrobiologists everywhere. At least three of the planets looked like they were within the star’s habitable zone. The latest analysis, by Eric Wolf from the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, US, has somewhat dampened expectations, suggesting that only one of the group has life-sustaining potential. But never mind: one chance in seven is still better than no chance at all.