In a tantalising first, scientists have discovered water at a planet outside our solar system that has temperatures suitable for life.
London researchers announced today they've found water vapour in the atmosphere of a planet 110 light-years away. This so-called Super Earth is the right distance from its star to conceivably harbour life.
The University College London scientists say it's the only exoplanet known so far to have both water and temperatures needed for life, making it a prime candidate for potential life. But they caution it's not another Earth.
It's twice the size of Earth with eight times the mass, and its star is unlike our sun. No one knows if water's flowing on the surface. Lead author Angelos Tsiaras says it could help determine, "Is the Earth unique?"
Its star and atmosphere are so different than ours that "Earth-like conditions are not possible," Tsiaras told reporters. "The only question that we're trying to ask here, and we're pushing forward, is the question of habitability."
A Canadian-led team announced similar findings today. In a paper just submitted to the Astronomical Journal for publication, these scientists suggest it might even be raining there.
"This represents the biggest step yet taken toward our ultimate goal of finding life on other planets, of proving that we are not alone," the study's lead astronomer, Bjorn Benneke of the University of Montreal, said.
Discovered in 2015, the planet known as K2-18b is thought to be rocky, but no one knows if water's flowing on the surface. Its star, a red dwarf, is considerably smaller and cooler than our sun, a yellow dwarf, and its atmosphere is also different than ours.
The results are doubly exciting, Tsiaras noted, given this is not only the first Super Earth with water detected in its atmosphere but the planet also resides within the habitable zone of its star.
The research teams used archived data from the Hubble Space Telescope and other spacecraft to analyse the planet's atmosphere. Further observations are needed to determine whether the planet is indeed a true water world, using next-generation observatories like NASA's James Webb Space Telescope and the European Space Agency's Ariel, both due to launch in the 2020s.
For now, scientists know K2-18b takes 33 days to orbit its star, so one year there is one month here. At this distance, temperatures range from minus 73 degrees to 47 degrees Celsius.
The star, glowing red in the day sky, is believed to bombard the planet with radiation harsh enough to quickly inflict any human visitors with cancer, although "life there may have evolved differently" in order to survive, noted the London team's Ingo Waldmann. A sister planet, meanwhile, orbits closer to the star and is likely too hot to be in the habitable zone.
The cloud cover isn't too thick on K2-18b, otherwise it would have obscured the water vapor in the atmosphere, according to the scientists.
The surface, meanwhile, could be wet or dry. The London data suggest water vapor makes up anywhere between 0.01% and 50% of the atmosphere — "quite a big range," Waldmann acknowledged. Either way, given the planet's mass, it would be difficult to walk on the surface.
"Maybe not quite your vacation destination just yet," Waldmann said.