Scientists discover water on planet outside solar system

Water discovered on ‘Super-Earth’ raises first real hope of alien life

Still, scientists warned that K2-18b isn't "Earth 2.0" - its atmosphere and surface are different than ours.

Though humans are unlikely to ever set foot on the remote world with current technologies, astronomer Jonti Horner of the University of Southern Queensland told ABC the discovery would help researchers understand other Earth-like planets going forward.

A group of astronomers may have found Earth's long-lost cousin, discovering the first ever "habitable" terrestrial planet with water in its atmosphere, according to new research aided by the Hubble telescope. K2-18b, which is eight times the mass of Earth, is now the only planet orbiting a star outside the Solar System, or exoplanet, known to have both water and temperatures that could support life.

This massive range stems from the fact that, with Hubble observations, researchers can only identify a water signature, the "fingerprint" observed using transit spectroscopy; they can't tell how much water is there, Giovanna Tinetti, a researcher on this study and a professor of astrophysics at UCL, said during a September 10 news conference.

"Even though it's in the habitable zone", Kreidberg said, "it's very different from the Earth, and it's not at all clear whether the planet is actually a hospitable environment for life to evolve [in]".

Professor Giovanna Tinetti (UCL CSED), co-author and Principal Investigator for ARIEL, said: "Our discovery makes K2-18b one of the most interesting targets for future study".

It's closer to its star than the Earth is to the Sun, meaning it has shorter years, and completing its orbit in 33 days while ours takes 365. "At first we weren't sure exactly what it meant, but we knew we had something exciting". As Ingo Waldmann, a researcher on the team, said: "It's maybe not quite your vacation destination just yet". Within this hydrogen, however, is the distinct mark of H2O.

"The Kepler Space Telescope first discovered K2-18 b, which is just 110 light-years away from us, in 2015". By separating the light into its component parts, the scientists could look for signatures of particular molecules. "Water has really strong absorption bands, especially in that wavelength they are looking at", Schaefer adds.

Apple CEO Tim Cook speaks on-stage during a product launch event at Apple's headquarters in Cupertino California
Apple CEO Tim Cook speaks on-stage during a product launch event at Apple's headquarters in Cupertino California

The Hubble isn't sensitive to the right types of light to detect other important molecules, such as nitrogen or methane, so the researchers can only speculate about the precise composition of the atmosphere.

The result is that the Nature Astronomy paper, which is peer-reviewed and more conservative in its findings, concludes there's a significant concentration of water within K2-18b's atmosphere, though the researchers speculate it could make up as little as 0.01% of the atmosphere or as much as 50%. The planet could have thick clouds, like Venus, that would heat its surface to an intolerable degree.

"The temperature of the atmosphere increases the deeper you go", Benneke says. As the water condenses into liquid, the drops would fall toward the core, then revert to gas as the atmospheric pressure increases. Drops of rain can fall over hot deserts and evaporate back into water vapor before they hit the ground, for example.

"There is higher UV radiation on the surface and for life on Earth that would be bad, as we we would all get cancer". So K2-18b would be a pretty humid place. So, while the team knows there's water in the atmosphere, its abundance remains unknown.

"We can not assume that it has oceans on the surface but it is a real possibility". There's still a chance it could be bathed in a huge ocean, though, which would be more suitable for life, Abel Mendez, director of the Planetary Habitability Laboratory at the University of Puerto Rico, who was not involved in either study, told Daniel Oberhaus at WIRED.

Their analysis of starlight filtered through K2-18b's atmosphere pointed to the unmistakable molecular signature of water vapor.

The uncertainty is because the Hubble can't probe the atmospheres of distant exoplanets in great detail.

"It's definitely pushing the limits of what's been done before", Schaefer says.

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