Water is crucial to life as we know it, so it’s one of the key things astronomers look out for on exoplanets. And now, water vapor has been detected in the atmosphere of a potentially habitable exoplanet for the first time.
Water vapor has turned up on planets outside our solar system before, but none of those were anything close to liveable. These worlds include broiling hot versions of our own Jupiter, Saturn and Neptune, and steamy Super-Earths that are more water than rock.
But this new discovery of atmospheric water vapor is more promising. The planet in question is known as K2-18b, and orbits a red dwarf star some 110 light-years away in the constellation of Leo. It’s rocky and Earth-like, measuring 2.25 times wider and eight times more massive than our home planet.
Most exciting of all, however, is that K2-18b orbits its star within the habitable zone, a region where conditions and temperatures are just right for water to pool as a liquid on the surface. This is the first time water has been found in the atmosphere of a planet within this zone, making it the most habitable exoplanet we know of so far.
But before you start packing your bags, it’s important to note that “potentially habitable” doesn’t necessarily mean for humans. Because of its larger size, the gravity at the surface would be much stronger than it is here on Earth. And red dwarf stars are known to be more active than our Sun, so the planet would be bombarded by stronger UV radiation than we’re used to.
Humans wouldn’t find K2-18b very homely, but it’s not always about us. This planet could be a paradise to any local life that evolved under those conditions, and as it stands it might currently be our best shot at finding extraterrestrial life.
“Finding water in a potentially habitable world other than Earth is incredibly exciting,” says Angelos Tsiaras, first author of the study, “K2-18b is not ‘Earth 2.0’ as it is significantly heavier and has a different atmospheric composition. However, it brings us closer to answering the fundamental question: Is the Earth unique?”
The planet itself was discovered by Kepler back in 2015, but the water was only just detected in archive Hubble data from 2016 and 2017. The team behind the find developed new algorithms that analyzed light from the host star as it filtered through the planet’s atmosphere. This revealed the molecular signature of water vapor, as well as hydrogen and helium.
The discovery makes K2-18b one of the most intriguing targets for future observations with more powerful telescopes, such as James Webb and ARIEL. Further study could help determine just how much water there is in the atmosphere, how much cloud coverage there is, and most importantly whether nitrogen and methane are also present. If so, this would strengthen the case for life on K2-18b.
The research was published in the journal Nature Astronomy. The team describes the discovery in the video below.
Sources: University College London, NASA, Hubble
