Researchers Find Water on an Exoplanet Twice the Size of Earth

This artist’s concept shows two super Earth exoplanets K2-18 b and c orbiting the red dwarf star K2-18. Image Alex Boersman

This artist’s concept shows two super Earth exoplanets K2-18 b and c orbiting the red dwarf star K2-18. Image Alex Boersman

Using the transit method, K2-18b was found to have a size of 2.7 times Earth's diameter, and using the reflex velocity method a mass of 8.6 times Earth's mass. K2-18b is now the only super-Earth exoplanet known to host both water and temperatures that could support life. Its orbital path is much tighter than the one Earth follows around our sun (out there, a year would be just 33 Earth days)-but this intimate distance means the planet is still within the red dwarf star's habitable zone, the life-friendly region where temperatures are conducive to liquid water. At nearly three times Earth's diameter and between 7 and 10 times its mass, K2-18b is a super-Earth, a type of planet abundant in the galaxy, even though it's absent from the solar system. The goal for discovery has always been to find a rocky exoplanet with water, and after studying thousands of possible destinations, K2-18b finally represents a possibility for supporting life.

As per the findings, the K2-18b exoplanet has water somewhere around 0.01% to 50% in the atmosphere. These worlds include broiling hot versions of our own Jupiter, Saturn and Neptune, and steamy Super-Earths that are more water than rock. This makes it bigger than Earth but smaller than Neptune; most exoplanets found are in this size range. Our biases about habitability, he noted, are now very "Earth-centric", which is reasonable given that Earth is the only habitable planet we know of.

Angelos Tsiaras, an astronomer at UCL, said the team is focusing its attention on identifying exoplanets with conditions similar to those on Earth.

Both teams found that water vapor is nearly certainly present in the atmosphere of this super-Earth.

The authors of the paper, published in Nature Astronomy, believe that other molecules, including nitrogen and methane, may be present but they remain undetectable with current observations. Scientists have spent a considerable amount of time trying to track down planets with traces of water in the atmosphere and have come up largely empty.

Sadly, exoplanets in orbit around red dwarfs are considered poor candidates for habitability, owing to the propensity of this group of stars to produce tremendously powerful and frequent solar flares. Data collected by the Hubble Space Telescope over 2016 and 2017 reveals that there is also hydrogen and helium.

However, the discovery brings astronomers closer to answering the fundamental question of how unique Earth is in the universe, the scientists said.

Further studies are required to estimate cloud coverage and the percentage of atmospheric water present, the researchers said.

"K2-18b receives only 5 per cent more radiation than the Earth, leaving it with an equilibrium temperature of 265 K (minus 8 degrees Celsius)", Lothringer wrote in the tweet.

K2-18b orbits a red dwarf star about 110 light years distant - a million billion kilometres - in the Leo constellation of the Milky Way, and is probably bombarded by more destructive radiation than Earth. So he and his colleagues developed new analysis techniques to provide evidence that clouds made up of liquid water droplets likely exist on K2-18 b.

The new generation of space-based star gazing instruments led by the James Webb Space Telescope and the European Space Agency's ARIEL mission will be able to describe exoplanet atmospheres in far greater detail.

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