Atmospheric analysis reveals exoplanet K2-18b may be livable

Astronomers have just analyzed the atmosphere of the exoplanet K2-18b and found a high probability of liquid water and even breeding life. K2-18b is believed to be in orbit 124 light-years from Earth and orbits the star in its habitable zone. In this case, its surface temperature may allow the presence of liquid water.

Atmospheric analysis reveals exoplanet K2-18b may be livable

(From: ESA / Hubble, M. Kornmesser)

In our solar system, Neptune is about 17 times the size of Earth. K2-18b is somewhere in between, about 2.6 times the width of Earth and about 8.6 times the weight of Earth.

As a planet made up mainly of rocks, is K2-18b more like a mini version of Neptune (smaller cores, denser atmosphere) or a sparse surface with liquid water?

The good news is that last year, astronomers detected a large amount of water vapor in their atmosphere, confirming the idea that extraterrestrial habitable planets don’t have to be strictly referenced to the size of the super-Earth.

Lead researcher Nikku Madhusudhan said: ‘We have detected water vapor in the atmospheres of many exoplanets, but even if the planet is in the habitable zone, it does not mean that its surface is really livable.


The main difference between Earth-like exoplanets and Neptune is the ratio of the atmosphere to the rock, and the composition of both.

To this end, astronomers at the University of Cambridge have conducted a special analysis of the K2-18b atmosphere to identify the most promising combinations.

The results confirmed that K2-18b is rich in hydrogen in the atmosphere and contains a large amount of water vapor. Interestingly, the levels of chemicals such as methane and ammonia were lower than scientists had expected.

Based on the data, the team was able to examine the range of conditions where K2-18b might allow life to exist, such as hydrogen, which can account for up to 6% of the planet’s mass and a minimum of less than one millionth of the total mass.

The latter part of the number, can be considered to be a perfect fit with the earth. In fact, many of the scenarios presented in the study depict K2-18b as a water world with the ocean at a livable and sustainable temperature and pressure.

Study co-author Matthew Nixon said: “We want to know the thickness of the hydrogen envelope, which is how deep hydrogen can spread.”

Although this is a problem involving multiple directions, new research has shown that extraterrestrial habitable planets do not need to have much hydrogen to present the similar observations we expect.

In addition, the new analysis may help to recover some of the exolifeable planets previously overlooked. Planets usually the size of Earth are considered the first choice, but outside the system are more common indeed super-Earths.

Details of the study have been published in the astrophysical journal Letters.

Originally published as The Interior and Atmosphere of Habitable-zone Exoplanet K2-18b