Following the discovery of water vapor in its atmosphere back in 2019, a research team from the University of Cambridge immersed itself on the question of whether life can exist on k2-18B

Artist's impression of K2-18b orbiting its red dwarf star - Image Credit: ESA/Hubble, M. Kornmesser via Wikimedia Commons - HDR tune by Universal-Sci

Back in 2015, scientists discovered an exoplanet that is now known as super-earth k2-18B. The planet is located approximately 120 light-years away from Earth and orbits a red dwarf star. One of its most exciting features was the fact that it has a moderate surface temperature and that it orbits within the so-called 'goldilocks zone' of its host star (the range of orbits around a star within which a planetary surface can sustain liquid water given adequate atmospheric pressure, making it potentially habitable).

There was some exciting news regarding k2-18B in 2019 as researchers discovered that it not only orbited within the habitable zone, but it also contained actual water vapor in its atmosphere. It was the first-ever confirmed exoplanet atmosphere containing liquid water. Raising the question, could there be life on this planet?

A research team from the University of Cambridge immersed itself on this question and came with a new study focusing primarily on the planet's habitability. They published their results in The Astrophysical Journal Letters, a well known Science Journal.

K2-18b has a radius of approximately two and a half times that of Earth, in addition, it has almost nine times its mass. Although water vapor was discovered in its surface back in 2019, the extent of the atmosphere and the conditions of the interior underneath remained a mystery.

Liquid water beneath the atmosphere

Dr. Nikku Madhusudhan, lead researcher, mentioned in an interview that even though water vapor has been detected in the atmospheres of multiple exoplanets within the habitable zone now, it does not necessarily mean there are habitable conditions on the surface of those exoplanets. According to him, it is crucial to obtain a consolidated understanding of the interior and atmospheric conditions on the planet (particularly whether liquid water can exist beneath the atmosphere), to establish the prospects for habitability.

This diagram explains the Goldilocks/Habitable Zone. Displayed is starlight received vs temperature - Image Credit: Chester Harman via Wikimedia Commons

In order to uncover more details about what the planet is like blow the atmosphere, the team looked at the size of the exoplanet, among other things. As K2-18 is almost nine times the mass of Earth, scientists have suggested that the planet would be more akin to a small Neptune than a large Earth. If the planet is, in fact, more like a mini-Neptune, it is to be expected that is has a notable hydrogen 'wrap' surrounding a layer of high-pressure water, with an internal core of iron and rock. If, for example, said hydrogen wrap is too dense, the pressure and temperature at the surface of the water layer underneath it would be far too high for supporting any form of life as we know it.

The Cambridge science team, looking at atmospheric observations and mass/radius data, confirmed that the atmosphere is hydrogen-rich and includes a substantial amount of water vapor. However, they also discovered that, despite its large size, its hydrogen wrap is not necessarily too dense. Additionally, its water layer might have the right conditions to support life. Moreover, the team found that levels of chemicals like ammonia and methane were lower than anticipated. Such levels could, in theory, be attributed to biological processes. A closer inspection would be required to confirm this.

All things considered, the results of the Cambridge study are fascinating. K2-18B may be a real ocean world with conditions that could be suitable for life. On top of that, the study shows that exoplanets don't necessarily need to be earth-sized to have the right conditions for life, even planets considerably larger could be viable. We can't wait for future, bigger space telescopes to take a closer look at K2-18B. We'll keep you posted!

Sources and further reading: The Interior and Atmosphere of the Habitable-zone Exoplanet K2-18b - Astronomers discovered the first exoplanet in a habitable zone with water in its atmosphere