For the first time, researchers have discovered water vapour in an atmosphere of an exoplanet 124 light-years away from our solar system. Exoplanet K2-18b is approximately 2.7 times the radius and 8.3 times the mass of Earth, but researchers continue to debate whether this planet is a super-Earth or a mini-Neptune.
Planets that fall under the category of mini-Neptunes have a thick hydrogen-filled atmosphere that surrounds a layer of water. However, temperatures would be too high and the water would be under too much pressure for life to survive. This is why planets that fall under this category are labelled to be inhabitable, at least by Earth’s standards.
A super-Earth is a reference to a planet’s size. Super-Earths are a class of planets that are larger than earth yet lighter than ice giants like Neptune. They are unlike any planets that are in our solar system, the Milky Way. To fall under this category, these planets must be up to 10 times Earth’s mass and between twice the size of Earth. The term super-Earth only refers to the size of a planet. It does not imply anything about a planet’s surface conditions or its habitability.
Could Exoplanet K2-18b be Habitable After All?
Given exoplanet K2-18b’s large size, people assumed that it is more like a mini-Neptune rather than a super-Earth.
However, assumptions might be changing – if researchers are correct.
Dr. Nikku Madhusudhan at Cambridge University, led a research group to learn more about exoplanet K2-18b. They discovered that the exoplanet’s hydrogen atmosphere might not be too thick and the water might actually be habitable. This discovery meant that K2-18b’s atmosphere would be more like a super-Earth than a mini-Neptune, making it more habitable than we thought.
The research team also found out that the levels of ammonia and methane were less than expected for such an atmosphere, creating a chemical disequilibrium. However, whether these levels can be attributed to a biosignature remains to be seen.
If these discoveries are in fact correct, and exoplanet K2-18b is a habitable super-Earth, I will be on the first ticket to travel 124 light-years to get there. Who’s with me?