What is K2-18 b?

K2-18 b is a super Earth exoplanet that orbits an M-type star red dwarf K2-18 . Its discovery was announced in 2015.

What is the mass of K2-18 b?

Its mass is 8.92 Earths.

How much time K2-18 b takes to complete one orbit of its star?

It takes 32.9 days to complete one orbit of its star, and is 0.1429 AU from its star.

It has a 33-day orbit within the star’s habitable zone, meaning that it receives about a similar amount of starlight as the Earth receives from the Sun and could have similar conditions, which allow the existence of liquid water.

What is unique about K2-18b?

In 2019 the presence of water vapour in K2-18b’s atmosphere was discovered,

In 2023, the James Webb Space Telescope detected carbon dioxide and methane in the atmosphere of exoplanet K2-18b. Webb’s data suggest the planet might be covered in ocean, with a hydrogen-rich atmosphere.

What is the density of K2-18b?

The density of K2-18b is about 2.67 g/cm3 which is intermediate between Earth and Neptune – implying that the planet has a hydrogen-rich envelope.

Why K2-18 b is classified as Mini-Neptune?

The planet, initially discovered with the Kepler space telescope, is about eight times the mass of Earth, and is thus classified as Mini-Neptune.

What is a Super-Earth?

A Super-Earth is a type of exoplanet with a mass higher than Earth’s, but substantially below those of the Solar System’s ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth’s, respectively.

The term “super-Earth” refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability.

The alternative term “gas dwarfs” may be more accurate for those at the higher end of the mass scale, although “mini-Neptunes” is a more common term.

What is an exoplanet?

An exoplanet or extrasolar planet is a planet outside the Solar System.

As of 1 September 2023, there are 5,506 confirmed exoplanets in 4,065 planetary systems,

The James Webb Space Telescope (JWST) is expected to discover more exoplanets, and also much more about exoplanets, including composition, environmental conditions and potential for life.

The discovery of exoplanets has intensified interest in the search for extraterrestrial life.