The planet K2-18 b, which is twice the size of Earth and orbits within the habitable zone around its host star, is located 120 light-years away from the Sun.
Simulation of the exoplanet K2-18 b within the habitable zone of its host star. Image: NASA.
The James Webb Space Telescope (JWST) has discovered evidence of carbon-containing molecules in the atmosphere of a candidate exoplanet with a potential ocean. This exoplanet, K2-18 b, has captured the attention of astronomers as they search for extraterrestrial life beyond our solar system. Previous research and observations using the Hubble Space Telescope had hinted at the possibility that this planet might be a world with a liquid ocean, a vital ingredient for life, as reported by Space on September 11th.
K2-18 b boasts a radius two to three times that of Earth and is situated 120 light-years away from the Sun. The latest research findings reveal traces of carbon dioxide and methane in K2-18 b’s atmosphere, without detecting ammonia, indicating the presence of a water-rich ocean beneath a hydrogen-rich atmosphere. This discovery underscores the importance of considering diverse environments when searching for extraterrestrial life, according to the research lead, Dr. Nikku Madhusudhan at the University of Cambridge.
With a mass approximately 8.6 times that of Earth and located in the habitable zone of its relatively cool star, where temperatures are not too hot or too cold for liquid water, K2-18 b serves as an example of a planet falling between Earth and Neptune in size. Such planets are often referred to as “mini-Neptunes” and differ significantly from any other planets in our solar system. They remain a mystery to astronomers, who are still debating their atmospheric nature. This research will help explore the atmosphere and environmental conditions of both mini-Neptune planets like K2-18 b and Hycean planets (worlds with massive liquid water oceans beneath hydrogen-rich atmospheres).
JWST has also seemingly detected dimethyl sulfide (DMS) in the atmosphere of K2-18 b, a compound primarily produced by biological processes on Earth. However, the research team remains cautious, with Dr. Madhusudhan noting that further observations with JWST will confirm whether DMS indeed exists in significant quantities on K2-18 b.
With a diameter about 2.6 times that of Earth, K2-18’s size suggests an internal structure with high-pressure ice layers akin to Neptune, along with a thinner atmosphere and a surface featuring a potential ocean. This implies that the planet may have a boiling, overly hot ocean unsuitable for life. Assessing the atmospheric composition of distant worlds like K2-18 b is not a straightforward task due to the faintness of the starlight reflected from the planet’s atmosphere in comparison to its host star. Madhusudhan and colleagues await K2-18 b to transit in front of its host star from JWST’s line of sight. This allows direct starlight to pass through the planet’s atmosphere.
Chemical elements and compounds absorb and emit light at characteristic wavelengths, leaving unique “fingerprints” in the star’s spectrum when present in a planet’s atmosphere. The research team’s discovery reflects data collected by JWST during two transits of K2-18 b in front of its host star. Researchers will continue to observe K2-18 b to learn more about the environmental conditions of this exoplanet. Their findings will be published in the Astrophysical Journal Letters. (Source: Space)