Methane and Carbon Dioxide Found in the Atmosphere of Exoplanet K2-18 b, Webb Telescope Reveals

Astronomers have made a groundbreaking discovery regarding the exoplanet K2-18 b, which is 8.6 times the mass of Earth. Using data from the NASA/ESA/CSA James Webb Space Telescope, an international team of astronomers has found carbon-bearing molecules, including methane and carbon dioxide, in the planet’s atmosphere. This finding has led to the suggestion that K2-18 b could be a Hycean exoplanet, meaning it has the potential for a hydrogen-rich atmosphere and a water ocean-covered surface.

The investigation into the atmospheric properties of K2-18 b began with observations from the NASA/ESA Hubble Space Telescope. These initial observations prompted further studies that have significantly expanded our understanding of the exoplanet. New observations were then made using the NIRISS and NIRSpec instruments aboard the James Webb Space Telescope. K2-18 b orbits a cool dwarf star called K2-18 in the habitable zone and is located 120 light-years away from Earth in the constellation Leo.

K2-18 b belongs to a class of exoplanets known as “sub-Neptunes,” which have sizes between Earth and Neptune. These types of planets are not present in our Solar System, making them poorly understood. The nature of their atmospheres has been a subject of active debate among astronomers. The suggestion that K2-18 b could be a Hycean exoplanet is particularly intriguing because some scientists believe that these worlds offer promising environments for the search for life on exoplanets.

The abundance of methane and carbon dioxide, along with the scarcity of ammonia, supports the hypothesis that K2-18 b may have an ocean beneath a hydrogen-rich atmosphere. The presence of a molecule called dimethyl sulphide (DMS) was also detected, which on Earth is only produced by life. The team of astronomers cautions that further validation is needed to confirm this finding. Future observations with the James Webb Space Telescope are expected to provide more insights into the presence of DMS in the exoplanet’s atmosphere.

Despite being located in the habitable zone and having carbon-bearing molecules, it’s uncertain whether K2-18 b can support life. The planet’s large size, with a radius 2.6 times that of Earth, suggests the presence of a mantle of high-pressure ice similar to Neptune. However, K2-18 b has a thinner hydrogen-rich atmosphere and a possible ocean surface. Hycean worlds like K2-18 b are predicted to have water oceans, but it is unclear if these oceans are habitable or even liquid due to the planet’s potential high temperatures.

Characterizing the atmospheres of exoplanets like K2-18 b is a challenging task because their parent stars outshine them. However, the team of astronomers overcame this challenge by analyzing light from K2-18 b’s parent star as it passed through the exoplanet’s atmosphere. This analysis allowed them to determine the gases present in the atmosphere. The fact that K2-18 b is a transiting exoplanet, meaning it passes across the face of its host star, enabled this study.

The team’s findings are significant because they provide valuable insights into the atmospheric composition of habitable-zone exoplanets. The observations were made possible by the extended wavelength range and unprecedented sensitivity of the James Webb Space Telescope. The researchers expect to conduct further research using the telescope’s Mid-InfraRed Instrument (MIRI) spectrograph to validate their findings and gain a deeper understanding of the environmental conditions on K2-18 b.

The ultimate goal of this research is to identify signs of life on habitable exoplanets, which would revolutionize our understanding of our place in the Universe. The team’s results have been accepted for publication in The Astrophysical Journal Letters. This study is just the beginning, as more observations of K2-18 b and other habitable-zone exoplanets are planned with the James Webb Space Telescope. These future observations hold the potential to provide even more exciting discoveries in the search for life beyond Earth.