A new investigation with NASA’s James Webb Space Telescope of K2-18 b, an exoplanet 8.6 times more massive than Earth, has revealed the presence of carbon-containing molecules, including methane and carbon dioxide. Webb’s findings add to recent studies suggesting K2-18 b may be a Hycean exoplanet, likely with a hydrogen-rich atmosphere and a surface covered with water and oceans. The first glimpses of the atmospheric properties of this habitable-zone exoplanet came from observations with NASA’s Hubble Space Telescope, leading to further studies that have since changed. change our understanding of this system. K2-18 b orbits the cool dwarf star K2-18 in the habitable zone and is 120 light-years from Earth in the constellation Leo. Exoplanets like K2-18 b, which range in size from Earth to Neptune, are unlike any other planet in our solar system. The lack of nearby equivalent planets means that these “sub-Neptunes” are poorly understood, and the nature of their atmospheres is the subject of active debate among astronomers.

The proposal that asteroid K2-18 b may be a Hycean exoplanet is intriguing, as some astronomers believe that these worlds are promising environments to search for evidence of life on exoplanets. “Our results highlight the importance of taking into account the diversity of possible environments,” explains Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper announcing the results. live while searching for life elsewhere. “Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but larger Hycean worlds are significantly easier to observe atmospherically.” The abundance of methane and carbon dioxide, as well as the lack of ammonia, support the hypothesis that there may be a water ocean beneath the hydrogen-rich atmosphere in K2-18 b. Webb’s initial observations also discovered a molecule called dimethyl sulfide (DMS). On Earth, this is only created by life. Most of the DMS present in Earth’s atmosphere is emitted by phytoplankton in marine environments.

DMS inference is less robust and requires additional validation. “Further observations by Webb will be able to confirm whether DMS is indeed present in the atmosphere of K2-18 b at significant levels,” explains Madhusudhan. Although K2-18 b is in the habitable zone and is currently known to contain carbon molecules, this does not necessarily mean the planet can support life. The planet’s large size – with a radius 2.6 times that of Earth – means its interior could contain a huge layer of high-pressure ice, like Neptune, but with an atmosphere thinner, hydrogen-rich, and ocean surface. Hycean worlds should have oceans of water. However, it is also possible that the ocean is too warm to be habitable or that there is no liquid at all. Subhajit Sarkar, a member of the research team from Cardiff University, explained: “Although this type of planet does not exist in our solar system, sub-Neptunian planets are the most common type of planet discovered. known to date in the galaxy”. “To date, we have obtained the most detailed spectra of the habitable zone under Neptune, which allows us to identify the molecules that exist in its atmosphere.” Characterizing the atmospheres of exoplanets like K2-18 b – that is, determining their gases and physical conditions – is a very active field in astronomy. However, these planets are actually dwarfed by the luminosity of their much larger parent stars, making exploration of the atmospheres of exoplanets especially difficult. The team overcame this challenge by analyzing light from K2-18 b’s parent star as it passed through the exoplanet’s atmosphere. K2-18 b is a transiting exoplanet, which means we can detect a decrease in brightness as it passes in front of its host star. This is how the exoplanet was first discovered in 2015 with NASA’s K2 mission. This means that during transit, a very small portion of starlight will pass through the exoplanet’s atmosphere before reaching telescopes like the Webb. The passage of starlight through an exoplanet’s atmosphere leaves a signature that astronomers can reconstruct to identify the gases in the exoplanet’s atmosphere.

“This result was only possible thanks to Webb’s extended wavelength range and unprecedented sensitivity, which allows robust detection of spectral features with just two transitions,” said Madhusudhan. “For comparison, one transit observation with the Webb provides the same precision as eight observations with Hubble taken over several years and over a relatively narrow wavelength range.” “These results are the product of just two observations of K2-18 b, with many more on the way,” explains team member Savvas Constantinou from the University of Cambridge. “This means that our work here is just the first demonstration of what Webb can observe in habitable zone exoplanets.” The team’s results have been accepted for publication in the Astrophysical Journal. The team now plans to conduct follow-up research with the telescope’s Mid-Infrared Instrument (MIRI) spectrometer, which they hope will further confirm their results and provide new information about environmental conditions. upper school K2-18 b. “Our ultimate goal is to identify life on a habitable exoplanet, which will transform our understanding of our place in the universe,” Madhusudhan concluded. “Our findings represent a promising step toward a deeper understanding of the Hycean world in this quest.”

source: https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b