World of Water? Massive exoplanet’s atmosphere contains methane and carbon dioxide.

Methane and carbon dioxide have been found in K2-18 b, an exoplanet 8.6 times as large as Earth, according to a recent study using NASA’s James Webb Space Telescope. Webb’s discovery supports recent research that K2-18 b may be a Hycean exoplanet, a type of planet that has the potential to have an atmosphere rich in hydrogen and a surface covered in water oceans.

Observations using NASA’s Hubble Space Telescope provided the first understanding of the atmospheric characteristics of this exoplanet in the habitable zone, which led to further research that has since altered our understanding of the system.

K2-18 b is 120 light-years away from Earth in the constellation Leo, orbiting the cool dwarf star K2-18 in the habitable zone. Exoplanets with sizes between those of Earth and Neptune, like K2-18 b, are unlike anything else in the solar system. These “sub-Neptunes” are poorly understood because there aren’t any neighboring planets that can be compared, and scientists are currently debating the makeup of their atmospheres.

It is exciting to speculate that the sub-Neptune K2-18 b could be a Hycean exoplanet because some astronomers think these worlds offer ideal settings for looking for signs of life on other exoplanets.

Nikku Madhusudhan, an astronomer at the Space Telescope Science Institute, said that “our observations underscore the importance of examining diverse habitable environments in the search for life elsewhere.”

The smaller rocky planets have historically received most of the attention in the search for extraterrestrial life, although the larger Hycean worlds are much more suited for atmospheric investigations. The presence of a water ocean beneath a hydrogen-rich atmosphere in K2-18 b is suggested by the abundance of methane and carbon dioxide and the lack of ammonia. Additionally, the earliest Webb observations allowed for the potential identification of the chemical dimethyl sulfide (DMS). This can only be made by life on Earth. Phytoplankton in maritime areas emit the majority of the DMS that is present in the Earth’s atmosphere.

The DMS inference is less reliable and needs additional validation.Future Webb observations should be able to determine whether DMS is actually present at considerable levels in the atmosphere of K2-18 b.

Although it is now established that K2-18 b contains carbon-containing molecules and is in the habitable zone, this does not necessarily suggest that the planet can sustain life. Because of the planet’s massive size, which is 2.6 times that of Earth, its interior is most likely made up of a thick mantle of high-pressure ice, similar to that of Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface. Oceans of water are expected on hycean worlds. It’s also conceivable that the ocean is too warm to support life or remain liquid.

Subhajit Sarkar of Cardiff University, a team member, noted that sub-Neptunes are the most prevalent type of planets so far identified in the galaxy, despite the fact that this type of planet is not present in our solar system.

We were able to determine the chemicals present in the atmosphere of the sub-Neptune by obtaining the most comprehensive spectra of one yet.

Astronomy is actively working on characterizing the atmospheres of exoplanets like K2-18 b, or determining their gases and physical characteristics. Exploring exoplanet atmospheres is particularly difficult since these planets are actually outshone by the brightness of their much larger parent stars. The team got around this problem by studying light from K2-18 b’s parent star as it traveled through the atmosphere of the exoplanet. Since K2-18 b is a transiting exoplanet, we can see a lowering of brightness as it crosses the face of its star. This is how NASA’s K2 mission discovered the exoplanet for the first time in 2015. As a result, during transits, a very little portion of the starlight will pass through the exoplanet’s atmosphere before it is captured by telescopes like Webb. Astronomers can put together the traces left by the starlight as it passes through the exoplanet’s atmosphere to discover the gases that make up the atmosphere.

According to Madhusudhan, “Webb’s unprecedented sensitivity and extended wavelength range allowed robust detection of spectral features with just two transits, making this result only possible.” For instance, “eight Hubble observations over a few years and in a relatively narrow wavelength range provided comparable precision to one transit observation with Webb.”

With many more observations of K2-18 b on the way, team member Savvas Constantinou of the University of Cambridge said, “These results are the result of just two observations of K2-18 b.” This means that what we’ve done here is just a preliminary example of what Webb can see on exoplanets in the habitable zone.

The team now plans to carry out more analysis using the telescope’s MIRI (Mid-Infrared Instrument) spectrograph in the hopes that it would further corroborate their results and offer fresh information about the conditions on K2-18 b.

“Our primary objective is to find evidence of life on a habitable exoplanet, which could change our understanding of our place in the universe,” Madhusudhan said in his conclusion. “In this endeavor, our findings are a promising first step towards a deeper understanding of Hycean worlds.”

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