James Webb Space Telescope’s latest investigation into the exoplanet K2-18 b has offered groundbreaking insights that could change our approach to searching for life beyond Earth. Situated 120 light-years away from our planet, in the constellation Leo, K2-18 b is unlike anything in our own solar system, offering scientists a unique challenge. This planet orbits a cool dwarf star, K2-18, in what is often described as the habitable zone—ideal conditions for hosting life as we know it.

The discovery of carbon-bearing molecules like methane and carbon dioxide in the atmosphere of K2-18 b adds a fresh dimension to our understanding of this unique exoplanet. The findings have fueled speculation that K2-18 b could be a Hycean world—an exoplanet with a hydrogen-rich atmosphere and an ocean covering its surface. It’s a classification that is fast becoming a hot topic among astronomers because these types of planets may hold the key to discovering extraterrestrial life.

Originally, K2-18 b was observed by NASA’s Hubble Space Telescope, opening the door for the more recent in-depth examination by Webb. The planet falls into a category known as sub-Neptunes, which are larger than Earth but smaller than Neptune. Given that we don’t have a planetary equivalent in our solar system, these sub-Neptunes are not yet fully understood.

According to Nikku Madhusudhan, an astronomer at the University of Cambridge and the lead researcher on the study, “The search for life has mostly been focused on smaller rocky planets. However, larger Hycean worlds are proving to be better candidates for atmospheric observation, which opens up a new frontier in our search for life.”

One of the most intriguing findings from Webb’s observations is the potential detection of dimethyl sulfide (DMS). On Earth, DMS is a molecule produced solely by living organisms, particularly phytoplankton in oceanic environments. Though the presence of DMS on K2-18 b is not confirmed, it has definitely piqued interest.

The abundant methane and carbon dioxide, coupled with a lack of ammonia, support the idea of a sub-Neptune with a water ocean beneath its hydrogen-rich atmosphere. This could be an exciting step in understanding the environmental conditions of such exotic worlds.

Yet, it’s important to note that a habitable zone location and the existence of carbon-bearing molecules do not automatically make K2-18 b a life-bearing planet. Due to its large size—2.6 times the radius of Earth—the planet likely has a significant mantle of high-pressure ice, similar to Neptune, but with a thinner atmosphere and a potentially liquid ocean on the surface.


Subhajit Sarkar, a team member from Cardiff University, highlighted, “This is the most comprehensive spectrum analysis of a habitable-zone sub-Neptune so far. It allows us to identify the molecules in its atmosphere, increasing our understanding of this fascinating category of planets.”

Studying these exoplanets is challenging because they are often outshone by their parent stars. However, the team maneuvered around this obstacle by analyzing light from the host star as it passed through K2-18 b’s atmosphere, offering crucial data about its composition.

Madhusudhan concluded, “Our primary aim is to eventually identify life on a habitable exoplanet. The data we have collected on K2-18 b is a promising start toward deeper understanding of these mysterious Hycean worlds, and what role they may play in our ongoing search for extraterrestrial life.”

With the Webb telescope’s unmatched sensitivity and extensive wavelength range, scientists now have an unprecedented tool at their disposal. It’s an exciting time in astronomy as we take these promising first steps in broadening our understanding of what life beyond Earth could potentially look like.

Source: NASA

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