Exoplanet K2-18b may harbor life

JWST detected in its atmosphere gas molecules that are produced by living organisms.

In September 2023, an astronomer at the University of Cambridge shocked the astronomy community by claiming that an exoplanet 124 light years from Earth may harbor life.

Using the James Webb Space Telescope (JWST), Nikku Madhusudhan said he discovered that K2-18b, an exoplanet circling a cool dwarf star K2-18 within the habitable zone, has dimethyl sulfide (DMS) molecules in its atmosphere. 

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Madhusudhan and his team also detected carbon-bearing molecules, including methane and carbon dioxide, according to the findings of a study published in the Astrophysical Journal Letters. 

The presence of carbon footprints in the hydrogen-rich atmosphere of this planet in the Leo Constellation suggest that it is a world covered by oceans, which corresponds to the Hycean class exoplanet.

K2-18b has a radius 2.6 times larger than that of rocky Earth and is likely to be a gas planet like Uranus or Neptun. Initially discovered with the Kepler Space Telescope in 2015, it was later observed by the James Webb Space Telescope in order to study the planet's atmosphere.

“Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere. Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger Hycean worlds are significantly more conducive to atmospheric observations,” explained Madhusudhan, the lead author of the paper announcing these results.

On Earth, DMS molecules are produced by living organisms, primarily by phytoplankton in marine environments. It is a colorless organic compound with the chemical formula (CH3)2S.

At standard temperature and pressure, it is a colorless liquid with a strong odor resembling that of cooked cabbage or rotting vegetables. However, it has a relatively low boiling point of around 37°C (99°F), which means it can easily evaporate into the air at room temperature, turning into gas. So, while it can exist as a liquid under certain conditions, it is more commonly encountered as a gas due to its volatility.

At the same time, the presence of methane and carbon dioxide, along with the shortage of ammonia, support the hypothesis that K2-18b may have a water ocean underneath the atmosphere. 

A study published last February suggests that the ocean on K2-18b may in fact be lava.

To answer the questions lingering K2-18b, the Madhusudhan team has asked NASA to point the JWST lenses again to this exoplanet in order to gather more data.

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