Webb studies planet K2-18 b again to confirm presence of gas 'only produced by life'

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As we continue to explore the cosmos, we are discovering an increasing number of exoplanets that could potentially harbor life. One such world is K2-18 b, an exoplanet that has recently captured the attention of astronomers due to the presence of intriguing DMS gas molecules in its atmosphere.

In September 2023, Nikku Madhusudhan, an astronomer at the University of Cambridge, announced a very intriguing discovery.

Using the powerful James Webb Space Telescope (JWST), Madhusudhan and his team detected the presence of carbon-bearing molecules, including methane and carbon dioxide, on exoplanet K2-18 b.

This discovery was added to other recent studies suggesting that K2-18 b could be a Hycean exoplanet, characterized by a hydrogen-rich atmosphere and a water ocean-covered surface.

"Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere," explained Madhusudhan, the lead author of the paper announcing these results.

"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," he continued.

Tantalizing hint of dimethyl sulfide (DMS)

The initial Webb observations also provided a possible detection of a molecule called dimethyl sulfide (DMS). On Earth, this molecule is "only produced by life", primarily by phytoplankton in marine environments.

The abundance of methane and carbon dioxide, along with the shortage of ammonia, support the hypothesis that K2-18 b may have a water ocean underneath a hydrogen-rich atmosphere.

"It was a real shock, I had sleepless nights for a week," enthused Dr. Madhusudhan, recalling the moment when the analysis showed a possible hint of DMS in the planet's atmosphere. "That week, I didn't even muster the courage to break it to my own team."

Why a whiff of DMS made astronomers look again

Dimethyl sulfide (DMS) is an organic compound with the chemical formula (CH3)2S. This colorless, flammable liquid possesses a characteristic odor often associated with the smell of the ocean.

DMS plays a crucial role in the Earth's sulfur cycle and has garnered significant attention due to its potential as a biomarker for extraterrestrial life.

Biological significance of DMS on Earth

On Earth, dimethyl sulfide is predominantly produced by marine organisms, particularly phytoplankton. These tiny, photosynthetic organisms release DMS as a byproduct of their metabolic processes.

When DMS enters the atmosphere, it undergoes oxidation, contributing to the formation of cloud condensation nuclei. This process influences cloud formation and, consequently, Earth's climate.

DMS as a biomarker for extraterrestrial life

Detecting DMS on distant exoplanets presents numerous challenges. The molecule's spectral signature is difficult to distinguish from other compounds, and its presence in an atmosphere may be masked by other gases.

The detection of DMS in the atmosphere of an exoplanet, such as K2-18 b, has significant implications for the search for extraterrestrial life.

On Earth, DMS is exclusively produced by biological processes, making it a compelling biomarker. The presence of DMS in an exoplanet's atmosphere suggests the possibility of marine life similar to Earth's phytoplankton.

K2-18 b: An exoplanet like no other

K2-18 b orbits the cool dwarf star K2-18 in the habitable zone, approximately 120 light-years from Earth in the constellation Leo. With a radius 2.6 times that of Earth, K2-18 b is unlike anything in our solar system.

These sub-Neptune exoplanets are poorly understood, and the nature of their atmospheres is a matter of active debate among astronomers.

"Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy," explained team member Subhajit Sarkar of Cardiff University.

"We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere," Sarkar concluded.

Cosmic detective story continues

The team is now conducting follow-up research with the JWST's MIRI (Mid-Infrared Instrument) spectrograph, hoping to further validate their findings and provide new insights into the environmental conditions on K2-18 b.

The inference of DMS on the exoplanet, though incredibly tantalizing, requires further validation. As Madhusudhan explained, "Upcoming Webb observations should be able to confirm if DMS is indeed present in the atmosphere of K2-18 b at significant levels."

"Our ultimate goal is the identification of life on a habitable exoplanet, which would transform our understanding of our place in the universe," concluded Madhusudhan. "Our past findings and future studies are a promising step towards a deeper understanding of Hycean worlds in this quest."

Implications of finding life on K2-18 b

As we stand on the precipice of a potentially transformational discovery, the tantalizing hint of alien life on K2-18 b reminds us of the boundless possibilities that await us in the vast expanse of the universe.

The tireless efforts of astronomers like Nikku Madhusudhan and his team, coupled with the unparalleled capabilities of the Webb Telescope, bring us closer than ever to answering one of humanity's most profound questions: Are we alone?

As we eagerly anticipate the upcoming observations and the revelations they may bring, we find ourselves inspired by the relentless curiosity and unwavering dedication of those who seek to unravel the mysteries of the cosmos, pushing the boundaries of our understanding and redefining our place in the universe.

The full study was published in The Astrophysical Journal Letters.

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