JWST Discovers Methane, CO2 On on K2-18b, Possible DMS Detection

In a groundbreaking announcement, NASA's James Webb Space Telescope has discovered the presence of carbon-bearing molecules, including methane and carbon dioxide, on the exoplanet K2-18b just a 120 light years away. 

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Zac Aubert

Zac Aubert

Published: 11th Sep 2023 15:18 GMT
Written by: Zac Aubert

In a groundbreaking announcement, NASA's James Webb Space Telescope has discovered the presence of carbon-bearing molecules, including methane and carbon dioxide, on the exoplanet K2-18b just a 120 light years away. 

In 2019 NASA discovered water vapors on K2-18b through observations with NASA's Hubble Space Telescope. These observations set in motion a series of further studies that have since revolutionized our understanding of this distant celestial system. The first of those studies is now complete and has been published.

K2-18b, orbits the cool dwarf star K2-18, 120 light-years away from Earth, within the constellation Leo. 

Credit: NASA Exoplanet Catalog

Credit: NASA Exoplanet  Catalog

K2-18b orbits K2-18 every 32.9 days. Its unique classification as a sub-Neptune, a category of exoplanets characterized by sizes falling between that of Earth and Neptune, sets it apart from anything within our solar system.

This exoplanet, approximately 8.6 times as Earth, has captured the attention of astronomers due to its potential as a Hycean exoplanet, boasting the intriguing possibility of a hydrogen-rich atmosphere and a surface concealed beneath a water ocean.

Credit: NASA Exoplanet Catalog

The notion that K2-18b might be a Hycean exoplanet has piqued the interest of astronomers. Many in the field believe that these planets hold great promise as potential environments to search for signs of life beyond our planet.

"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." - Nikku Madhusudhan, Lead Resercher & Astronomer at the University of Cambridge

The abundance of methane and carbon dioxide, coupled with the absence of ammonia, lends credence to the hypothesis that K2-18b might host a water ocean beneath its hydrogen-rich atmosphere.

Initial Webb observations also hinted at the presence of dimethyl sulfide (DMS), a molecule only that is only produced by life on Earth. DMS is predominantly emitted by phytoplankton in marine environments, suggesting the potential for biological activity on K2-18b.

The detection of DMS requires further validation through upcoming Webb observations, which will ascertain its presence in significant quantities.

While K2-18b occupies the habitable zone and now boasts the presence of carbon-bearing molecules, it remains uncertain whether the planet can truly support life. Its substantial size, with a radius 2.6 times that of Earth, suggests the likelihood of a mantle composed of high-pressure ice, akin to Neptune. This is coupled with a thinner hydrogen-rich atmosphere and the possibility of a water-covered surface, characteristics typical of Hycean worlds. Yet, questions linger regarding the habitability of its ocean, which may be too hot to sustain life or remain in a liquid state.

"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. 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." - Subhajit Sarkar of Cardiff University

Characterizing the atmospheres of exoplanets like K2-18b, including identifying their gases and physical conditions, presents a significant challenge as these planets are often overshadowed by the intense glare of their parent stars, making the study of their atmospheres particularly complex.

The research team ingeniously circumvented this challenge by analyzing the light from K2-18b's parent star as it passed through the exoplanet's atmosphere during transits. These transits, or passages of the exoplanet in front of its host star, were first detected in 2015 during NASA's K2 mission. This phenomenon allowed astronomers to observe minute changes in the star's brightness as it traversed the exoplanet's atmosphere, revealing vital information about its composition.

 "This result was only possible because of the extended wavelength range and unprecedented sensitivity of Webb, which enabled robust detection of spectral features with just two transits." - Nikku Madhusudhan, Lead Resercher & Astronomer at the University of Cambridge

The precision of a single Webb transit observation is equal that of eight Hubble observations conducted over several years and in a narrower wavelength range.

These findings represent only the initial steps in the research, with numerous additional observations of K2-18b planned.

"This means our work here is but an early demonstration of what Webb can observe in habitable-zone exoplanets." -  Savvas Constantinou, University of Cambridge

The team's K2-18b discovery and research have been accepted for publication in The Astrophysical Journal Letters, and they intend to conduct further research using the telescope's Mid-Infrared Instrument (MIRI) spectrograph, which promises to validate their discoveries and provide fresh insights into K2-18 b's environmental conditions.

"Our findings are a promising step towards a deeper understanding of Hycean worlds in this quest." - Nikku Madhusudhan, Lead Resercher & Astronomer at the University of Cambridge

As scientists continue to unravel the mysteries of distant exoplanets, the search for life beyond Earth, has taken a significant leap forward today!

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