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Scientists have uncovered further indications of potential biosignature gases on the nearby exoplanet K2-18b, bolstering the argument that it could potentially support extraterrestrial life. This discovery, utilizing the James Webb Space Telescope (JWST), focuses on the presence of molecules like dimethyl sulfide (DMS), further fueling interest in the habitability of this distant world.
Background of Initial Findings
In 2023, researchers employing NASA’s James Webb Space Telescope (JWST) initially reported the possible existence of dimethyl sulfide (DMS) on K2-18b. This exoplanet, approximately nine times the mass of Earth, orbits within the “habitable zone” of a star located roughly 120 light-years from our solar system.
On Earth, DMS is predominantly generated by living organisms — particularly phytoplankton and other marine microbes. Consequently, the 2023 study sparked considerable enthusiasm. However, this excitement was tempered by the preliminary aspect of the discovery. JWST’s observations were consistent with DMS presence but didn’t definitively confirm it. As a result, the research team conducted further investigation, employing a slightly modified approach.
New Study and Methodology
JWST can analyze exoplanet atmospheres during a “transit” event, which occurs when these planets pass in front of their host stars from the telescope’s viewpoint. By observing the wavelengths of starlight absorbed, the telescope can identify specific molecules present in the atmosphere.
The original, tentative DMS detection utilized JWST’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph) instruments. For this latest study, the scientists used the telescope’s Mid-Infrared Instrument (MIRI), a $10 billion instrument designed to examine different wavelengths of light.
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Confirmation with MIRI
The MIRI instrument also detected the spectral signature of DMS (and/or dimethyl disulfide, or DMDS, a chemically related compound and another potential biosignature), as reported by the researchers in their new study published in The Astrophysical Journal Letters.
“This represents an independent line of evidence, employing a different instrument and a distinct light wavelength range, with no overlap with prior observations,” stated Nikku Madhusudhan, a professor at Cambridge University’s Institute of Astronomy, who spearheaded both K2-18b studies. “The signal obtained was both robust and unambiguous.”
Hycean World Hypothesis
Based on its dimensions and other characteristics, astronomers suggest K2-18b might be a “Hycean” world. This proposed class of exoplanet, introduced in 2021, is characterized by a vast liquid-water ocean and an atmosphere rich in hydrogen. “Hycean” is a combination of “hydrogen” and “ocean.”
High DMS Levels on K2-18b
According to the new research, K2-18b’s atmosphere is abundant in DMS and/or DMDS. Researchers estimate concentrations exceeding 10 parts per million by volume, significantly higher than the less than one part per billion found on Earth.
“Previous theoretical studies predicted the possibility of high concentrations of sulfur-based gases like DMS and DMDS on Hycean worlds,” Madhusudhan explained. “Our current observations align with these predictions. Considering our collective knowledge of this planet, the scenario that best fits the available data is that of a Hycean world with an ocean teeming with life.”
Skepticism and Further Research
Madhusudhan and his team emphasize that they have not definitively detected alien life. They maintain that further research is necessary to validate and expand upon their current findings. Other scientists concur, with some expressing increased skepticism regarding K2-18b and its potential to harbor life.
Ongoing Debate
Astronomer Chris Lintott, for instance, challenged Madhusudhan’s description of the DMS/DMDS signal as “strong and clear.”
Lintott, an astrophysics professor at the University of Oxford, commented on social media, “Conversely, the peer-reviewed publication states that ‘While [the presence of molecules] DMDS and DMS best explains the current observations, their combined significance… is at the lower end of robustness required for scientific evidence.'”
Identifying signals of extraterrestrial life is inherently complex, and substantiating these signals is even more challenging, particularly on a planet like K2-18b. Close-range investigation remains unattainable for the foreseeable future, if ever. Consequently, it is expected that both the scientific debate and data collection efforts will persist.