Did the James Webb Space Telescope (JWST) pick up on "alien emissions" on an Earth-like exoplanet's atmosphere last year, or were they merely methane clouds? A recent study argues for the latter, potentially dimming hopes of confirming life beyond our solar system.
The disputable exoplanet, dubbed K2-18b, is a temperate, aqueous celestial body with a hydrogen-rich atmosphere. Situated roughly 120 light-years away from Earth, it orbits within the habitable zone of its parent star, where liquid water — and thus, potentially life — could exist.
K2-18b made waves in the news last year following observations with JWST's Near Infrared Spectrograph (NIRSpec) instrument, which hinted at the presence of a biologically generated gas called dimethyl sulfide (DMS) in its atmosphere. On Earth, this compound is exclusively produced by microscopic marine organisms like phytoplankton, sparking speculation that K2-18b's oceans might teem with life.
However, the detection came with uncertainties, primarily stemming from the faintness of the chemical signals at such vast distances from Earth.
Shang-Min Tsai, the lead author of the study and a project scientist at the University of California, Riverside, remarked, "The DMS signal from the Webb telescope was not very strong and only showed up in certain ways when analyzing the data. We wanted to know if we could be sure."
The latest research, published in The Astrophysical Journal Letters on Thursday (May 2), further casts doubt on this intriguing discovery. Taking into account that organically produced DMS swiftly dissipates in Earth's atmosphere before accumulating in significant quantities, the researchers conducted computer simulations to assess whether DMS could ever reach detectable levels in the atmosphere of a hydrogen-rich exoplanet.
The team concluded that DMS could indeed reach detectable levels — provided that the hypothetical creatures in K2-18b's oceans emit DMS at rates 20 times higher than plankton do on Earth.
While this finding doesn't necessarily rule out the possibility of life on the potentially habitable waterworld, Tsai noted, "Everything else we know about it makes the planet an ideal situation in which to find life."
However, the team's analysis also indicated that JWST would likely struggle to distinguish a DMS signal from other, more prevalent atmospheric gases at the specific wavelengths examined with NIRSpec.
"The signal strongly overlaps with methane, and we think that picking out DMS from methane is beyond this instrument's capability," Tsai explained.
In essence, while there could indeed be biological compounds in K2-18b's atmosphere and abundant life in its oceans, JWST likely hasn't detected them.
Fortunately, JWST is equipped with another instrument — the Mid-Infrared Instrument (MIRI) — which can detect a wider range of wavelengths and might be better suited for differentiating DMS from methane, the study authors pointed out. Follow-up observations of K2-18b using MIRI are already slated for this year, with scientific findings anticipated before the year's end. If life does exist on K2-18b — whether emitting gases or not — we may soon gain clearer insights.
