In 2023, astronomers reported a tentative detection of dimethyl sulfide — which is predominately produced by marine microbes on Earth and regarded as a biosignature gas — in the atmosphere of the super-Earth exoplanet K2-18b. In a paper published in the Astrophysical Journal Letters, University of California, Riverside astronomer Shang-Min Tsai and colleagues challenge this finding, but also outline how the NASA/ESA/CSA James Webb Space Telescope might verify the presence of dimethyl sulfide.
K2-18 is a red dwarf located approximately 111 light-years away in the constellation of Leo.
Also known as EPIC 201912552, the star hosts two massive exoplanets: K2-18b and K2-18c.
First discovered in 2015, K2-18b has a radius of 2.2 times that of Earth and is about 8 times as massive.
The planet orbits its star every 33 days at a distance of approximately 0.15 AU and has an Earth Similarity Index of 0.73.
It receives 1.28 times the light intensity of Earth, and its equilibrium temperature is 28 degrees Fahrenheit (minus 2 degrees Celsius).
K2-18c, discovered in 2017, has a mass about 7.5 times that of Earth, orbits the host star one every 9 days, and is probably too hot to be in the habitable zone.
In 2023, astronomers reported a tentative detection of dimethyl sulfide (DMS) in the atmosphere of K2-18b.
“K2-18b gets almost the same amount of solar radiation as Earth,” Dr. Tsai said.
“And if atmosphere is removed as a factor, K2-18b has a temperature close to Earth’s, which is also an ideal situation in which to find life.”
“K2-18b’s atmosphere is mainly hydrogen, unlike our nitrogen-based atmosphere.”
“But there was speculation that K2-18b has water oceans, like Earth. That makes K2-18b a potentially Hycean world, which means a combination of a hydrogen atmosphere and water oceans.”
“What was icing on the cake, in terms of the search for life, is that last year researchers reported a tentative detection of DMS in the atmosphere of that planet,…
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