In 2023, astronomers tentatively detected dimethyl sulfide, which is primarily produced by marine microorganisms on Earth and is considered a biosignature gas, in the atmosphere of super-Earth exoplanet K2-18b. reported.in paper Published in Astrophysics Journal LetterUC Riverside astronomer Xiangming Tsai and others dispute this finding, but also how NASA/ESA/CSA’s James Webb Space Telescope will test for the presence of dimethyl sulfide. Outlined.
K2-18 is a red dwarf star located approximately 111 light-years away in the constellation Leo.
Also known as EPIC 201912552, this star is home to two giant exoplanets, K2-18b and K2-18c.
First discovered in 2015, K2-18b has a radius 2.2 times that of Earth and about eight times the mass.
The planet orbits at a distance of approximately 0.15 astronomical units every 33 days and has an Earth similarity index of 0.73.
It receives 1.28 times more light intensity than Earth, and its equilibrium temperature is 28 degrees Fahrenheit (-2 degrees Celsius).
Discovered in 2017, K2-18c has about 7.5 times the mass of Earth and orbits its star every nine days, but it’s probably too hot to enter the habitable zone.
In 2023, astronomers report provisional detection dimethyl sulfide (DMS) In the atmosphere of K2-18b.
“K2-18b receives about the same amount of solar radiation as Earth,” Dr. Tsai said.
“And, excluding atmospheric influences, K2-18b’s temperature is close to Earth’s, which is also an ideal situation for finding life.”
“K2-18b’s atmosphere is primarily hydrogen, unlike our nitrogen-based atmosphere.”
“However, there has been speculation that K2-18b has an ocean of water, similar to Earth. So K2-18b potentially represents a Hycean world, meaning a combination of a hydrogen atmosphere and a water ocean.”
“In a further blow to the search for life, researchers last year reported preliminary detection of DMS, produced by terrestrial marine phytoplankton, in the planet’s atmosphere. .”
“DMS is the main source of sulfur in the air on Earth and may play a role in cloud formation.”
Telescope data were inconclusive, so Dr. Tsai and his coauthors wanted to understand whether enough DMS could accumulate to detectable levels on K2-18b.
“The DMS signal from the web was not very strong and only appeared in a certain way when we analyzed the data,” Dr. Tsai said.
“I wanted to see if I could be certain of things like the hints about DMS.”
This artist’s impression shows planets K2-18b and c and their host stars. Image credit: NASA / ESA / Hubble / M. Kohnmesser.
Based on the physics and chemistry of DMS and computer models that describe a hydrogen-based atmosphere, the researchers found that the data was unlikely to indicate the presence of DMS.
“The signal overlaps strongly with methane, suggesting that detecting DMS from methane is beyond the capabilities of this instrument,” Dr. Tsai said.
However, scientists believe that DMS can accumulate to detectable levels.
For that to happen, plankton or other life forms would have to produce 20 times the amount of DMS that exists on Earth.
Detecting life on exoplanets is a difficult task given their distance from Earth.
To find DMS, Webb will need to use equipment that can better detect infrared wavelengths in the atmosphere than the one he used last year.
Fortunately, the telescope is scheduled to use such instruments later this year to definitively reveal whether DMS is present on K2-18b.
“The best biosignatures on exoplanets may be very different from the most abundant biosignatures found on Earth today,” said Dr. Eddie Schwieterman, an astrobiologist at the University of California, Riverside. Stated.
“Planets with hydrogen-rich atmospheres may be more likely to find DMS produced by life, rather than oxygen produced by plants and bacteria as on Earth.”
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Tsai Xiangming other. 2024. Biogenic sulfur gases as biosignatures of temperate sub-Neptunian waterworlds. APJL 966, L24; doi: 10.3847/2041-8213/ad3801
