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An artist’s rendering of a view of the Hycean world. Credit: Shang-Min Tsai/UCR
Recent report NASA’s James Webb Space Telescope’s discovery of signs of life on a distant planet has understandably caused excitement. The new study disputes this finding, but also outlines how telescopes verify the presence of life-forming gases.
Research at the University of California, Riverside; Astrophysics Journal Letterwhich may be a disappointment for extraterrestrial enthusiasts, does not rule out the possibility of a discovery in the near future.
In 2023, there were interesting reports of the presence of biosignature gases in the atmosphere of planet K2-18b. This gas appears to have several conditions that make life possible.
Many exoplanets, or planets orbiting other stars, cannot easily be compared to Earth. Its temperature, atmosphere, and climate make it difficult to imagine the existence of Earth-like life.
However, K2-18b is a little different. “The planet receives about the same amount of solar radiation as Earth. And, excluding atmospheric effects, K2-18b’s temperature is close to Earth’s, which is also an ideal situation for finding life.” said UCR project scientists. and paper author Shang-Min Tsai.
K2-18b’s atmosphere is primarily hydrogen, unlike its nitrogen-based atmosphere. However, there has been speculation that K2-18b has an ocean of water, similar to Earth. Therefore, K2-18b could be a “hycean” world, meaning a combination of a hydrogen atmosphere and a water ocean.
Last year, a Cambridge research team used JWST to reveal methane and carbon dioxide in K2-18b’s atmosphere, other elements that could show signs of life.
“In a further blow to the search for life, these researchers last year discovered preliminary detections of dimethyl sulfide (DMS), produced by terrestrial marine phytoplankton, in Earth’s atmosphere. ”, Tsai said. DMS is the main source of atmospheric sulfur on Earth and may be involved in cloud formation.
Telescope data was inconclusive, so the UCR researchers wanted to understand whether enough DMS could accumulate to detectable levels on K2-18b, which is about 120 light-years from Earth. . As with other distant planets, it is impossible to obtain physical samples of the chemicals in the atmosphere.
“The DMS signal from the Webb telescope was not very strong and only appeared in a certain way when we analyzed the data,” Tsai said. “I wanted to see if I could be certain of things like the hints about DMS.”
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,” Tsai said.
However, researchers 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, the Webb telescope will need to use instruments that can better detect infrared wavelengths in the atmosphere than those 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 are likely to be very different from those most abundantly found on Earth today. Planets with hydrogen-rich atmospheres may have less oxygen produced by plants and bacteria. Instead, we may be more likely to find DMS made by life on Earth,” said UCR astrobiologist Eddie Schwieterman, lead author of the study.
Given the complexity of searching for signs of life on distant planets, some question the researchers’ continued motivations.
“Why do we continue to search the universe for signs of life? Imagine you’re camping in a Joshua tree at night, and you hear something. Your instinct is , to shine a light to see what’s out there. That’s what we’re doing too, in a sense,” Tsai said.
For more information:
Biogenic sulfur gas as a biosignature of temperate sub-Neptune waters; Astrophysics Journal Letter (2024). DOI: 10.3847/2041-8213/ad3801