A New Way Of Discovering Signs Of Alien Life On Distant Planets Has Been Discovered
Exoplanets with deep oceans and large amounts of hydrogen in the atmosphere could contain signs of life if such worlds exist. They are the best chance that the James Webb Space Telescope (JWST) has at detecting biosignatures.
The potential signs of life are methyl halides, a group of chemicals that are also produced by some bacteria and ocean algae on Earth. The hypothetical worlds on which these biosignatures may be found are called hycean planets.
Their name is a combination of “hydrogen” and ocean.” It was first coined in 2021 by Nikku Madhusudhan, a planetary scientist from the University of California, Riverside.
“Unlike an Earth-like planet, where atmospheric noise and telescope limitations make it difficult to detect biosignatures, hycean planets offer a much clearer signal,” said Eddie Schwieterman, an astrobiologist at the University of California, Riverside.
Hycean planets are expected to orbit red dwarf stars. The planet K2-18b is the best candidate for a hycean world.
It is categorized as a “sub-Neptune” world and orbits in the habitable zone of a red dwarf star. It is located 124 light-years away from Earth in the constellation of Leo.
In 2019, the Hubble Space Telescope discovered water vapor in K2-18b’s atmosphere. JWST has also detected the presence of carbon dioxide and methane in the atmosphere, as well as the absence of carbon monoxide and ammonia.
In addition, there was some possible evidence of a compound called dimethyl sulfide, which is only produced by ocean plankton on Earth. It exists in K2-18b’s atmosphere, too.
A team of researchers from the University of California, Riverside, and ETH Zurich in Switzerland proposed that another family of compounds called methyl halides could produce a chemical signature of biological life in a hycean planet’s atmosphere. It would be more easily detected than the signature of oxygen on a planet similar to Earth.
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“Oxygen is currently difficult or impossible to detect on an Earth-like planet,” said Michaela Leung, the first author of the study from the University of California, Riverside. “However, methyl halides on hycean worlds offer a unique opportunity for detection with existing technology.”
Methyl halides are molecules that consist of carbon atoms and three hydrogen atoms attached to a halogen atom, such as bromine, chlorine, or fluorine. Methyl halides are produced by life on Earth, but they are still relatively rare in our planet’s atmosphere.
It could be different on hycean worlds, though. If hycean worlds did indeed exist, the conditions on the planets would allow methyl halides to accumulate in the atmosphere. They would also have strong absorption features in infrared light, so the JWST would be able to observe them.
Hycean worlds were proposed as a way to explain some properties of warm sub-Neptune-type planets, so scientists don’t really know yet if they truly exist. If life does exist in such a world, it would have to breathe hydrogen instead of oxygen.
The details of the research were published in The Astrophysical Journal Letters.
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