(Image credit: Amanda Smith, Nikku Madhusudhan)
Heisei worlds, which are a potential type of exoplanet with vast oceans and a thick shell of hydrogen, may provide the James Webb Space Telescope (JWST) with the best chance of detecting biosignatures, according to a new study.
Potential indicators of life are thought to be groups of chemical compounds known as methyl halides, which are produced by some bacteria and algae on Earth.
“Unlike Earth-like planets, where atmospheric interference and telescope limitations make it difficult to detect biosignatures, gycean planets provide a much clearer signal,” said Eddie Schwieterman, an astrobiologist at the University of California, Riverside.
For now, the existence of Gicey planets remains theoretical. Their name is a combination of the words “hydrogen” and “ocean,” first proposed in 2021 by planetary scientist Nikku Madhusudhan of the University of Cambridge.
Hycean planets are expected to orbit red dwarf stars, and the most likely candidate for a Hycean world is K2-18b. This exoplanet, classified as a “sub-Neptune” world, orbits in the habitable zone of a red dwarf star 124 light years from Earth in the constellation Leo.
The Hubble Space Telescope detected water vapor in K2-18b’s atmosphere in 2019, and JWST found carbon dioxide and methane in the planet’s atmosphere, but no carbon monoxide or ammonia — just as the Geeky Planet hypothesis predicted. There’s also preliminary evidence that a compound called dimethyl sulfide, which is only produced by ocean plankton on Earth, may be present in K2-18b’s atmosphere, though this remains a matter of debate.
Now, a team of scientists from the University of California, Riverside, and ETH Zurich have taken this a step further. They suggest that another family of compounds called methyl halides, which are produced by microbial ocean life on Earth, may create a biosignature — a chemical signature of biological life — in the atmosphere of a Hycian world that is easier to detect than the oxygen signature on an Earth-like planet.
“Currently, oxygen is difficult or impossible to detect on an Earth-like planet,” said Michaela Leung of the University of California, Riverside, first author of a new paper describing the research. “However, methyl halides on hycyanic worlds provide a unique opportunity for detection using existing technology.”
Methyl halides are molecules containing carbon atoms and three hydrogen atoms bonded to a halogen atom such as bromine, chlorine, or fluorine. (Halogens are a group of reactive non-metallic elements.) On Earth, methyl halides are produced by living organisms, but their amounts in our planet's atmosphere are far from significant.
However, the situation may be different on Gisei worlds. Ljung's team suggests that conditions on such worlds, if they exist, would allow methyl halides to accumulate in significant quantities in the atmosphere. In addition, methyl halides would have strong infrared absorption characteristics at the same wavelengths that JWST is designed to detect.
“One of the major advantages of searching for methyl halides is that they can potentially be detected in as little as 13 hours with James Webb. That’s about the same or less time than it takes the telescope to detect gases like oxygen or methane,” Leung said. “Less telescope time means less cost.”
There are two caveats to Ljung's team's proposal. First, we don't yet know whether Gytzean worlds actually exist. They have been proposed as a way to explain certain
Sourse: www.livescience.com
