Planetary scientists at the University of California, Riverside, believe the gases produced by marine organisms and from plants similar to broccoli could also be reliable indicators of life on other worlds.
These gases are produced naturally through a process called methylation, which turns potential waste into gases that float into the atmosphere. A study in The Astrophysical Journal argues these gases are closely associated with life; they could indicate life if they were detected in the atmospheres of exoplanets.
“Methylation is so widespread on Earth, we expect life anywhere else to perform it,” said Michaela Leung, UCR planetary scientist, in a statement. “Most cells have mechanisms for expelling harmful substances.”
The study argues that methyl bromide should be considered a leading biosignature over other gases produced by methylation. The gas lingers in the atmosphere for shorter periods of time than other traditional biosignature gases. If it was found in the atmosphere of an exoplanet and likely made recently. Whatever produced it is still around.
Methyl bromide is also more likely to have been made by living organisms. Methylated gases produced naturally on Earth are usually found in marine and terrestrial life. The gas also absorbs light with a similar biosignature to methyl chloride, which makes them gases and their emitters easier to find.
“There are limited ways to create this gas through non-biological means, so it is more indicative of life if you find it,” Leung said.
Earth is abundant in natural sources of methyl bromide, but it is not easily detectable in our atmosphere because of intense ultraviolet radiation from the Sun. Ultraviolet radiation breaks apart water molecules in the atmosphere, which splits them into products that destroy the gas.
The study suggests the gas might be easily found in the atmospheres of exoplanets orbiting an M dwarf star. These stars are smaller and cooler than our Sun, produce less of the ultraviolet radiation that breaks water molecules apart, and are 10 times more common than stars like our own.
“An M dwarf host star increases the concentration and detectability of methyl bromide by four orders of magnitude compared to the Sun,” said Leung.
The James Webb Space Telescope is not designed to detect planetary atmospheres similar to Earth’s, but plans for large ground-based telescopes will be. The UCR research team is also investigating other methylated gases as potential biosignature candidates for extraterrestrial life.
“We believe methyl bromide is one of many gases commonly made by organisms on Earth that may provide compelling evidence of life from afar,” said Eddie Schwieterman, UCR astrobiologist and the study co-author, in a statement. “This one is just the tip of the iceberg.”