The scientific community and UFO enthusiasts are excited following a recent announcement by researchers using NASA’s James Webb Space Telescope (JWST) about their study of an exoplanet named K2-18 b. They reported detecting high levels of a chemical known as dimethyl sulfide or a closely related compound in the planet’s atmosphere, suggesting the possibility of extraterrestrial life. Though dimethyl sulfide may not be a household name, it is quite prevalent on Earth. But what exactly is this compound, and could it really indicate life elsewhere in the universe?

Understanding Dimethyl Sulfide

Dimethyl sulfide is a chemical compound consisting of one sulfur atom linked to two methyl groups, each made up of a carbon atom and three hydrogen atoms. This seemingly simple molecule has a significant impact due to its potent odor, often compared to the smell of garlic or rotten eggs. “Sulfur compounds typically have a very strong smell,” explains Eleanor Browne, a chemist at the University of Colorado Boulder.

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On Earth, dimethyl sulfide is constantly produced by microscopic plankton in the oceans. It enters the atmosphere, where it represents about one in every billion molecules. Once airborne, it only survives for a few hours or at most a day, being broken down by sunlight and other atmospheric chemicals.

This breakdown process is crucial, Browne notes, because it leads to the formation of aerosols that act as cloud condensation nuclei. Thus, understanding dimethyl sulfide is vital for climate modeling and other aspects of atmospheric science.

Journey from Earth to K2-18 b

Microorganisms are responsible for all detectable amounts of dimethyl sulfide in Earth’s atmosphere, and its rapid degradation makes it a potential biosignature—a marker of life detectable from afar. “It’s considered a very clear biosignature on Earth,” states Nora Hänni, a chemist at the University of Bern in Switzerland.

The JWST’s capabilities allow it to detect atmospheric chemicals on distant planets, an ability that led researchers to study K2-18 b, an exoplanet discovered in 2015 orbiting a cool, small star about 124 light-years away. The planet, which is sized between Earth and Neptune, is unlike any other we have observed closely.

In 2023, a team led by Nikku Madhusudhan from the University of Cambridge reported initial signs of dimethyl sulfide in the atmosphere of K2-18 b. Subsequent observations confirmed the presence of this compound or a related one, dimethyl disulfide, at levels much higher than those found on Earth. These findings were published on April 17 in the Astrophysical Journal Letters.

“The concentrations found are thousands of times higher than those on Earth,” Madhusudhan explained in a YouTube presentation on April 17.

Rethinking the Role of Biosignatures

Based on the new JWST data and K2-18 b’s potential for harboring liquid water, Madhusudhan suggested that the planet might be covered in oceans bustling with life. However, recent studies by Browne and Hänni suggest caution. They managed to produce dimethyl sulfide and similar compounds in lab simulations of Earth’s early atmosphere without any biological activity and even detected the molecule on a comet explored by the European Space Agency’s Rosetta mission.

Both researchers warn that not enough is known about K2-18 b to conclude whether its dimethyl sulfide comes from biological sources or mere chemical coincidences. Moreover, they note that the compound may not dissipate as quickly on K2-18 b, which has a carbon dioxide-dominated atmosphere, unlike Earth’s nitrogen-rich one.

“The diversity in chemistry and planetary processes means there are many ways to produce such compounds without biological activity,” Browne adds.

If life were responsible for the dimethyl sulfide on K2-18 b, other related chemical signatures should also be detectable, points out Chris Lintott, an astronomer at the University of Oxford. “If it’s a product of biology, it should be part of a wider chemical network. Yet, we don’t see that happening based on the spectra,” he explains.

Lintott emphasizes that context is crucial in determining what constitutes a biosignature. “What signifies biological activity on Earth may not necessarily apply elsewhere in the universe,” he concludes.