Last month, scientists reported the possible detection of dimethyl sulfide (CH₃-S-CH₃), or DMS, in the atmosphere of a planet outside our solar system—a finding that drew widespread media attention. On Earth, DMS is produced exclusively by biological processes, prompting the researchers to cautiously suggest the potential presence of life on the exoplanet K2-18b. The media, however, largely overlooked the caution, hailing it as evidence of life just 124 light-years away. However, several independent research teams that closely examined the data have concluded that the evidence falls far short of indicating signs of life.

To date, astronomers have identified around 5,000 exoplanets beyond our solar system. Most of these planets cannot be seen directly through telescopes; instead, they’re detected using indirect methods. One approach measures the gravitational pull a planet exerts on its host star, causing subtle shifts in the star’s motion. Another, more common method tracks tiny, periodic dips in a star’s brightness as a planet crosses in front of it—a transit. It was through this latter technique that, in 2015, astronomers discovered K2-18b, a planet roughly eight times the mass of Earth, orbiting the red dwarf star K2-18.

2 View gallery ( Illustration: NASA )

In 2022, the James Webb Space Telescope (JWST) began operations. Among its advanced tools are spectrometers, which can analyze the composition of light across different wavelengths. Because each molecule absorbs and emits light in a unique pattern—its “spectral signature”—scientists can infer the chemical makeup of a planet’s atmosphere by studying how starlight is altered as it passes through it. These are highly sensitive and challenging measurements, especially across such vast distances.

Previous studies had already identified carbon dioxide (CO₂) and methane (CH₄) in K2-18b’s atmosphere. A study published in April determined, with a relatively high degree of probability, that DMS and dimethyl disulfide (CH₃-S-S-CH₃) may also be present, though the researchers acknowledged the statistical confidence was below typical scientific standards. Lead researcher Nikku Madhusudhan of the University of Cambridge noted that the probability of the results being due to chance was approximately 0.3%.

Interpreting the data

As mentioned, everyone agrees with the original conclusion about possible signs of life on K2-18b. A research team led by Rafael Luque at the University of Chicago reanalyzed all available James Webb Space Telescope data for the planet and reported in a preprint that there is “insufficient evidence for the presence of DMS (dimethyl sulfide) and/or DMDS (dimethyl disulfide) in its atmosphere.” In another preprint on the subject, Jake Taylor from the University of Oxford examined the statistical strength of the original findings and similarly concluded that there is “no strong statistical evidence” to support the presence of DMS in K2-18b’s atmosphere.

A third group, led by Luis Welbanks of the University of Arizona—a former PhD student of Madhusudhan—took a different approach. They searched for molecules with infrared absorption patterns similar to that of dimethyl disulfide, which could potentially mislead researchers. In their manuscript, also shared as a preprint before peer review, they identified no fewer than 59 such compounds.

2 View gallery ( Illustration: AP )

The closest match to the spectral signal reported in the original study wasn’t dimethyl disulfide, but rather the gas propyne (CH₃C≡CH). Welbanks and his team did not claim that propyne is present in the atmosphere of K2-18b—only that the identification of DMS is inconclusive, as multiple molecules could produce similar spectral features. “Their claim just absolutely vanishes,” Welbanks said of his former advisor’s study.

Madhusudhan responded. In a reply paper, he and his team analyzed 650 compounds using a similar method. They found that three molecules produced comparable spectral signatures—one of them DMS, and the other two slightly more complex. But according to Welbanks, this only reinforces the argument that the evidence is too ambiguous to conclude DMS is present in K2-18b’s atmosphere. “They’re essentially refuting their own claim,” Welbanks concluded.

Vast distances

A clear scientific consensus on the atmospheric composition of K2-18b may still take time to emerge—though perhaps not too long. At the end of last year, researchers at NASA’s Jet Propulsion Laboratory (JPL) conducted new infrared observations of the exoplanet’s atmosphere. The data is still being processed, but according to team leader Renyu Hu “It will include substantially more data than previously published.”

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In the meantime, it’s worth remembering that K2-18b, while relatively “close” in cosmic terms, remains far beyond the reach of practical exploration. At 124 light-years away, even if life did exist there, any attempt at communication would require nearly 250 years for a round trip. A question sent today—assuming an immediate response—would not be answered until the time of our great-great-grandchildren.

Even if we could travel at speeds approaching that of light, the journey would still take 124 years from Earth’s perspective. Due to relativistic effects, astronauts aboard such a mission might experience only a few years in transit. But we are still light-years away—literally—from achieving light-speed travel. With current technology, a journey to K2-18b would take hundreds of thousands of years—longer than the entire history of modern humans.

Content distributed by the Davidson Institute of Science Education .