With the news about the planet K2-18b, announced in April, researchers sparked excitement by detecting what could be a biosignature — a molecule linked to life — in the atmosphere of the planet located 124 light-years away. Using the James Webb Space Telescope, a team from university of Cambridge identified possible traces of dimethyl sulfide (DMS) – a compound on Earth produced only by living organisms. However, a new study by the scientists from University of Chicago challenges this interpretation, warning that the evidence remains inconclusive.

The UChicago team reanalyzed the data, including additional observations from Webb and Hubble, and found that the signal could be explained by other, more common molecules. “The data is too noisy to definitively claim detection of DMS,” said lead author Rafael Luque. “There simply isn’t enough certainty yet.”

Detecting molecules on distant exoplanets is incredibly difficult. Scientists rely on indirect methods, such as observing how starlight filters through a planet’s atmosphere. Different molecules block specific wavelengths of light, creating a unique fingerprint. However, as co-author Michael Zhang noted, many compounds share similar spectral features. Dimethyl sulfide contains a carbon bonded to three hydrogens, but so do countless other molecules, like ethane — a gas found on lifeless planets like Neptune.

The researchers emphasized the importance of ruling out ordinary explanations before invoking extraordinary ones. “We should only consider exotic molecules after eliminating more likely candidates,” said co-author Caroline Piaulet-Ghorayeb. In this case, ethane — a molecule common in planetary atmospheres — fits the data just as well as DMS.

Another issue is that the initial detection relied on a single observation. When combining multiple datasets, the evidence for DMS weakened significantly. The team stressed the need for further observations to confirm or refute the finding.

“Searching for life beyond Earth is one of science’s most profound questions,” said Luque. “But premature claims risk overshadowing the careful progress being made in this field.” The study, submitted to Astronomy and Astrophysics Letters, highlights the challenges of interpreting faint signals from distant worlds—and the importance of patience in the hunt for extraterrestrial life.

For more details read the full article by University of Chicago.