Whether or not we’re alone in the universe is one of the biggest questions in science.

A recent study, led by astrophysicist Nikku Madhusudhan at the University of Cambridge, suggests the answer might be no. Based on observations from NASA’s James Webb Space Telescope, the study points to alien life on K2-18b, a distant exoplanet 124 light years from Earth.

The researchers found strong evidence of a chemical called dimethyl sulfide (DMS) in the planet’s atmosphere. On Earth, DMS is produced only by living organisms, so it appears to be a compelling sign of life, or “biosignature”.

While the new findings have made headlines, a look at the history of astrobiology shows similar discoveries have been inconclusive in the past. The issue is partly theoretical: scientists and philosophers still have no agreed-upon definition of exactly what life is.

Unlike the older Hubble telescope, which orbited Earth, NASA’s James Webb Space Telescope is placed in orbit around the Sun. This gives it a better view of objects in deep space.

When distant exoplanets pass in front of their host star, astronomers can deduce what chemicals are in their atmospheres from the tell-tale wavelengths they leave in the detected light. Since the precision of these readings can vary, scientists estimate a margin of error for their results, to rule out random chance. The recent study of K2-18b found only a 0.3% probability that the readings were a fluke, leaving researchers confident in their........

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