The idea that life exists on the planets of other stars was once only fanciful science fiction. It’s just been 30-years since astronomers have even known for sure that other stars besides the sun have planets. We now know that there are probably hundreds of billions of these exoplanets in our galaxy. The possibility that some host life is very real.
In 2025, a team of American and British astronomers reported that they had found possible evidence of life on an exoplanet one hundred and 24 light years from Earth, called K2-18b.
Finding evidence of life on an exoplanet is hard. Because they are so far away, most can’t be directly imaged by a telescope. Instead, astronomers hope to find out whether exoplanets have life by searching for telltale chemical traces in the composition of their atmospheres.
When an exoplanet passes in front of its star, some of its light passes through the planet’s atmosphere on the way to Earth. Gases in the atmosphere absorb a characteristic pattern of light wavelengths indicating its chemical composition. Measuring this spectral pattern in the light is difficult, challenging the limits of our technology.
The researchers made their measurement for K2 18b using the James Webb Space Telescope. They found spectral evidence that the planet’s atmosphere contained two chemicals that, on Earth, are made only by marine algae. Based on other evidence, they also think the planet could have an ocean of liquid water. Both claims are exciting but controversial. Much further research will be needed to know for sure whether the planet actually hosts life.
A special thanks to Dr. Caty Pilachowski, Professor and Kirkwood Chair in Astronomy, Department of Astronomy, Indiana University for reviewing today's episode!
Further Reading
- Possible hints of life found on exoplanet K2-18b
- A possible sign of life on K2-18b? Here’s… | The Planetary Society
- Did we actually find signs of alien life on K2-18b? 'We should expect some false alarms and this may be one' | Space
- Scientists found a potential sign of life on a distant planet – an astronomer explains why many are still skeptical
- K2-18b: Scientists using Webb telescope detect signature of life on an exoplanet, study suggests | CNN
N. Madhusudhan et al. 2025, New constraints on DMS and DMDS in the atmosphere of K2-18b from JWST MIRI. The Astrophysical Journal letters, 983:L40 DOI: 10.3847/2041-8213/adc1c8