Astronomy
The Search for Biosignatures in Exoplanet Atmospheres
Quick fact
The James Webb Space Telescope detected carbon dioxide and methane in the atmosphere of a distant planet, a first step toward finding biosignatures.
Why this is interesting
Imagine looking at a tiny dot of light and knowing it might be a world with life. How can we tell if a planet like Earth is out there, even from hundreds of light-years away?
Read the full explanation
Understanding The Search for Biosignatures in Exoplanet Atmospheres
When a planet passes in front of its star (a transit), a thin ring of its atmosphere is backlit by the star. As starlight filters through this atmosphere, certain wavelengths are absorbed by its molecules, creating a 'fingerprint' in the starlight. By splitting this light into a spectrum, astronomers can identify which gases are present. If they find a mixture like Earth's—oxygen and methane together, which are out of balance unless life produces them—it suggests the presence of life.
A deeper explanation
The search hinges on the concept of biosignatures: gases that, when found in a planet's atmosphere, are strong indicators of biological activity. For example, oxygen is highly reactive and would quickly combine with other molecules, so a large amount of it must be continuously produced—likely by photosynthesis. Similarly, methane, which is short-lived in oxidizing atmospheres, can indicate a biological source such as microbes. Finding both simultaneously is especially promising because these gases would destroy each other without a constant source. Telescopes like JWST use spectroscopy to detect these gases, and planned observatories will be even better at probing rocky exoplanets in the habitable zone, bringing us closer to answering whether we are alone.