Alien planets may be home to purple life

A recent study suggests that the “light fingerprint” of life on other planets might be purple rather than green.

Some microbes on Earth are purple, but in our oxygen-rich environment, green life prevails in most ecosystems. Researchers from Cornell University say that life elsewhere may likely make energy with different types of light from the sun, and use compounds with purple pigments rather than green.

About 2.4 billion years ago, cyanobacteria, the first-known photosynthesizing species, began harnessing sunlight using chlorophyll. Before this, microorganisms relied on a purple-pigment molecule called retinal for energy production. This molecule, if present on other planets, could leave a unique signature detectable by advanced telescopes.

Scientists selected over 20 purple-coloured bacteria from different ecosystems, measuring their vibrant pigments and how they give off light. Then, they simulated the “light signatures” — the unique colour and chemical fingerprints that would be visible in an alien planet’s reflected light — and found these purple bacteria would generate vivid, identifiable signatures.

Space observatories could look for these signs of purple life when observing exoplanets — distant planets beyond the sun. Upcoming powerful telescopes, such as the Extremely Large Telescope and the Habitable Worlds Observatory, will look into the atmospheres of such far-off worlds to determine their composition and habitability.