In fact, scientists hypothesize that early Earth might have been purple. In a 2018 study, researchers concluded that purple archaea, another type of microorganism that uses a molecule called retinal to photosynthesize, could have dominated our planet before it was filled with oxygen. “What this new study does is expand potential lifeforms that might provide a purple signature,” says Shiladitya DasSarma, a molecular biologist at the University of Maryland and lead author of the 2018 paper.
Now, the scientists behind the most recent paper have added spectral data on 20 species of purple bacteria, collected from places like marshes and lakes. The researchers measured the wavelengths of light the bacteria reflected and modeled how those patterns could look when seen on a faraway planet.
The result is a collection of light signatures that the team is adding to an ongoing database. These data are publicly available, says Kaltenegger, where scientists can use these signatures to inform their own projects.
Signatures of habitable worlds
Astronomers look for life on other planets using markers called biosignatures. The color of a planet’s surface can be one such biosignature. To see it, astronomers use a technique called reflected light spectroscopy.
But “this type of observation cannot be done with the types of telescopes that we have available today,” says Edward Schwieterman, an astronomer at University of California Riverside who was not involved with the study. For instance, the James Webb Space Telescope can only detect biosignatures in an exoplanet’s atmosphere, like whether it has oxygen, methane, or other gases. It’s unable to measure the reflected light from the planet’s surface.
Dr. Thomas Hughes is a UK-based scientist and science communicator who makes complex topics accessible to readers. His articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
