Life may exist on “purple exoplanets”, researchers say

A team of researchers from Cornell University suggests that purple bacteria may serve as alternative biosignals indicating the presence of life on exoplanets. The study was published in the journal Monthly Notices of the Royal Astronomical Society.

Traditionally, the search for life beyond Earth has focused on “red-colored” vegetation, a distinctive spectral characteristic caused by the chlorophyll content of plants. However, a new study expands this search by examining the spectra of purple bacteria.

Researchers have discovered that purple bacteria exhibit a wide range of colors, including yellow, orange, brown and red, thanks to their diverse pigments. Using the measured spectra, they simulated the reflectance of Earth-like exoplanets dominated by purple bacteria.

“Purple bacteria can thrive in a wide range of conditions, making them a leading candidate for life that could dominate a wide variety of worlds,” explained study lead author Ligia Fonseca of the Carl Sagan Institute’s Coelho Institute.

Models have shown that evidence of surface biopigmentation by purple bacteria can be observed on a wide variety of terrestrial planets, including frozen planets, ocean worlds, and Earth analogues.

The study also suggests that purple bacteria could potentially thrive on exoplanets orbiting red dwarf stars, also known as M stars. This discovery further expands the search for life beyond Earth.

“We need to build a database of signs of life to make sure our telescopes don’t miss life if it doesn’t look exactly like what we encounter every day,” said study co-author Lisa Kaltenegger.

This study highlights the importance of expanding our understanding of the diversity of life on Earth and its potential manifestations on other worlds, the researchers say. By going beyond traditional “green” biosignals, we are increasing our chances of discovering life on exoplanets.