For the first time ever, scientists have created a detailed catalogue of color swatches that correspond to nearly 140 known microorganisms, including those that can live in the most extreme environments. Armed with this knowledge, astrobiologists can now scan the atmospheres of distant exoplanets in hopes of finding a match.

"This database gives us the first glimpse at what diverse worlds out there could look like," noted astronomer and study co-author Lisa Kaltenegger in the Cornell Chronicle. "We looked at a broad set of life forms, including some from the most extreme parts of Earth."


Indeed, as witnessed on our planet, the history of life involves microbes. Lots of microbes — enough to influence the reflective signature of our planet when seen from a distance. The Cornell astronomers conjecture that a similar thing must happen on other habitable planets, and that life evolves through single-celled stages prior to multicellular creatures. Their database, which is freely available here, is the first to catalogue the spectral biosignatures that would be generated by such life.

In each panel, the top is a regular photograph of the sample and the bottom is a micrograph, a version of the top image zoomed-in 400 times. (Caption and photo credit: Cornell Chronicle/Hegde et al./Max Planck Institute).

Using the next generation of telescopes, astronomers and astrobiologists will be able to measure the light shimmering off the surface of a planet. They should be able to see pigmentation on an exoplanet and determine its chemical makeup by looking at the color.


Related: Why scientists should look for purple planets


In total, the astronomers collected and catalogued the cultures of 137 cellular life forms in the 0.35- to 2.5-μm spectral range. The samples ranged from from Bacillus gathered at the Sonoran Desert to Halorubrum chaoviator found at Baja California, Mexico, to Oocystis minuta, which was collected in an oyster pond at Martha's Vineyard.

"Our results show the amazing diversity of life that one can detect remotely on exoplanets," added study co-author Siddharth Hegde. "We explore for the first time the spectral signatures of a diversity of pigmented microorganisms isolated from various environments on Earth — including extreme ones — which will provide a more broad guide, based on Earth life, for the search for surface features of extraterrestrial life."


This is great, but what would make the catalogue even more complete would be to include the biosignatures generated by intelligent life, such as unnaturally elevated levels of carbon dioxide and other tell-tale signatures.


Read the entire study at PNAS: "Surface biosignatures of exo-Earths: Remote detection of extraterrestrial life."

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