Some of the 137 single-cell organisms in the color catalog inhabit Earth's most extreme environments.
Image credit: NASA
The new catalog is the work of scientists from research centers in the US and Germany, including the Institute for Pale Blue Dots in the Department of Astronomy at Cornell University in Ithaca, NY, and the Max Planck Institute for Astronomy in Heidelberg.
An account of the new catalog, and how it came about, is reported in the Proceedings of the National Academy of Sciences.
The catalog contains the surface biosignatures - in terms of their unique pigmentation - of over 100 microorganisms, including ones isolated from Earth's most extreme environments.
When seen from outer space, the light that reflects from Earth gives away the fact there is life on the planet.
The new catalog is based on the idea that if life exists on other planets, its beginnings - as on Earth - are likely to be dominated by microbes, evolving from single-celled creatures to more complex organisms.
Catalog gives 'first glimpse' of what diverse exoplanets with life might look like
One of the team members, Lisa Kaltenegger, professor of astronomy and director of the Institute for Pale Blue Dots at Cornell University, says:
"This database gives us the first glimpse at what diverse worlds out there could look like. We looked at a broad set of life forms, including some from the most extreme parts of Earth."
Pale Blue Dots is a new institute that studies and models habitable rocky "exoplanets" - that is, planets not in our solar system.
While the Institute will be hosting the catalog of surface biosignatures, the researchers have also made it freely available to other teams in search of life on exoplanets. In their paper, they note:
"Here, we present the first database for a diverse range of life - including extremophiles (organisms living in extreme conditions) found in the most inhospitable environments on Earth - for such surface features in preparation for the next generation of telescopes that will search for a wide variety of life on exoplanets."
If you could magic yourself to the Andromeda Galaxy and take one of the new generation of telescopes with you, you would see that Earth shimmers with a unique blend of pigments as sunlight reflects off our planet's vegetation.
Conversely, astronomers on our planet can see pigmentation on exoplanets and analyze their makeup by looking at their color. Prof. Kaltenegger explains:
"On Earth these are just niche environments, but on other worlds, these life forms might just have the right [makeup] to dominate, and now we have a database to know how we could spot that."
Catalog contains data and spectral signatures of 137 single-cell life forms
The catalog contains information on the pigmentation of 137 single-cell life forms, ranging from the yellow-pigmented Amphidinium carterae found on the coasts of the Atlantic and Pacific oceans, to the orange-tinted Halorubrum chaoviator found at Baja California, Mexico, to the cream-colored Escherichia coli abundant in sand, soil, and sediments.
Each entry of the catalog also has a graph showing the spectral shape of the organism's biosignature across the wavelengths of light.
First author Siddharth Hegde, one of Prof. Kaltenegger's former doctoral students, says their paper shows the "amazing diversity of life that one can detect remotely on exoplanets," and notes:
"We explore for the first time the reflection 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."
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