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Astronomers develop the cosmic "cheat sheet" in the hunt for life

ITHACA, NY – Cornell University astronomers have created a cosmic "cheat sheet" from Earth's early Earth color palette to understand where exoplanets discovered can fall into their own spectrum. scalable.

Jack O-Malley-James, Research Associate at the Carl Sagan Institute, and Lisa Kaltenegger, Professor of Astronomy and Director of the Carl Sagan Institute, co-author of "Extending the Timeline of the red edge biosignature of photosynthesis of the Earth ", published in The letters of the astrophysical journal.

"In our quest to understand the exoplanets, we are using the beginnings of the Earth and its biological milestones in history as a Rosetta stone," said O-Malley-James. "Scientists can observe surface biosignatures beyond vegetation on Earth-like exoplanets using our own planet as the key to what to look for."

For half a billion years – about 10% of the life of our planet – chlorophyll, present in many known plant forms, such as leaves and lichen, is the key element of the biosignature of the Earth. But other flora, such as cyanobacteria and algae, are much older than terrestrial vegetation, but their chlorophyll-containing structures leave their own indicia on the surface of the planet.

"Astronomers have been focused on vegetation previously, but with a better color palette, researchers can now look beyond half a billion years and up to 2. , 5 billion years back on the history of the Earth, to match similar periods on exoplanets, "said Kaltenegger. "If an alien had used colors to observe if our Earth had life, it would see very different colors throughout the history of our planet – going back billions of years – when different forms of life dominated the surface of the Earth. "

O & # 39; Malley-James & Kaltenegger modeled terrestrial-type exoplanets with different surface organisms using chlorophyll.

Lichens (a symbiotic fungal and photosynthetic partnership) may have colonized the land masses of the Earth about 1.2 billion years ago and would have painted the Earth in mint green sage. This cover would have generated a "non-vegetative" photosynthetic red edge signature. A red signature is the part of the spectrum that helps planets stay burned by the sun.

"When we discover an exoplanet, this research gives us a much wider range of hindsight over time," Kaltenegger said. "We are extending the search time of surface biota from 500 million years (widespread terrestrial vegetation) to about 1 billion years with lichen and up to 2 or 3 billion years ago. years with cyanobacteria. "


Funding for this research was provided by the Simons Foundation.

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