Astronomers develop the cosmic "cheat sheet"

Cornell's astronomers have drawn on the Earth's color palette since the early days of Earth to create a cosmic "reminder" for viewing distant worlds. By correlating hues and tints, researchers seek to understand where the discovered exoplanets can reasonably be located in their own evolutionary spectrum.

"In our quest to understand the exoplanets, we use the Rosetta Stone of the Early Earth and its biological milestones in history," said Jack O. Malley-James, research associate at the University of Toronto. Carl Sagan Institute, Cornell.

O 'Malley-James co-authored with Lisa Kaltenegger, Professor of Astronomy and Director of the Sagan Institute's "Expanding the Chronology of Photosynthetic Red Edge Biosynthesis of the Earth". The document was published on July 9 in the Astrophysical Journal.

"If an alien had used colors to see if our Earth had life, this alien would see very different colors throughout the history of our planet – going back billions of years – when different shapes of life dominated the surface of the Earth, "said Kaltenegger.

"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 ago on the history of the Earth to match similar periods on exoplanets, "she said.

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.

"Scientists can observe surface biosignatures beyond vegetation on earth-like exoplanets using our own planet as the key to what to look for," said O-Malley-James.

"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. "

O & # 39; Malley-James & Kaltenegger modeled terrestrial-type exoplanets with different surface organisms using chlorophyll. Scenarios may include places where a few organisms dominate the entire surface of a planet similar to Earth, such as the fictional and swampy world of Dagobah, Yoda's home in the "Star Wars" movies.

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 (the part of the spectrum that helps prevent planets from being burned by the sun) before the modern Earth's biota takes over.

O 'Malley-James and Kaltenegger stated that cyanobacteria – surface algae – could have been shed about 2 to 3 billion years ago, producing a photosynthetic red border and could be found on the planet's surface. 39, other exoplanets similar to the Earth.

This research shows that lichens, algae and cyanobacteria could have provided a detectable trait at the red edge of the surface for a younger Earth, long before the terrestrial vegetation spread 500 to 750 million years ago. years, said O-Malley-James.

"This article extends the use of a red-bordered photosynthetic surface bio-trait to earlier periods in the history of the Earth," he said, "as well as". to a wider range of livable extrasolar planet scenarios ".