“Identifying Early-to-Modern Earth-Like Exoplanets”

Earth from the ISS

 

“Our Earth and the air we breathe have changed drastically since Earth formed 4.5 billions years ago,” said Lisa Kaltenegger, associate professor of astronomy and director of the Carl Sagan Institute about a new study that created five models representing key points from our planet’s evolution, like chemical snapshots through Earth’s own geologic epochs that will allow astronomers identify young to modern Earth-like planets in transit, using our own Earth’s history as a template.

“Using our own Earth as the key, we modeled five distinct Earth epochs to provide a template for how we can characterize a potential exo-Earth – from a young, prebiotic Earth to our modern world,” she said. “The models also allow us to explore at what point in Earth’s evolution a distant observer could identify life on the universe’s ‘pale blue dots’ and other worlds like them.”

New generation of space- and ground-based telescopes coupled with our models will allow us to identify planets like our Earth out to about 50 to 100 light-years away, said Kaltenegger.

Kaltenegger and her team created atmospheric models that match the Earth of 3.9 billion years ago, a prebiotic Earth, when carbon dioxide densely cloaked the young planet. A second throwback model chemically depicts a planet free of oxygen, an anoxic Earth, going back 3.5 billion years. Three other models reveal the rise of oxygen in the atmosphere from a 0.2% concentration to modern-day levels of 21%.

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In Earth’s history, the timeline of the rise of oxygen and its abundance is not clear, Kaltenegger said. But, if astronomers can find exoplanets with nearly 1% of Earth’s current oxygen levels, those scientists will begin to find emerging biology, ozone and methane – and can match it to ages of the Earth templates.

“Our transmission spectra show atmospheric features, which would show a remote observer that Earth had a biosphere as early as about 2 billion years ago,” Kaltenegger said.

Using forthcoming telescopes like NASA’s James Webb Space Telescope, scheduled to launch in March 2021, or the Extremely Large Telescope in Antofagasta, Chile, scheduled for first light in 2025, astronomers could watch as an exoplanet transits in front of its host star, revealing the planet’s atmosphere.

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“Once the exoplanet transits and blocks out part of its host star, we can decipher its atmospheric spectral signatures,” Kaltenegger said. “Using Earth’s geologic history as a key, we can more easily spot the chemical signs of life on the distant exoplanets.”

Kaltenegger, doctoral student Jack Madden and Zifan Lin authored the study,”High-Resolution Transmission Spectra of Earth through Geological Time,” published in Astrophysical Journal Letters.

The Daily Galaxy, Sam Cabot, via Cornell University/Carl Sagan Institute