New Exoplanet Climate ‘Decoder’ Will Advance the Search for Alien Life

After analyzing a dozen types of suns and numerous planet surfaces, Cornell astronomers have come up with a practical model, or a decoder, to unravel climate clues for potentially habitable exoplanets in distant galaxies.

“We looked at how different planetary surfaces in the habitable zones of distant solar systems could affect the climate on exoplanets,” said Jack Madden, Ph.D., who works in the lab of Lisa Kaltenegger, associate professor of astronomy and director of Cornell’s Carl Sagan Institute. “Reflected light on the surface of planets plays a significant role not only on the overall climate but also on the detectable spectra of Earth-like planets.”

Madden and Kaltenegger are co-authors of “How Surfaces Shape the Climate of Habitable Exoplanets,” paper, released on May 18th, 2020, in the Monthly Notices of the Royal Astronomical Society.

It’s the Same For Stars and Planets

In their study, the two scientists merge information of a planet‘s surface color and the light from its host star to measure the climate. For example, a rocky, black basalt planet consumes light well and would be incredibly hot, but with sand or clouds, the planet can cool down. Also, a planet with vegetation and orbiting a red K-star will probably have cool temperatures because of the way those surfaces reflect their suns’ light.

“Think about wearing a dark shirt on a hot summer day. You’re going to heat up more because the dark shirt is not reflecting light. It has a low albedo (it absorbs light), and it retains heat,” Madden explained. “If you wear a light color, such as white, its high albedo reflects the light – and your shirt keeps you cool.

Different kinds of suns are shown as they interact with various Earth-like surfaces in distant solar systems. The combinations create an array of climates. [Image: Jack Madden/Cornell]
The same goes for stars and planets, Kaltenegger said: “Depending on the kind of star and the exoplanet’s primary color – or the reflecting albedo – the planet’s color can mitigate some of the energy given off by the star. What makes up the surface of an exoplanet, how many clouds surround the planet, and the color of the sun can change an exoplanet’s climate significantly.”

Madded added that upcoming advanced instruments such as the Earth-bound Extremely Large Telescope would enable researchers to collect data in order to test a catalog of climate predictions.

“There’s an important interaction between the color of a surface and the light hitting it,” he said. “The effects we found based on a planet’s surface properties can help in the search for life.”

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