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The dark sides of hot Jupiters feature similar temperatures, astronomers find

By
Brooks Hays
Pictured is a schematic of clouds on the night side of a hot Jupiter exoplanet, where the underlying atmosphere is over 800 degrees Celsius -- hot enough to vaporize rocks. The rock vapor then travels to cooler conditions, where it condenses into clouds and possibly rains down. Photo by Dylan Keating/McGill University
Pictured is a schematic of clouds on the night side of a hot Jupiter exoplanet, where the underlying atmosphere is over 800 degrees Celsius -- hot enough to vaporize rocks. The rock vapor then travels to cooler conditions, where it condenses into clouds and possibly rains down. Photo by Dylan Keating/McGill University

Aug. 27 (UPI) -- The night sides, or dark sides, of hot Jupiters boast similar temperatures, according to a new survey of the extrasolar gas giants.

Hot Jupiters are Jupiter-sized gas giants living in close proximity to other stars. Unlike Jupiter, which migrated away from the sun, scientists estimate hot Jupiters moved closer to their host stars after formation, becoming hotter.

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Astronomers at the McGill Space Institute used the Spitzer Space and the Hubble Space telescopes to measure the night-side temperatures of 12 hot Jupiters. All 12 were roughly 800 degrees Celsius.

Scientists concluded the gas giants host clouds similarly composed of minerals and rocks.

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Hot Jupiters orbit their host stars so closely that they are gravitationally locked, like the moon and Earth, which means they rotate and orbit at the same speeds, ensuring the same sides always face toward and away from the star.

Because hot Jupiters orbit their host stars at such a close distance, the side cast permanently in sunlight is especially hot. Until now, scientists knew less about the temperature of the night sides of the gas giants.

Scientists had previously relied on models to predict the temperature on the dark sides of hot Jupiters. The latest research -- published this week in the journal Nature Astronomy -- suggests the models were flawed.

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"Atmospheric circulation models predicted that nightside temperatures should vary much more than they do," Dylan Keating, the study's first author and a doctoral student in physics at McGill, said in a news release. "This is really surprising because the planets we studied all receive different amounts of irradiation from their host stars and the day side temperatures among them varies by almost 1700 degrees Celsius."

The research suggests cloud formation among hot Jupiters is universal, with their clouds boasting some combination of manganese sulfide, silicates and other rocks.

Scientists hope to study exoplanet cloud formation in greater detail using the James Webb Space Telescope, scheduled to come online in 2021.

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"Observing hot Jupiters at both shorter and longer wavelengths will help us determine what types of clouds are on the night sides of these planets," Keating said.

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