WASP -121b, which is about 900 light-years from Earth, is an egg-shaped exoplanet. Temperatures on its dayside can reach up to 2,538 degrees Celsius. It is so hot that heavy metals, such as iron and magnesium, exist as gases and are constantly flowing out of the atmosphere and into space.
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In a new study, published in the journal Nature Astronomy on February 21, astronomers shared their first look at the planet's dark side using NASA's Hubble Space Telescope
Telescopes at the South African Astronomical Observatory discovered WASP-121b in 2015. The planet, which is slightly larger and heavier than Jupiter, is on the verge of being torn apart by the gravitational forces of its host star, known as WASP 121.It makes a complete orbit of that star once every 1.3 days, and one side of it is constantly bathed in starlight, while the other forever stares out into space.
"This is one of the most extreme systems we've seen," says Ben Montet, an astrophysicist at the University of New South Wales who was not involved with the study. He notes that the extremely hot dayside is hotter than some stars.
NASA's Hubble played a key role in learning more about WASP-121b's atmosphere, first revealing in 2017 that it contains water vapor and suggesting that the planet has a stratosphere. The new study turns once again to Hubble and reveals, in detail, the planet's atmosphere and how the change in temperature from day to night affects the elements flying around Jupiter's hot upper layers.
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Hubble trained its cosmic eye on WASP-121b for two full orbits of its star, once in 2018 and a second time a year later. Hubble's "eye" collects light data, which scientists can break down into wavelengths that correspond to specific elements and molecules. The team looked for water vapor on the night side of WASP-121b and used it to determine how "cold" the dark side is getting.
The night side drops to 1,204 degrees Celsius . Not too cold compared to Earth, but extremely cold compared to the day side of WASP-121b. They were also able to calculate wind speeds on the planet that exceeded 11,000 miles per hour.
With this information, the team then modeled what other types of chemicals and molecules might be present in the exoplanet's atmosphere. They found that the night side likely contains exotic clouds of iron and titanium, as well as corundum, the same mineral found in ruby and sapphire gemstones on Earth. The clouds are transported from the night side to the day side and find themselves in an extremely hostile environment where they condense and fall, like rain.
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"All these exotic compounds are raining down from the planet's atmosphere," Montet said. Essentially, if you could survive on WASP-121b, you could see the liquid version of rubies and sapphires falling from the sky.
NASA's recently launched James Webb Space Telescope is also expected to observe WASP-121b later this year, for a more detailed analysis of its conditions.
