First observations of the dark side of the hot Jupiter

(ORDO NEWS) — For the first time, astronomers have been able to observe the night side of an exoplanet, permanently in shadow as the planet is tidally locked to its parent star.

These observations, together with observations of the day side of the planet, which is constantly illuminated by a star, make it possible for the first time to get an idea of ​​the entire atmosphere of the planet as a whole.

“Now we can not only take isolated images of specific regions of exoplanet atmospheres, but study them as the 3D systems they really are,” said study lead author Thomas Mikal-Evans of the Institute for Astrophysics and Research. space them. Kavli of the Massachusetts Institute of Technology.

This planet is called WASP-121b and is a massive gas giant, about twice the size of Jupiter. The planet belongs to the class of superhot Jupiters and was discovered in 2015 in orbit around a star located at a distance of about 850 light years from Earth.

Planet WASP-121b is in the closest orbit around a star known to date, making one revolution around the parent star in just 30 hours. It is also in a tidal lock with respect to the star, so that its day side is eternally illuminated by the rays of the star, and its night side is eternally turned towards space.

Astronomers have previously detected water vapor and studied changes in the temperature of the planet’s atmosphere with altitude on the day side of the planet.

The new study provides a more detailed picture. With the help of spectroscopic observations, the researchers were able to map the significant temperature changes during the transition from the day side of the planet to the night side and estimate the changes in these temperatures with altitude.

They also tracked the presence of water in the atmosphere to show for the first time how water circulates between the day and night sides of the planet.

While on Earth the water cycle involves first evaporating, then condensing into clouds and then falling to the surface in the form of rain, on the planet the water cycle is much more turbulent.

On the day side, the atoms that make up the water molecule dissociate at temperatures above 3000 Kelvin. These atoms are then moved by the winds to the night side, where lower temperatures promote the recombination of hydrogen and oxygen atoms into water molecules, which are then transported by the winds to the day side, where the cycle resumes.

The team calculated that the water cycle on the planet WASP-121b is supported by winds blowing at speeds up to 5 kilometers per second.

The authors also found that there is more than just water in the planet’s atmosphere – most likely, it is cold enough on the night side for iron and aluminum oxide to condense to form exotic clouds that are carried by winds to the day side of the planet, where these clouds turn into gas.

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