Sapphires and rubies rain on this planet WASP-121b

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It is a new illustration of the fascinating diversity of worlds that populate the universe. Using the Hubble Space Telescope, an international team of researchers headed by the prestigious Massachusetts Institute of Technology (MIT) has obtained the most precise image of the night side of an exoplanet called WASP-121b. Located about 850 light years from Earth, in the constellation of the Pupus (visible from the southern hemisphere), this extrasolar planet is well known to astronomers because its atmosphere contains water.

Discovered in 2015, this gas giant, with a mass comparable to Jupiter’s twice as large, is what scientists call a hot Jupiter. Indeed, the temperature there is particularly high because the planet orbits very close to its parent star, of which it completes a complete revolution in just 30 hours. A great proximity which also has the consequence of locking its orbit, so that it always shows the same face to its star, the other half remaining constantly in darkness.

By lifting the veil on this part of WASP-121b condemned to perpetual darkness and by combining its data with measurements made on the day side of the planet, the scientific team was able to obtain a first overview of the phenomena that occur. in its atmosphere, via simulations. Enough to make it the first detailed view of the global atmosphere of an exoplanet. Results which have just been the subject of a publication in the journal Nature Astronomy and which do not lack panache as this world they describe is exotic!

While in 2017, Nasa researchers detected water vapor in the atmosphere of WASP-121b, the new study traces the cycle of this water while drawing a detailed map of the enormous temperature changes that exist. between the day and night faces of the planet at different altitudes. The water cycle of WASP-121b’s atmosphere is very intense. On the day side, it is so hot that the atoms that make up the water are literally torn apart. After which these atoms – hydrogen and oxygen – are blown towards the night side by powerful winds of up to 5 kilometers per second. Plunged into the shadows and the cold, these same atoms then recombine into water molecules, on the night side. Which in turn are blown towards the day side and so on.

By establishing this water cycle on the planet, the researchers also assessed the temperatures on both sides with relative precision. According to them, the dayside temperature increases with altitude and ranges between 2,225°C in the deepest observable layer and 3,226°C in the uppermost layer. On the night side, it is absolutely the opposite, the temperature drops with altitude, going from 1,525°C near the surface to 1,227°C in the uppermost layer of the atmosphere. But that’s not all…

The study’s authors also determined that it was cold enough on the night side of the planet to form clouds of iron and corundum, a mineral that makes up rubies and sapphires. Clouds which would also be brought to circulate towards the day side, where the high temperatures vaporize the metals in the form of gas. Along the way, exotic rains could therefore very well occur, causing liquid gemstones to fall from the famous corundum clouds. This is enough to motivate new observations of the planet WASP-121b, which scientists hope to see soon with the infrared eyes of the James Webb Space Telescope, which is about to open a new window on the cosmos.