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Artistic imagination of WASP-121b. Image credit: NASA, ESA, and G. Bacon / STScIWASP-121b is probably the most thoroughly studied exoplanet. Discovered in 2015, it has a mass of 1.18 times Jupiter's, a radius of 1.81 times Jupiter's, and an orbital period of 30.6 hours. In 2017, astronomers even found water in its stratosphere. Today, anomalous data in spectral analysis revealed that the planet could even rain gems.

Of course, that doesn't mean you should go to this star to look for opportunities to make a fortune. As you may have noticed, WASP-121b orbits in only 30.6 hours. Unfortunately, its host star, WASP-121, is an F6 star, close to the Sun's G2 star. So, according to Kepler's third law, the shorter the period, the smaller the orbit radius, and WASP-121b is very close to its host star. According to observations, its surface temperature can even reach more than 3000 Kelvin. WASP-121b doesn't make you rich, it just kills you.

So far, nearly 5000 exoplanets have been identified, of which more than 300 are gaseous planets with orbital periods less than 10 days, which astronomers call "hot Jupiters." But even among the more than 300 hot Jupiters, WASP-121b's environment is so extreme that astronomers are even planning to create a new category for it as a "superhot Jupiter."

Astronomers mainly use the transit method to find exoplanets. If the plane side of the exoplanet orbiting the star is facing us, then when the exoplanet passes in front of the star, it will block some of the starlight, causing the star to decrease in brightness, and we can find the exoplanet.

Planetary movements affect the brightness of stars. When a planet obscures a star, the light emitted by the star penetrates the planet's atmosphere and changes the star's spectrum, allowing us to analyze the elements contained in the planet's atmosphere. Thomas Mikal-Evans, an astronomer at the Max Planck Institute for Astronomy in Germany, said: "Despite the discovery of thousands of exoplanets, we can only study a small part of the atmosphere due to the challenging nature of the observations. "WASP-121b's extreme temperature makes it so bright that astronomers may even be able to study the light emitted by the planet itself.

In 2016, a paper published in Astrophysical Letters said they found water in WASP-121b's atmosphere-certainly not in liquid form. To be precise, the spectral analysis astronomers use only allows astronomers to detect water molecules. However, this is the first time astronomers have found water in the atmosphere of an exoplanet.

It is at such short distances that the tidal effects on the planet are very strong. This puts the planet into a tide-locked state--orbiting at the same time as it rotates, with only one planet always facing its host star. This created a huge temperature difference on WASP-121b, with temperatures of 3000 Kelvin in the daytime hemisphere and only 1500 Kelvin in the night hemisphere. The temperature difference between the two hemispheres is very strong, and astronomers are eager to know what kind of impact such extreme conditions will have, but its night hemisphere is only about 1/10 of the brightness of the day hemisphere, which makes observation more difficult.

To obtain information on both hemispheres, Mical-Evans 'team used the Hubble Space Telescope to observe WASP-121b for more than two years--more than two years on WASP-121b, and observed it for about 80 hours. It also gave astronomers the first insight into how the atmosphere works on such extreme stars. The paper was published in Nature Astronomy.

Computer simulation of WASP-121b observation images, but now all human telescopes resolution is difficult to image exoplanets, generally only observe the image of the light curve brightness effect. Photo source: NASA / JPL-Caltech / Aix-Marseille University (AMU)/Vivien Parmentier On Earth, water molecules participate in the water cycle in solid, liquid and gas states, while in the day hemisphere of WASP-121b, water vapor at 3000 Kelvin may even cause water molecules to decompose into hydrogen atoms and oxygen atoms. Only in the night hemisphere, the "low temperature" of 1500 Kelvin can make it "condense" again into water vapor.

The 1500-degree temperature difference between the star's two hemispheres creates a permanent pressure differential across the planet, which produces extreme westerly winds that orbit the entire planet. "The winds on WASP-121b are much faster than those on our planet, and could sweep the entire planet in 20 hours," said Tansu Daylan, an astrophysicist at MIT. "

Astronomers have found vanadium, iron, chromium, calcium, sodium, magnesium, nickel, aluminum and titanium in its atmosphere, the most thoroughly studied exoplanet. In the atmosphere of the night hemisphere, however, aluminum and titanium disappear. The team believes that aluminum and titanium have been carried deep into the planet's atmosphere in the night hemisphere. Aluminum easily combines with oxygen to form alumina. Given that WASP-121b's atmosphere contains multiple metallic elements, it is likely that these aluminas carry vanadium, iron, chromium or titanium "impurities," which are the conditions for the formation of rubies and sapphires.

This means that in the night hemisphere of WASP-121b, there is a good chance that it is raining gems-or gemstone "hail," after all, it takes only twenty hours for the wind to sweep the entire planet and the temperature of 1500 Kelvin to make you "rich" there.

For researchers, however, carbon monoxide is more likely to be found. Carbon monoxide is the most common molecule in nebulae after hydrogen, and because of its asymmetric structure, it is easier to observe and is often used by astronomers to study how stars form. Mikal-Evans, who is looking forward to using the James Webb Space Telescope to find traces of carbon monoxide on WASP-121b, said: "The abundance of carbon and oxygen in the atmosphere will give us clues to the formation of such planets. "

Reference link:

https://www.nature.com/articles/s41550-021-01592-w

http://www.mpia.de/news/science/2022-05-wasp121b

https://www.eurekalert.org/news-releases/943920

https://news.berkeley.edu/2020/05/26/astronomers-create-cloud-atlas-for-hot-jupiter-like-exoplanets/

https://www.sciencealert.com/the-atmosphere-of-one-of-the-hottest-exoplanets-in-the-galaxy-is-full-of-metal

https://www.sciencealert.com/a-wild-laboratory-experiment-supports-diamond-rain-on-neptune-and-uranus

https://iopscience.iop.org/article/10.3847/2041-8205/822/1/L4/pdf

This article comes from Weixin Official Accounts: Global Science (ID: huanqiukexue), written by Wang Yu, revised by Bai Defan

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