The dark side of “Hot Jupiter” revealed in detail for the first time

“Hot Jupiter” The concept of an artist on an exoplanet. Credit: NASA / JPL-Caltech

MIT astronomers have ever taken the clearest view of the permanent dark side of an exoplanet that is “properly anchored” to the star. Their observations, combined with permanent sun-side measurements of the planet, provide the first detailed view of the global atmosphere of exoplanets.

“We are currently not only taking isolated snapshots of specific areas of the atmosphere of exoplanets, but also studying them as true 3D systems,” said a postdoc at MIT’s Kavli Astrophysics and Space Institute. Thomas Mikal-Evans, who led the program, said. research.

The planet at the center of new research is Nature AstronomyIs WASP-121b, a giant gas giant that is almost twice the size of Jupiter.The planet is Jupiter, which is extremely hot and was discovered in 2015 by orbiting about 850 stars. Light year From the earth. WASP-121b is one of the shortest orbits ever detected, orbiting the star in just 30 hours. It is also neatly locked so that the “day” side facing the stars is permanently roasted and the “night” side is forever directed into space.

“Hot Jupiter is famous for having a very bright day side, but the night side is another beast. The night side of WASP-121b is about 10 times darker than the day side,” said Tansu Daylan, co-authored by MIT’s TESS postdoc. Says. the study.

Astronomers have previously detected water vapor and studied how atmospheric temperature changes with the altitude of the planet’s day.

New research captures much more detailed images. Researchers were able to map dramatic temperature changes from day to night and see how these temperatures change with altitude. They also tracked the presence of water in the atmosphere for the first time to show how water circulates between day and night on the planet.

On Earth, the water cycle evaporates first, then condenses into clouds, and then circulates by rain. In WASP-121b, the water cycle is much more intense. During the day, the atoms that make up water are torn at temperatures above 3,000. Kelvin. These atoms are blown to the night side, and when the temperature is low, hydrogen and oxygen atoms are recombined into water molecules, which are blown back to the day side and the cycle is restarted.

The team calculates that the planet’s water cycle is maintained by winds that whip atoms around the planet at speeds of up to 5 kilometers per second, or more than 11,000 miles per hour.

Also, it seems that water is not the only thing that circulates around the earth. Astronomers have found that the night side is cold enough to host the exotic clouds of iron and corundum. This is the mineral that makes up ruby ​​and sapphire. These clouds, like water vapor, can swirl on the sun side where high temperatures vaporize metal into the form of gas. Along the way, it can rain exotic, such as liquid gems from corundum clouds.

“This observation actually gives us a global view of the meteorology of exoplanets,” says Michal Evans.

Co-authors of this study include collaborators at MIT, Johns Hopkins University, California Institute of Technology, and other institutions.

Day and night

The team observed WASP-121b using a spectroscopic camera onboard NASA’s Hubble Space Telescope. This device observes the planet and the light from that star and breaks it down into its constituent wavelengths. Its strength gives astronomers clues to the temperature and composition of the atmosphere.

Through spectroscopic studies, scientists have observed details of the daytime atmosphere of many exoplanets. But it’s much harder to do the same on the night side. That’s because as a planet orbits the star, it is necessary to monitor small changes in the entire spectrum of the planet.

In a new study, the team observed WASP-121b in all two orbits. One is 2018 and the other is 2019. In both observations, researchers examined optical data to characterize specific lines or spectra that indicate their presence. Of steam.

“We looked at the characteristics of this water and mapped how it changed in different parts of the planet’s orbit,” says Michal Evans. “This encodes information about what the temperature of the planet’s atmosphere is doing as a function of altitude.”

Change water This feature helped the team map both day and night temperature profiles. They found that the range during the day ranged from 2,500 Kelvin in the deepest observable layer to 3,500 Kelvin in the top layer. The night side ranged from the deepest 1,800 Kelvin to the upper atmosphere of 1,500 Kelvin. Interestingly, the temperature profile rose with altitude on the day side, meteorologically a “heat inversion layer”, and appeared to fall with altitude on the night side.

Researchers then passed temperature maps through various models to identify chemicals that are likely to be present in the planet’s atmosphere given a particular altitude and temperature. This modeling revealed the possibility of metal clouds such as iron, corundum, and titanium on the night side.

From them temperature In the mapping, the team also observed that the hottest regions of the planet were shifting east of the “substellar” region beneath the stars. They speculated that this change was due to extreme winds.

“The gas is heated at the point below the stars, but it is blown eastward before it re-radiates into space,” explains Michal Evans.

From the size of the shift, the team estimates that the wind speed will clock in at about 5 kilometers per second.

“These winds are much faster than our jet stream and can probably move clouds across the planet in about 20 hours,” said NASA’s MIT-led mission TESS before on the planet. Says Daylan, who led the work.

Astronomers have reserved time with the James Webb Space Telescope to observe WASP-121b later this year, as well as mapping changes. water vapor Carbon monoxide, which scientists suspect should be in the atmosphere.

“This is the first time we have been able to measure carbon-containing molecules in the planet’s atmosphere,” says Michal Evans. “The amount of carbon and oxygen in the atmosphere provides clues as to where these types of planets are formed.”

James Webb Space Telescope maps the atmosphere of exoplanets

For more information:
Thomas Mikal-Evans, Diurnal Cycle in the Stratosphere of the Ultra-Hot Giant Exoplanet WASP-121b, Nature Astronomy (2022). DOI: 10.1038 / s41550-021-01592-w..

Quote: The dark side of “Hot Jupiter” was first acquired from https: // on February 21, 2022 (February 2022). 21st) It was revealed in detail. html

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The dark side of “Hot Jupiter” revealed in detail for the first time

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