Giant eccentric planet has the density of fluffy cotton candy, study shows | CNN

K. Ivanov

An extremely low-density planet called WASP-193b is larger than Jupiter, but weighs only a fraction of its mass.

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What’s big, with a fluffy, cotton candy-like composition? It turns out to be a planet.

An international coalition of astronomers recently discovered an unusual planet called WASP-193b, which is about 50% larger than Jupiter and somehow still remains the second-lightest planet ever found.

But WASP-193b, located outside our solar system, about 1,200 light-years from Earth, isn’t just a scientific oddity. The exoplanet could also hold the key to future research into atypical planetary formation, according to a study describing the find published Tuesday in the journal Nature Astronomy.

This cotton candy planet is not alone; there are other similar planets that belong to a class that scientists funnily call “swollen Jupiters.” The lightest planet ever discovered is the super puffy Kepler 51d, which is almost the size of Jupiter but a hundred times lighter than the gas giant.

Swollen Jupiters have been largely a mystery for 15 years, says lead researcher Khalid Barkaoui. But WASP-193b’s size makes it an ideal candidate for further analysis by the James Webb Space Telescope and other observatories.

“The planet is so light that it is difficult to think of an analogous solid material,” Barkaoui, a postdoctoral fellow in earth, atmospheric and planetary sciences at the Massachusetts Institute of Technology, said in a press release. “The reason why it is close to cotton candy is because both are composed largely of light gases rather than solids. The planet is actually super fluffy.”

WASP-193b, which researchers believe is composed mainly of hydrogen and helium, has been a huge puzzle for researchers to put together. Because the exoplanet’s density is so light relative to its size, calculating its mass became a challenge.

Typically, scientists determine mass using a technique called radial velocity, in which researchers analyze how a star’s spectrum, a graph that indicates the intensity of light emission in wavelengths, shifts as a planet orbits it. The larger the planet, the more the star’s spectrum can shift – but this didn’t work for WASP-193b, which is so light that the team didn’t exert any pull on the star that the team could detect.

Because the mass signal was so small, it took the team four years to collect data and calculate WASP-193b’s mass, Barkaoui explained. Because the extremely low numbers they found were so rare, the researchers ran multiple tests of data analysis to be sure.

“We initially got extremely low densities, which was very hard to believe at first,” said co-lead author Francisco Pozuelos, a senior researcher at the Spanish Institute of Astrophysics of Andalusia, in a press release.

Ultimately, the team found that the planet’s mass is only 14% that of Jupiter, despite being so much larger.

But a larger size means a larger “extended atmosphere,” says co-author Julien de Wit, an associate professor of planetary science at MIT. This means that WASP-193b provides particularly useful insight into the formation of these puffy planets.

“The larger a planet’s atmosphere, the more light can pass through it,” De Wit told CNN. “So it’s clear that this planet is one of the best targets we have for studying atmospheric effects. It will be a Rosetta stone to solve the mystery of the swollen Jupiters.”

But it’s also not clear how WASP-193b emerged in the first place, Barkaoui said. The “classical evolution models” of gas giants do not fully explain the phenomenon.

“WASP-193b is an outlier among all planets discovered so far,” he said.

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