The fluffy giant: New planet ‘WASP-193b’ defies expectations with cotton candy-like density

WASP-193b, located 1,200 light-years from Earth, is a real outlier among the more than 5,000 exoplanets found so far. This new planet has a density similar to cotton candy since it is 50% bigger than Jupiter but seven times less dense.

"WASP-193b is the second least dense planet discovered to date, after Kepler-51d, which is much smaller," said Khalid Barkaoui, the study's first author and postdoctoral researcher at ULiege's EXOTIC Laboratory. The study was published in Nature Astronomy.

Even under the implausible premise of a coreless structure, traditional models of irradiated gas giants cannot account for the planet's very low density. "Its extremely low density makes it a real anomaly among the more than five thousand exoplanets discovered to date," Barkaoui continues.

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The first to identify the new planet was the Wide Angle Search for Planets (WASP), an international initiative that used two robotic observatories to examine hundreds of stars' brightness in the sky. A transiting planet was detected by periodic dips in the brightness from the star WASP-193.

Subsequently, the group measured the planetary signal at several wavelengths and confirmed that the eclipsing object was really planetary using the Chilean observatories TRAPPIST-South and SPECULOOS-South. The planet's mass was determined using spectroscopic measurements made with the CORALIE and HARPS spectrographs in Chile.

With a mass and size of around 0.14 and 1.5 times that of Jupiter, respectively, the planet's density was found to be very low based on the cumulative measurements: 0.059 grams per cubic centimeter, or approximately the same as cotton candy.

According to co-author and MIT professor Julien de Wit, "the planet is so light that it's difficult to think of an analogous, solid-state material." "The planet is basically super fluffy."

Scientists believe that WASP-193b is primarily composed of hydrogen and helium, and that its massively inflated atmosphere stretches tens of thousands of kilometers beyond the atmosphere of Jupiter. Nevertheless, how a planet may expand to such a degree is still outside the current understanding of planetary formation theories.

"We don't know where to put this planet in all the formation theories we have right now, because it's an outlier of all of them. We cannot explain how this planet was formed," added Francisco Pozuelos, astronomer at the Instituto de Astrofisica de Andalucia.

(With inputs from agencies)