Astronomers Discover Cotton Candy-Like Planet That Defies Explanation

In a cosmic discovery that has left scientists scratching their heads, an international team of researchers led by the EXOTIC Laboratory at the University of Liège in Belgium has found an extraordinarily fluffy planet orbiting a distant star. This peculiar world, named WASP-193b, is unlike anything astronomers have seen before. The planet is about 50 percent larger than Jupiter but seven times less massive, giving it an extremely low density comparable to that of cotton candy.

Located 1,200 light-years away from Earth, WASP-193b is the second-least dense planet discovered to date. The remarkable findings have been published in the journal Nature Astronomy.

“WASP-193b is the second least dense planet discovered to date, after Kepler-51d, which is much smaller,” says first study author Khalid Barkaoui, a postdoctoral researcher at the University of Liège’s EXOTIC Laboratory. “Its extremely low density makes it a real anomaly among the more than 5,000 exoplanets discovered to date. This extremely low density cannot be reproduced by standard models of irradiated gas giants, even under the unrealistic assumption of a coreless structure.”

In the past few decades, astronomers have discovered thousands of these cosmic worlds, but WASP-193b stands out due to its mind-bogglingly low density.

The planet was first spotted by the Wide Angle Search for Planets (WASP), an international collaboration that uses robotic observatories to monitor the brightness of thousands of stars. Between 2006 and 2012, the WASP-South observatory detected periodic dips in light from the star WASP-193, indicating that a planet was passing in front of the star every 6.25 days.

To confirm their findings and measure the planet’s size and mass, the team used the TRAPPIST-South and SPECULOOS-South observatories in Chile, as well as data from the HARPS and CORALIE spectrographs. The results were stunning: WASP-193b’s mass and size were about 0.14 and 1.5 that of Jupiter, respectively, resulting in a density of just 0.059 grams per cubic centimeter — similar to that of cotton candy.

“The planet is so light that it’s difficult to think of an analogous, solid-state material,” explains study co-author Julien de Wit, professor at Massachusetts Institute of Technology (MIT). “The reason why it’s close to cotton candy is because both are pretty much air. The planet is basically super fluffy.”

Scientists believe that WASP-193b is primarily composed of hydrogen and helium, like most other gas giants in the galaxy. However, its atmosphere is likely hugely inflated, extending tens of thousands of kilometers farther than Jupiter’s. The exact mechanism behind this extreme inflation remains a mystery, as no existing theory of planetary formation can fully explain it.

“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. Looking more closely at its atmosphere will allow us to constrain an evolutionary path of this planet,” adds study co-author Francisco Pozuelos, astronomer at the Instituto de Astrofisica de Andalucia (IAA-CSIC, Granada, Spain).

The discovery of WASP-193b has opened up a new frontier in the study of exoplanets, challenging our understanding of how these cosmic worlds form and evolve.

“WASP-193b is a cosmic mystery,” concludes Barkaoui. “Solving it will require some more observational and theoretical work, notably to measure its atmospheric properties with the JWST space telescope and to confront them to different theoretical mechanisms that possibly result in such an extreme inflation.”


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