Scientists discover “super fluffy” exoplanet with cotton candy-like density

Researchers have discovered a “super fluffy” exoplanet, 50 per cent larger than Jupiter and weighing only a seventh of it, giving it a “cotton candy”-like density.

The new, “fluffy” planet has been named ‘WASP-193b’ and was found to be located about 1,200 light years away from Earth, roughly equivalent to 10,800 trillion kilometres. Exoplanets exist outside the solar system and help us understand a bit more about how the universe works.

“The planet is so light that it’s difficult to think of an analogous, solid-state material,” said study co-author Julien de Wit, a professor at Massachusetts Institute of Technology (MIT), US.

“The reason why it’s close to cotton candy is because both are pretty much air. The planet is basically super fluffy,” he said.

The international team of researchers said that the exoplanet is the second least dense planet discovered and its extremely low density makes it a “real anomaly” among the more than five thousand 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,” said Khalid Barkaoui, a postdoctoral researcher at the University of Lige, Belgium, and first author of the study published in the journal Nature Astronomy.

The exoplanet was initially spotted by the Wide Angle Search for Planets (WASP), an international collaboration of academic institutions. Dips in light or “periodic transits” had been detected from the star WASP-193 in the data taken between 2006 and 2008, and again from 2011 to 2012.

Astronomers had determined that the star’s periodic dips in brightness were consistent with a planet passing in front of it every 6.25 days. They estimated the planet’s size by measuring the light from the star it blocked each time it passed in front of it.

In this study, the researchers used data from observatories based in the Atacama Desert, Chile, to measure the planet’s weight.

Their calculations revealed an “extremely low density” for the planet – 0.059 grams per cubic centimetre.

The substance closest in density, according to the researchers – the cotton candy – has a density of about 0.05 grams per cubic centimetre, they said. Water is known to have a density of 1 gram per cubic centimetre.

Providing more context, the researchers said that while Jupiter has a density of about 1.33 grams per cubic centimetre, Earth is a more substantial 5.51 grams per cubic centimetre.

The researchers suspected the fluffy planet to be made largely of hydrogen and helium gases, similar to most other gas giant planets in the Milky Way galaxy. The planet’s mass and size were also calculated to be about 0.14 and 1.5 that of Jupiter, respectively.

They also explained that the gases on the planet likely formed a hugely inflated atmosphere extending to tens of thousands of kilometres farther than Jupiter’s atmosphere.

However, how a planet can inflate so much is something that no existing theory of planet formation can yet answer, because of which the researchers have described the planet as a “cosmic mystery” and an “outlier”.

“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,” said Francisco Pozuelos, an astronomer at the Instituto de Astrofisica de Andalucia, Spain.