Meet a planet as light as cotton candy

An international team has just discovered WASP-193b, an extraordinarily low-density giant planet orbiting a distant Sun-like star.

Meet WASP-193b, an exoplanet discovered 1,232 light-years away, orbiting a Sun-like star named WASP-193. It is 50 percent bigger than Jupiter but is light and fluffy as cotton candy.

“WASP-193b is the second least dense planet discovered to date, after Kepler-51d, which is much smaller,” explains Khalid Barkaoui, a Postdcotral Researcher at ULiège’s EXOTIC Laboratory and first author of the article published in Nature Astronomy. 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.”

WASP-193b was spotted by the the Wide Angle Search for Planets (WASP), an international collaboration of academic institutions that together operated two robotic observatories, one in the northern hemisphere and the other in the south.

According to the statement: “Each observatory used an array of wide-angle cameras to measure the brightness of thousands of individual stars across the entire sky.  In data taken between 2006 and 2008, and again from 2011 to 2012, the WASP-South observatory detected periodic transits, or dips in light, from the star WASP-193. Astronomers determined that the star’s periodic dips in brightness were consistent with a planet passing in front of the star every 6.25 days. The scientists measured the amount of light the planet blocked with each transit, which gave them an estimate of the planet’s size.”

An artist’s impression of a puffy cotton-candy world. (NASA/ESA/STScI)

The measurements conducted by the team revealed the planet to have extremely low density. The mass and size were about 0.14 and 1.5 that of Jupiter, respectively. Which means that its density is about 0.059 grams per cubic centimeter. On the other hand Jupiter’s density is about 1.33 grams per cubic centimeter; and Earth is even higher at 5.51 grams per cubic centimeter. Cotton candy has a density of about 0.05 grams per cubic centimeter.

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

The researchers think that WASP 193b is made mostly from from hydrogen and helium, like most other gas giants in the galaxy.

As per statement: “For WASP-193b, these gases likely form a hugely inflated atmosphere that extends tens of thousands of kilometers farther than Jupiter’s own atmosphere. Exactly how a planet can inflate so much is a question that no existing theory of planetary formation can yet answer. It certainly requires a significant deposit of energy deep into the planet’s interior, but the details of the mechanism are not yet understood.”

“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 Francisco Pozuelos, astronomer at the Instituto de Astrofisica de Andalucia (IAA-CSIC, Granada, Spain).”

“WASP-193b is a cosmic mystery. 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”, concludes Khalid Barkaoui.

Saima Baig

I am a Chartered Environmentalist from the Royal Society for the Environment, UK and co-owner of DoLocal Digital Marketing Agency Ltd, with a Master of Environmental Management from Yale University, an MBA in Finance, and a Bachelor of Science in Physics and Mathematics. I am passionate about science, history and environment and love to create content on these topics.