Astronomers Find Massive Planets As Light As Cotton Candy

Three new exoplanets as big as Jupiter have been discovered trillions of miles from Earth. But unlike other giants, these planets are so light astronomers compared them to floating cotton candy.

The team at the University of Colorado Boulder used the Hubble Space Telescope to observe  the three super lightweight planets in the Kepler 51 star system 2,400 light years from Earth. The “super-puff” worlds of Kepler 51 were first described in 2014, The Weather Channel reported.

Researchers said cotton-candy-like planets are still rare in the Milky Galaxy. Astronomers currently have only 15 of them explored. 

“They’re very bizarre,” Jessica Libby-Roberts, lead researcher at the University of Colorado Boulder, said in a press release. “We knew they were low density. But when you picture a Jupiter-sized ball of cotton candy – that’s really low density.”

Data from Hubble showed that the planets' atmospheres are filled with hazy smog. Libby-Roberts said the team did not see signatures of any molecule. 

The study suggests that the cotton candy planets are potentially mostly hydrogen and helium by mass, which made them super lightweight. Estimates show that three planets have a density less than 0.1 grams per cubic centimeter of volume. 

Researchers said the Kepler 51 trio could be the lowest density exoplanets ever discovered in the galaxy. Another surprising finding in the study is that the planets appeared releasing gas into space at a rapid pace.

If that activity continues, researchers expect the cotton candy worlds to shrink over the next billion years. That would eventually make them lose their puffiness and become "mini-Neptunes."

“This is an extreme example of what’s so cool about exoplanets in general,” Zachory Berta-Thompson, study co-author and an assistant professor at the University of Colorado Boulder, said. “They give us an opportunity to study worlds that are very different than ours, but they also place the planets in our own solar system into a larger context.”

The Kepler 51 star system is currently 500 million years old, which astronomers consider as a young system and still developing. The study will be published in The Astronomical Journal.

Kepler 51 An artist's depiction of the Kepler 51 star system. NASA/ESA/STScI