These Exoplanets Are As Fluffy As Cotton Candy!


An illustration depicting the Sun-like star Kepler 51 and three giant Jupiter-sized planets, discovered by NASA's Kepler Space Telescope discovered in 2012-2014 (Credit: NASA, ESA, and L. Hustak, J. Olmsted, D. Player and F. Summers (STScI))

Cotton candy is probably the last thing that comes to mind when one thinks of exoplanets. But the three giant worlds orbiting the Kepler 51 star system, about 2,600 light-years away from Earth, are so "light and fluffy" that they warrant a comparison to the beloved spun-sugar confection.

The exoplanets named Kepler 51 - b, c, and d, detected by NASA's Kepler Space Telescope between 2012 and 2014, belong to a rare class of low-density "super-puffs" — only 15 of which are known to exist. Curious about the composition of the exoplanets’ atmospheres and to find clues around how these lightweight worlds may have formed, a team led by the University of Colorado (CU), graduate student, Jessica Libby-Roberts, decided to investigate.

The scientists began by using the Hubble Space Telescope to zoom in on the 500-million-year-old Kepler 51-star system, which hosts the planets. The data enabled the team to develop accurate estimates for the three planets' masses and densities. The researchers' calculations revealed the three "super-puffs" had a density of less than 0.1 g/cm³ of volume — almost identical to that of the sweet pink carnival treat. In contrast, the similar-sized Jupiter boasts a density of 1.33 g/cm³. “We knew they were low density,” said Libby-Roberts. “But when you picture a Jupiter-sized ball of cotton candy—that’s really low density.”

While confirming the planets' "super puff" status was easy, using the Hubble to peer into their atmosphere proved impossible due to a high-altitude opaque shell around each of their outer layers. “This was completely unexpected. We had planned on observing large water absorption features, but they just weren’t there. We were clouded out,” Libby-Roberts said.

Artist's illustration comparing the size of the "super-puff" Kepler-51 planets to some of the planets in our Solar System (Credit: NASA / ESA / L. Hustak & J. Olmsted, STScI.)

Computer simulations and other tools led the researchers to theorize that the Kepler-51 planets most likely comprise lightweight gases like hydrogen and helium, which also explains their puffiness. They suspect that similar to Saturn's moon Titan, the worlds are encompassed by a layer of methane. “If you hit methane with ultraviolet light, it will form a haze,” Libby-Roberts said. “It’s Titan in a nutshell.”

Libby-Roberts and study co-author, CU assistant professor Zachory Berta-Thompson, maintain that the "super-puff" worlds may not be as unusual as was first thought. Their observations showed the trio were shedding as much as tens of billions of tons of gas into space every second. The researchers say if the pace continues, the planets will lose their cotton-candy puffiness within the next billion years and end up looking more like the normal class of exoplanets called “mini-Neptunes.”

“People have been really struggling to find out why this system looks so different than every other system,” Libby-Roberts said. “We’re trying to show that, actually, it does look like some of these other systems.” Berta-Thompson agreed: “A good bit of their weirdness is coming from the fact that we’re seeing them at a time in their development where we’ve rarely gotten the chance to observe planets.”

Only time will tell if the scientists are right. For now, it is just fun to imagine three ginormous balls of cotton candy floating around in our universe.


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  • viviane
    vivianeSunday, January 19, 2020 at 4:25 pm
    I'm confused but cotton candy is awesome
    • viviane
      vivianeSunday, January 19, 2020 at 3:52 pm
      How cotton candy 👅
      • queen_onyx
        queen_onyxSaturday, January 18, 2020 at 6:24 pm
        Omg I want cotton candy!!
        • reagan223
          reagan223Friday, January 17, 2020 at 2:43 pm
          Wow! Those planets look so much like cotton candy!
          • slytherin222
            slytherin222Friday, January 17, 2020 at 1:48 pm
            OMG this is so cool. Imagine that in a billion years the whole earth may be covered in fluff.
            • janseldanoob
              janseldanoobFriday, January 17, 2020 at 11:57 am
              Eatable because if I will eat it!!!!!
              • hjhjhoihoihoi
                hjhjhoihoihoiFriday, January 17, 2020 at 6:24 am
                yum yum
                • gomobaco-157106077766
                  gomobaco-157106077766Friday, January 17, 2020 at 11:18 am
                  wait how many layers of fluffieness does it have why is the planet not frozen? accualy why arent all the planets frozen ms b
                • bananaqueen
                  bananaqueenThursday, January 16, 2020 at 5:28 pm
                  I WANNA EAT IT!!!!!!
                  • beeberlin
                    beeberlinSunday, January 19, 2020 at 5:02 am
                    Me too girl! Like if you agree!!! 😛😜😝😋
                  • snowflake3478
                    snowflake3478Thursday, January 16, 2020 at 11:45 am
                    Can i eat them???????
                    • chillz_slashez
                      chillz_slashezThursday, January 16, 2020 at 11:30 am
                      I actually thought they were cotton candy.