Scientists Unravel the Mysteries of 'Cotton Candy' Planets

This illustration depicts the sun-like star Kepler 51 and three giant planets that Hubble discovered in 2012–2014. NASA, ESA, and L. Hustak, J. Olmsted, D. Player and F. Summers (STScI)

"Super-puffs" may sound like a sweet treat you'd find at the grocery store, but these "cotton candy" exoplanets are much more interesting.

Scientists at NASA, fueled by ever-increasing data from the Hubble Space Telescope, are studying new data that shows the existence of three super-puffs orbiting a young sun-like star called Kepler-51.

These puffy exoplanets are roughly the size of Jupiter and have a similar density to cotton candy, thus the name.

They were discovered in 2012 and their densities were determined in 2014. However, it wasn't until this week that data from Hubble allowed astronomers to refine and independently confirm the mass and size estimates of these worlds.

The super-puffs were labeled by astronomers as Kepler-51 b, Kepler-51 c and Kepler-51 d. As you can see in the photo below, their hydrogen and/or helium atmospheres are so bloated they're nearly the size of Jupiter.

NASA's Kepler space telescope detected the shadows of these planets in 2012–2014 as they passed in front of their star.
This illustration depicts the three giant planets orbiting the sun-like star Kepler 51 as compared to some of the planets in our solar system. NASA, ESA, and L. Hustak and J. Olmsted (STScI

Researchers at NASA also used Hubble to examine the chemical components of the atmospheres of these new puff planets.

They expected to find traces of water, but to their surprise, they only found clouds of salt crystals and photochemical hazes. This composition is similar to Saturn's largest moon, Titan.

"This was completely unexpected," said Jessica Libby-Roberts of the University of Colorado, Boulder. "We had planned on observing large water absorption features, but they just weren't there. We were clouded out!"

The team of researchers compared the super-puffs to other gas-rich planets. They were able to determine the cooler a planet is, the cloudier it becomes.

Another part of the study concluded the lower densities are due to the young age of the system.

Their system is roughly 500 million years old, which pales in comparison to our 4.6-billion-year-old sun.

Scientists believe these young exoplanets formed outside their star's "snow line," where a planet's orbit allow the existence of icy materials. Then, the super-puffs migrated inward.

Over time, NASA researchers believe the low-density atmospheres will evaporate. That would turn a super-puff like Kepler-51 b into a smaller and hotter version of Neptune.

"This system offers a unique laboratory for testing theories of early planet evolution," said Zach Berta-Thompson of the University of Colorado, Boulder.

While many details of these "cotton candy" planets still remain a mystery, NASA is relying on the soon-to-be launched James Webb Space Telescope to learn even more about what they're made of.