Jupiter is definitely the Big Planet on Campus here in our solar system, what with that huge moon and its own significant size. But in the wider galaxy, Jupiter is a small fish in a big pond. And it’s not even the most interesting Jupiter-sized planet in that big pond!

In a new paper appearing in The Astronomical Journal, a team led by Caroline Piaulet presents the discovery of a puffed up planet. Roughly the size of Jupiter, the world has ten times less mass than Jupiter. It’s basically just a lot of hot gas with a less than 4.6 Earth-mass core. 

It is thought that it normally takes significantly more mass in the core for a planet to gravitationally pull in enough material to be this big. This object has been cataloged as WASP-107b and has been dubbed a super puff or cotton candy planet. Co-author Bjorn Benneke states: This work addresses the very foundations of how giant planets can form and grow. It provides concrete proof that massive accretion of a gas envelope can be triggered for cores that are much less massive than previously thought.

It’s unclear if the team has considered any other ways of getting a puffed-out planet than forming it that way; this is after all a discovery paper saying, “Hey, look at what we found.” 

I have to admit, this work reminds me of a paper last year that pointed out that Jupiter’s core is fluffier than expected, probably because of a collision between Jupiter and an earlier proto-planet. That paper has me wondering if you can get really fluffy planets with bigger collisions. I can’t wait to see what theorists do with this discovery.

More Information

University of Montreal press release

“WASP-107b’s Density Is Even Lower: A Case Study for the Physics of Planetary Gas Envelope Accretion and Orbital Migration,” Caroline Piaulet et al., 2021 January 18, The Astronomical Journal