The Exoplanet WASP-107b is a Real Super-Puff

James Maynard
Jan 21 · 4 min read

The super-puff planet WASP-107b has a density so low, it was thought impossible. Evidentially not.

Image for post
Image for post
A look at how the cotton candy planet WASP-107b might look. Image credit: The Cosmic Companion / Created in Universe Sandbox

The exoplanet WASP-107b may be as large as Jupiter, but this super-puff planet only contains one-tenth as much mass as the king of our Solar System. The density of this world is lower than what astronomers thought possible.

The discovery of this bizarre exoplanet — sometimes called a cotton candy planet — provides astronomers with a unique target for further study.

“With a mass in the Neptune regime and a radius of Jupiter, WASP-107b presents a challenge to planet formation theories. Meanwhile, the planet’s low surface gravity and the star’s brightness also make it one of the most favorable targets for atmospheric characterization,” researchers explain in The Astronomical Journal.

This study, headed by Caroline Piaulet, a Ph.D. student at the Université de Montréal’s (UdeM) Institute for Research on Exoplanets (iREx), suggests other such cotton candy worlds may be found in other solar systems.

Planets form within protoplanetary disks of gas and dust surrounding young stars. Astronomers seeking to understand the formation of gas giants is largely based on the only examples we knew until recently — Jupiter and Saturn.

Calculations suggested planetary cores needed to have masses at least 10 times greater than Earth in order to collect the vast amounts of gas needed to form a gas giant — far greater than WASP-107b. So, how did this cotton candy planet take shape?

“For WASP-107b, the most plausible scenario is that the planet formed far away from the star, where the gas in the disc is cold enough that gas accretion can occur very quickly. The planet was later able to migrate to its current position, either through interactions with the disc or with other planets in the system,” Eve Lee of McGill University stated.

Image for post
Image for post
An artistic rendition of the exoplanet WASP-107b and its star, WASP-107. Some of the star’s light streams through the exoplanet’s extended gas layer. Image credit: ESA/Hubble, NASA, M. Kornmesser

Super-puff planets are the least dense of all exoplanets. Even these, however, were thought to have a lower limit to their densities. This new study challenges these old assumptions.

Piaulet’s team analyzed data recorded at the Keck Observatory in Hawai’i, in order to better understand the mass and composition of this exoplanet, discovered in 2017.

They utilized the radial velocity method, examining the wobble created by as star as a planet orbits around it. The team determined that WASP-107b is centered on a solid core just four times more massive than Earth.

This would suggest that over 85 percent of the mass of the world is contained in its atmosphere. Neptune — the most similar planet in our solar system — holds just 10 to 15 percent of its mass in its atmosphere.

“We had a lot of questions about WASP-107b. How could a planet of such low density form? And how did it keep its huge layer of gas from escaping, especially given the planet’s close proximity to its star?” Piaulet descibes.

Examination of the atmosphere of WASP-107b, using the Hubble Space Telescope, showed little methane in the air surrounding this unusual exoplanet, where researchers expected to find higher concentrations.

“Cotton candy is the perfect snack for when I’m in the mood to eat dry, scratchy fabric.” — Demetri Martin

A look at what the exoplanet WASP-107b might look like in its orbit around its parent star. Video credit: Hubble ESA

Detailed observations of the WASP-107 planetary system also reveal the presence of a second exoplanet in the system. This larger planet, WASP-107c, is roughly one-third as massive as Jupiter, and orbits the central star in an elliptical orbit once every three years, compared to 5.7 days for WASP-107b.

“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,” Björn Benneke, astrophysics professor at UdeM, stated.

Once the James Webb Space Telescope launches and becomes operational, astronomers will be able to get more-detailed studies of exoplanets and their atmospheres, including the worlds of WASP-107.

James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.

Did you like this article? Join us on The Cosmic Companion Network for our podcast, weekly video series, informative newsletter, news briefings on Amazon Alexa and more!

The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

Medium is an open platform where 170 million readers come to find insightful and dynamic thinking. Here, expert and undiscovered voices alike dive into the heart of any topic and bring new ideas to the surface. Learn more

Follow the writers, publications, and topics that matter to you, and you’ll see them on your homepage and in your inbox. Explore

If you have a story to tell, knowledge to share, or a perspective to offer — welcome home. It’s easy and free to post your thinking on any topic. Write on Medium

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store