Webb Gets To The Core Of Puffy Microwaved Marshmallow Planet Mystery

NASA’s James Webb Space Telescope (JWST), along with help from its tried and true sibling Hubble, have given researchers the data needed to explain why some giant gassy exoplanets are so puffy. Results of the study were mainly because of Webb’s “extraordinary sensitivity,” along with its ability to measure light passing through exoplanet atmospheres.

The most recent of these puffy planets to be discovered, often called “cotton candy” planets because of their density, was WASP-193b. Until now, scientists and astronomers have remained baffled as to these exoplanets came to exist, as standard models can not reproduce their extremely-low-density. New research, however, seems to answer that question.

Data collected by Webb, combined with prior observations from Hubble, of gas-giant exoplanet WASP-107b indicate there is little methane in the planet’s atmosphere, meaning that the interior of the exoplanet might be significantly hotter and the core more massive than previously estimated.

“Based on its radius, mass, age, and assumed internal temperature, we thought WASP-107 b had a very small, rocky core surrounded by a huge mass of hydrogen and helium,” explained Luis Welbanks from Arizona State University (ASU), lead author on a paper published today in Nature. “But it was hard to understand how such a small core could sweep up so much gas, and then stop short of growing fully into a Jupiter-mass planet.”


Researchers remarked that if WASP-107b has more of its mass in the core, the atmosphere should have contracted as the planet cooled over time. They added that without a source of heat to re-expand the gas, WASP-107b should in theory be much smaller. While the planet orbits its star at one-seventh of the distance between Mercury and the Sun, it still does not receive enough energy from its star to be so inflated.

“WASP-107 b is such an interesting target for Webb because it’s significantly cooler and more Neptune-like in mass than many of the other low-density planets, the hot Jupiters, we’ve been studying,” remarked David Sing from the Johns Hopkins University (JHU), lead author on a parallel study also published today in Nature. “As a result, we should be able to detect methane and other molecules that can give us information about its chemistry and internal dynamics that we can’t get from a hotter planet.”

By combining observations from Webb’s NIRCam and MIRI cameras, as well as Hubble’s WFC3 camera, the team was able to build a broad spectrum of micron light absorbed by WASP-107b’s atmosphere. The precision of the data made it possible to not just detect, but also measure the abundances of a “wealth of molecules, including water vapor, methane, carbon dioxide, carbon monoxide, sulfur dioxide, and ammonia."

“This is evidence that hot gas from deep in the planet must be mixing vigorously with the cooler layers higher up,” explained Sing. “Methane is unstable at high temperatures. The fact that we detected so little, even though we did detect other carbon-bearing molecules, tells us that the interior of the planet must be significantly hotter than we thought.”

With all the new data in hand about WASP-107b, researchers were able to determine that the core is at least twice as massive as originally estimated, making the entire picture make more sense.