Mystery of puffy exoplanet solved

WASP-107b Illustration (Download Image)

An artistic impression of WASP-107b. (Illustration: NASA, ESA, CSA, and Ralf Crawford [STScI])


A recent study of the atmosphere of the exoplanet WASP-107b suggests tidal heating is responsible for the exoplanet’s inflated nature and reveals a previously unseen combination of molecules in an exoplanet.

A Lawrence Livermore National Laboratory (LLNL) scientist and international collaborators have characterized the atmosphere of the exoplanet, WASP-107b, using a technique called transmission spectroscopy with the James Webb Space Telescope. The results show surprisingly little methane (CH4) in the planet’s atmosphere, indicating that the interior of WASP-107 b must be significantly hotter and the core much more massive than previously estimated. The research appears in Nature.

WASP-107b is nearly as large as Jupiter but has only a tenth of its mass, making it one of the lowest-density planets known and difficult to explain using planet formation theories. The study finds that the surprising lack of methane in the atmosphere of WASP-107b suggests that the planet’s core must be tidally heated by its eccentric orbit around its host star. While puffy planets are not uncommon, most are hotter and more massive, and therefore easier to explain.

"The study solves a long-standing challenge in exoplanet science,” said LLNL scientist Peter McGill, a co-author of the paper. “For the first time, we are linking the chemical composition of an exoplanet’s atmosphere to its internal properties.”

In addition to solving the mystery of WASP-107b’s inflated appearance, the study revealed that the planet has an array of previously unseen, yet expected, molecules in its atmosphere.

“For the first time in a transiting exoplanet we have simultaneously detected carbon-, oxygen-, nitrogen- and sulfur- bearing molecules,” McGill said. “The high-precision observations we have from the James Webb Space Telescope means we are now often playing catchup with our theoretical models to explain the data. Therefore, it was important to robustly validate the detection of molecules we found with this planet.”

Using the James Webb Space Telescope and the Hubble Space Telescope, the team was able to produce the broadest panchromatic exoplanet spectrum to date (0.8 to 12.2 microns).

Other institutions involved in the research include Arizona State University, NASA's Ames Research Center, Space Telescope Science Institute, University of Wisconsin-Madison, University of California, Santa Cruz, National Astronomical Observatory of Japan, University of Arizona, University of Michigan, Université Côte d’Azur and Université Paris Cité.

The conclusions of this work are corroborated by the results of an independent, parallel study on WASP-107b, that also is published in Nature today and led by researchers at Johns Hopkins University.