NASA’s JWST Solves Mystery of Super-Fluffy Planet With Cotton Candy-Like Density

NASA has finally cracked the mystery as to how a marshmallow planet got so big despite being extremely light compared to its size.

Cotton Candy Exoplanet

In 2017, NASA announced the discovery of WASP-107b, a Neptune-like exoplanet that orbits a K-type star about 200 light years away from Earth in the constellation Virgo. It has a mass of 30.5 Earths and takes 5.7 days to orbit its host star at a distance of 5.1 million miles (8.21 million kilometers).

Using infrared spectroscopy, astronomers working with NASA's Hubble Space Telescope discovered helium in the escaping atmosphere of this planet in 2018. This led to the first detection of helium in the atmosphere of an exoplanet. A follow-up observation in 2020 revealed that the helium absorption extends beyond transit-egress.

WASP-107b is about the same size as Jupiter but has only around one-tenth of its mass. This means that this gas giant is one of the least dense planets ever discovered.

Solving the Mystery of a Pluffy Planet

In the paper "A warm Neptune's methane reveals core mass and vigorous atmospheric mixing," explained how this exoplanet gained such a low-density "floofy" atmosphere.

According to Luis Welbanks from Arizona State University, they initially thought that WASP-107b possesses a very tiny, rocky core surrounded by a large mass of hydrogen and helium. This assumption was based on the planet's age, mass, radius, and assumed internal temperature. However, it was hard to understand how such a tiny core could accumulate so much gas and stop growing fully into a Jupiter-mass planet.

The research team believe that WASP-107b may have grown to such a large size despite having a lower mass because its core is a lot hotter than expected. This is supported by the fact that the planet possesses less methane in its atmosphere than initially thought.

Data collected by the James Webb Space Telescope reveals that WASP-107b has 1,000 times less methane than expected, an indication of an intensely hot interior. This is also evidence that hot gas from the deep region of the planet mixes vigorously with the cooler layers near the surface.

Methane gas is unstable at high temperatures, and the fact that astronomers detected so little, even if they detected other carbon-bearing molecules, tells something about the planet's temperature. Aside from this, the lower methane levels and higher temperatures suggest that WASP-107b has a large core, which is 12 times the mass of the Earth's core.

The high internal temperature of WASP-107b possibly allowed the planet to puff up much more, contributing to its exceptionally large size. This heat could have been generated by tidal heating, which resulted from its elliptical and close orbit with its host star.

The data from JWST suggests that planets like this one did not have to form in some strange way with a super small core and large gassy envelope. The research team plan to use these techniques in examining the atmosphere and temperature of other distant exoplanets across the Milky Way galaxy in the search for signs of alien life.