NASA cracks mystery of ‘marshmallow’ planet thanks to James Webb Space Telescope

NASA has finally cracked it when it comes to explaining how a 'marshmallow' planet got so big despite being extremely light compared to its size.

Through the pioneering James Webb Space Telescope, the American space agency has figured out how it got so big while staying light and 'floofy'.

Dubbed WASP-107 b, the massive planet lies some 200 light-years away from Earth.

It was first discovered back in 2017 by the Hubble Space Telescope.

The planet itself is massive, some three-quarters the size of Jupiter yet it holds less than 10% of the planet's mass - meaning it's somewhat of a balloon in comparison floating through the cosmos.

The problem with the planet

While puffy planets are not uncommon, most are hotter and more massive, and therefore easier to explain. Hence the head-scratching from scientists for the past seven years when trying to explain how it ballooned but stayed so light.

"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 in Nature.

WASP-107 b (NASA, ESA, CSA, Ralf Crawford (STScI))

“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.”

David Sing from the Johns Hopkins University (JHU), lead author on a parallel study also published in Nature, said: "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.

"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."

NASA strikes again (EVA MARIE UZCATEGUI/AFP via Getty Images)

What was found?

WASP-107 b’s giant radius, extended atmosphere, and edge-on orbit make it ideal for something called transmission spectroscopy; a method used to identify the various gases in a planet atmosphere based on how they affect starlight.

The precision of the data from both studies has made it possible to not just detect, but actually measure the abundances of a wealth of molecules on the planet.

This includes water vapour (H2O), methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (SO2), and ammonia (NH3).

There was a huge lack of methane in the planet's atmosphere; one-thousandth the amount expected based on its assumed temperature.

Researchers were also able to estimate the size of the planets core, which is now thought to be at least twice as big as originally thought.

CGI of the James Webb Space Telescope floating in space (NASA/Getty Stock Images)

What does this mean to the ordinary person?

All together, WASP-107 b is not as mysterious as it once appeared.

“The Webb data tells us that planets like WASP-107 b didn’t have to form in some odd way with a super small core and a huge gassy envelope,” explained Mike Line from ASU.

“Instead, we can take something more like Neptune, with a lot of rock and not as much gas, just dial up the temperature, and poof it up to look the way it does.”