NASA's James Webb may have found answers to planets' extreme puffiness around stars

NASA’s James Webb Space Telescope (JWST) may have found the answer to why some planets swell at staggering amounts in the presence of a star, a mystery that puzzled scientists when recently they spotted a puffy exoplanet, WASP-107 b.

A surprisingly low reservoir of methane in a planet might unravel the mystery of a planet growing weirdly puffy near a star. The observations made by JWST show that planetary atmospheres can inflate immensely, which defies some of the existing planet formation theories.

"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," explains Michael Line, an extrasolar planetologist at Arizona State University.

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"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."

WASP-107 b was discovered in 2017 by the Wide Angle Search for Planets (WASP) consortium, roughly 200 light-years away from Earth in the constellation Virgo. It was found to be the lightest of known exoplanets.

Despite being as large as Jupiter, WASP-107 b weighs just 12 per cent of the planet's mass, which is equivalent to only 30 Earths. For context, one Jupiter mass is equal to about 318 Earth masses. This planet is so puffy, the team says, that its density can be compared to a microwaved marshmallow.

James Webb suspects low methane in planets ascause of their puffiness

The study was conducted on the basis of data from JWST and previous observations from the Hubble Space Telescope- divided among two independent teams.

In a nutshell, the teams discovered that methane in the planet’s atmosphere is 1,000th of what would be expected for the world. As methane is unstable at high temperatures, researchers say the astonishingly low amount of it is evidence that the gas from deep within the planet is “mixing vigorously with cooler layers higher up,” says David Sing of John Hopkins University (JHU) in Maryland, who led one of the two studies.

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"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."

One thing that could explain this extra heat is the fact that WASP-107 b zips around its star every 5.7 days in an orbit that is not a perfect circle, the researchers say. The star's constant gravitational pull on WASP-107 b, whose distance from its star keeps varying throughout, stretches and contracts the planet’s profile, thereby heating it up. On Earth, a similar force by the moon causes high and low tides.

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The planet's hot core combined with tidal heating from its star is also changing the chemistry of the gases deep within the planet, Zafar Rustamkulov, who is a graduate student at JHU and a co-author of one of the two new studies, said in a statement. "We think this heat is causing the chemistry of the gases to change, specifically destroying methane and making elevated amounts of carbon dioxide and carbon monoxide."

The planet’s extremely puffy nature helps astronomers look about 50 times deeper into its atmosphere than they can for a world like Jupiter.

This research is described in two studies published Monday (May 20) in the journal Nature.

(With inputs from agencies)