A surprisingly low methane reservoir could explain how a planet around a nearby star became strangely puffy, according to new observations from the James Webb Space Telescope (JWST). The finding shows that planetary atmospheres can inflate to remarkable amounts without resorting to esoteric theories of planet formation, astronomers say.
“The Webb data tells us that planets like WASP-107 b didn’t have to form in a strange way with a super small core and a huge gaseous envelope,” said Michael Line, an extrasolar planetologist at Arizona State University, in a declaration. . “Instead, we can take something that looks more like Neptune, with a lot of rock and not as much gas, just increase the temperature and raise it to look like this.”
Discovered in 2017 by the Wide Angle Search for Planets (WASP) consortium, WASP-107 b is located about 200 light-years from Earth in the constellation Virgo and is among the lightest of the more than 5,000 exoplanets found so far. Despite being almost as big as Jupiter, WASP-107 b weighs just 12% of the gas giant’s mass, equivalent to just 30 Earths. For context, one Jupiter mass is equal to approximately 318 Earth masses. This planet is so swollen, the team says, that its density could be likened to a microwaved marshmallow.
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Based on previous observations of WASP-107 b’s size, mass and age, astronomers suspected that the planet had a small, rocky core surrounded by a rich reservoir of hydrogen and helium gases. However, such a scenario could not fully explain the remarkably inflated sphere, which, despite orbiting its star at one-seventh the distance between Mercury and our Sun, does not receive enough energy from its star to explain its cotton production. such as density. Alternatively, if the planet’s core actually had more mass than expected, scientists say the atmosphere would have shrunk as the planet cooled over time, meaning it would have become smaller than what is observed.
Using the JWST data – combined with previous observations from the Hubble Space Telescope – two independent teams of astronomers may have solved the puzzle. In short, they found that methane in the planet’s atmosphere is one-thousandth of what would be expected for this world. Because methane is unstable at high temperatures, astronomers say the surprisingly low amount is evidence that the gas deep within the planet is “mixing vigorously with cooler layers higher up,” says David Sing of Johns Hopkins University (JHU) in Maryland, who led the charge. indicated an investigation. of the two new studies, the statement said. “The fact that we detected so little, even though we did detect other carbonaceous molecules, tells us that the interior of the planet must be significantly hotter than we thought.”
The extra heat is likely because WASP-107 b orbits its star every 5.7 days in an orbit that is not a perfect circle, the researchers say. The star’s constant pull on WASP-107 b, whose distance from its star constantly varies, stretches and contracts the planet’s profile, causing it to heat up. On Earth, a similar force from the moon causes ebb and flow.
The planet’s hot core, combined with the star’s tidal heating, also changes the chemistry of gases deep within the planet, said Zafar Rustamkulov, a graduate student at JHU and co-author of one of the two new studies. statement from the university. “We think this heat causes the chemistry of the gases to change, specifically destroying methane and making increased amounts of carbon dioxide and carbon monoxide.”
In 2020, a team of astronomers including Sing discovered helium in WASP-107 b’s atmosphere, marking the discovery as the first time this gas has been spotted on an exoplanet. The element, which was tentatively spotted on Earth in 2018 before its existence was confirmed there two years later, extended far into space like a tenuous cloud. Because this planet’s atmosphere has been flung so far, astronomers say ultraviolet radiation from WASP-107 b’s star is slowly stripping the world of its air – about 0.1% to 4% of its atmospheric mass per billion years, to to be more specific, resulting in a comet-like tail hanging behind the sphere.
The planet’s extraordinarily puffy nature allows astronomers to see about 50 times deeper into its atmosphere than on a world like Jupiter. For example, last year JWST observations of WASP-107 b’s atmosphere showed sand raining down on the planet.
This research is described in two studies published Monday (May 20) in the journal Nature.
Originally published on Space.com.