The James Webb Telescope solves the mystery of inflated exoplanets – NBC New York

With more than three-quarters the size of Jupiter but less than a tenth its mass, exoplanet WASP-107 b is one of the least massive planets known.

Now, new data from the James Webb Telescope has helped understand why this giant gas body “bloated.”

Webb’s data, combined with previous observations from the Hubble Space Telescope, show there is “surprisingly” little methane (CH4) in the atmosphere of WASP-107 b, suggesting that the planet’s interior must be noticeably hotter. The planet’s core is much hotter than previously estimated.

The results, which show that the exoplanet is not as mysterious as it seemed, have been published in two articles in the journal Nature, based on observations by NASA and the European Space Agency ESA.

These results, made possible by Webb’s “extraordinary ability” to measure light passing through exoplanetary atmospheres, may explain the inflation of dozens of low-density exoplanets.

Although puffy or “spongy” planets are not uncommon, most are hotter and more massive, and therefore easier to explain.

“Based on its radius, mass and age, we thought WASP-107 b had a very small rocky core surrounded by a huge mass of hydrogen and helium, but it was difficult to understand how this could happen,” explains Lewis Wilbanks of Arizona State University. “Such a small core could absorb so much gas and not become a planet with the mass of Jupiter.”

On the other hand, if WASP-107 b had more mass in the core, the atmosphere should have contracted as the planet’s temperature cooled in the time that has passed since its formation.

Without a heat source to re-expand the gas, the planet would have to be much smaller.

Although WASP-107 b has an orbital distance of only 8 million kilometers (one-seventh of the distance between Mercury and the Sun), it does not receive enough energy from its star to inflate that much.

WASP-107 b’s giant radius, vast atmosphere, and edge-on orbit make it ideal for transmission spectroscopy, a method used to identify different gases in an exoplanet’s atmosphere based on how they affect starlight.

Thus, the abundance of a large number of molecules was not only detected, but also measured, such as water vapor, methane, carbon dioxide, carbon monoxide, sulfur dioxide, and ammonia.

The two spectra – obtained by measurements from several Webb and Hubble instruments – show a surprising lack of methane in the atmosphere of the planet WASP-107 b: a thousandth of the amount expected based on its assumed temperature.

“This shows that the hot gas deep inside the planet must be mixing strongly with the cold layers above,” says David Singh of Johns Hopkins University.

Methane is unstable at high temperatures. “The fact that we have detected so little, even though we have detected other carbon-bearing molecules, tells us that the interior of the planet must be much hotter than we thought,” he says.

The likely source of WASP-107 b’s additional internal energy is tidal heating generated by its slightly elliptical orbit.

As the distance between the star and the planet constantly changes throughout its 5.7-day orbit, the force of gravity also changes, causing the planet to expand and heat up.

Researchers had previously suggested that tidal heating could be a cause of the swelling of WASP-107 b, but until Webb’s results, there was no evidence.

The core mass is at least twice what was originally estimated, which makes more sense in terms of how planets form.

Overall, it turns out that WASP-107 b is not as mysterious as it seems. “Webb’s data tells us that planets like WASP-107 b didn’t have to form in a strange way, with a very small core and a massive gaseous envelope,” says Mike Line of Arizona State University.

“Instead, we could take something that looks like Neptune, with a lot of rock and not a lot of gas, and just increase the temperature and give it the shape it looks like.”