James Webb Telescope Unravels Mystery of Inflated Exoplanet – NBC New York

With more than three-quarters of Jupiter’s volume but less than one-tenth its mass, exoplanet WASP-107 b is one of the least dense planets known.

Now, new data from the James Webb Telescope has helped explain why this giant gas body is so “inflated.”

Webb’s data, combined with previous Hubble Space Telescope observations, show “surprisingly” little methane (CH4) in the atmosphere of WASP-107 b, indicating that the planet’s interior should be significantly hotter, with a core much hotter than previously assumed. .

The results, which show that the exoplanet is not as mysterious as it seemed, have just been published in two papers in the journal Nature, according to notes from the US space agency NASA and the European Space Agency ESA.

The results, made possible by Webb’s “extraordinary ability” to measure light passing through the atmospheres of exoplanets, could explain the swelling of dozens of low-density exoplanets.

While 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 that WASP-107 b had a very small rocky core surrounded by a huge mass of hydrogen and helium,” explains Louis Welbanks of Arizona State University, but “it was difficult to figure out how.” Such a small core could absorb so much gas and not become a planet with the mass of Jupiter.”

If, on the other hand, WASP-107 b has more mass at its core, the atmosphere should have contracted as the planet cooled in the time since its formation.

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

Although WASP-107 b has an orbital distance of only 8 million kilometers (one-seventh 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, extensive atmosphere and marginal orbit make it ideal for transmission spectroscopy, a technique used to identify different gases in an exoplanet’s atmosphere based on how they affect starlight.

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

Two spectra obtained from measurements from multiple Webb and Hubble instruments show a surprising absence of methane in WASP-107 b’s atmosphere: one thousandth the amount expected based on its estimated temperature.

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

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

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

As the distance between the star and the planet changes constantly throughout its 5.7-day orbit, so does the gravitational pull that stretches the planet and warms it.

Previously, researchers had suggested that tidal heating might be the cause of WASP-107 b’s swelling, but there was no evidence until Webb’s results.

The core is at least twice as massive as originally thought, which makes more sense in terms of planet formation.

All in all, it turns out that WASP-107 b is not as mysterious as it seemed. “Webb’s data tells us that planets like WASP-107 b shouldn’t have formed in some strange way, with a super-small core and a huge envelope of gas,” says Mike Line of Arizona State University.

“Instead, we can take something similar to Neptune, with more rock and less gas, and just raise the temperature and give it the appearance that it does.”