Astronomers believe they have solved a remarkable and widely known cosmic mystery, NASA announced this week. Two groups of researchers, mainly using observations from the James Webb Space Telescope, have discovered what causes certain planets to form to look “swollen” or bloated much larger than the dimensions suggested by their remarkably low density.
It’s a phenomenon that seems to boil down to the surprising internal composition of exoplanets like WASP-107b, a “warm” Neptune gas giant identified in 2017 that orbits a star about 200 light-years from Earth. Although scientists have identified thousands of low-density exoplanets, this one was different from the previously studied “hot Jupiters” and even the unusual “hot Neptunes.”
Astronomers looked at the composition of WASP-107b in hopes of understanding how it could be so massive while weighing so little, because based on characteristics such as its size and distance from the star, they assumed it was internally cooler than it turned out to be. .
“Based on its radius, mass, age and presumed internal temperature, we thought WASP-107 b had a very small, rocky core surrounded by a huge mass of hydrogen and helium,” said Luis Welbanks of Arizona State University, who led indicated an investigation. of the new studies on the exoplanet, in a statement to NASA. ‘But it was difficult to understand how such a small core could suck in so much gas and then not fully develop into a planet with the mass of Jupiter.’
NASA, ESA, CSA, Ralf Crawford (STScI)
WASP-107b is almost the size of Jupiter, but only about one-tenth the density. The exoplanet weighs about the same as 30 Earths, while Jupiter weighs more than 300 Earths, making WASP-107b one of the least dense known planets, NASA said. That was strange because it is less hot and less massive than other “puffy” exoplanets, such as the Jupiter-like gas giant WASP-193b, which was discovered last year and is also known for its extraordinarily low density.
While there was also no evidence-based explanation for the puffiness of larger, hotter exoplanets, scientists said WASP-107b was particularly difficult to explain because it doesn’t get enough energy from the star it orbits to pass through the gases that make it up to function. blowing up so much. But new data from Webb, combined with older data from the Hubble Space Telescope, revealed another cause for the expansion.
The telescope observations detected only a small fraction of the methane gas that astronomers expected to find in WASP-107b’s atmosphere, which “tells us that the planet’s interior must be significantly hotter than we thought,” says David Sing of Johns Hopkins University. who led a second new study on WASP-107b.
That supports a theory astronomers have previously proposed about why WASP-107b is “swollen,” suggesting that a process called tidal heating is responsible for both its warmer internal temperature and its bloated size. Learning about WASP-107b’s atmosphere could also provide crucial insight into dozens of other low-density ‘swollen’ planets and what makes them expand, potentially helping to clarify what NASA has called a ‘long-standing mystery in exoplanet science’ mentioned.