Astronomers believe they have solved a strange and well-known cosmic mystery, NASA announced this week. Two groups of researchers may have figured out what causes certain planets to appear, using observations from the James Webb Space Telescope appearing “bloated” or bloated far beyond the sizes suggested by their remarkably low density.
It’s a phenomenon that appears to stem from 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 already identified thousands of low-density exoplanets, this one was different from the previously studied “hot Jupiters” and even the unusual “hot Neptunes.”
Astronomers studied WASP-107b’s structure in hopes of understanding how it could be so massive while weighing so little, as they assumed it would be cooler inside than due to features such as its size and distance from its star it turned out.
“Based on its radius, mass, age and assumed internal temperature, we assumed that WASP-107 b had a very small, rocky core surrounded by a huge mass of hydrogen and helium,” said Luis Welbanks of the Arizona State University, which led the study of the new studies on the exoplanet, in a statement to NASA. “But it was difficult to understand how such a small core could entrain so much gas and then not fully grow into a Jupiter-mass planet.”
NASA, ESA, CSA, Ralf Crawford (STScI)
WASP-107b is almost as large as Jupiter, but only about a tenth as dense. The exoplanet weighs about 30 Earths, while Jupiter weighs more than 300, making WASP-107b one of the least dense planets known, according to NASA. That’s odd, because it’s less hot and less massive than other “puffy” exoplanets, such as the Jupiter-like gas giant WASP-193b, discovered last year and also known for its exceptionally low density.
Even though there hasn’t been an evidence-based explanation for the swelling of larger, hotter exoplanets, scientists said WASP-107b is particularly difficult to explain because it doesn’t absorb enough energy from the star it orbits for the gases that make it up to inflate so much. But new data from Webb, combined with older data from the Hubble Space Telescope, revealed another reason for its expansion.
The telescope observations detected only a tiny fraction of the methane gas that astronomers had expected in WASP-107b’s atmosphere, which “tells us that the interior of the planet must be significantly hotter than we thought,” said David Sing of Johns Hopkins University. who led a second new study on WASP-107b.
This supports a theory astronomers had previously put forward as to why WASP-107b is “bloated,” suggesting that a process called tidal heating is responsible for both the higher internal temperature and the inflated size. Learning WASP-107b’s atmosphere could also provide crucial insights into dozens of other low-density, “bloated” planets and what causes them to expand, potentially helping to solve what NASA calls a “long-standing mystery in exoplanet science.” designated.