Kepler-51 Super-Puff Planets Baffle Scientists as JWST Finds No Atmosphere Clues

Some planets defy everything we know about how worlds are built. The Kepler-51 system, located 2,615 light-years away, contains three so-called "super-puff" exoplanets — worlds roughly the size of Saturn but so astonishingly lightweight that their density is comparable to cotton candy. Discovered by NASA's Kepler Space Telescope, these bizarre worlds have now stumped even the most powerful observatory ever launched.

Planets So Light They Should Not Exist

According to the new research, the three planets, 51b, c, and d, each have a radius seven to ten times that of Earth, but their masses are only 3.7 to 5.6 times that of Earth. Saturn, which has a similar size to the three new planets, has a mass 95 times that of Earth. According to planet formation theory, gas giants form by first forming dense and massive cores, which then gravitationally attract gas from the surroundings. However, the three new planets have small cores and enormous atmospheres, which cannot be explained by any known theory. Moreover, the three planets are closer to their star than Venus in our solar system.

A Haze Too Thick for Webb to See Through

Astronomers had hoped the James Webb Space Telescope's Near Infrared Spectrometer would finally solve the mystery by detecting the chemical signature of the atmosphere of Kepler-51d. When a planet passes in front of its star, the light passing through the atmosphere leaves behind the "signature" of the molecules. However, the JWST did not detect anything. It is now thought that a haze of hydrocarbons, perhaps similar to the haze of Titan, the moon of Saturn, is obscuring the view. Scientists are now waiting to see the atmospheric signature of the sister planet 51b.