When you buy through links on our articles, Future and its syndication partners may earn a commission.An artist’s impression of the Kepler-51 system. | Credit: NASA/ESA/L. Hustak, J. Olmsted, D. Player and F. Summers (STScI)An exoplanet so light that it would float on water, were there an ocean large enough, is continuing to frustrate astronomers by concealing its closest secrets with a layer of haze thicker than any ever seen on a planet before.The haze is so thick that not even the vision of the James Webb Space Telescope (JWST) can penetrate it, leaving the mystery of how this ultra-low density world and its sibling planets all formed unsolved for now.AdvertisementAdvertisement”These ultra-low density planets are rare and they defy conventional understanding of how gas giants form,” said Jessica Libby-Roberts of the University of Tampa in Florida in a statement. “And if explaining how one formed wasn’t difficult enough, this system has three!”Kepler-51d is a member of a four-planet system orbiting a young Sun-like star 2,615 light years away. They were discovered by NASA’s Kepler Space Telescope, which observed the planets transiting their star. From the amount of the star’s light blocked during the transits, astronomers deduced the size of the worlds, and from transit timing variations — the way each planet’s gravity pulls and pushes on the other planets, varying exactly when they are seen to transit — their masses were measured. Planets 51b, c and d have 7.1, 9 and 9.7 times the radius of Earth, respectively, making them about the same size as Saturn.However, planets b, c and d have masses only 3.7, 5.6 and 5.6 times greater than Earth’s, respectively. Saturn, on the other hand, has a mass 95 times more than Earth. So, these worlds are a similar size to Saturn, but much (much) less massive. (The fourth planet in the system, e, was only discovered in 2024 and its mass and radius are yet to be measured to any degree of accuracy.)It is remarkable that the densities of planets 51b, c and d have more in common with cotton candy (or candy floss as we call it in the U.K.!) than with the planets we are more familiar with.Advertisemen …
