Neptune and Uranus are twins in some respects. They're very close to one other in size, mass, and composition. They're also distinctly different to the two larger giant planets, Jupiter and Saturn, in that they contain more molecules like methane, ammonia, and water. While the larger gas giants are mostly hydrogen and helium, these light gasses make up only 20 percent of their colder sister worlds.
PHOTOS: Cosmic Hotshots from Keck Observatory
Understanding the atmospheres of giant planets can tell us a great deal about how those planets work, but we still know very little about them. Only a handful of spacecraft have ever visited our solar system's largest worlds, and only one (the Galileo probe in 1995) has ever given us a glimpse of a giant planet, Jupiter, from inside its atmosphere. For a long time, a big question has been whether the winds reach deep into a planet's atmosphere, or if they're only found near the surface.
For this study, Kaspi and his colleagues used an ingenious trick. They analysed the gravitational fields of the two ice giant planets to look for how they were affected by winds. The gravitational field of any planet is affected by how dense it is.