Free Astronomy Magazine September-October 2018

PLANETOLOGY 21 L et’s face it, Uranus is hardly ever a leading topic in the popularization of astronomy, perhaps more famous as the brunt of childish humor than scientific inquiry. There are not comparatively many exciting things to say about the seventh planet of our solar system. After the fast flyby performed by the Voyager 2 probe on January 24, 1986, which produced a leap in our knowledge of Uranus, only a few other pieces of information were added thanks to sporadic observations SEPTEMBER-OCTOBER 2018 using large ground-based telescopes and, above all, the Hubble Space Telescope. Even today, the modern profile of Uranus is only approximate: it is a frozen giant 50 thousand km in diameter; it is slightly larger but slightly less massive than Nep- tune; it probably has a small rocky nucleus topped by a dense and fluid ocean of water, methane and ammonia; it has an atmos- phere dominated by hydrogen and helium, with a small percentage of methane that gives the planet its typical blue-green color. S pectacular photomontage made by Jimmy Wallebring (Öre- bro, Sweden), which shows Uranus, some large moons, and rings as seen from the huge canyon Messina Chasma that characterizes the surface of the satellite Titania.