Stars and Planets Book


Although the provisional designation of 2005 FY9 was given to Makemake when its discovery was made public, before that Dr. Brown's team had used the playful codename "Easter Bunny" for this small world, because of its discovery shortly after Easter. A Moon Made Of Lightweight Fluff! Methone is small and oval--and unlike other tiny objects, composed of rock and ice, that scurry around our Solar System. Methone, which was observed up close for the very first time in 2012, is not pockmarked by impacts like other worldlets of its kind. Instead, this strange little moon, is very smooth--it shows not a hill nor an impact crater anywhere on its weirdly smooth surface. This shiny, white, icy egg in Space, residing in a peaceful nest of ice crystals, is an enigma wrapped in a bewildering mystery that some astronomers may have solved. The answer to the bewitching riddle of Methone? It is composed of lightweight fluff! However, it was little Enceladus that gave astronomers their greatest shock. Even though the existence of Enceladus has been known since it was discovered by William Herschel in 1789, its enchantingly weird character was not fully appreciated until this century. Indeed, until the Voyagers flew past it, little was known about the moon. However, Enceladus has always been considered one of the more interesting members of Saturn's abundantly moonstruck family, for a number of very good reasons. First of all, it is amazingly bright. The quantity of sunlight that an object in our Solar System reflects back is termed its albedo, and this is calculated primarily by the color of the object's ground coating. The albedo of the dazzling Enceladus is almost a mirror-like 100%. Basically, this means that the surface of the little moon is richly covered with ice crystals--and that these crystals are regularly and frequently replenished. When the Voyagers flew over Enceladus in the 1980s, they found that the object was indeed abundantly coated with glittering ice. It was also being constantly, frequently repaved. Immense basins and valleys were filled with pristine white, fresh snow. Craters were cut in half--one side of the crater remaining a visible cavity pockmarking the moon's surface, and the other side completely buried in the bright, white snow. Remarkably, Enceladus circles Saturn within its so-called E ring, which is the widest of the planet's numerous rings. Just behind the moon is a readily-observed bulge within that ring, that astronomers determined was the result of the sparkling emission emanating from icy volcanoes (cryovolcanoes) that follow Enceladus wherever it wanders around its parent planet. The cryovolanoes studding Enceladus are responsible for the frequent repaving of its surface. In 2008, Cassini confirmed that the cryovolanic stream was composed of ordinary water, laced with carbon dioxide, potassium salts, carbon monoxide, and a plethora of other organic materials. Tidal squeezing, caused by Saturn and the nearby sister moons Dione and Tethys, keep the interior of Enceladus pleasantly warm, and its water in a liquid state--thus allowing the cryovolcanoes to keep spewing out their watery eruptions. The most enticing mystery, of course, is determining exactly how much water Enceladus holds. Is there merely a lake-sized body of water, or a sea, or a global ocean? The more water there is, the more it will circulate and churn--and the more Enceladus quivers and shakes, the more likely it is that it can brew up a bit of life.