The first planetary nebula discovered (though not yet termed as such) was the Dumbbell Nebula in the constellation of Vulpecula. It was observed by Charles Messier in 1764 and listed as M27 in his catalogue of nebulous objects. To early observers with low-resolution telescopes, M27 and subsequently discovered planetary nebulae resembled the giant planets like Uranus. William Herschel, discoverer of Uranus, perhaps coined the term “planetary nebula”. However, in as early as January 1779, the French astronomer Antoine Darquier de Pellepoix described in his observations of the Ring Nebula, “a very dull nebula, but perfectly outlined; as large as Jupiter and looks like a fading planet”. Whatever the true origin of the term, the label “planetary nebula” became ingrained in the terminology used by astronomers to categorize these types of nebulae, and is still in use by astronomers today.
"Titan is a very active moon. We already know that about its geology and exotic hydrocarbon cycle. Now we can add another analogy with Earth and Mars: the active dust cycle, in which organic dust can be raised from large dune fields around Titan's equator," Dr. Sebastien Rodriguez explained in a September 24, 2018 NASA Jet Propulsion Laboratory (JPL) Press Release. Dr. Rodriguez is an astronomer at the Universite Paris Diderot, France, and the paper's lead author. The JPL is in Pasadena, California. A moon is defined as a natural satellite in orbit around another body that, in turn, is in orbit around its Star. The moon is kept in its position by both its own gravity, as well as its host's gravitational grip. Some planets have many moons, some have only a small number, and still others have none at all. Several asteroids inhabiting our Solar System are circled by very small moons, and some dwarf planets--such as Pluto--also host moons. The findings of the two missions are presented in papers published on April 13, 2017, by planetary scientists with NASA's Cassini mission to Saturn and the venerable Hubble Space Telescope (HST). In one of the papers, Cassini scientists announced their discovery that a form of chemical energy life can feed on appears to exist on Enceladus. In the second paper, HST researchers report additional evidence of plumes erupting from Jupiter's moon, Europa, whose fascinating frozen crust of ice resembles a cracked eggshell. It has long been recognized by planetary scientists that beneath Europa's bizarre cracked shell of ice, there is a sloshing global ocean of liquid water.