Neptune is not visible to the unaided eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to gravitational perturbation by an unknown planet. The position of Neptune was subsequently calculated from Bouvard’s observations, independently, by John Couch Adams and Urbain Le Verrier after his death. Neptune was subsequently observed with a telescope on 23 September 1846 by Johann Galle within a degree of the position predicted by Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the planet’s remaining known 13 moons were located telescopically until the 20th century. The planet’s distance from Earth gives it a very small apparent size, making it challenging to study with Earth-based telescopes. Neptune was visited by Voyager 2, when it flew by the planet on 25 August 1989. The advent of the Hubble Space Telescope and large ground-based telescopes with adaptive optics has recently allowed for additional detailed observations from afar.
The Face Behind The Veil. Titan is a little larger than Mercury--the smallest major planet inhabiting our Solar System. Indeed, Titan would have been classified as a major planet in its own right if it orbited our Sun instead of Saturn. The Huygens Probe images lifted the veil from the face of this distant moon-world, revealing a youthful surface that is both smooth and relatively free of impact craters. Huygens also found that this icy, hydrocarbon-saturated moon's climate includes those heavy rains of gasoline, as well as raging, roaring winds. Some of Titan's surface features were found to be hauntingly akin to certain surface features on Earth.
The team's findings can also be applied to exoplanets, which are planets that circle stars beyond our own Sun. Some super-Earth exoplanets, which are rocky planets more massive than our own, have been proposed as "water worlds" covered with churning oceans. Could they have life? Perhaps. The potential would certainly be there. Dr. Vance and his team believe laboratory experiments and more sophisticated modeling of exotic oceans might help to find answers to these very profound questions.
Earth's mysterious large Moon is our nearest neighbor in space, dominating our clear night sky with its beguiling and bewitching cold golden glow. Earth's Moon is the only body beyond our planet that we have visited, leaving our footprints embedded in its alien dust. Despite its close proximity to our planet, our mysterious Moon has still managed to keep some ancient secrets from us very well. However, in October 2014, using data derived from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, a team of planetary scientists announced that they may have solved a lunar mystery almost as old as our Moon itself.