Uranus is an odd planet. Its rotational axis is tilted more than 90 degrees. Its pale blue orb is mostly featureless. Most peculiar, though, is that at times in its orbit, it moves faster than it should. At other times, slower. It’s as if some unknown force is pulling on it from the far reaches of space.
That mysterious force belongs to Neptune, the last planet in our fine solar system.
A Frenchman by the name of Alexis Bouvard was the first to notice that Uranus was not where it should be. Having made tables depicting the orbits of Jupiter and Saturn, he knew that something must be impacting Uranus that was, as of yet, unknown to astronomers, though he was unable to prove it himself. That honor was for another Frenchman, Urbain Le Verrier. Or was it John Couch Adams? History says both. Adams was the first to do the calculations and even sent his prediction of the mystery object’s location to an observatory. When the observatory replied asking for clarification, he neglected to answer. Le Verrier was the first to both do the calculations and have someone verify his results. In September 1846, Johann Gottfried Galle, upon receiving a letter from Le Verrier, pointed his telescope to the sky and found a faint blue disk, less than a degree from where it was predicted to be. The solar system gained a new planet — Neptune.
Now, here’s where it gets tricky: Galle wasn’t the first to actually see Neptune. The observatory that acted under Adams’ instruction viewed Neptune months earlier, but, lacking accurate star charts or a follow-up from Adams, they were unable to definitively know what they saw. Similarly, John Herschel, son of the discoverer of Uranus, claims to have noticed a disk-like blue object during an observation, but he assumed it was a star. Going even further back, drawings made by Galileo in the 1600s show that he, too, saw Neptune, but due to its faintness and apparent lack of motion, he also mistook it for a star — though that might be up for debate. Because all of these people saw Neptune but failed to recognize its true identity, they are not credited with the discovery. That goes to Urbain Le Verrier.
Now, on to the planet itself. Neptune is what’s known as an ice giant, which is a gas giant with a high amount of heavier elements that condense at a lower temperature. Because of its distance from the Sun (roughly 30 times as distant as Earth), Neptune’s atmosphere is among the coldest places in the solar system. The extreme cold is what allows the heavier elements to “freeze out,” hence the term ice giant. The atmosphere is also very windy, which allows for massive storm systems to form and move across the surface rapidly. Most notable was the Great Dark Spot, which is featured in most photographs of Neptune. It was similar to the Jupiter's Great Red Spot in many ways — the main difference between the two is that Jupiter’s spot has remained for hundreds of years (though it is getting smaller). Neptune’s spot has disappeared from the atmosphere since subsequent observation in 1994. A smaller spot, aptly named the Small Dark Spot, has also formed on the surface, but it is unknown how long it will last. A personal favorite storm of mine is called Scooter, a small white storm that had formed near to the Great Dark Spot but moved even more rapidly along the surface than either Spot.
As of now, Neptune is the furthest known planet from the Sun, but it hasn’t always been that way. Current models of the formation of the solar system suggest that Neptune was actually interior to Uranus after formation. After Jupiter and Saturn, the two most massive, and therefore gravitationally-dominant planets, formed an orbital resonance and flung Neptune to the outer solar system and into the newly formed Kuiper Belt. Such a dramatic introduction of a massive object sent many smaller bodies into the inner solar system. Much of the cratering seen throughout the solar system is thought to have been from this series of perturbations, known as the Heavy Late Bombardment. It is also thought that many of the icy objects in the Kuiper Belt struck Earth and introduced much-needed water to our planet (thanks, Neptune).
Jupiter, being the most massive object nearest to the asteroid belt, causes various orbital gaps and eccentricities (or how oval-like the orbit) is among the much smaller asteroids. Neptune has a similar effect on the Kuiper Belt, shaping the orbits of the small objects found there. Many objects orbit in a simple ratio with respect to Neptune. Pluto is one that orbits twice for every three orbits of Neptune, meaning it has a 2:3 orbital resonance. Other dwarf planets share orbital resonances with Neptune, but they are generally not as even (Eris is in a 5:17 resonance, for example).
Of the seven major moons in the solar system, Neptune has one. Discovered shortly after Neptune itself, Triton was the only known moon for nearly a century until the discovery of tiny Nereid. Along with being the coldest surface in the solar system, Triton has the distinction of being the only large moon with a retrograde orbit. Every major body in the solar system orbits either the Sun or its primary in a counterclockwise motion — Triton does not. It is thought that during Neptune’s migration, it captured Triton from the Kuiper Belt, which would lead to its unusual orbit. A rather new notion of cryovolcanism — when supercooled ices behave like molten rock and can erupt, naturally, from cryovolcanoes — is present on Triton. Voyager 2, the only flyby of Neptune, was the first to discover such phenomena, but it is now known that Europa, a moon of Jupiter, and Titan and Enceladus, moons of Saturn, all exhibit something like cryovolcanism, with suspected occurrences on Pluto as well.
@ThinkinAbtSpace
