by DM Zwack

Created on: May 17, 2009   Last Updated: May 23, 2009

In the middle of the 19th Century, two scientists, John Couch Adams of Great Britain and Urbain Le Verrier of France, concluded independently that, due to irregularities in the orbit of Uranus, another planet must exist beyond it. Both men calculated this new planet's approximate position before it was ever seen through a telescope, making Neptune the only planet discovered through calculation rather than observation. In 1846, German astronomer Johann Gottfried Galle used Le Verrier's figures to identify the new planet, though it had actually been seen before but thought to be a faint star. There followed an international controversy over who should get credit for the discovery.

Since the demotion of Pluto to dwarf status in 2006, Neptune now holds the official title of most distant planet, although between 1979 and 1999, Pluto's bizarrely elliptical orbit brought it temporarily closer to the sun. The fourth largest planet in the Solar System, Neptune is named for the Roman God of the sea and, indeed, the small but significant composition of methane in the planet's atmosphere makes it appear a deep ocean blue. Neptune is large enough for 60 Earths to fit inside it and so far from the sun that the planet itself generates more than twice as much energy as the meager solar contribution provides.

Unlike the almost inert and inactive Uranus, its near twin in size and composition, Neptune is alive with vast storms and powerful winds that blow against the rotation of the planet. Wind speeds of 1,200 miles per hour have been observed, the fastest in the Solar System. Like the other three planets known as gas giants, Neptune probably has no solid surface. A faint set of rings orbiting the planet has also been detected. Neptune is unique among the planets in that it has not even made one revolution around the sun since its discovery (Again, this is since the demotion of Pluto, which takes even longer to orbit the sun). Neptune takes an agonizing 165 years to complete an orbit.

Neptune has more than a dozen moons, and perhaps more that are too tiny and dark to be seen. Most of these are fairly small, but the planet's largest satellite qualifies as one of the strangest in the Solar System. Triton, discovered by William Lassell only a few weeks after the planet itself was first observed, is the largest known object to exhibit a retrograde orbit-that is, an orbit in the opposite direction of the planet's rotation. Because of this, Triton may have been captured from the Kuiper Belt, the source of the Solar System's dwarf planets, including Pluto and Eris. In fact, according to data gathered by Voyager 2 in the late 1980s, Triton's composition is very similar to that of Pluto's. Triton, locked in an almost circular orbit and always facing the same side toward the planet, raises significant tides on Neptune's surface and may contribute to the forceful winds mentioned earlier. Some astronomers believe Triton may some day draw close enough to Neptune to destroy the moon and irrevocably alter the planet.

Despite the obvious high levels of activity on Neptune, it is one of the coldest places in the Solar System, with Celsius temperatures of negative 200 degrees below zero not uncommon. Triton is colder still, with temperatures of -240 C, making it the most frigid locale yet discovered. Yet, as the above information attests, one should never assume cold means dead. Despite being 2.8 billion miles from the sun, Neptune is a lively and vibrant planet.

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