While most of our solar system’s planets were discovered through telescopic observations, Neptune was the first planet discovered through mathematical predictions. When analyzing Uranus’s trajectory, the French mathematician Urbain Le Verrier and the English astronomer John Adams detected surprising differences between the planet’s hypothesized and observed orbit. To resolve this dilemma, they proposed the existence of an eighth planet to explain Uranus’s unexpected orbit. By using Le Verrier’s and Adams’s calculations, Johann Galle of the Berlin observatory was able to locate the planet just one degree above its predicted location.
Neptune orbits the sun every 164.79 years. Thus in 2010 the planet will have completed one orbit since Galle’s observation, on September 23, 1846. While Neptune’s neighbouring Pluto has recently been reclassified as a dwarf planet, even when it possessed its majestic place as the ninth member of our solar system, its elliptical orbit temporarily positioned it closer to the Sun than Neptune. This routine occurs once every 248 years, and the two planets exchange positions for approximately 20 years, making Pluto the eighth and Neptune the ninth planetary body during that period.
Due to its great distance from the Sun, prior to the 1989 Voyager 2 mission, astronomers were unable to delve into Neptune’s details, and consequently presumed it to be a dull and featureless planet. Yet as Voyager 2’s cameras demonstrated, the fierce storms raging across its surface make it anything but bland.
In the southern hemisphere of the planet, Voyager 2 observed a gigantic dark storm adequately named the Great Dark Spot, similar in characteristics to Jupiter’s Great Red Spot. While the dark spot was presumed to be a large stationary version of Earth’s hurricanes, to astronomers’ surprise in 1994, the Hubble Space Telescope was unable to locate the storm. On various occasions, similar dark spots were observed but never in the same location, nor of the same magnitude. One such reoccurrence happened in 2007 when Mate Adamkovics of the University of California re-spotted a cloudy patch in Neptune’s South Pole, and observed that over the course of a few days it split into two smaller entities.
Neptune’s atmosphere is made up of layers of clouds of frozen methane, helium, and hydrogen sulfide, which at lower altitudes and higher pressure compress into a liquid layer that surrounds the planet’s rock and ice core. While this layer is virtually liquid-like, an abundance of hydrogen molecules prevent the formation of true liquid water by inserting themselves into the water molecules. This keeps them from condensing into water, and yet forms a water-like substance.
Similar to the rest of the outer planets of our solar system, Neptune also possesses a system of rings. Although they are comparable to Jupiter’s rings, the difference lies in the uneven spread of the dust they are composed of. The most distinguishable example is Adams ring, which is composed of discrete arcs named Liberty, Equality, Brotherhood, and Courage. Astronomers believe that the stability of the arcs may be due to the ring’s interaction with Galatea, one of Neptune’s thirteen moons.
Although Neptune’s original nine satellites were observed by Voyager 2, the final four were discovered in 2002 by Mathew Holman and his team. The largest of Neptune’s moons, Triton, was discovered in 1846 by William Lassell, and is the coldest place in the solar system, with temperatures reaching -235 degrees Celsius. Triton’s surface is covered with active volcanoes which erupt nitrogen ice crystals up to ten kilometers above its surface. It is hypothesized that the volcanoes may once have spewed the mixture of ammonia and water which now coats the Triton’s surface in a frozen layer.
After plunging into Neptune, we set course for an asteroid belt extending past Neptune and surrounding our entire solar system. Until then, the night sky awaits your exploration.
