Neptune
When Uranus was discovered, astronomers noticed that its orbit was not shaped the way
they expected. They guessed (correctly) that this could be due to the gravitational force
of another, more distant planet. This planet turned out to be Neptune, which was
discovered in 1846. As it turns out, the astronomers that discovered Neptune were
incredibly lucky: if they had looked where they predicted a few years earlier or later, the
planet would have been nowhere in sight!
Neptune orbits the sun at a distance of approximately 2.8 billion miles. It has a diameter
of 30,777 miles.
Neptune is similar to composition to Uranus: Mostly ice and rock with some hydrogen
and a small amount of helium. Also like Uranus, Neptune is not layered, but is instead
uniform in composition, although it may have a small core of rock. Neptune’s
atmosphere is composed mainly of hydrogen and helium with a little bit of methane.
Neptune’s magnetic field, like Uranus’, is oriented differently from most planets’ and is
probably the result of conducting material (like water) moving around below its surface.
Neptune’s blue color is partly due the absorption of red light by the methane gas in its
atmosphere. There is also an unidentified substance that gives Neptune’s clouds their
blue color.
Neptune, like the other gas planets has very turbulent winds. In fact, Neptune’s winds are
the fastest in the solar system, reaching speeds of over 1,200 miles per hour!
Many pictures we have of Neptune came from the Voyager 2 mission in 1989. The
pictures taken by Voyager show a large dark spot in the planet’s southern hemisphere.
This spot was a storm, similar to Jupiter’s Great Red Spot, that was moving across
Neptune’s surface at a speed of 700 miles per hour. Unlike Jupiter’s spot, however, this
storm was more short-lived. Pictures taken by the Hubble Space Telescope in 1994
show that the Great Dark Spot has disappeared and a new storm has formed in the
northern hemisphere!
Neptune has several rings and 13 known moons. Its rings are similar to those of Jupiter
and Uranus: they are dark and their composition is unknown. Eight of Neptune’s moons
have names, including the largest, Triton, which was discovered just weeks after Neptune
itself. The five remaining moons were discovered in 2002 and 2003 and have yet to
receive names.