Neptune has a shorter day than the Earth. One day measures about sixteen Earth hours. Since it is the eighth planet from the sun, it has the second longest year. It takes one hundred sixty-five Earth years for Neptune to make one complete orbit around the Sun.
Scientists believe Neptune has a hot, rocky core about the size of Earth. It is covered with an ocean of water and other chemicals. The atmosphere is mainly hydrogen and helium. The high heat inside Neptune causes convection currents. Neptune probably gets as much heat from its central core as it does from the Sun. However, the average surface temperature is only 355 degrees fahrenheit. That is very cold.
Several dark spots have been seen on Neptune. The largest is
about the size of Earth. It is called The Great Dark Spot. It
may be a gigantic storm like the Great Red Spot on Jupiter. The
Great Dark Spot was first seen by the Voyager 2 space probe in
1989. In the 1990s, the Hubble Space Telescope could not find
it. Astronomers are not sure why it disappeared or whether it
will reappear. Long wispy clouds race around Neptune. They are
blown by the fastest winds in the solar system. Near the Great
Dark Spot winds blow up to 1,200 mph! One cloud zooms around the
planet once every 16 hours. Scientists have nicknamed it Scooter
because it moves so quickly.
Even though Neptune diameter is 30,200 miles, it is the smallest
of the four gas planets. Neptune actually looks like a star through
has 8 moons. The biggest ones are Triton and Nereid. Triton is even bigger than the planet Pluto! Unlike most moons, Triton orbits in the opposite direction of Neptune's spin. We now know that Neptune may have faint rings. Neptune's rings were found in 1989.