Last Call

• Named after the God of The Seas
• Galileo observed Neptune when it was closer to Jupiter in 1613, but discounted it as a star
• Is an ice giant
• One day is 16 hours
• One year is 165 Earth years
• Has 13 moons

Neptune was predicted to exist before it was found. Something was pulling/pushing Uranus out of it's theoretical orbit by another celestial body, and scientists theorised Neptune's existence. However, the planet was first observed in a location very close to that predicted in the year 1846. 

Much of our information about Neptune comes from the spacecraft Voyager 2, which visited Neptune in 1989. Voyager 2 recorded the most information about our solar system of any other spacecraft to date.

Models suggest that Neptune probably holds a very similar composition to Uranus, both of which are often called “ice giants” based on the large quantities of hydrogen and other less volatile materials than the other two gas giants in the Outer Solar System. It has a small, rocky core. The atmospheric composition of Neptune is 74% hydrogen, 25% helium, with trace amounts of methane and heavier elements such as carbon, oxygen, and nitrogen. The methane gas is mostly responsible for Neptune’s blue color, as it absorbs the red spectrum of light that hits it. However, there is likely another unknown substance that enhances Neptune’s blue colouring.

When the Voyager 2 visited Neptune in 1989, it photographed a great dark spot similar to Jupiter’s famous Red Spot. It was thought to be a similar hurricane-like storm, possessing winds of up to 1,500 miles per hour. However, in 1994, when the Hubble Space Telescope again tried to photograph the Great Dark Spot, as it was named, it had apparently disappeared! Eventually, a storm of approximately the same size and magnitude emerged on Neptune farther to the north, and that is now referred to as the Northern Great Dark Spot and remains visible to this day.

Neptune has 13 known moons, the largest and most famous of which is Triton. An astronomer named William Lassell discovered this moon in 1846, and it possesses a unique orbital trait: it is the only known moon that orbits its planet retrograde. That is to say that while Neptune rotates in one direction, Triton orbits it in the opposite direction. Triton is slightly smaller than the Earth’s moon, and has a somewhat elliptical orbit. The gravitational pull Neptune exerts on Triton varies due to the moon’s elliptical orbit, and it also provides frictional resistance, pushing and stretching the moon.

This friction has created a warm inner core to the moon, and as a result, the surface has a number of active ice volcanoes and frozen lakes.

It is thought that the white, snow-like substance that covers Triton is frozen nitrogen. Also unusual for a satellite, Triton has a thin nitrogen atmosphere: most moons are much too small to have an atmosphere of their own.

There are four thin rings consisting of dust, ice particles, and bits of sand that encircle the planet Neptune. It is thought that, similar to other ringed planets we have studied, these rings were formed by inner satellites colliding and causing chunks of debris to fly loose and enter into orbit around the blue planet. Neptune’s outermost ring has three bright arcs that may be a result of another of Neptune’s moons, Galatea, and its gravitational interference with the rings causing bits of ice to tend to clump together in certain patterns.