Neptune

The planet Neptune
The planet Neptune showing a Great Dark Spot (photo: NASA) – click to enlarge

Neptune is the eighth, and furthest, planet from the Sun, now that Pluto has been demoted to dwarf planet status. Since Neptune is so far from the Sun, one Neptunian year takes 164.8 Earth years or 89,000 of Neptune’s 16-hour days.

Neptune is roughly eight times the diameter of the Earth and 17 times as massive. Neptune is similar in size and composition to Uranus and just slightly smaller, making it the fourth largest planet in the Solar System. Both Uranus and Neptune are  classed as “ice giants”.

Neptune Stats:

Diameter Distance from Sun Mass Day Year Surface temp
49,244 km
7.8 Earths
29.8 to 30.3 AU 17.1 Earths

Neptune’s Discovery

Neptune’s existence was first predicted by Alexis Bouvard, several years before its discovery, from its gravitational effects on the orbit of Uranus. In 1846 Johann Gottfried Galle observed the new planet within 1° of where mathematian Urbain Le Verrier had predicted it to be, and about 12° from a position predicted by John Couch Adams; all three men are now credited with Neptune’s discovery. Many astronomers, including Galileo, had previously observed Neptune but failed to identify it as a planet, marking it on charts as a faint star.

Composition

Neptune, like Uranus, is classed as an ice giant planet. It is thought to consist of a rocky core – of similar mass to the Earth – a thick mantle of water, ammonia and methane ice and an atmosphere of hydrogen (80%), helium (19%) and trace amounts of methane, giving the planet its beautiful blue colour. White clouds of methane ice are often visible as well as storm systems such as Neptune’s Great Dark Spots – anticyclones roughly the diameter of the Earth, which appear to last several years at a time. Neptune’s high internal heat energy, compared to its sister planet Uranus, drives the fastest planetary winds in the Solar System.

Neptune’s Rings

Neptune, like the other giant planets in the Solar System, has a ring system, however the rings are faint and the outermost consists of five separate arcs, due to the gravitational effects of the moon Galatea.

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Astronomy, Cosmology, Astrophysics and Space Exploration

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