Neptune is the eighth planet from the sun and the outermost known planet in our solar system, given Pluto's disputed status. The planet is mostly ocean, which is appropriate because it was named after Neptune, the Roman god of the sea.
Neptune was discovered in 1846 by Johann Gottfried Galle. His discovery was based on oddities in the orbit of Uranus, the most distant known planet at that time.
Similar to Uranus, Neptune's core is liquid rock, and its surface is an ocean of water, hydrogen, helium, methane and ammonia.
Neptune's atmosphere consists of hydrogen, helium, methane and ammonia. It appears blue in color because of the methane, and it has many large clouds over its surface.
Day and Year
Neptune spins on its axis faster than Earth, completing a full day every 16.11 hours. Its year is much longer, taking 59,800 days to orbit the sun.
Great Dark Spot
A distinctive characteristic of Neptune is its Great Dark Spot, which is thought to be a depression in the atmosphere moving at high speeds in a direction opposite Neptune's spin.