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Neptune is the eighth planet from the sun, the fourth largest, and a gas planet. It is named after the Roman god of the sea. Neptune is four times the size of Earth, and its day lasts a little more than16 hours. Its year is about 165 Earth years. Neptune's orbit is a perfect circle. The last stop on spacecraft Voyager's epic trip through the solar system was the gas giant Neptune.
Since humans have observed strange phenomena, they have tried to explain them. UFO theories vary as widely in their credibility as in their imagination. Learn about theories of UFOs, aliens, spaceships, and the government.