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	Pluto: The First Dwarf Planet
	Pluto is named for the ruler of the underworld in classical mythology.

Pluto was discovered in 1930 by astronomer Clyde Tombaugh. However, it was not until the year 2015 that we finally got a close-up look at the dwarf planet. After a nine-year journey, NASA's New Horizons spacecraft flew by Pluto, taking pictures and collecting data. We now know that the surface of the dwarf planet is a tannish-red color. Scientists also observed a large bright area shaped like a heart and dark regions near the equator. There are high mountains made out of water ice. These mountains are covered by layers of frozen gases. While a few craters were seen, there was not nearly as many as expected. This means that something must be changing the surface of Pluto. Scientists do not yet know what could be causing these changes. From the data collected by the spacecraft, scientists also learned that Pluto has a rocky core surrounded by a thick mantle of ice. Some scientists wonder if there might be a thin liquid ocean beneath the frozen surface. Data from the experiments on-board New Horizons determined Pluto's diameter to be 2,372 kilometers. It has an atmosphere of gases that expands when Pluto is nearer to the Sun. When Pluto is at its greatest distance from the Sun, the atmosphere freezes and falls to the surface. It takes 6.39 Earth days for Pluto to make one spin on its axis. It takes Pluto 248 Earth years to make one orbit around the Sun. Pluto is about 40 times farther from the Sun than Earth. Pluto has five known moons: Charon, Nix, Hydra, Kerberos, and Styx.

A Question What is the name of the spacecraft that flew by Pluto in 2015?