l l Learning Objective
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      Pluto was discovered in 1930. It is the smallest planet in the solar system, about 1/5th the size of Earth, and it is the furthest away from the Sun. It takes Pluto an incredible 248 years to make one of its highly elongated orbits of the Sun. It rotates on its axis once every 6.4 days. Due to its small size and great distance from Earth, Pluto’s true nature is a mystery. In 1978, a moon called Charon was discovered orbiting Pluto. The average temperature of Pluto is estimated to be -210°C. This is cold enough to solidify most gases. It is suggested that Pluto has a meager atmosphere comprised mainly of nitrogen. Pluto has been described as a large, dirty ice ball made up of a mixture of frozen gases with lesser amounts of rocky substances.