This is an image of Pluto with its moon Charon.
Click on image for full size
After the discovery of Neptune in 1846, mathematical theory suggested that there still might be a ninth planet. Scientists set out to discover it, and it was finally identified in 1930 by Clyde Tombaugh after a careful search of the sky.
Finding Pluto was difficult. It had to be done by noticing its motion against the background of stars. Because Pluto is so small, it is also very dim in the sky. At 39 Astronomical Units from the sun, and with 248 years to complete its orbit around the sun, Pluto also moves very slowly. So it was many years before the 9th planet could be identified by its motion.
Pluto is named after the Roman god of the underworld. It has one moon named Charon. The two objects act more like a double planetary system. They orbit each other, as if they were in a standoff, waiting for the other to turn their back. Some people say that Pluto isn't a planet at all, but rather a satellite that escaped Neptune's gravitational pull.
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