THE BOYS' BRIGADE

Pluto

Our Sun would look like a small dot of light if you were standing on the surface of Pluto. But Pluto is so far away that no spacecraft has ever visited it. Pluto is the ninth planet in our solar system. Astronomers know less about Pluto than about any other planet.

Pluto is usually the farthest planet from the Sun. It goes around the Sun in an oval-shaped path called an orbit. It takes almost 248 Earth years for Pluto to go around the Sun once. Sometimes Pluto’s orbit brings Pluto closer to the Sun than the eighth planet, Neptune. During that time, Pluto is the second farthest planet from the Sun. Neptune is farther.

HOW WAS PLUTO DISCOVERED?

An American astronomer named Percival Lowell observed that the orbits of the distant planets Neptune and Uranus changed slightly as they went around the Sun. Lowell decided that the changes were being caused by an unseen planet. He called it Planet X.

Lowell died before he found Planet X. A young astronomer named Clyde Tombaugh found Pluto in 1930. It was not in the same place that Lowell predicted, and it turns out that Lowell made mistakes in his math. But because he called attention to it, Tombaugh worked hard to find another planet and did. He saw Pluto on pictures taken with a powerful telescope. Even with a powerful telescope, Pluto looks like just a tiny dot of light.

Astronomers in 1978 found that Pluto has a moon. They named the moon Charon. Charon is almost as big as Pluto. In 2005 astronomers discovered two small moons.

WHAT IS PLUTO MADE OF?

Scientists are not sure what Pluto is made of. They think it’s made of rock and ice. They know that Pluto is very cold because it is so far from the Sun.

Pluto has a thin atmosphere sometimes, when it comes closest to the Sun. An atmosphere is a layer of gases around a planet. The Sun warms frozen gases on Pluto’s surface. Some frozen nitrogen, carbon monoxide, and methane turn to gas and become an atmosphere. When Pluto moves farther from the Sun, the gases freeze again. For most of its orbit, Pluto has no atmosphere.

In 1994, the Hubble Space Telescope, orbiting high above Earth, took pictures of Pluto. The pictures showed that there are ice caps at Pluto’s north and south poles. They showed that there are bright and dark areas on Pluto.

Scientists are not even sure exactly how big Pluto is. They know that it is smaller than Earth’s moon. There are many things left to learn about Pluto. The New Horizons spacecraft was launched in 2006, and scientists hope it will fly past Pluto in 2015.