As you look at this long lost planet, what do you see? Do you just look at it as another planet? Or do you see something else, a planet debated on by scientists for almost three fourths of a century. Who actually discovered it? Is it just a moon that escaped Neptune’s orbit, or one of the most unknown objects in the solar system?

Basic Facts

Pluto is usually the ninth planet from the sun. I said "usually" because sometimes Pluto switches positions with Neptune because of the planets’ odd orbit around the sun. Pluto becomes the eighth planet while Neptune becomes the ninth. Don’t worry though, that won’t happen again until the 23^rd century. Neptune and Pluto last switched positions back in 1995.

It takes about 18 years for a space probe to travel to Pluto. How old will you be by the time you reach the planet if you left now? What year will it be?

It is very cold on Pluto, with temperatures reaching as low as –400 degrees Fahrenheit! Most of the time the average temperature there is about –370 degrees Fahrenheit.

The Discovery

After the discovery of Neptune in 1846, scientists thought that there was still another planet in our solar system. So, they set out to look for it. Finding Pluto was very difficult because it is very small and a long distance away from the Sun. Pluto looks very dim in the sky when you look at it through a telescope.

Lowell and Planet X

An astronomer named Percival Lowell began looking in the early 1900’s for the ninth planet, which he called Planet X. He constructed a private observatory lab in Flagstaff, Arizona, hoping to find the planet. He made many attempts to discover this unknown planet, but he was not successful. His first search ended in 1909, but he started a second search in 1913. Lowell and many other astronomers searched for the planet from 1913 to 1915. In 1915, he published the results from his search. Unknown to him, or anyone else, the very same year, two small photographs of Planet X were recorded at his observatory. Along with the two pictures of Planet X, he also discovered 515 asteroids and 700 different stars that no one had ever seen before. Even though he found all of this, Lowell was very disappointed that he did not find the far away planet. He died the following year, 1916, not knowing that he had actually discovered the long lost planet.

The Good Luck of Clyde Tombaugh

No one looked for Planet X for another 12 years. Finally, in 1927, the search was on once again. In 1929, an astronomer named Clyde Tombaugh was hired to find Planet X. Tombaugh took photographs of the solar system every one or two weeks to look for anything that shifted or moved. This method was very successful. This 24-year-old lab assistant from Kansas discovered Planet X on February 18, 1930. During the earlier searches, Lowell didn’t expect the planet to be so small, which is perhaps why it was overlooked in the photographs he recorded years earlier. Tombaugh was lucky to find Planet X because it was so far away and moves very slowly. Clyde Tombaugh became the first, and only, American to discover a planet.

The Name

Since Tombaugh found the planet, he was very excited, but he had to do just one more thing – name it! (Whoever discovers a planet has the privilege to name it.) Many ideas for the name were given, like Lowell, Apollo, and Constance. Finally, he chose a name suggested by an 11 year-old girl from England, Venetia Burney. She named the tiny planet Pluto, after the Greek God of the Underworld. Another reason Planet X was named Pluto was because it is so far away from the sun, and it is always in darkness. So naming it after the God of the Underworld seemed most appropriate.

Is Pluto Really A Planet?

It took a long time to confirm that Pluto was a planet because scientists must see that an object orbits a star in order to be a planet. In this case, that star would be the sun. (Remember, it takes 248 years to orbit the sun for Pluto.) Scientists did not watch the planet for 248 years. They just watched it for a short period of time to see if it was in some type of an orbit with the Sun. Objects also have to meet two other requirements to be called a planet:

It must be small enough to not be undergoing internal nuclear fusion; the process stars use to create light by combining hydrogen atoms to make helium atoms.

It must be large enough to be able to maintain its own self-gravity; it has its own gravitational pull to orbit the sun.

Unlike asteroids located in the asteroid belt, every planet has at least a thin atmosphere. Asteroids are also called "minor planets" because they are thought to be remains of another planet that tried to form millions of years ago. This is not a requirement to be a planet. This is why asteroids are not planets. Comets are not planets because they have a possibility of disintegrating while in orbit.

"Inside Scoop"

Although scientists know very little about Pluto’s surface, they believe the planet has three layers. The first layer is made up of frozen-methane. The second layer may be ice. Scientists do not know what makes up the third layer.

Pluto’s Moon

Pluto has one moon, Charon. Jim Christy discovered it in 1978. Before Charon was discovered, Pluto looked like it had a very large lump on its side. But in later years, when technology improved, scientists found that Pluto and its moon were actually two separate things. Pluto looked much larger because Charon blurred together with Pluto. Actually, Charon is only slightly smaller than Pluto.

Future

Pluto has not been visited by anyone or anything from Earth, and remains one of the most mysterious objects in space. Maybe in 2006, though, when NASA launches a probe to Pluto, scientists might be able to answer some questions that they have about the planet. Some scientists still believe that Pluto was once one of Neptune’s moons that escaped its gravitational pull. But until that is proven as a fact, Pluto will remain our solar system’s ninth, and darkest planet.

"Pluto." Encarta Encyclopedia, 1996.

Kerrod, Robin. Uranus, Neptune, and Pluto. Minneapolis: Grahm Beehag Books, 2000.

Space: Everything You Need To Know and Beyond. </J0112388> Last visited: December 2001.

Space: Today, Tomorrow, and Always. </J0112188> Last visited: December 2001.

Send us an email

All pictures courtesy of NASA unless otherwise noted