The Planet That Was Considered a Moon

For many years people have looked at Pluto as a moon rather than a planet. It is believed that it may have been a moon of Neptune that simply broke away. We now have more evidence that proves that Pluto is more a planet than a moon.

Scientist have now looked at the orbit of Pluto and have determined that it has the same orbit as Kuiper belt. This is a distant region that consists of thousands of miniature icy worlds with diameters of at least 1,000 km and is also believed to be the source of some comets. Pluto is thought to be the biggest of these small icy worlds. An astronomer named Clyde Tombaugh discovered Pluto in 1930. He also discovered that it takes 248 earth years for Pluto to orbit the sun.

Pluto has a rocky core that is surrounded by a mantle of thick frozen water. This consists of a bright layer of frozen methane, nitrogen, and carbon monoxide on its surface. When Pluto comes to it closets point to the sun some of this outer layer melts to form a thin pink atmosphere. This holds stable for 20 years while Pluto orbits the sun. As it moves away from the sun the thin atmosphere begins to disperse.

In 1978, American astronomers James Christy and Robert Harrington discovered that Pluto has a satellite (moon), which they named Charon. Charon is almost half the size of Pluto and shares the same orbit. Pluto and Charon are considered a double planet. Charon's surface is covered with dirty water ice and doesn't reflect as much light as Pluto's surface. Charon is difficult to observe against the glare from nearby Pluto, and only recently has this smaller member of the "double planet" been viewed as a world with its own personality and puzzles. Although Pluto and Charon were both formed in the outer solar system, they are very different. Charon is much more uniform, its surface mainly frozen water and its atmosphere very thin or nonexistent.

No spacecraft have visited Pluto. NASA is currently considering a mission called New Horizons that would explore both Pluto and the Kuiper Belt region. The earliest it would launch is 2006. It will take and send pictures of Pluto's surface and thin atmosphere. It will also take readings of the planets temperature and weather. Pluto's atmosphere was detected in 1988. We know that its surface pressure is about 100,000 times smaller than that on Earth but still large enough for us to expect weather, winds, haze, chemistry, and an ionosphere. At the