Continuing Our Astronomy 101 - Solar System Tour
Next, we come to the Kuiper Belt. Often called our Solar System's "final frontier," the Kuiper (pronounced Ki-Per) Belt is a disk-shaped region of icy debris is about 12 to 15 billion kilometers (7.5 billion to 9.3 billion miles) from our Sun.More than 1,000 Kuiper Belt Objects (KBOs) have been identified since 1992. (They are sometimes called Edgeworth Kuiper Belt objects, acknowledging another astronomer who also is credited with the idea, or they are simply called transneptunian objects (TNOs.)
Probably the most famous of the Kuiper Belt Objects (KBOs) is Pluto, once considered a planet. Pluto was discovered by American astronomer Clyde Tombaugh in 1930, while working at Lowell Observatory in Flagstaff, AZ. The founder of the observatory, Percival Lowell had theorized that a planet beyond Neptune was affecting its orbit as well as that of Uranus. Tombaugh spent months studying images of the sky, looking for that needle in a haystack. Although Lowell was wrong about a planet affecting Uranus and Neptune's orbit, Tombaugh discovered Pluto, anyway.
After many other suggestions and much debate, the planet was named Pluto partly due to its distance from the sun, which keeps it perpetually in the dark, and partly because "PL" are the initials of Percival Lowell.
Pluto takes 248 years to orbit the Sun. Pluto's most recent close approach to the Sun was in 1989. Between 1979 and 1999, Pluto's highly elliptical orbit brought it closer to the Sun than Neptune, providing rare opportunities to study this small, cold, distant world and its companion moon, Charon.
On August 24, 2006, the International Astronomical Union (IAU) formally downgraded Pluto from an official planet to a dwarf planet. According to the new rules a planet meets three criteria: it must orbit the Sun, it must be big enough for gravity to squash it into a round ball, and it must have cleared other things out of the way in its orbital neighborhood. The latter measure knocks out Pluto.
Pluto can only be seen through large telescopes. Even the Hubble Space Telescope can only make out the largest features on Pluto. It's the only planet not yet visited by a spacecraft.
In January of 2006, the New Horizons Mission launched. It will swing past Jupiter for a gravity boost and scientific studies in February 2007, and reach Pluto and its moons, Charon, Nix and Hydra, in July 2015. Then, as part of an extended mission, the spacecraft would head deeper into the Kuiper Belt to study one or more of the icy mini-worlds in that vast region beyond Neptune's orbit. Sending a spacecraft on this long journey will help us answer basic questions about the surface properties, geology, interior makeup and atmospheres on these bodies.
Comets and Meteors:
Comets have been known to man since we first began looking to the skies; however, it took some time to recognize patterns in these visits. Sometimes called dirty snowballs, they are a mixture of ice and dust, which have highly elliptical orbits about the sun. As a comet nears the Sun, some of the ice turns into gas, which along with the freed loose dust make up the famous tail that streams behind the comet. Comets are only visible as they near the sun. Each pass by the sun wears away more of the comet substance, which may eventually leave a rocky object similar to an asteroid. In fact, some of the asteroids in our part of the galaxy may have been comets at one time. Perhaps the most famous comet is Halley's, which returns approximately every 75 - 79 years.
Meteors are basically space debris, often left behind by comets, that enters the atmosphere of the earth. The friction of the atmosphere creates tremendous heat, causing the objects to glow and appear as what is often called a shooting or falling star. Generally these objects burn up before they reach the ground, but if they make it, they are called meteorites. Those that don't get caught in the earth's gravity and pulled into the atmosphere are often called meteoroids. If you watch the sky, generally you can spot one or two meteors an hour. Occasionally, during certain peak times, like the Leonid, Lyrid, Geminid, and Perseid meteor showers, you may be able to see up to 100 per hour.
Conclusion:
Well, you made it to the end. This course wasn't meant to be a complete study of the field of astronomy, merely an overview, and a chance to pick up some new information about the universe, our solar system, and the planets. I hope it has piqued your interest enough that you will consider more study. If it has, here are a few resources to help you learn more:
Assignment
Read more about Gas Giants, Pluto, and Meteors. Don't forget the discussion Forum.Congratulations, now pass a simple 20 question quiz to get your certificate of completion.