In the outer limits of our solar system there is a planet unlike any other, Pluto. Pluto was discovered in February of 1930 by an American astronomer, Clyde Tombaugh. It is the only planet to have been discovered by an American. All though we have known of the existence of Pluto for over thirty years now, there are still many mysteries surrounding this celestial body. Being the farthest planet has made it difficult to study Pluto, Adding to the obscurity of this strange planet is that the capability to send spacecraft such distances has never been achieved. Through the wonders of science and astronomy, there are many things that can be determined, concluded, and hypothesized about this obscure planet.

Pluto's discovery was actually a fortunate accident. Clyde Tombaugh was searching for a ninth planet to explain inconsistencies in the orbits of Neptune and Uranus. Once further research was done regarding Pluto it was determined that the size of Pluto was too small to account for the irregularities of the orbits. Astronomers continued to search for a tenth planet, "Planet X." The calculations that made scientists to believe this have since been proven incorrect by the Voyager 2. With the more accurate mass of Neptune that Voyager 2 was able to produce, the discrepancies of the orbit were explained. It is no longer believed that there is a tenth planet.

Since it's discovery, the legitimacy of Pluto as actually being a planet, has long been debated. The numerous irregularities found when studying Pluto, coupled with its minuscule size has made it the object of controversy. For a while it was believed that Pluto could have possibly been another moon of the planet Neptune. This was often believed due to similarities between Pluto and the Neptune moon Triton. Triton and Pluto have similar surface and atmospheric properties, both being of near equal temperatures. Many believe that Triton was also once independent from Neptune, and that Triton, like Pluto, came from the Kuiper Belt explaining such relations.

Also, both Pluto and Triton have very unusual orbits which does lead some to believe that there is a cosmic connection between the two. Upon ruling out the possibility of Pluto being another moon of Neptune, Pluto was then classified by the International Astronomical Union (IAU) as a Trans-Neptunian Object, or TSO. With the discovery of the Kuiper Belt, and many small objects with properties similar to Pluto, questions arose about whether or not Pluto was just another one of these objects. To be qualified as a planet and object must orbit a star, is not star-like in that it is undergoing internal nuclear fusion, and has a gravitational force that will allow it to retain a spherical shape. Pluto certainly fulfills these requirements, however, there are Kuiper objects that also meet the same criteria. These objects have been classified as minor planets and have been assigned a numerical designation.

Despite all the argument for demoting Pluto to a minor planet, its status has remained the same, even if solely contributed to maintaining historical context. As mentioned earlier, Pluto has a rather unusual orbit. Pluto, while it is the furthest planet from the sun, for twenty years during its two-hundred and forty nine year orbit, it is actually the eighth planet, crossing over Neptune's orbit. Regardless of the fact that the orbits of the two planets cross, their orbits will not allow for them to ever collide.

This is mainly due to Pluto's orbiting not staying in the elliptic plane. Because of its unusual orbit, Pluto travels above and below Neptune as the cross, avoiding collision. What also allows these two bodies to cross paths and avoid impact is that when Pluto is at one side of the sun, Neptune is at the other. This is a result of Pluto taking three times as long to make one orbit around the sun in comparison to Neptune. Pluto crossed in front of Neptune most recently in January of 1979 and crossed back out in February of 1999. Its orbit is not only unique in it's crossing path, but also that its poles nearly lay in the orbital plane.

This gives Pluto the appearance that it is tipped on its side, which, in essence, it virtually is. Pluto's rotation also has notable qualities. Pluto's rotation period is 6. 387 days, the same as its satellite / moon Charon. Although it is common for a moon to travel in a synchronous orbit with its planet, Pluto is the only planet to rotate synchronously with the orbit of its satellite. Thus being tidally locked, Pluto and Charon continuously face each other as they travel through space.

From 1985 to 1990, the Earth lined up with Pluto and Charon to cause and eclipse every Pluto day. This occurrence allowed astronomers to gather a multitude of valuable information about Pluto and its moon. The eclipses lasted as much as four hours and by carefully timing their beginning and ending, measurements for their diameters were taken. Photograph's later taken by the Hubble telescope confirms Pluto's diameter of 1413 miles, and Charon's, at nearly half the size, 728 miles across within one percent accuracy.

Astronomers where also able to determine the density of Pluto during the daily eclipses. By discovering the density to be approximately two grams per cubic centimeter, astronomers where able to hypothesize the make up of the planet. They concluded that Pluto is fifty to seventy percent rock with mixed with ice. Astronomers are also confident in the density of Charon. If correct, the approximate density of one gram per cubic centimeter would mean that Charon contains little rock, and therefore Charon truly formed independently from Pluto. These numbers however, are still being challenged.

The albedo, or reflectivity of the planet was another feature astronomers observed during the eclipses. By measuring the brightness of the distinct regions of Pluto, astronomers were able to postulate many things about the features of the planet. Pluto has a large albedo range of. 49 to.

66. Pluto's surface consists of a highly reflective south polar cap to a dimmer, darker north polar cap. Charon's albedo range on the other hand is marginal, reaching from. 36 to only.

39. This eventually led to a widespread use of albedo maps. Further research of the surface of Pluto has given scientists a distinctive idea of what the make up of the planet is. The have found that the icy surface is ninety percent nitrogen, and has traces of methane and carbon monoxide. The solid methane lead scientists to claim that the temperature on Pluto is below seventy degrees Kelvin.

However, this may not always be true. Due to its awkward orbit, Pluto can be as close as thirty AU from the sun, and as distant as fifty AU. This actually causes a melting and freezing of Pluto's atmosphere. As it approaches nearer to the sun the Atmosphere melts and then freezes as it moves further away. In 2001, NASA had hoped to launch the Pluto Express, a spacecraft to study the atmosphere during the period the atmosphere was unfrozen. Unfortunately however, this project did not get the necessary funding, and was never able to leave the ground.

Another mission is being planned for 2006. The mission named, "New Horizons," is planned to be launched in January of 2006, but will not arrive in the depths of the solar system until July of 2015. The spacecraft will not only be studying Pluto and Charon, but also a couple of the Kuiper Belt objects. It will also be gathering information on Jupiter as it pass the planet in February of 2007. This will also allow the spacecraft to gain energy from Jupiter gravitational force to help it make its long journey to the outer limits.

Once positioned, New Horizons will use wavelength cameras to study the make up of the surface using spectra in the near infrared. The atmosphere will be studied using radio and ultraviolet rays. Astronomers will be focusing on studying the particles leaving the atmosphere and the effect the solar winds has on the atmosphere. Pluto is the most ambiguous planet in the solar system.

The time at which we can best observe Pluto is when it is at its point closest to the sun. This is known as a planet's perihelion. Even at perihelion, Pluto is still an enormous 4. 4 billion kilometers away. In comparison, it greatly differs from the Earth's distance of 147. 5 kilometers from the sun at perihelion.

Astronomers can best study Pluto when it is at perihelion, unfortunately, it only happens once in its 248. 8 year orbit. As we continue to extend out reach to the outer solar system, we are constantly learning more and more about Pluto. While the information that astronomers have is limited, every piece helps them to make further hypothesis about the planet. In just a short time Astronomers have been able to make great leaps gathering information to better understand Pluto. Hopefully, with continued space travel and research, we can continue to learn about the unusual planet.

Sources web web. gs fc. nasa. gov / planetary /planets / pluto page.

html o web IAU press release from January 1999. "The status of Pluto: A clarification.