Pluto / Introduction

Pluto is the outermost planet of our Solar System with a mean distance from the sun of nearly six billion kilometers. It features no rings and there seems to be only one satellite called Charon. Pluto is the smallest planet of our Solar System and has a diameter of only 2300 kilometers. It is therefore even considerably smaller than some of the larger moons.

Similar to Neptune, its existence was postulated based on calculations before the planet was first seen. In 1930, the search for Pluto came to a successful conclusion when the planet was finally observed by the American astronomer Tombaugh.

Pluto has an exceptionally eccentric orbit. Therefore, Pluto is at certain times located inside the orbit of Neptune.Its orbit plane is inclined by approximately 17 degrees towards the orbits of the other planets. Pluto and its satellite Charon form a double planet system. They orbit a common center of gravity located between the two objects.

Scientists assume that Pluto consists mainly of rock and ice. Its surface temperature is minus 220 ░C. It completes a full rotation on its own axis every 6.4 days and it takes Pluto more than 248 years to complete one revolution around the sun. The mean density of Pluto is twice the density of water.

Orbit of Pluto

Every 6.5 days, Pluto completes a full rotation on its own axis. This is the same period of time that the satellite Charon requires to revolve around Pluto once. The planet has an orbit cycle around the sun of 248.4 years, The orbit of Pluto is unique in our Solar System.

It is of a highly elliptical shape and extremely eccentric. Therefore, thereis a great difference in distance between its closest and outermost position to the sun (4.4 billion and 7.38 billion kilometers respectively).

The orbit of Pluto is inclined by 17 degrees in relation to the orbits of the other planets.

This particular feature results in the strange situation that Pluto is not always the outermost planet of our Solar System.

For approximately 20 of the 248 years that make a full orbit cycle of Pluto, the planet is found inside the orbit of Neptune. Therefore, Neptune was the outermost planet of the Solar System for a while until spring 1999.


Charon and Pluto form a double planet system. The two objects revolve around a common center of gravity, whichis located between the two bodies.

The fact that the two objects influence each other to such an extentis due to the relatively short distance between them of less than 20,000 kilometers.

Another contributing factor is the size of Charon, which is the largest satellite in relation to its planet in the Solar System. It has a diameter of 1200 kilometers, which is half the size of Pluto (ratio 1:2). The size ratio moon : earth is for example 1:4. During a period of 6.4 days, Pluto completes a full rotation on its own axis while Charon revolves once around its bigger partner planet. Charon therefore always faces the same part of Pluto and the other side of Charon is never visible from Pluto.

The surface of Charon, which has a dark appearance is believed to be more structured than that of Pluto. It consists mainly of heavily packed ice. Frozen methane that is found on Pluto seems not to appear on Charon, due to its smaller mass.

Most of the knowledge on Pluto and Charon was gathered by observation through the Hubble Space Telescope. Pluto is the only planet in the Solar System that has not yet been visited by a spacecraft from the earth. The first spacecraft to explore the double planet system will pass near Pluto and Charon in 2010.

Planet X

Uranus and Neptune show certain irregularities in their orbits. For many years, astronomers believed that these effects were the result of gravitational interference by an as yet unknown planet. They therefore predicted the existence of Pluto, which was then eventually also detected.

Today however, scientists know that these irregularities cannot be fully explained by the existence of Pluto as the mass of this planet, even taking into account the mass of Charon, is not sufficient to cause the observed effects. The question therefore remains: is there another planet beyond Pluto?

There are several indications for such a body. Besides the irregularities of orbits of outer planets, the very existence of comets leads scientists to believe that there must be a planet with considerable gravitational force out there, able to capture matter from the Oort Cloud and to channel it into orbit inside the Solar System.

This mysterious planet has been given the name Planet X or Transpluto. Its size is believed to be close to the size of Neptune. Its orbit is predicted asbeing highly eccentric and at right angle to the orbits of the other planets. If Planet X exists, there is a good chance that spacecraft sent out to the distant planets might be influenced by its gravitational force and deviate from their planned route.

ęby megasystems



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