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.
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
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
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.
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.
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.
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
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.