Pluto

Pluto is the ninth and smallest planet in our Solar System. It is also one of the most disputed over planet. Scientists have disputed over the status as far as to even say it is not actually a planet. It is even smaller than earth’s moon.
Pluto was discovered on February 18, 1930 by Clyde W. Tombaugh. Originally it was thought to have only one moon, which was named Charon. Charon was discovered by astronomer James Christy in 1978. Later in 2005 two more moons of Pluto were discovered. They are yet to be designated names and so far are provisionaly called of S/2005 P 1 and S/2005 P 2. Scientists workng with the Hubble Space telescope are credited with this discovery. The discovery of Charon allowed astronomers to determine the mass of the Pluto-Charon pair from their observed orbital period and separation by a straightforward application of Kepler's third law of planetary motion. The mass was found to be lower than even the lowest earlier estimates.The discovery also led astronomers to alter their estimate of Pluto's size. Originally, it was believed that Pluto was larger than Mercury but smaller than Mars, but that calculation was based on the premise that a single object was being observed. Once it was realized that there were in fact two objects instead of one, the estimated size of Pluto was revised downward.
Pluto follows an orbit that is unique in many respect. . It is highly inclined above the plane of the ecliptic, and highly eccentric. This in effect makes Pluto only the eighth planet if distance from sun alone is taken into consideration. This is because during its revolution Pluto for a certain period of its journey is closer to the sun than Neptune.

Pluto's thin atmosphere is most likely nitrogen and carbon monoxide, in equilibrium with solid nitrogen and carbon monoxide ices on the surface. The existance of an atmosphere was only confimed in1988 from an occultation observation. This reinforced Pluto’s status as a planet. The Hubble Space telescope was widely used to study the planets surface. It s remarkaly found to be hetrogeneous. The main constitunts of the surface are ice of metane, nitrogen and carbon dioxide.

So far no exploration vehicle has reached Pluto. The New Horizons spacecraft, which lifted off from Cape Canaveral, Florida on January 19, 2006, is expected to become the first unmanned spacecraft to fly by Pluto on July 14, 2015.


Source: Some dates are from Britanica 2006

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