Pluto

   Pluto is the farthest planet from the sun. It is also the coldest. Most of the planet is frozen gasses. The gasses are so cold that they make a solid. Pluto is also the smallest of all the planets. Pluto is so small that if you looked from a normal tellescope (150X) you would see it so small that you would not be able to tell that you were looking at a planet. Pluto is so far away that it would take you years to reach the planet, even if you had the newest of the space shuttles.

   Unlike most planets, but similar to Uranus, Pluto rotates with its poles almost in its orbital plane. Pluto's rotational axis is tipped 122 degrees. When Pluto was first discovered, its relatively bright south polar region was the view seen from the Earth. Pluto appeared to grow dim as our viewpoint gradually shifted from nearly pole-on in 1954 to nearly equator-on in 1973. Pluto's equator is now the view seen from Earth.

   Pluto's icy surface is 98% nitrogen (N2). Methane (CH4) and traces of carbon monoxide (CO) are also present. The solid methane indicates that Pluto is colder than 70 Kelvin. Pluto's temperature varies widely during the course of its orbit since Pluto can be as close to the sun as 30 AU and as far away as 50 AU. There is a thin atmosphere that freezes and falls to the surface as the planet moves away from the Sun. NASA plans to launch a spacecraft, the Pluto Express, in 2001 that will allow scientists to study the planet before its atmosphere freezes. The atmospheric pressure deduced for Pluto's surface is 1/100,000 that of Earth's surface pressure.

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