Plutonian Facts

Pluto

Pluto's existence was predicted in the early twentieth century as astronomers tried to find a reason for the orbit of Uranus not following the path they had predicted. Neptune alone could not account for all the discrepancies in the orbit of Uranus. The American astronomer Clyde Tombaugh spent thousands of hours searching photographs with millions of stars, before he found Pluto in 1930. It appears only as a speck even in the largest telescopes, and has not been visited by any space probes, so astronomers have had to work out as best they can what Pluto might be like. Observations from Earth show that its surface is covered with frozen water and methane at about -446�F.

Pluto has one moon, Charon, which was discovered in 1978 as a small bulge in an image of Pluto, made by J. Christy, an astronomer at the United States Naval Observatory. It is about 740 miles (1,190 km) in diameter, about half the size of Pluto itself. Some astronomers have labeled Pluto as a binary planet due to the similar size and proximity to Charon even. Charon's surface is icy but darker than Pluto's, and it seems to have water ice on it but no methane.

In 1987 and 1988, Charon's orbit carried it behind and directly in front of Pluto on each circuit, as seen from Earth. This is a rare series of events that can only be witnessed every 200 years. Observations made at this time were a great help to astronomers, in working out the size and nature of this remote pair.

Pluto rotates once on its axis, in exactly the same time that it takes Charon to complete one orbit: 6 days, 9 hours, and 67 minutes. This means that Charon is always in the same place in the sky above Pluto.

Pluto is usually described as the planet farthest from the Sun, but this is not always true. Its orbit is such a stretched-out ellipse that the planet comes to within 2.8 million miles of the Sun, closer than the orbit of Neptune. Its furthest point from the Sun is over 4 million miles (7 million km) away.

For twenty years of each orbit Pluto is closer to the Sun than Neptune. During the years 1979 to 1999, Neptune is the outermost planet of the Solar System.

Mass (kg)	1.29 x 10^22
Diameter (km)	2300
Mean Density kg/m^3	2030
Escape Velocity (m/sec)	1100
Average Distance from Sun (AU)	39.53
Rotation Period (length of day in Earth days)	6.39
Revolution Period (length of year in Earth years)	247.7
Obliquity (Tilt of Axis)	122.5�
Orbit Inclination	17.15�
Orbit Eccentricity (Deviation from Circular)	0.248
Mean Temperature	37�K
Visual Geometric Albedo (Reflectivity)	About 0.5
Atmospheric Components	Perhaps Methane and Nitrogen
Surface Materials	Perhaps Methane Ice

This page hosted by

� Get your own Free Home Page

Hosted by www.Geocities.ws