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P L U T O (9th planet from the Sun)
In Roman mythology, Pluto (Greek: Hades) is the
god of the underworld.


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1 MOON

INTRODUCTION
I

The planet received this name (after many other suggestions) perhaps because it's so far from the Sun that it is in perpetual darkness and perhaps because "PL" are the initials of Percival Lowell. The 9 th planet from the sun and outermost known member of the solar system. Pluto was discovered as the result of a telescopic search inaugurated in 1905 by the American astronomer Percival Lowell, who postulated the existence of a distant planet beyond Neptune as the cause of slight perturbations (see Orbit) in the motions of Uranus. Continued by members of the Lowell Observatory staff, the search ended successfully in 1930, when the American astronomer Clyde William Tombaugh found Pluto near the position Lowell had predicted. Pluto revolves about the sun once in 247.7 Earth years at an average distance of 5.9 billion km (3.67 billion mi) from the sun. The orbit is so eccentric that at certain points along its path Pluto is closer to the sun than is Neptune. No possibility of collision exists, however, because Pluto's orbit is inclined more than 17.2° to the plane of the ecliptic and never actually crosses Neptune's path. Visible only through large telescopes, Pluto appears to have a yellowish color. For many years very little was known about the planet, but in 1978 astronomers discovered a relatively large moon orbiting Pluto at a distance of only about 19,000 km (about 12,000 mi) and named it Charon. The orbits of Pluto and Charon caused them to pass repeatedly in front of one another from 1985 through 1990, enabling astronomers to determine their sizes fairly accurately. The Hubble Space Telescope allowed astronomers to determine the sizes of Pluto and Charon even more accurately in 1994. Pluto is about 2320 km (1440 mi) in diameter, about two-thirds the size of Earth's moon. Charon is about 1270 km (790 mi) in diameter, making Pluto and Charon the planet-satellite pair closest in size in the solar system. Pluto was also found to have a thin atmosphere, probably of methane, exerting a pressure on the planet's surface that is about 100,000 times weaker than the Earth's atmospheric pressure at sea level. In 1994 the Hubble Space Telescope imaged 85 percent of Pluto's surface, revealing bright and dark areas of startling contrast. Astronomers believe that the bright areas are shifting fields of nitrogen ice and the dark areas are fields of methane ice colored by interaction with sunlight. Some of the dark areas may also be valleys or fresh impact craters. These images support the theory that extensive ice caps form on Pluto's poles, especially when the planet is farthest from the sun. With a density about twice that of water, Pluto is apparently made of much rockier material than are the other planets of the outer solar system. This may be the result of the kind of chemical combinations that took place during the formation of the planet under cold temperatures and low pressure. Many astronomers think Pluto may be a former satellite of Neptune, knocked into a separate orbit during the early days of the solar system. Charon could be an accumulation of the lighter materials resulting from the collision.


Pluto is farther from the sun than the other planets in the solar system, although it occasionally moves in closer than Neptune due to an irregular orbit. The small, rocky, and cold planet takes 247.7 years to revolve around the sun. This artist's rendition depicts Pluto, foreground; its moon, Charon, background; and the distant sun, upper right.
Photo Researchers, Inc.



























The never-before-seen surface of the distant planet Pluto is resolved in these NASA Hubble Space Telescope pictures, taken with the European Space Agency's (ESA) Faint Object Camera (FOC) aboard Hubble.

Pluto Video 615 KB - MPG


















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MOON
CHARON
II

Charon is named after the boatman who took the souls of the dead
across the River Styx into the underworld, or Hades, in Greek mythology.
According to Christy, he selected the name in part because the first
syllable is the nickname of his wife, Charlene.

orbit: 19,640 km from Pluto
diameter: 1172 km
mass: 1.90e21 kg

Charon ( "KAIR en" ) is Pluto's only known satellite:

Though officially named for the mythological figure, Charon's discoverer was also naming it
in honor of his wife, Charlene. Thus, those in the know pronounce it with the first syllable
sounding like 'shard' ("SHAHR en").

Charon was discovered in 1978 by Jim Christy. Prior to that it was thought that
Pluto was much larger since the images of Charon and Pluto were blurred together.

Charon is unusual in that it is the largest moon with respect to its
primary planet in the Solar System (a distinction once held by Earth's
Moon). Some prefer to think of Pluto/Charon as a double planet
rather than a planet and a moon.

Charon's radius is not well known.
JPL's value of 586 has an error margin of +/- 13, more than two percent.
Its mass and density are also poorly known.

Pluto and Charon are also unique in that not only does Charon
rotate synchronously but Pluto does, too: they both keep the
same face toward one another. (This makes the phases of
Charon as seen from Pluto very interesting.)

Charon's composition is unknown, but its low density (about 2 gm/cm3)
indicates that it may be similar to Saturn's icy moons (i.e. Rhea).
Its surface seems to be covered with water ice.
Interestingly, this is quite different from Pluto.

Unlike Pluto, Charon does not have large albedo features,
though it may have smaller ones that have not been resolved.

It has been proposed that Charon was formed by a giant impact
similar to the one that formed Earth's Moon.

It is doubtful that Charon has a significant atmosphere.

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RECOMMENED READING
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