Charon (moon)

119.591 ± 0.014 ° ( orbital plane ) 112.783 ± 0.014 ° ( ecliptic ) °

J. W. Christy

Charon is the innermost of the five known moons of the dwarf planet Pluto. He was discovered in 1978. Its mean diameter is 1212 km, representing slightly more than half the diameter of Pluto. Compared with other moons in the solar system so that Charon is unusually large in relation to its main body.

Discovery and designation

Charon was on 22 June 1978 by the astronomer James Walter Christy from the United States Naval Observatory in Washington, DC discovered during the evaluation of photographic plates that months had previously been made ​​by the 1.55 -meter " Kaj beach Astrometric Reflector". Christy discovered that Pluto had a slight bulge periodically on the photographs ( see figure). This phenomenon, pointing to a moon of Pluto, could later be detected on photographic plates which had been exposed already on 29 April 1965. The bulge corresponded to the rotation period of Pluto, which was known by its light curve, and thus pointed out to a synchronous orbit. All doubts were removed when Pluto and Charon covered each other between 1985 and 1990, which only happens twice within the 248 -year orbital period of Pluto. So it was a happy coincidence that this so soon took place after Charon's discovery. The discovery was announced on July 7, 1978; of the heavenly bodies initially received the provisional designation S/1978 P 1

On January 3, 1986, the moon, named along with the Saturn 's moons Prometheus and Pandora, by the International Astronomical Union ( IAU) officially by Charon (Greek for " Flash " ), the ferryman of the underworld in Greek mythology, which of the shadows deceased for a mite (coin) over the dead river Acheron (often the rivers Lethe or Styx are called ) placed so that they could enter the realm of the dead god Hades (Latin Pluto). The IAU preferred so that the name of Christy's proposal, which thus also on the first four letters of the name of his wife Charlene, called by him Char alluded. Therefore, all who know about it, the name of the moon Sharon from talking. The naming is thus also in herein by reference to Pluto, whose first two letters refer to Percival Lowell's initials, the Clyde Tombaughs search for the Planet X inspired and supported.

When naming was at the suggestion of Christy's colleagues at the Naval Observatory also Persephone for discussion, the wife of Pluto in mythology.

Charon's discovery allowed the astronomers, Pluto's mass and size to determine more accurately.

In August 2006, the IAU discussed whether Charon and Pluto should get together as a double planet the status of the planet Plutonenklasse. However, it was decided to classify Pluto as a dwarf planet, Charon, therefore, remains, by definition, a moon of Pluto.

Web properties

Orbit

Pluto and Charon orbit each other in a retrograde with respect to the solar system, almost perfectly circular orbit at 17,536 ± 4 km average distance ( distance between the centers of the two bodies 19571.4, about 17 Pluto or 32.3 Charonradien ) around the common center of gravity which is due to the relatively small mass difference about 1200 km above the surface of Pluto (2360 km from the center ) is located. Thus, Charon and Pluto represent physically a dual system dar. This leads to an average distance between the two surfaces of 17,812 km. The orbital eccentricity is at most 0.00007, the orbit is inclined 0.001 degrees from the equator of Pluto. Like the equator Pluto is therefore very strongly inclined with 119.591 ° relative to the orbital plane of the dwarf planet Charon's orbital plane.

Charon and Pluto orbit each other in 6 days, 9 hours, 17 minutes and 36.7 ± 0.1 seconds, which is in a Pluto year equals approximately 14186.63 rounds (about 248.09 Earth years ).

Rotation

Charon also rotates in 6 days, 9 hours, 17 minutes and 36.7 ± 0.1 seconds on its own axis and in the same period and with the same sense of rotation around the center of mass. He leads into how the Earth's moon synchronous rotation and shows its main body is always the same page. In contrast to Earth and Moon rotation times of Pluto and Charon were slowed down by tidal forces on both sides and synchronized, Pluto, Charon, therefore, it makes use of the same page. This is the only confirmed case of so-called double-bonded rotation in the solar system. Among pairs of approximately equal size asteroid is such a synchronous rotation probably fairly common.

Physical Properties

Charon has a diameter of 1212 km ( according to other data 1207.2 ± 2.8 ), corresponding to about 52.6 %, slightly more than half of the central body, based on the assumed albedo of 37.2 %. This is in comparison to other Kuiper Belt objects rather bright and folows the albedo of the earth. Charon's mass is about 11.6 % of the mass of Pluto, the average density was determined to be 1.71 g/cm3. It should thus be about 55 - 45 % consists of water ice - 60% rock and 40; a striking contrast to Pluto, the stone content is about 70 %.

There are internal structure of Charon two theories: either Charon is a differentiated body constructed with a rocky core and ice mantle, or it consists of a single ice - rock mixture. Through the discovery of evidence of Kryovulkanismus the first theory is favored.

Unlike Pluto surface which is covered by frozen nitrogen and methane, Charon surface seems to consist of the less volatile water ice. In addition, Charon appears in contrast to the reddish, inhomogeneous Pluto in a uniform neutral gray. The surface temperature could be determined on 1 July 2005 with a stellar occultation by Charon to minus 210 ° C. This corresponds to the expected at this distance radiative equilibrium. The pressure of a possible, very thin atmosphere may be higher than 0,11 millionth of a bar.

The Gemini Observatory announced on 17 July 2007 announced that it had discovered on Charon cryovolcanoes that involve a mixture of crystalline water ice and ammonium hydroxide to the surface, which then deposited globally. The fact that the ice is still present in crystalline form, points to recent deposits, since the solar radiation would have weathered the ice within about 30,000 years ago in an amorphous state.

The relatively high proportion of rocky material and the lack of an appreciable atmosphere support the assumption on these relatively large Trabant analogous to the formation of the Moon is the product of the great collision of a predecessor of Pluto with another pluto large body of the Kuiper belt.

Research

The first images that Pluto and Charon as showed two separate bodies were made ​​by the Hubble Space Telescope in the 1990s. Same from ground-based telescopes was later possible through the use of adaptive optics.

It is planned to have the space probe launched on January 19, 2006 New Horizons fly by on July 14, 2015, 27,000 km distance to Charon and 9600 km distance to Pluto. However, these are only objective parameters that can be changed during the flight easily. Two weeks after the flyby, the observations are completed, and the probe will begin to transmit the data collected during the flyby to Earth. Since the transmission rate over this distance is very small, a few months will pass before all data has arrived on Earth.

The 2005 discovered satellites Nix and Hydra can also be regarded as the first " real" Pluto moons when they favor the status of Pluto and Charon as a "dwarf double planet system."

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