Charon is the largest and innermost moon of Pluto. It was discovered in 1978 by astronomer James Christy, using photographic plate. It is the twelfth largest natural satellite in the Solar System. Charon is nearly 1/8 the mass of Pluto and is the sixth-largest trans-Neptunian object, after Pluto, Eris, Haumea, Makemake, and Gonggong.
It orbits a common center of gravity with Pluto, and the two worlds are tidally locked together as they orbit. It is a very large moon in comparison to its parent body.
History[]
Discovery[]
Charon was discovered by astronomers James Christy and Robert Harrington, using the telescope at the United States Naval Observatory Flagstaff Station (NOFS), around six miles from where Pluto itself was discovered at the Lowell Observatory.
The moon was discovered on June 22, 1978 after Christy had been examining photographic plates that were taken with the telescope about two months prior. He noticed that there were cases in which Pluto appeared strangely elongated. The bulge was also seen on plates dating back to April 29, 1965. They confirmed that the object was indeed a satellite on July 2, 1978, and the International Astronomical Union formally announced Christy's discovery on July 7, 1978.[1]
Name[]
The name Charon was suggested by Christy, as a scientific-sounding version of his wife's nickname "Char". While his colleagues at the Naval Observatory proposed Persephone, Christy stuck with Charon after discovering it referred to a Greek mythological figure. In Greek mythology, Charon is the ferryman of the dead, closely associated with the god Hades or Pluton.
The IAU officially adopted the name in late 1985 and it was announced on January 3, 1986.[2]
Orbit[]
Charon and Pluto orbit each other every 6.387 days. Both objects are gravitationally locked to each other, so each object shows the same face towards the other. This is known as "mutual tidal locking", and is somewhat similar to the Earth and Moon, though the Moon always shows the same face to Earth, but not vice versa. Typically, the distance between Charon and Pluto is 19,570 kilometers (12,160 miles).[3]
Size and geology[]
Charon is about 1,212 kilometers, or 753 miles, in diameter, a little half the size of Pluto. This makes it the twelfth largest natural satellite and larger than the dwarf planet Ceres.
Charon's surface is primarily composed of water ice, as opposed to its companion Pluto which is primarily composed of nitrogen and methane ices. The New Horizons probe revealed that the north polar region of the moon is dominated by a large dark red area, named Mordor Macula by the team. The reddish hue is generally accepted to be condensation of gases that escaped from Pluto's atmosphere. The southern pole of Charon entered polar night in 1989 and will not see sunlight again until 2107.[4]