Charon

Attic Red Figure (White Ground) Lekythos with Charon, attributed to the Tymbos painter, ca 500 - 450 BC, Ashmolean Museum, Oxford, UK (22681344331)

CarontediMichelagelo

Gustave Doré - Dante Alighieri - Inferno - Plate 10 (Canto III - Charon herds the sinners onto his boat)

Charon is one of the largest moons of Pluto, and it is a significant body in the Kuiper belt, a region of the Solar System beyond the orbit of Neptune filled with numerous small bodies. Discovered in 1978 by astronomer James Christy, Charon revolutionized our understanding of the outer solar system and prompted discussions about the classification of celestial bodies.

Discovery and Naming

Charon was discovered on June 22, 1978, by James Christy at the United States Naval Observatory in Flagstaff, Arizona. The discovery was made by examining photographic plates taken at the observatory, where Christy noticed a bulge on the side of Pluto, which was later confirmed to be a separate body. The moon was named after the ferryman of the dead in Greek mythology, who carries souls across the river Styx to the underworld—a fitting companion to Pluto, the Roman god of the underworld.

Physical Characteristics

Charon is about half the size of Pluto, making it the largest satellite relative to its planet in the Solar System. This size ratio has led some astronomers to refer to Pluto and Charon as a double dwarf planet system. Charon's diameter is about 1,212 kilometers (753 miles), and it has a mass of approximately 1.52 × 10^21 kilograms.

The surface of Charon is primarily composed of water ice, with regions rich in ammonia compounds. Its surface is relatively young and less cratered than other moons in the outer Solar System, suggesting a history of geological activity. Charon's north pole has a reddish color, likely due to tholins, organic molecules formed by ultraviolet radiation from the Sun hitting methane on Charon's surface.

Orbit and Rotation

Charon orbits Pluto at a distance of about 19,640 kilometers (12,200 miles), completing a revolution every 6.4 Earth days. The moon is tidally locked with Pluto, meaning the same side always faces its planet, just as Pluto's same hemisphere always faces Charon. This synchronous orbit is a result of gravitational forces between the two bodies, leading to a stable and circular orbit.

Exploration

The most significant exploration of Charon came with the NASA's New Horizons mission, which flew by the Pluto system in July 2015. The spacecraft provided detailed images and data on Charon's surface, revealing a complex and varied landscape, including canyons, mountains, and plains. New Horizons' observations have been crucial in understanding Charon's geology and its relationship with Pluto.

Significance in Astronomy

Charon's discovery and subsequent observations have played a crucial role in the debate over the definition of a planet. The Pluto-Charon system's characteristics challenged traditional views, contributing to the eventual reclassification of Pluto as a dwarf planet by the International Astronomical Union in 2006. Additionally, studying Charon and Pluto provides valuable insights into the conditions and processes in the outer Solar System, particularly in the Kuiper belt.

See Also

• Pluto
• Kuiper belt
• New Horizons
• Dwarf planet
• Solar System