Charon

Charon is Pluto’s largest moon and the largest known moon relative to its planet. The two bodies are so close in size that they are often considered a double dwarf planet system or binary planet.

A Binary System

Charon and Pluto orbit each other around a common center of mass that lies outside Pluto. This makes them a true binary system, unlike most planet-moon pairs where the moon orbits around the planet.

The distance between Charon and Pluto is only about 19,640 kilometers—less than the distance from Earth to the Moon. This close proximity means that from Pluto’s surface, Charon would appear much larger in the sky than our Moon does from Earth.

Surface Features

Charon’s surface is covered in water ice, with a thin layer of hydrocarbon molecules that give it a reddish-brown color. The northern polar region is particularly dark and red, possibly due to tholins—organic compounds formed when ultraviolet light interacts with nitrogen and methane.

The surface shows evidence of extensive fracturing and possible past cryovolcanic activity. There are large chasms and valleys that may have formed from the moon’s expansion as it cooled, or from tectonic activity.

Geological History

Charon appears to have been geologically active in the past. The presence of smooth plains and the absence of large impact craters suggest that the surface has been resurfaced, possibly by cryovolcanism or the eruption of subsurface water.

Unlike many other moons, Charon shows no signs of tidal heating from its parent body, suggesting that any internal activity was driven by radioactive decay rather than tidal forces.

Exploration

Charon was discovered in 1978 by astronomer James Christy. It was visited by NASA’s New Horizons spacecraft in 2015, which provided detailed images and data about its surface and composition.

The study of Charon helps scientists understand the geology and evolution of Kuiper Belt objects, and provides insights into the early history of the solar system.