Since the New Horizons probe flew through the Pluto system on July 14, most of the attention has been on Pluto itself. But it also has a comparatively large and—as we now know—fascinating moon called Charon.
The vast haul of data from New Horizons is now being transmitted to Earth at a slow rate because the signal is so weak. Yet some amazingly detailed images have been released, helping researchers trace the moon’s violent history through its ridges and craters.
Charon is usually pronounced “Shairon” or even “Sharon,” though “Kairon” would be a more faithful rendering of the name of the ferryman of the classical underworld after whom it is named. Charon and Pluto are locked in a tidal embrace that matches their rotation rates to their orbital period about each other, so that the same side of Charon always faces Pluto, and vice versa.
Our prior understanding is that Charon’s surface is mostly water-ice, tainted by ammonia and lacking the more exotic methane, carbon monoxide and nitrogen ices that so spectacularly coat parts of Pluto. Charon is a darker, drabber world than Pluto when you see an identically processed image of each (below).
