Charon’s Ancient Ridges Reveal a Dramatic Planetary Slowdown

Analysis of imagery from NASA’s New Horizons mission suggests that Charon once completed a rotation every 14.3 hours. Over eons, gravitational interactions with Pluto forced the moon into a tidally locked state, stretching its current day to 153.3 hours. As the moon’s spin slowed, its equatorial bulge collapsed, causing the crust to buckle and compress by roughly 1%.

Led by Hanzhang Chen of the University of California, Los Angeles, the study identified asymmetric slopes and north-south compressional ridges within the Oz Terra region. Unlike active moons such as Enceladus, Charon lacks a thick atmosphere or significant volcanic resurfacing, preserving these ancient tectonic scars for over four billion years. This geological record supports a “cold start” theory for the moon’s formation, providing a rare window into the early thermal evolution of icy satellites in the outer Solar System.