A newly released image of Charon, Pluto’s largest moon, reveals a heavily fractured surface that may have formed when a subsurface ocean froze and expanded to split an exterior shell of ice. High-resolution images show that much of the moon’s northern hemisphere is cracked, nowhere more dramatically than in an equator-straddling series of chasms that includes Serenity Chasma (shown in the 175-km-by-386-km close-up seen at right above, and color coded for elevation at bottom right). Altogether, the low-latitude system of cracks and valleys is the longest known anywhere in our solar system (about four times the length and in some places almost five times the depth of Earth’s Grand Canyon), the researchers report. Because Charon’s modern-day surface is mostly water ice, it makes sense that the 1212-km-diameter moon once had a subsurface ocean kept liquid by heat from the radioactive decay of elements in its core, as well as by the heat generated from collisions of smaller bits when the moon first accumulated. Later, surface waters exposed to space were the first to freeze. As the moon aged its icy shell got thicker. Eventually, possibly a few hundred million years after the moon formed, the deepest parts of the ocean froze, swelling to crack surface ice—which may have been 10 km thick or more—just as ice cubes in a freezer often do. The image released yesterday, obtained just 100 minutes before the New Horizons craft swooped past Charon last 14 July, was taken from a range of about 78,700 km.