Analysis of the images captured during NASA’s New Horizon mission last year has revealed that Pluto’s largest moon Charon was home to an ancient subsurface ocean that has since frozen, expanding during the process. This, according to the scientists, caused to the moon’s surface to stretch outward, creating massive canyon-like fractures that are clearly visible in the images.
In July 2015, NASA launched its New Horizons spacecraft as part of a six-month-long flyby study of the Pluto system. Charon’s surface, as seen in the images, is characterized by several “pull apart” tectonic faults, in the form of valleys, scarps and ridges running up to 4 miles (around 6.5 km) in depth. The crevices, the researchers believe, developed sometime in the past when the celestial body underwent expansion in size.
Charon’s outer surface is made almost entirely of water ice. When the satellite was still quite young, its internal heat, coupled with the heat produced as a result of the decay of radioactive elements, kept this layer warm, causing the ice to melt into an enormous ocean deep inside the ground. Since then, however, the moon has cooled substantially, due to which the once flowing water has now frozen and expanded. This has in turn forcibly lifted Charon’s outermost surface, creating deep gorges along the way.
Of the images taken by NASA’s spacecraft, one shows part of what is known as the Serenity Chasma, belonging to a vast belt of chasms located along the moon’s equator. Believed to be one of the largest in the entire solar system, this system of canyons is around 1,100 miles (approx. 1,800 km) long and nearly 4.5 miles (or 7.5 km) deep. Arizona’s Grand Canyon, by comparison, is only 277 miles (about 446 km) in length and slightly more than one mile (or 1.6 km) in depth.
According to the researchers, the unique shape of these chasms suggests that at least part of Charon’s water ice layer may have been liquid, mostly likely during its early history. This part, however, has since refrozen and consequently, expanded. This particular image was taken on July 14, 2015, using the Long-Range Reconnaissance Imager (or LORRI) on board the New Horizons spacecraft. Boasting a resolution of nearly 1,290 feet (approx. 394 m) per pixel, the photo shows an area measuring around 240 miles (386 km) long and up to 110 miles (about 175 km) wide.
As the team points out, the image was captured at a distance of 48,900 miles (around 78,700 km) from Pluto’s Charon, only a hour and 40 minutes before the spacecraft made its closest approach to this distant moon.