Frozen ocean caused Pluto's moon to stretch like 'Hulk': NASA

Washington, Feb 20: Pluto's largest moon Charon once had a subsurface ocean which has frozen long ago and expanded, pushing and stretching the natural satellite's surface like 'Hulk' while causing massive fractures, a new NASA image has shown.

The new image from NASA's New Horizons spacecraft suggest that Charon's tectonic landscape shows that, somehow, the moon expanded in its past, and – like the fictional superhero Bruce Banner tearing his shirt as he becomes the Incredible Hulk – Charon's surface fractured as it stretched, researchers said.

The side of Pluto's largest moon viewed by NASA's passing New Horizons in July 2015 is characterised by a system of "pull apart" tectonic faults, which are expressed as ridges, scarps and valleys — the latter sometimes reaching more than 6.5 kilometres deep. The outer layer of Charon is primarily water ice.

This layer was kept warm when Charon was young by heat provided by the decay of radioactive elements, as well as Charon's own internal heat formation. Scientists said Charon could have been warm enough to cause the water ice to melt deep down, creating a subsurface ocean.

However, as Charon cooled over time, this ocean would have frozen and expanded (as happens when water freezes), lifting the outermost layers of the moon and producing the massive chasms we see today. The image released by NASA shows part of the feature informally named Serenity Chasma, part of a vast equatorial belt of chasms on Charon.

This system of faults and fractures runs at least 1,800 kilometres long and in places there are chasms 7.5 kilometres deep. By comparison, the Grand Canyon is 446 kilometres long and just over 1.6 kilometres deep. Using measurements of shape of this feature, scientists suggest that Charon's water ice layer may have been at least partially liquid in its early history, and has since refrozen.

The image was obtained by the Long-Range Reconnaissance Imager (LORRI) on the New Horizons spacecraft. The image resolution is about 394 meters per pixel. It measures 386 kilometres long and 175 kilometres wide. It was obtained at a range of approximately 78,700 kilometres from Charon, about an hour and 40 minutes before New Horizons' closest approach to Charon on July 14 last year.

PTI