Pluto's largest moon Charon may have been a home to an ancient ocean.

NASA's New Horizons flyby was able to capture images suggesting that Charon once had a subsurface ocean that froze and expanded outward, resulting in the surface to stretch out. The space agency compared this possibility to Bruce Banner turning into the big green beast that is the Incredible Hulk.

New Horizons has been giving earthlings so much information about Pluto and its moons since it arrived there in 2015. Now, new images reveal that there may be another explanation to this distinct surface characteristic of Charon.

New Horizons New Image

At the uppermost part of the New Horizons image, experts were able to discover that Charon has a 1,100-mile surface, temporarily dubbed Serenity Chasma. Such surface has chasms that are approximately 4.5 miles in depth.

Because Charon's diameter is estimated at 1,440 miles, Serenity Chasma looks like Earth's Grand Canyon running across the moon's entire surface. To be specific, the Grand Canyon runs 277 miles in distance and slightly over a mile in depth.

"The lower portion of the image shows color-coded topography of the same scene," NASA writes. Measurements indicate that the water ice layer of Charon may have been partially liquid back in the day, but has refrozen.

The photo was captured by the New Horizons' Long-Range Reconnaissance Imager (LORRI). The flyby is said to be 48,900 miles from Charon when the image was taken. Such distance is approximately an hour and 40 minutes before its closest approach to the moon in July 14, 2015.

Turning From Warm To Cold

Pluto's moons may have been formed by the collision of the planet with another cosmic object from the Kuiper belt. Charon, in particular, has an outer layer composed mainly of water ice. This layer was kept warm by its internal heat generation and the radioactive elements that decayed when it was still young.

Experts say that this warmth was sufficient enough to melt the water ice and let it seep deep down the surface, creating a subsurface ocean.

Charon eventually cooled down, freezing the liquid layer. Because water expands when it freezes, the said layer fractured the outermost region of the moon, creating the chasms observed at present.

New Horizons is expected to provide more information about Pluto and its moons in the future. The flyby downloads information back to NASA at about one to four kilobytes per second, hence more data from spacecraft are coming later in 2016. Who knows? Pluto may also have a subsurface ocean too, as signalled by geologic activity at the Sputnik Planum.

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