NASA released more photos of Pluto and its moon Charon that were taken by their New Horizons spacecraft. The image of the dwarf planet was taken on July 13, 2015 from 1.7 million kilometres away and shows Pluto's "heart" region.

NASA says the image provides new details to help map the Krun Macula, the dark spot on the bottom of the image.

The image of Charon details a crater, informally named Organa, and reveals unprecedented concentrations of ammonia surrounding it - shown in green on the picture.

The lead for the New Horizons Geology, Geophysics and Imaging team from Washington University in St. Louis, Bill McKinnon, said in a statement, "This is a fantastic discovery...Concentrated ammonia is a powerful antifreeze on icy worlds, and if the ammonia really is from Charon's interior, it could help explain the formation of Charon's surface by cryovolcanism, via the eruption of cold, ammonia-water magmas."

The image of Charon and its craters was taken on July 14, 2015 when New Horizons was 81,000 kilometres from Charon.

New Horizons became the first spacecraft to visit Pluto and is currently 3.1 billion miles from Earth.

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