NASA has revealed an image of the dark side of Pluto, six years after it was captured by the New Horizons spacecraft.
The image – taken in July 2015 when Pluto was 3 billion miles from Earth – shows a portion of the dwarf planet’s landscape that was not directly illuminated by sunlight.
The researchers were able to create the image using 360 images taken by New Horizons, looking back at Pluto’s southern hemisphere while flying past it.
The photo was captured by taking advantage of the light that was reflected off Pluto’s five largest moons, Charon.
The image reveals a large, “conspicuously bright” region halfway between Pluto’s south pole and the equator, which may be precipitation of nitrogen or methane ice, similar to Pluto’s icy “core” on its opposite side.
“At the time, Charon’s illumination on Pluto was similar to that emitted by our moon on Earth when it was in its first quarter,” said Todd Lauer, an astronomer at the National Science Foundation’s Optical Infrared Astronomy Research Observatory in Tucson, Arizona.
Pluto is a complex world of frozen plains and icebergs the size of the Rocky Mountains.
Pluto was considered the ninth planet, the largest member of the Kuiper belt and the most famous of a new class of worlds called dwarf planets.
NASA’s New Horizons spacecraft launched in January 2006, and made history by returning the first close-up images of Pluto and its moons in the following decade.
After flying within 7,800 miles (12,550 km) of Pluto’s icy surface on July 14, 2015, New Horizons continued at nine miles per second to the Kuiper Belt.
As it left Pluto, the spacecraft looked at the dwarf planet and took a series of photos of its dark side, backlit by the distant sun.
Although Pluto’s hazy atmosphere represented a luminous ring of light, the dark side itself was, of course, hidden.
Fortunately, part of Pluto’s dark southern hemisphere is illuminated by faint sunlight reflecting off the icy surface of Pluto’s largest moon, Charon, about the size of Texas.
This part of the “Charon light” was enough for the researchers to elicit details of Pluto’s southern hemisphere that could not be obtained any other way.
Recovering details on Pluto’s surface in the dim moonlight wasn’t easy – which is part of the reason the image was released more than six years after the flyby.
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