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What causes the dark color of Cthulhu Regio on Pluto?
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Pluto
Pluto as observed by the New Horizons spacecraft, July 13, 2015.
The dark color of Cthulhu Regio on Pluto is caused by the presence of organic compounds known as tholins. These compounds contribute to the region's low reflectivity, which ranges between 0.1 and 0.2, making it the darkest area on the dwarf planet.1