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How does the brightness of Tombaugh Regio differ from that of Cthulhu Regio?
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Pluto
Pluto as observed by the New Horizons spacecraft, July 13, 2015.
Tombaugh Regio and Cthulhu Regio exhibit significant differences in their surface reflectivity, or albedo.
Tombaugh Regio, a prominent heart-shaped plain, is highly reflective, with a reflectivity ranging from 0.8 to 1. In contrast, Cthulhu Regio is the darkest region on Pluto, possessing a much lower reflectivity of 0.1 to 0.2. This dark coloration in Cthulhu Regio is attributed to the presence of organic compounds known as tholins.1