Pluto's blue sky. New Horizons image of the atmospheric haze (blue) around the dwarf planet Pluto. The high-altitude haze is thought to be similar in nature to that seen at Saturn's moon Titan. The source of both hazes likely involves sunlight-initiated chemical reactions of nitrogen and methane, leading to relatively small, soot-like particles (called tholins) that grow as they settle toward the surface. This image, which includes near-infrared data, was obtained by Multispectral Visible Imaging Camera (MVIC) on the Ralph sensor on NASA's New Horizons spacecraft. The New Horizons spacecraft flew past Pluto in 2015, beaming data back to Earth.