Pluto's blue twilight revealed by NASA New Horizons imagery

Researchers analyzing high-resolution images from NASA’s New Horizons spacecraft have revealed that Pluto possesses a blue twilight. This phenomenon was observed when the spacecraft turned its instruments back toward the dwarf planet following its July 14, 2015, closest approach, placing Pluto directly between the camera and the Sun.

The blue color is caused by sunlight scattering through a thin, tenuous nitrogen-dominated atmosphere. Specifically, aerosol haze particles scatter light along long slant paths through the atmosphere when viewed against the silhouette of the planet. This high-phase geometry allowed the Multispectral Visible Imaging Camera (MVIC) to detect more than a dozen distinct atmospheric layers and low-lying haze.

Additionally, analysis of the data suggests that liquid nitrogen may have risen from beneath Pluto’s frozen surface and briefly flowed across the Sputnik Planitia region, a vast nitrogen glacier larger than Texas and Oklahoma combined.