In 2015, NASA’s New Horizons spacecraft passed in front of Pluto. All the images released by the mission managers were from the side of the dwarf planet that is illuminated by the Sun.
According to the researchers, a part of Pluto’s dark southern hemisphere was illuminated by faint light reflected off the icy surface of this dwarf planet’s moon Charon.
That little light from Charon was enough for the researchers to reveal some details of the planet that could not have been obtained otherwise.
“In a surprising coincidence, the amount of light from Charon on Pluto is close to that of the Moon on Earth, in the same phase for each one,” explained Tod Lauer, one of the mission managers.
“At that time, the illumination of Charon on Pluto was similar to that of our own Moon on Earth when it is in the waxing phase.”
While the available map still contains digital noise, it shows some important features of Pluto’s shaded surface.
The most prominent is a dark crescent-shaped area where neither sunlight nor Charon’s light was projected when New Horizons took the images.
Also striking is a large, bright region that lies between the south of Pluto and its equator. The team in charge thinks that it may be a deposit of nitrogen or methane ice similar to the frozen “heart” of the dwarf planet on its opposite side.