For the first time ever, humanity has gotten a glimpse of Pluto's dark side. NASA's New Horizons probe beamed back images of the dwarf planet's side that faces its largest moon, Charon. The picture reveals four dark spots roughly 300 miles across. “It’s weird that they’re spaced so regularly,” one scientist said. “We can’t tell whether they’re plateaus or plains, or whether they’re brightness variations on a completely smooth surface,” said another. It will be the last time this side of Pluto is seen as New Horizon is on a flyby path. The probe will come closest to Pluto on Tuesday.