Until 2015, Pluto, the former ninth planet of the classical solar system, was largely a mystery—a tiny speck 3.6 billion miles from the sun. When NASA's New Horizons spacecraft arrived at the ...

Pluto is so far away from Earth that everything we know about it can be written down on a couple of 3 x 5 inch index cards. But Pluto will come into clearer focus in a few years' time, though, as NASA ...