On Jan. 19, 2006, the Earth lost half a ton. More precisely, it lost 1,054 lbs (478 kg), but it’s O.K. to round down, since the 13 octillion-pound planet hardly noticed the missing weight. The flyweight fleck of matter was very much born of the planet, a collection of metal and silicon and copper and…

After Visiting Pluto, NASA’s New Horizons Spacecraft Reaches Another Cosmic Milestone