What may be the most threatening asteroid known to humankind was discovered in 1999, tumbling through space on an unstable orbit that periodically intersects that of Earth around the sun. Astronomers eventually named the half-kilometer-wide object Bennu, after a creation god from Egyptian mythology. And indeed, if Bennu, filled with organic compounds and water-rich minerals, fell on a barren world, it might sow the seeds of life. Instead it may be destined to cause immense suffering and death. Astronomers have projected that in 2135, Bennu will pass nearer to Earth than the moon, in a flyby that could tweak the asteroid's trajectory to guarantee a strike on our planet in the late 22nd century.