NASA is planning to launch a probe to study an asteroid that could one day pulverize the Earth. The asteroid, named Bennu, crosses Earth's orbit once every six years and has gotten ever closer since it was discovered in 1999, astronomers told the Sunday Times of London (paywall). In 2135, Bennu will fly between the moon and Earth — a hair's breadth in space terms, the Times reported. That's so close that gravity from the Earth could effect Bennu's orbit, "potentially putting it on course for the Earth later that century," said Dante Lauretta, a professor of planetary science at Arizona University. Bennu is about 1,600 feet in diameter and travels around the sun at an average of 63,000 mph. The chance of an impact is small but significant, and if it happens, would be equivalent to triggering 3 billion tons of high explosive, 200 times the strength of the atomic bomb dropped on Hiroshima. "Bennu falls on the boundary, in terms of size, for an object capable of causing a global