I mean really.....400m asteroid, a mere fender bender in astronomical terms. "a drop in the ocean" LOL. but seriously NEO's are probably more common that we think. ya can't make a planetary system without having lots of bits left over. I wonder how many times over the course of human history we have been blissfully unaware of thier existance and any near miss?
That's not the one that Brian Marsden at the Minor Planet Centre gave an "Official Asteroid Number" to and issued a warning about recently, only to discover that it was the ESA's Rosetta Spacecraft returning to Earth for another fly-by.
  