アテン群
is a small Aten asteroid first observed in 2000. It is assumed to have a diameter of approximately – or roughly twice that of the Chelyabinsk meteor – and an assumed mass of 7.1 kg (71,000 tonnes). But the size is only known within about a factor 2. It is the largest object known to have a better than 1/1000 chance (0.1%) of impacting Earth. The next good chance to observe the object will be in May 2028 when it passes from Earth.