2005 NB56

, also written as 2005 NB56, is a near-Earth asteroid of the Apollo group. In 2009, research physicist Edward Drobyshevski and colleagues have suggested that could be a possible source of the meteoroid that caused the Tunguska event on 30 June 1908. It has been also suspected to be a dormant comet.

Possible source of the Tunguska event bolide
One study "suggests that a chunk of a comet caused the 5-10 megaton fireball, bouncing off the atmosphere and back into orbit around the sun."

This object made a close approach to Earth when it was discovered in 2005 and will do so again in 2045. This object has a poorly known orbit and was only observed over an observation arc of 17 days, not sufficient to predict its position in 1908 with sufficient accuracy.