On 27 January 2012, at approximately 3.30 pm GMT, Asteroid 2012 BX 34 is will be at its closest point to Earth on its current orbital cycle, passing within 59 000 km of the Earth (the Moon never comes within 370 000 km of the Earth). It is not thought likely that it will hit us, as it is too small (11m across) to survive the trip through our atmosphere. An asteroid would have to be about 140 m across to cause significant damage at the impact sight, and a lot larger still to cause global effects.
2012 BX34 was discovered earlier this year by NASA's Asteroid Watch program (the name means the 873rd asteroid discovered in the second half of January 2012). The program is intended to search for near-Earth objects large enough to do us harm, but (obviously) it finds plenty of smaller objects in the process. To date the project has detected 911 objects large enough to be a potential threat, though none of these is predicted to collide with the Earth in the near future.