Closest Detected Asteroid Approach
A small near-Earth asteroid (NEA), discovered the night of March 15, 2004 by the NASA-funded LINEAR asteroid survey, maked the closest approach to Earth ever recorded. The object, designated 2004 FH, is roughly 30 meters (100 feet) in diameter and passed just 43,000 km (26,500 miles, or about 3.4 Earth diameters) above the Earth's surface on March 18, 2004 at 5:08 PM EST (22:08 UTC). Asteroid 2004 FH's point of closest approach with the Earth was over the South Atlantic Ocean. The object was bright enough to be seen a good pair of binoculars during this close approach from areas of Europe, Asia and most of the Southern Hemisphere.
The orbit of asteroid 2004 FH (shown in blue below) is almost entirely within the Earth orbit. Because the asteroid orbit intersects Earth's orbit, 2004 FH will again pass close to Earth. The next relatively close encounter will be in 2044, when it will be within 930,000 miles.
On average, objects about the size of 2004 FH pass within this distance roughly once every two years, but most of these small objects pass by undetected. This particular close approach is unusual only in the sense that scientists know about it. The fact that an object as small as asteroid 2004 FH has been discovered now is mostly a matter of perseverance by the LINEAR team, which is funded by NASA to search for larger kilometer-sized NEAs, but also routinely detect much smaller objects.