Highest Impact Probability of Colliding With Earth: 99942 Apophis

In 2004, a newly discovered 320-m asteroid, 99942 Apophis (previously called 2004 MN4), achieved the highest impact probability of any potentially dangerous object. The probability of collision on 13 April 2029 was estimated to be as high as 1 in 17 by Steve Chesley of NASA's Jet Propulsion Laboratory though the worst published figure was 1 in 37 calculated in December 2004.

Later observations showed that the asteroid will miss the earth by 25,600 km (within the orbits of communications satellites) in 2029, but its orbit will be altered unpredictably in a way which does not rule out a collision on 13 or 14 April 2036 or later in the century.

These possible future dates have a cumulative probability of 1 in 45,000 for an impact in the 21stcentury.