The Monte Carlo method of the nominal orbit clonning was applied to the case of 2007 WD5, the asteroid from the Apollo group. Calculations based on 33 observations from the time interval of 2007 11 08 - 2008 01 02 showed that the asteroid will pass near planet Mars at the minimum distance of 10.9\pm 2.9 R_{Mars}, what implies that probability that 2007 WD5 strike the planet decreased to the value of 0.03% from the value of about 3--4% previously announced by NASA. The additional observations taken on January 3--9 reduce further the asteroid's impact chances, effectively to nil: the asteroid will pass near planet Mars at the minimum distance of 8.4\pm 1.1 R_{Mars}.
Cite
@article{arxiv.0801.1771,
title = {Asteroid 2007 WD5 will not impact Mars on January 30!},
author = {Malgorzata Krolikowska and Grzegorz Sitarski},
journal= {arXiv preprint arXiv:0801.1771},
year = {2008}
}