"Mars sees these kinds of near-miss encounters every 10 or 20 years, but the impact rate for asteroids this size is about once in a thousand years" - Steve Chesley, an astronomer at the Jet Propulsion Lab in Pasadena, California.
Asteroid 2007 WD5 that had been predicted to crash into Mars, has sailed past the Red Planet. Additional position observations for asteroid 2007 WD5 taken through January were used to improve the accuracy of the asteroid's orbit. The refined orbit had ruled out a collision. The asteroid came less than 20,000 km from the surface of Mars at ~ at 10:56 UT (2:56 a.m. PST), 30th January, 2008 Astronomers estimate that the 164-foot space rock will pass by the Earth on the 10th September, 2011. On March 31, 2004, a small asteroid, designated 2004 FU162, passed within 6,500 kilometres, or roughly one Earth radius from the Earths surface. It was only five to 10 metres in diameter, however.
2008-Jan-30 00:00 RA 05 32 26.56, Dec +26 41 15.0 mag 25.90 2008-Jan-31 00:00 RA 05 33 37.60, Dec +26 41 12.5 mag 25.96
Title: Asteroid 2007 WD5 will not impact Mars on January 30! Authors: Malgorzata Krolikowska, Grzegorz Sitarski
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 ± 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 ± 1.1 R_{Mars}.
2007 WD5 Mars Collision Effectively Ruled Out - Impact Odds now 1 in 10,000 Since our last update, we have received numerous tracking measurements of asteroid 2007 WD5 from four different observatories. These new data have led to a significant reduction in the position uncertainties during the asteroid's close approach to Mars on Jan. 30, 2008. As a result, the impact probability has dropped dramatically, to approximately 0.01% or 1 in 10,000 odds, effectively ruling out the possible collision with Mars.
The orbit of the asteroid 2007 WD5 has been updated by using new observations. Although the best estimate of the distance from approach remains constant with approximately 30.000 kilometres, uncertainty in position for the close approach decreased by a factor of three. Consequently, the estimate of the probability of impact fell to 2.5%, or a 1 in 40 chance.
Additional position observations for asteroid 2007 WD5 taken on December 29 through January 2 have been used to improve the accuracy of the asteroid's orbit. As a result, the range of possible paths past Mars has narrowed by a factor of 3 and the most likely path has moved a little farther away from the planet, causing the Mars impact probability to decrease slightly to 3.6% (about one chance in 28). The new positional observations were made using the 2.4 meter telescope at New Mexico Tech's Magdalena Ridge Observatory and reported by astronomer Bill Ryan. It seems likely that as additional observations further shrink the uncertainty region of this asteroid, the region will no longer intersect Mars and the impact probability will quickly drop to zero.
An asteroid that has a one in 20 chance of striking Mars on Jan 30, might just fly past, which would probably make it target Earth at some point in the future.