page_title: 2007 WD5
section_title: Estimates of resulting impact
hierarchical_section_title: 2007 WD5 / Mars encounter: chance of impact / Estimates of resulting impact
caption_attribution_description: This artist rendering uses an arrow to show the predicted path of asteroid 2007 WD5 on Jan. 30, 2008, and the orange swath indicates the area it is expected to pass through. Mars may or may not be in its path.
context_page_description: 2007 WD₅ is an Apollo asteroid some 50 m in diameter and a Mars-crosser asteroid first observed on 20 November 2007, by Andrea Boattini of the Catalina Sky Survey. Early observations of 2007 WD₅ caused excitement amongst the scientific community when it was estimated as having as high as a 1 in 25 chance of colliding with Mars on 30 January 2008. However, by 9 January 2008, additional observations allowed NASA's Near Earth Object Program to reduce the uncertainty region resulting in only a 1-in-10,000 chance of impact. 2007 WD₅ most likely passed Mars at a distance of 6.5 Mars radii. Due to this relatively small distance and the uncertainty level of the prior observations, the gravitational effects of Mars on its trajectory are unknown and, according to Steven Chesley of NASA's Jet Propulsion Laboratory Near-Earth Object program, 2007 WD₅ is currently considered 'lost'.
context_section_description: If the asteroid had collided with Mars, it would have hit with a velocity of about 13.5 km/s (8.4 miles per second), and would have produced an explosion equivalent to about 3 megatons of TNT. Due to the thin atmosphere of Mars, it was predicted that the asteroid would have reached the surface intact and blasted out a crater approximately 0.8 km (0.5 mi) in diameter. A crater this size would be equal to the size of the Meteor Crater in Arizona, United States. NASA officials say if it had hit Mars, it would have done so north of the location of the Opportunity rover.
  2007 WD₅ is roughly the size of the cometary object that caused the Tunguska event in 1908, in remote central Siberia, Russia. Due to the Earth's greater gravity, an impact with the power of Tunguska is expected to occur once every few hundred years. Since Mars has only 1/10 the mass to attract objects, these types of impacts occur roughly every one thousand years on Mars.
caption: Track of asteroid 2007 WD5 over Mars (NASA/JPL)
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