2007 WD5 is a 48.77 m (160.0 ft) diameter Near-Earth object and a Mars-crosser asteroid discovered on November 20, 2007 by the NASA-funded Catalina Sky Survey on Mt. Lemmon, near Tucson, Arizona, USA, using a 1.5m telescope.  2007 WD5 is roughly the size of the cometary object that caused the Tunguska event in 1908, in remote central Siberia, Russia.

On November 1, 2007, this small asteroid passed within 7.5 million km (5 million miles or 0.0477 AU) of the Earth.

By December 21, 2007, 2007 WD5 was approximately half way between Earth and Mars traveling at 27,900 mph, and was estimated by NASA's Near Earth Object Program (NEOP) to have a 1-in-75 chance of colliding with Mars on January 30, 2008 at approximately 10:55 UT. It should pass within 50,000 km (0.000345AU) of Mars. If the asteroid were to collide with Mars, it would hit with a velocity of about 13.5 km/s (8.4 miles per second), and would produce an explosion equivalent to about 3 MT of TNT. Due to the thin atmosphere of Mars, it is predicted that the asteroid would reach the surface intact and blast out a crater approximately 0.8 km (0.5 mi) in diameter. A crater this size would be equal to the size of the famed Meteor Crater in Arizona, USA.

Previously, in July of 2003, this asteroid passed within 0.07AU of Mars. If 2007 WD5 passes Mars, as is expected, it could return to swing past Earth and/or Mars years or decades in the future.

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