A computer-generated image showing the possible paths of asteroid 2007 WD5. On January 30, 2008, the asteroid may pass through any point seen in the dotted area.
This story was updated at 11:04 p.m. EST.
The chances of an asteroid smacking into Mars this month are slipping away as astronomers continue to refine its course toward the red planet.
The space rock, an asteroid called 2007 WD5, is now expected to miss Mars by about 18,641 miles (30,000 km), according a Tuesday report by NASA's Near Earth-Object (NEO) program office.
Scientists now estimate the space rock's odds of walloping Mars on Jan. 30 at 2.5 percent, about a 1-in-40 chance, after a series of observations taken by astronomers using Spain's 11.5-foot (3.5-meter) Calar Alto Observatory. The new analysis lowered the asteroid's odds of a martian impact from a 3.6 percent chance released last week.
"If the estimated miss distance remains stable in future updates, the impact probability will continue to fall as continuing observations further constrain the uncertainties," said the report, which was compiled by researchers at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
Astronomers at the University of Arizona first glimpsed Asteroid 2007 WD5 last month while performing the Catalina Sky Survey. At the time, the space rock was hurtling through space at about 8 miles per second, which is about 28,800 miles per hour (46,349 kph) and 15 times faster than a rifle bullet, researchers said.
With an estimated diameter of about 164 feet (50 meters), the asteroid is similar in size to the object that slammed into northern Arizona about 50,000 years ago to create Meteor Crater, NASA scientists have said. Earlier analysis of the space rock's trajectory suggested that, if it did impact Mars, it could slam into the planet's surface at about 30,000 miles per hour (48,280 kph), release about 3 megatons of energy and leave a crater about a half-mile (0.8-km) wide, they added.
Such an impact could be observed by the multiple spacecraft currently orbiting Mars, such as NASA's Mars Reconnaissance Orbiter, and provide a wealth of information on the formation of craters and the red planet's interior, researchers have said.
"We estimate such impacts occur on Mars every thousand years or so," said JPL researcher Steve Chesley, who released the refined asteroid course with colleagues Paul Chodas and Don Yeomans, in a NASA announcement last week.
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