BEIJING, Jan. 9 (Xinhuanet) -- The up-and-down odds of an asteroid striking Mars this month are down again as astronomers continue to refine its course toward the Red Planet.

    The asteroid, named 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.

Gully channels in a crater in the southern highlands of Mars, taken by the High Resolution Imaging Science Experiment (HiRISE) camera on the Mars Reconnaissance Orbiter, are shown in this image released by NASA Sept. 20, 2007. The gullies emanating from the rocky cliffs near the crater's rim (upper L) show meandering and braided patterns typical of water-carved channels. (Xinhua/Reuters Photo) Photo Gallery>>>

    Scientists now estimate the space rock's odds of hitting 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 in December 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.

    (Agencies)