The odds of a collision between asteroid 2007 WD5 and Mars later this month have gone down, scientists said Wednesday.

The chances of a collision on Jan. 30 are currently about 3.6 percent, according to Don Yeomans, manager of NASA’s Near-Earth Objects Program at the Jet Propulsion Laboratory in Pasadena, Calif.

In late December, Yeomans said, the odds of a collision between the Red Planet and the 160-foot-wide space rock rose as high as 3.9 percent. Those were the best odds ever recorded by the nine-year-old Near-Earth Objects office, which was set up to track objects that might threaten Earth.

Most of the time, astronomers in the office root against a collision. This time, they were hoping for one.

“The chances of it happening were always a long-shot,” Yeomans said.

Even though a collision remains a possibility, the object’s most likely course would cause it to miss the planet by 22,000 miles. For space, that’s a near-miss; it’s about one-tenth as far as the moon is from Earth.

Were it to hit, it would provide a bonanza of scientific results. One of the two Martian rovers, exploring opposite sides of the planet, might be able to take pictures of any resulting dust plume rising from the surface.

Also, the Mars Reconnaissance Orbiter, which is mapping the planet, would be able to study the impact with its high-resolution camera.

An asteroid about the same size flattened forests in Siberia when it exploded above ground in 1908.

Because the Martian atmosphere is so thin, 2007 WD5 would likely plummet to the ground, digging a half-mile-wide crater, according to Steve Chesley, an astronomer with the Near-Earth Objects office.

The object was spotted in late November.

Since then, it has been followed by several telescopes in Arizona and New Mexico. As is typical for space flotsam tracked by the Near-Earth Objects office, the chances for a collision “went up and up and up. Then it drops precipitously. I think (the chance of a collision) has already peaked.”

To Yeomans, the incident shows just how crowded space is. “There’s a vast population of objects out there that routinely come close to Earth, and Mars,” he said.

AP-NY-01-02-08 2009EST