An asteroid discovered by The University of Arizona's Catalina Sky Survey has a one-in-75 chance of hitting Mars Jan. 30, scientists tracking it say.

Catalina Sky Survey team member Andrea Boattini discovered the asteroid, designated 2007 WD5, with UA's Mount Lemmon 60-inch telescope in the Santa Catalina Mountains north of Tucson on Nov. 20.

At the time, the asteroid was at 20th magnitude brightness, which is about 400,000 times fainter than the faintest object most people can see with their naked eye on a dark night, survey team member Ed Beshore said. The asteroid is now 16 times dimmer than it was when it was discovered, he added.

Astronomers monitoring the trajectory of the asteroid estimate it to be 164-feet wide. Observations provided by the astronomers and analyzed by NASA's Near-Earth Object Office at the Jet Propulsion Laboratory in Pasadena, Calif., indicate the object may pass within 30,000 miles of Mars at about 6 a.m. EST on Jan. 30, 2008.

The Mars-approaching asteroid is about the size of the object that blasted out Meteor Crater, Ariz., 50,000 years ago. The object that created Meteor Crater is believed to be a metallic asteroid - more like a ball bearing that a rock, Beshore said. The newly found Mars-approaching asteroid is probably a stony asteroid, as are most asteroids, Beshore said.

Scientists calculate it is traveling at eight miles a second, or 15 times faster than a rifle bullet, he added.

Asteroid 2007 WD5 is also being compared to the object that exploded over Tunguska, Siberia, with the energy of a three megaton bomb in 1908. The Tunguska object is believed to be the midair explosion of a cometary fragment, Beshore said.

In the unlikely event that 2007 WD5 does hit Mars, it would hit somewhere within a broad swath across the planet north of where the Opportunity rover is, according to NASA.

"We estimate such impacts occur on Mars every thousand years or so," Steve Chesley, an astronomer with the Near Earth Object Program at NASA's Jet Propulsion Laboratory, said in a NASA news release. "If 2007 WD5 were to thump Mars on Jan. 30, we calculate it would hit at about 30,000 miles per hour and might create a crater more than a half-a-mile wide."

The Mars Reconnaissance Orbiter, which is mapping the planet, would have a front-row seat, Chesley added.

The orbiter's science payload includes the High Resolution Imaging Experiment, or HiRISE, which operates the most powerful camera ever to orbit another planet.

"If the asteroid hits Mars we'll get a great look at the crater within a few days of impact," HiRISE principal investigator Alfred S. McEwen of UA's Lunar and Planetary Laboratory said.

HiRISE images of recent Martian impact craters can be found on the HiRISE Website.

The Catalina Sky Survey broke all records for discoveries of near-Earth objects, or NEOs, for any NEO survey this year. The survey found 450 NEOs in 2007, although that number will rise slightly when the final count is in, Beshore said. That tops its ealier record 400 NEO discoveries in 2006 and record 310 NEO discoveries in 2005.

The team's growing success in making NEO discoveries reflects that the survey continues to improve its technique and technologies, said the Lunar and Planetary Laboratory's Steve Larson, Catalina Sky Survey director.

The Catalina Sky Survey, known as the CSS, is conducted in the northern hemisphere by the Mount Lemmon Survey north of Tucson, Ariz., and in the southern hemisphere by the Siding Spring Survey near Coonabarabran, New South Wales, Australia.

CSS is one of four surveys funded by NASA to carry out a U.S. congressional mandate to find and catalog at least 90 percent of all near-Earth objects, larger than one kilometer across (six-tenths mile) by the end of 2008.

The impact of a kilometer-diameter asteroid would have global consequences to civilization as we know it, Larson said. If an object even a third as large hit Earth, it would explode with 24 times the energy of the world's largest thermonuclear bomb explosion, a 58 megaton Soviet bomb exploded in 1961.

The technology to detect and track these objects has been available for only a decade, and although impacts of these large NEOs are rare, we can for the first time quantify any potential danger as the first step in possibly mitigating a disaster, he said.