Mars could be in for an asteroid hit.

A newly discovered hunk of space rock has a one-in-75 chance of slamming into the Red Planet on Jan. 30, scientists said Thursday in Los Angeles.

This true-colour image of Mars was generated using the European Space Agency's OSIRIS camera's red, green and blue colour filters.
(European Space Agency)

"These odds are extremely unusual. We frequently work with really long odds when we track … threatening asteroids," said Steve Chesley, an astronomer with the Near Earth Object Program at NASA's Jet Propulsion Laboratory.

The asteroid, known as 2007 WD5, was discovered in late November and is similar in size to an object that hit remote central Siberia in 1908, unleashing energy equivalent to a 15-megaton nuclear bomb and wiping out 60 million trees.

Scientists tracking the asteroid, currently halfway between Earth and Mars, initially put the odds of impact at one in 350 but increased the chances this week. Scientists expect the odds to diminish again early next month after new observations of the asteroid's orbit, Chesley said.

"We know that it's going to fly by Mars and most likely going to miss but there's a possibility of an impact," he said.

If the asteroid does smash into Mars, it will probably hit near the equator close to where the rover Opportunity has been exploring the Martian plains since 2004.

The robot is not in danger because it lies outside the impact zone. Speeding at 13 kilometres a second, the asteroid would carve a hole the size of the famed Meteor Crater in Arizona.

In 1994, fragments of the comet Shoemaker-Levy 9 smacked into Jupiter, creating a series of overlapping fireballs in space. Astronomers have yet to witness an asteroid impact with another planet.

"Unlike an Earth impact, we're not afraid but we're excited," Chesley said.

NASA's Mars Reconnaissance Orbiter satellite currently circles the planet and could be in a good position to monitor the potential impact.

NASA also announced on Friday its decision to delay until 2013 the launch of a half-billion-dollar Martian probe called Scout. The $475-million US Scout atmospheric probe was originally scheduled to launch from Earth in 2011.

NASA chose to delay the launch over what it called a "serious" conflict of interest in one of the proposals submitted for the mission from one of two Colorado research institutions, but declined to elaborate.