You might want to mark your calendar for Oct. 12, 2017, just in case an asteroid approaching Earth decides to come closer than its near miss in October 2012, one astronomer says.

Estimates of the size of asteroid 2012 TC4 vary from 40 feet to 130 feet across; the space rock that exploded above the city of Chelyabinsk in Russia in February 2013, resulting in injuries to 1,500 people and damage to thousands of buildings, was estimated to be around 65 feet across.

That means if 2012 TC4 doesn't slide on by in 2017 but instead follows the Chelyabinsk example, the results could be devastating, says Judit Györgyey-Ries, a University of Texas astronomer.

"It is something to keep an eye on," she says. "We could see an airburst, maybe broken windows, depending on where it hits."

The asteroid was first detected Oct. 4, 2012, with a telescope at an observatory located in Hawaii, and less than a week later made a close pass by Earth, coming within 69,000 miles of our planet.

Analysis of the orbit of the rapidly-spinning space rock suggests it has made a number of close passes by the Earth in the past, astronomers say.

So far, analysis of its probable 2017 fly-by suggests another near-miss, they say, with the longest of odds against a collision.

"It has a 0.00055 percent cumulative chance that it will hit," Györgyey-Ries says.

Other experts agree the chances of a collision, although not impossible, are highly unlikely.

"There is one in a million chance that it could hit us," says Detlef Koschny, who heads the Near-Earth Object Segment in the European Space Agency's Space Situational Awareness program.

However, it's the uncertainty about the asteroid's size that adds an element of risk, he says.

"The size was estimated from the brightness, but we don't know the reflectivity. So it could be smaller or larger, assume from 10 meters (around 40 feet) to 40 meters (about 130 feet.)

"A 40-meter iron object would go through the atmosphere and make a crater; a 10-m rocky object would be hardly noticed," he explains.

Györgyey-Ries acknowledges the need for additional observations to narrow the uncertainties.

"Although it has a large uncertainty along the orbit, it is much less than the radial uncertainty, so it just changes the time of the closest flyby," she points out. "I would say based on this, that there is no chance of impact in 2017, but more observations could help to reduce the uncertainties."