Elizabeth Howell Space.com Astronomers say they'll have to keep an eye on the near-Earth asteroid Apophis to see how much of a danger the space rock poses to our planet during a close pass in 2068. But don't panic: The chances of an impact still seem very low. Under certain circumstances, the sun can heat an asteroid unevenly, causing the space rock to radiate away heat energy asymmetrically. The result can be a tiny push in a certain direction — an effect called Yarkovsky acceleration, which can change the path of an asteroid through space. Since astronomers hadn't measured this solar push on Apophis before, they didn't take it into consideration when calculating the threat the asteroid poses to us in 2068. Those previous calculations showed a tiny impact probability — around 1 in 150,000. Now, a new study shows the asteroid is drifting away from its previously predicted orbit by about 557 feet (170 meters) a year due to the Yarkovsky effect, lead author and University of Hawaii at