It's not large bodies we need to be concerned about
Scientists with the Institute of Astronomy of the Russian Academy of Sciences have recalculated the path of a large asteroid, Apophis; the refined data indicates a significantly low likelihood of a hazardous encounter with Earth, the institute's leading research fellow Viktor Shor said on Wednesday.

The Apophis asteroid is approximately the size of two-and-a-half football fields; its orbit is slightly offset to that of Earth's. Discovered in 2004, astronomers have determined that the asteroid will make a very close flyby in 2029 and might even hit Earth.

The initial calculation for the asteroid Apophis orbit was made using only two sets of observations.

Russian scientists recalculated its path taking into account a subtle effect changing the orbit of the asteroid - the thrust from sunlight absorbed and re-radiated as heat by the asteroid (the so-called Yarkovsky effect).

"Scientists give various orbital determinations for Apophis. But earlier calculations for the orbit did not include the Yarkovsky effect. This effect could strongly deflect the path of the asteroid," Shor said speaking at the International Aerospace Congress in Moscow.

The refined orbital determination indicates the significantly low likelihood of a hazardous encounter with Earth in 2029, Shor continued.

The exact path Apophis follows on its flyby in 2029 will determine whether it smashes into Earth seven years later, the scientist said.

The science of predicting asteroid orbits is based on a physical model of the solar system which includes the gravitational influence of the sun, moon, other planets and the three largest asteroids.