Sunlight could push killer rocks toward Earth

Artist's concept of a killer asteroid impact on Earth

By Richard Stenger
CNN Sci-Tech

(CNN) -- For eons our planet has dwelled among giant boulders that occasionally smack into it with catastrophic results. Why do the killer stones orbit nearby? According to a new report, the sun could be to blame.

The hordes of rocks, known as Near Earth Objects, most likely originated from a stable dense reservoir of gigantic, spinning rocks between Mars and Jupiter.

But scientists have had a hard time explaining what might have dislodged many of them from the generally stable asteroid belt and sent them into the neighborhood of the Earth.

A new U.S.-Czech study theorizes that an unexpectedly subtle cause could be responsible, the absorption and re-absorption of sunlight over millions or billions of years.

The slow process could gently nudge asteroids into new orbital zones, where they become vulnerable to the gravitational forces of the planets, which kicks them into paths that cross that of the Earth.

Like a sunlit sidewalk, a tumbling object in space would be expected to heat up slowly and reradiate the energy back into space.

Because radiation carries some momentum, the reradiated energy could slowly push the asteroids, similar to an effect first described by Russian engineer I.O. Yarkovsky a century ago.

Computer models used to study numerous asteroid belt bodies -- suspected fragments from the collision of large asteroids -- lent support to the idea that the heated bodies experienced altered orbits, the researchers said.

Many of the fragments seem to have been swept into narrow chaotic zones known as resonances, where tiny gravitational kicks produced by nearby planets such as Mars, Jupiter, or Saturn can push asteroids out of the asteroid belt, according to the study.

The team, led by William Bottke of the Southwest Research Institute in Boulder, Colorado, reported its findings in the November 23 edition the journal Science.