Paris, May 25 (AFP): A jarring game of planetary billiards in the solar system’s early years created the man-in-the-Moon, astrophysicists believe.

Rocks picked up by the Apollo astronauts suggest that the basins which appear to form the Moon’s “face” when seen from Earth resulted from a massive flurry of impacts by space rocks some four billion years ago.

If the dating is right, the lunar bombardment occurred around 600 million years after the Sun burst into light and the planets start to form. By that time, most of the solar system’s construction debris should have settled in stabilised orbits or been mopped up by the planets, sucked in by gravitational pull.

So how could this bombardment of the Moon have arisen? Writing in the journal Nature, scientists say the key is in the formation of Jupiter and Saturn around 4.5 billion years ago. When Saturn completed exactly one orbit of the Sun for every two orbits made by Jupiter, the two would trigger a phenomenon called mean-motion resonance.

It edged the two planets into wider orbits around the Sun, and, in turn, eventually scattered Uranus and Neptune. When Neptune was flung outwards, it in turn scattered an orbiting cloud of rocky debris towards the Sun, some of which smacked into the Moon.