The Moon may have been flying around our Earth in an oval-shaped, eccentric orbit 100 million years after its formation, US astronomers reported on Thursday.

This scenario could explain why the Moon's far side bulges at its equator, a mystery that has puzzled scientists since French mathematician Pierre-Simon Laplace first noticed it in year 1799, according to the astronomers at the Massachusetts Institute of Technology (MIT).

Scientists have not yet put forward a persuasive model both to explain the Moon's odd shape and fit its dimension. It is said that British physicist Isaac Newton suffered severe headaches when he attempted to provide a more complete theory of the Moon's motion.

According to the MIT team led by planetary science professor Maria Zuber, the Moon's peculiar shape may indicate a different orbit early in its history,

The excess material around the lunar equator, the "fossil bulge," can be explained if the satellite moved in an eccentric oval-shaped orbit 100 million years after its violent formation, when the satellite hadn't yet fully solidified, the MIT researchers said in the Aug. 4 edition of the journal Science.

Around that time, the Moon was like a big ball of molasses and all around the equator it got deformed. Conditions such as orbit shape and position were optimal for this "ball of molasses" to cool down and become the solid moon that we now know, the researchers said.

In one of their models, the Moon's orbit would be similar to present orbit of Mercury, which rotates three times about its own axis for every two revolutions about the Sun, the researchers said.

"The Moon may have once been in a 3:2 resonance of orbit period to spin period, similar to Mercury's present state," they wrote in the Science paper.

"The possibility of past high-eccentricity orbits suggests a rich dynamical history and may influence our understanding of the early thermal evolution of the Moon."

These results also dovetail in a reasonable way with the prevailing theory of the Moon's origin through a giant impact of a Mars-like object with Earth, the researchers said.

(Xinhua News Agency August 4, 2006)