`Earth had 2 moons, but 1 destroyed in collision`

A new theory has come up that the earth might once have had two moons - the one that shines at night today and a smaller companion, which was destroyed in a slow collision between the two satellites.

Updated: Aug 04, 2011, 13:23 PM IST

London: A new theory has come up that the earth might once have had two moons - the one that shines at night today and a smaller companion, which was destroyed in a slow collision between the two satellites.

While the side of the moon facing the Earth has relatively low and flat topography, the side facing away is high and mountainous with a much thicker crust.

Scientists have proposed different theories to explain this lack of symmetry. One leading idea is that gravitational tidal forces reshaped the moon’s crust and made it lopsided.

But the new theory builds on the “giant impact” model that explains the moon’s creation.

Many experts believe a Mars-sized object collided with the Earth early in the solar system’s history, ejecting debris that was later drawn together by gravity to form the moon.

The “second” moon is also thought to have been generated by the giant impact, remaining in orbit for tens of millions of years.

The two moons collided relatively slowly, according to the theory.

Such low velocity impacts do not produce craters or cause much melting. Instead, most of the colliding material is piled onto the impacted hemisphere as a thick new layer of solid crust.

This could have formed the mountainous region now seen on the far side of the moon.

“Our model works well with models of the moon-forming giant impact, which predict there should be massive debris left in orbit about the Earth, besides the moon itself,” the Daily Mail quoted lead researcher Professor Erik Asphaug, from the University of California at Santa Cruz, as saying.

“It agrees with what is known about the dynamical stability of such a system, the timing of the cooling of the moon, and the ages of lunar rocks,” he stated.

The study has been described in the journal Nature.

ANI