Earth ‘once had two moons’

EARTH may once have had two moons, the one that shines at night today and a smaller companion, according to a new theory.

A collision between the two is believed to have created the mountainous highlands on the moon’s far side that have long puzzled scientists.

The side of the moon facing the Earth and the side facing away have strikingly different topographies.

While the near side is relatively low and flat, the far side 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.

The new US 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 impact.

As the two moons collided, material piled onto the impacted hemisphere as a thick layer of solid crust.

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