A Fresh Theory On The Formation Of The Moon

A computer model of the cataclysmic impact event which formed the moon over 4 billion years ago

The formation of the moon began with an event cataclysmic in nature. Just 600 million years after the solar system began to form, our Earth was struck by an object of massive size. Molten material blasted into orbit, and under the influence of gravity, came together, then slowly cooled to form the moon. This is a summary of the current theory which describes the origins of our natural satellite.

Known as the Big Whack or the Big Splash, the hypothesis was put forward in the 1970s by several independent groups of scientists. Yet despite this, the subject is still contentious. Recent studies suggest that the Earth once had two moons, one of which engaged in a slow disintegration across the surface of the other, to become one single body.

Samples of lunar material sued in the isotopic study

The theory revolves around a Mars-sized body called Theia colliding with the young Earth, blasting out the material which would form the moon/moons. While Theia's iron core sinking to the centre of the planet, compensating for the molten rock lost to the moon, remained the same.

Now, new research suggests a rather different scenario. One way of linking a substance to its place of origin is to examine the ratio of isotopes (atoms of an element with a varying number of neutrons) within it.

A team of geochemists led by Andreas Reufer, from the Center for Space and Habitability in Bern, Switzerland, examined the oxygen isotope ratios in samples of rock brought back by the Apollo moon mission. They found they were uncannily similar to the ratio found in Earth rocks. Earlier this year, another research team came up with similar results based on titanium isotopes.

If Theia's core became part of the Earth the isotope ratios in the two bodies should be different. This forced the Swiss researchers to find a different solution to the problem. In the end they suggested that the collision may have been a glancing blow at a much higher velocity. Using computer and gravitational modelling, they suggest that this would have super heated magma and blasted a great enough volume of magma into orbit without altering the isotopic composition with its own material. What is more, the theory does not interfere with other ideas such as the collision altering the angle of the Earth's axis or stabilizing and slowing down what was originally a vicious and erratic orbit.

The conclusion to the story is still open. The researchers have stated that more analysis and possibly even fresh samples will be required to provide strong foundational evidence. The theory is not outlandish by any means. Yet the event is so far back in time during the primordial days of the solar system that it is likely the origins of the moon will always be shrouded in mystery.