Moon Born from a Violent Head-On Collision

The astronomers found that the isotopes share a unique fingerprint, something that could only happen if matter from Theia and Earth thoroughly mixed together in a head-on collision.

The only issue however is that most of the oxygen on Earth is made up of eight protons and eight neutrons within each atom, necessitating the need to call this composition O-16; but there is O-17 composition of heavier oxygen isotopes where the proton-neuron combination has an extra neutron; and O-18 with two extra neurons.

If the moon had formed from just a glancing blow between Earth and Theia, like in the video simulation below, we would not see an identical ratio, the scientists say. Young and some other scientists think Theia was roughly Earth-sized; others believe it was smaller, perhaps more Mars-sized.An interesting question is whether the collision removed any water that the early Earth may have contained, Young and colleagues said. Specifically, they wanted to see if the ratio of oxygen isotopes in lunar rocks was the same as that in the terrestrial rocks. Had Earth and Theia collided in a glancing blow, Young said, the vast majority of the moon would have been made mainly of Theia, and the Earth and moon should have different oxygen isotopes. Scientists already knew about the high-speed collision, but many thought it more of a powerful side-swipe than a head-on impact.

The researchers analysed seven rocks brought to the Earth from the moon by the Apollo 12, 15 and 17 missions, as well as six volcanic rocks from the Earth’s mantle – five from Hawaii and one from Arizona. He also revealed the Theia could have developed into a planet had the collision not taken place.

The new research suggests that the collision was actually very violent that the so-called planetary embryo fused with both the Moon and the Earth. In fact, it was thought that the Moon was created when Theia grazed the Earth and broke up.

This is called the giant impact hypothesis. A direct collision with another planet would probably strip any water from Earth, leaving scientists to ponder whether it only came back to the planet thanks to small asteroids colliding with us millions of years down the road. But in the new work, published January 29 in the journal Science, scientists argue that the side-swipe wouldn’t have led to such a similar makeup between Earth and Moon.

Professor Young also spoke about what would have happened to Theia if it had not slammed head-on into the young Earth.