The Moon was born from head-on collision between two worlds
Friday, January 29, 2016, 6:57 PM - According to a new study, the formation of the Moon was far more violent than previous research has shown, involving a head-on impact between Earth and proto-planet that blasted apart both worlds.
The widely-held hypothesis for the formation of the Moon is that a Mars-sized planet, which astronomers have dubbed Theia, hit the Earth with a hard, glancing blow roughly 100 million years after Earth formed.
Based on that scenario, Theia's core, along with most of its mantle and crust were then mixed into the Earth, while a large glob of its outer layers was thrown into space to cool and coalesce into the Moon.
Watch Below: This simulation by the Southwest Research Institute demonstrates the glancing blow by Theia that produced the Moon.
As a result of this, it was expected that Earth and the Moon should have fairly different surface compositions, especially with the ratios of certain chemical isotopes in the surface rocks and soil.
Isotopes are atoms of an element which have a different number of neutrons in the nucleus than normal. For example, over 99 per cent of stable oxygen atoms have a nucleus with 8 protons and 8 neutrons (atomic number 16, denoted as 16O). The remaining are split between atoms with 9 neutrons (thus 17O) or 10 neutrons (18O). These are the stable isotopes of oxygen.
Since the composition of objects in the solar system can vary greatly based on where they formed, if two objects were to have the same ratio of oxygen isotopes, there's a very good chance that they would be from the same source.
In June of 2014, a team of German researchers, led by Daniel Herwartz of the University of Cologne, reported using a new technique to separate out oxygen isotopes from samples, and that their technique had detected a very small difference in the number of 17O and 18O isotopes in Moon samples when compared to Earth samples. At the time, this was hailed as the first detectable "signature" of Theia, and their findings supported this "glancing blow" hypothesis for the formation of the Moon.
Now, another team of scientists, led by Edward Young, a UCLA professor of geochemistry and cosmochemistry, has found some very different results from that earlier study. Using state-of-the-art methods to examine 7 different Moon rocks brought back by the Apollo 12, 17 and 18 astronauts, and confirming those results with the university's new mass spectrometer, they found a remarkable similarity between the Earth and Moon samples.
"We don't see any difference between the Earth's and the Moon's oxygen isotopes; they’re indistinguishable," Young said in a UCLA news release.
This introduced a new potential scenario for the formation of the Moon, a much more violent one that involved a head-on collision rather than just a glancing blow. This would have melded Earth and Theia together completely, with the glob that formed the moon coming from this thorough mixture of the two worlds.
"Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them," Young said. "This explains why we don't see a different signature of Theia in the moon versus the Earth."
This isn't the first time this head-on collision formation scenario has been proposed for the Moon. Back in 2012, SETI Institute researcher Matija Ćuk and UC Davis' professor Sarah Stewart suggested it, as well as Robin Canup of the Southwest Research Institute. This new research lends strength to that hypothesis.
Watch Below: See every phase of the Moon for 2016, courtesy of NASA Goddard's Scientific Visualization Studio