The Moon may have formed almost immediately following a devastating impact between Earth and a Mars-sized world in the ancient past, according to the results of a new supercomputer study.
Earth’s moon is a silent witness to the history of our entire species. Its gravitational influence is responsible for the tides, and its simple presence in the night sky has profoundly influenced humanity’s cultural development.
Yet despite its ever present nature, the scientific community have yet to come to a consensus on how exactly Earth’s largest natural satellite came to form.
It is widely agreed that the Moon was created when a roughly Mars-sized solar system body — which has been dubbed Theia — collided with Earth roughly 4.5 billion years ago. This impact devastated both our planet, and primordial Theia, and sent vast amounts of material from both worlds hurtling into Earth’s orbit.
Many of the previous theories surrounding the Moon’s formation suggest that it slowly coalesced from this soup of orbital debris, until finally the remainder of the material not accumulated by the satellite fell back in towards Earth.
In this scenario, the orbital debris would have been largely comprised of the remains of Theia. However, rock samples recovered from the Moon’s surface by Apollo-era astronauts showed a surprising structural and isotopic similarity to those found on Earth.
Whilst it is possible, the authors of a new study found it unlikely that the material from Theia would have such a close match with that of the Earth.
In the new study, a team of researchers from Durham University in the UK used the powerful DiRAC supercomputing facility to run a range of simulations that could account for the creation of Earth’s moon.
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The supercomputer used a significantly larger number of particles to simulate the ancient collision compared to previous studies. According to the team, lower resolution simulations can omit important aspects of the collision process.
Over the course of the study, the scientists ran hundreds of these high-resolution simulations while varying a range of key parameters, including the masses, spins, angles, and speeds of the two unfortunate worlds.
The simulations revealed that a large body with a Moon-like mass and iron content could have coalesced almost immediately in orbit following the Earth-Theia collision. The detailed simulation showed that the newly born hypothetical satellite would have been created beyond the Roche limit – which is the orbital distance at which a satellite can orbit a planet without being shredded by its gravity.
Furthermore, the outer layers of such a world would be rich in material ejected from Earth, thus explaining the similarities between the Apollo-era rocks and those from our planet.
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“This formation route could help explain the similarity in isotopic composition between the lunar rocks returned by the Apollo astronauts and Earth’s mantlle,” explains study co-author Vincent Eke, an Associate Professor in the Department of Physics at the University of Exeter. “There may also be observable consequences for the thickness of the lunar crust, which would allow us to pin down further the type of collision that took place.”
If the Moon did form quickly following the impact, then its internal structure would likely be different than if it had grown gradually from a circumplanetary disk of debris. Astronauts returning to the Moon in the coming decades under NASA’s Artemis Program will collect fresh samples from the lunar surface that can be used to test the quick formation theory.
The research could help update scientist’s understanding as to how moons form in the orbits of distant worlds spread throughout the universe.
Anthony Wood is a freelance science writer for IGN
Image Credit: Dr Jacob Kegerreis
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