The moon may have formed in the immediate aftermath of a cataclysmic impact that ripped off a chunk of Earth and threw it into space, a new study has suggested.
Since the mid-1970s, astronomers have believed that the moon could have been made by a collision between Earth and an old one Mars-large protoplanet called Theia; The colossal impact would have created a vast debris field from which our lunar companion slowly formed over thousands of years.
But a new hypothesis, based on supercomputer simulations created at higher resolution than ever before, suggests that the moon’s formation may not have been a slow and gradual process after all, but happened in a matter of hours. The scientists published their findings in the journal on Oct. 4 The Letters of the Astrophysical Journal.
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“What we’ve learned is that it’s very difficult to predict how much resolution you’ll need to reliably simulate these violent and complex collisions – you just have to keep testing until you see that increasing the resolution further makes no difference.” get more power in your answer,” Jacob Kegerreis, a computational cosmologist at Durham University in England, told Live Science.
Scientists got their first clues about the moon’s formation after the return of the Apollo 11 mission in July 1969, when NASA astronauts Neil Armstrong and Buzz Aldrin returned 47.6 pounds (21.6 kilograms) of lunar rock and dust to Earth . The samples are from about 4.5 billion years ago, which places the moon’s formation in the turbulent period about 150 million years after the formation of the solar system.
Other evidence suggests that our largest natural satellite was born from a violent collision between Earth and a hypothetical planet that scientists named after the mythical Greek titan Theia – the mother of Selene, goddess of the moon. This evidence includes similarities in the composition of lunar and terrestrial rocks; The Earth’s rotation and the Moon’s orbit have similar orientations; the high combined angular momentum of the two bodies; and the existence of debris disks elsewhere in our solar system.
But exactly how the cosmic collision happened is up for debate. The conventional hypothesis holds that when Theia crashed to Earth, the planet-destroying impact shattered Theia into millions of pieces and reduced them to floating debris. Theia’s shattered remains, along with some vaporized rocks and gas ripped from our young planet’s mantle, slowly mixed into a disk around which the Moon’s molten sphere coalesced and cooled over millions of years.
However, some parts of the picture remain elusive. An open question is why, even though the moon is composed mostly of Theia, do many of its rocks bear striking similarities to those on Earth? Some scientists have suggested that more of Earth’s vaporized rock went into the moon’s formation than Theia’s pulverized remains, but that idea brings its own problems, such as why other models suggest that a moon composed mostly of crumbled Earth rocks would have a completely different orbit than what we see today.
To explore various possible scenarios for post-collision moon formation, the authors of the new study turned to a computer program called SPH With Inter-dependent Fine-grained Tasking (SWIFT), designed to map the complex and ever-changing web of the moon Accurately simulate gravitational and hydrodynamic forces acting on large amounts of matter. Doing this precisely is no easy math, so the scientists used a supercomputer to run the program: a system nicknamed COSMA (short for “Cosmology Machine”) at Durham University’s Distributed Research Utilizing Advanced Computing Facility (DiRAC).
By using COSMA to simulate hundreds of Earth-Theia collisions with different angles, spins and speeds, the lunar detectives were able to model the aftermath of the astronomical collapse with higher resolution than ever before. The resolutions in these simulations are determined by the number of particles the simulation uses. According to Kegerreis, the standard simulation resolution for giant impacts is usually between 100,000 and 1 million particles, but in the new study he and his fellow researchers were able to model up to 100 million particles.
“With higher resolution, we can examine more detail – similar to how a larger telescope can take higher-resolution images of distant planets or galaxies to discover new details,” said Kegerreis.
“Second, and perhaps more importantly, using too low a resolution in a simulation can lead to misleading or even wrong answers,” he added. “You can imagine that if you build a model car out of toy blocks to simulate how the car might break in an accident, then if you just use a few dozen blocks, you could just split it perfectly in half . But with a few thousand or a million, then you could start crumpling and breaking it in more realistic ways.
The higher-resolution simulation left researchers with a moon that formed within hours from the ejected chunks of earth and shattered pieces of Theia, and provided a one-step theory of formation that offered a clean and elegant answer to the moon’s visible properties. like its wide, inclined orbit; its partially melted interior; and its thin crust.
However, researchers need to study rock and dust samples excavated deep below the moon’s surface – a target of NASA’s future Artemis missions – before they can confirm how mixed its mantle might be.
“More samples from the lunar surface could be extremely helpful in making new and more reliable discoveries about the composition and evolution of the moon, which we can then backtrack to model simulations like ours,” Kegerreis said. “Missions and studies like this and many others are helping us rule out more possibilities and narrow the true history of the Moon and Earth and learn more about how planets form in and outside our solar system.”
Such studies could also shed light on how Earth took shape and became a life-supporting planet.
“The more we learn about how the moon formed, the more we learn about the evolution of our own Earth,” study co-author Vincent Eke, associate professor of physics at Durham University, said in a statement. “Their histories are intertwined – and may be mirrored in the histories of other planets altered by similar or very different collisions.”
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