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For its size and location in the solar system, Earth has a surprisingly large moon. But how exactly the blue planet got its companion has vexed researchers for a long time. Researchers at the Southwest Research Institute and the University of Arizona used state-of-the-art computational techniques that revealed fundamental differences in how the moon may have formed from the collision between a Mars-sized object and Earth roughly 4.5 billion years ago.
Published in The Astrophysical Journal Letters, the results – for the first time – factor in the material strength of the two ancestral bodies and may change how researchers think the planetary collision happened. These impact simulations could change how researchers understand moon formation and may help constrain the timing of the event.
"We discovered that the preexisting geology of the Mars-sized proto-moon matters," said Adeene Denton, a former postdoctoral researcher at Lunar and Planetary Laboratory who is now at SwRI. "When you simulate the Earth and the moon as colliding bodies with geologic properties, it changes how the moon forms out of that impact – that's something we considered unnecessary before."
Earlier studies of the giant impact scenario include a foundational 2001 paper by Robin Canup, vice president of SwRI’s Solar System Science and Exploration Division in Boulder, Colorado, and Erik Asphaug, a professor at the Lunar and Planetary Laboratory and co-author of the current study. In the giant impact scenario, the debris from the collision of a Mars-sized body known as Theia with the early Earth obliterated Theia, scattering its remains into a disk around Earth. However, those simulations and subsequent giant impact modeling ignored material strength, which was thought to be insignificant for such high-energy events. Denton and her team revisited this hypothesis, using modern computational methods that incorporate temperature-dependent geologic strength for the first time.
