The Moon is Earth’s twin, but not from a simple collision
In short: Every celestial body in our solar system has a unique chemical signature, except for the Earth and the Moon. They share a nearly identical composition, a mystery that defies the standard textbook explanation of how our satellite was born. A new theory suggests a much more violent, high-energy beginning.
The standard 'giant impact' theory proposes that a Mars-sized object grazed the early Earth, throwing off a mass of material that condensed to form the Moon. While this explains the system's angular momentum and the Earth's early five-hour day, it fails to account for two major anomalies. First, the Moon is unexpectedly similar in chemistry to Earth. Second, if the Moon had formed from a disk of material rotating around the equator, it should align with the plane of the ecliptic. Instead, it sits at a 5-degree tilt, suggesting a massive injection of energy occurred during its formation.
To solve this, planetary scientist Sarah T. Stewart and her colleagues proposed a new model involving a 'synestia.' Rather than a simple graze, they suggest a high-energy collision occurred that left behind a massive amount of vaporized and molten material. This molten mass eventually cooled and differentiated into the Earth and the Moon. This process explains why the two bodies share such a close chemical relationship—they essentially formed from the same pool of vaporized matter.
The model also accounts for the Moon's orbital tilt. The model suggests a more powerful primary impact occurred because a portion of the Earth-Moon system's angular momentum shifted toward the Earth-Sun system. This research, published in the journal Nature on October 31, provides a framework to understand how our unique celestial partnership emerged from a chaotic, high-energy past.
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Sources
- Summary by Intellect · source: Where did the Moon come from? A new theory | Sarah T. Stewart
- Also: The Earth and Moon are twins! A discovery that explains their origin
- Also: New Theory Explains How the Moon Got There
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