A new moon formation theory suggests the lunar satellite came out of the same big bang event that produced the Earth, rather than just being a chunk of Earth knocked loose later on during a celestial collision.
The current theory is that a Mars-like object grazed what would become the Earth early in the solar system's formation, throwing off a mass of material from which the moon condensed, said a study by the University of California, Davis.
"But there are a couple of problems with the textbook theory," the study found. "One is the moon's surprisingly Earth-like composition. Another is that if the moon condensed from a disk of material rotating around Earth's equator, it should be in orbit over the equator. But the moon's current orbit is tilted five degrees off the equator, meaning some more energy must have been put in to move it."
The new theory, published Tuesday in the science journal Nature, suggests there was "a more energetic collision" that "left a mass of vaporized and molten material from which the Earth and moon formed."
"We present a tidal evolution model starting with the moon in an equatorial orbit around an initially fast-spinning, high-obliquity Earth, which is a probable outcome of giant impacts," the study said. "Using numerical modelling, we show that the solar perturbations on the moon's orbit naturally induce a large lunar inclination and remove angular momentum from the Earth–Moon system."
"Our tidal evolution model supports recent high-angular-momentum, giant-impact scenarios to explain the Moon's isotopic composition and provides a new pathway to reach Earth's climatically favorable low obliquity."
The theory explains why the composition of Earth and the moon is so similar, making it unique in the solar system, said a study author, Sarah Stewart, professor of earth and planetary sciences.
"There are many potential paths from the moon's formation to the Earth-moon system we see today," said co-author Douglas Hamilton of the University of Maryland. "We've identified a few of them, but there are sure to be other possibilities.
"What we have now is a model that is more probable and works more cleanly than previous attempts. We think this is a significant improvement that gets us closer to what actually happened."
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