New simulations suggest a planetary collision between Earth and Theia could have formed the moon in hours.

Astronomers widely believe the moon formed when a Mars-sized protoplanet named Theia collided with the early Earth over 4.4 billion years ago. This leading explanation, known as the giant-impact hypothesis, suggests the powerful collision blasted material into orbit that later coalesced into our natural satellite. Support for this planetary-scale impact comes from several lines of evidence, including similar stable-isotope ratios in Earth and moon rocks and the high angular momentum of the Earth-moon system.

Additionally, the moon features a relatively small iron core and is depleted of volatile substances that easily turn to gas, traits consistent with a massive merging of mantles and crusts during an energetic event. A recent study led by Adeene Denton of the Southwest Research Institute and University of Arizona researchers suggests that the impact may have depended heavily on the heat and physical strength of the colliding bodies.

Simulations show that under certain conditions, the moon could have formed in a timeframe as short as five hours. Uncertainty remains regarding the precise timing of the collision, with current age estimates ranging from 40 to 120 million years after the solar system formed. Co-author Erik Asphaug notes that an earlier collision would involve a hotter Theia,