New Simulations Suggest Moon Formed in Five Hours After Giant Impact

Moon formed in five hours: Revised Impact Model

Researchers at Southwest Research Institute have run the most granular simulations yet of the cataclysmic collision that birthed Earth’s satellite. By feeding temperature‑dependent material strength into the equations, the team discovered that a scorching Theia, striking less than ↓ 60 million years after the solar system’s birth, would shatter and spawn a debris disk that coalesces into a moon in under ↑ 5 hours. The finding challenges the slower accretion picture that has dominated for decades.

Lead author Adeene Denton explains,

“When we matched the temperature profiles used in classic models, the disk collapsed almost instantaneously, delivering a complete moon in a handful of hours.”

The result dovetails with earlier work by planetary scientist Robin Canup, whose 2001 simulations first demonstrated that an oblique impact by a Mars‑sized protoplanet, dubbed Theia, could loft material into orbit.

Warmer interiors make planetary bodies more pliable, allowing impact energy to disperse differently. In the new runs, a hot Theia deforms dramatically, dumping most of its iron core into Earth while ejecting a massive mantle‑rich ring. That ring, according to the models, spreads and settles within a few revolutions, birthing the moon almost immediately.

If the impact occurred later—around 100‑150 million years after planet formation—Theia would have cooled, behaved like a sturdier projectile, and the debris disk would linger, permitting a gradual accretion over thousands of years. The thermal state, therefore, could explain lingering compositional puzzles, such as the moon’s volatile inventory and subtle isotopic offsets from Earth’s mantle.

The implications extend beyond our backyard. Should moon‑forming disks be as fleeting as these simulations suggest, astronomers hunting exomoons around rocky exoplanets may need to adjust expectations, because the observable signatures would vanish within days. By contrast, disks around gas giants, which arise from leftover nebular material, remain detectable for far longer.

For further details, see the study published 1 September in The Astrophysical Journal Letters and follow coverage on Reuters and NASA.

Intel provided by: Nova Stirling

Aerospace & Space Tech Correspondent