NASA Research Says Moon May Have Formed in Mere Hours

The solar system is peppered with space rocks that could really ruin your day if they happen to intersect with Earth, which is why we’re smashing them with probes and stealing bits for study. Even the most dangerous asteroid of today is nothing compared with the object that (probably) walloped Earth a few billion years ago to create the moon. Researchers from NASA’s Ames Research Center have created the most detailed simulations of this impact ever, and the results are surprising. Instead of taking months or years, the new research suggests the moon may have formed almost immediately.

Scientists have known for decades that the moon shares many chemical properties with Earth, but it’s unlikely that the impactor had a matching signature. Some theories have held that the impactor, a Mars-sized planetoid known as Theia, knocked material off of Earth, contributing to the moon’s crust. That hypothesis only matches reality if Earth contributed much more material to the moon, particularly the outer crust. However, it does explain the moon’s tilted orbit. Others have suggested that the moon simply formed in a swirl of vaporized rock from the collision. That could explain its composition but not the orbit.

The single-stage formation theory examined by the Ames team could explain the composition and orbit in a more elegant way, and it wouldn’t take months. The newly published research relies on some of the most advanced computational models of giant impacts. The simulation below demonstrates how the single-stage formation would have happened. Theia’s impact causes a massive disruption in the primordial Earth, ejecting material that initially forms two bodies. The larger inner one descends below the reforming Earth’s Roche limit, at which point it falls and re-merges with Earth. The smaller body remains in orbit, and that’s how you get the moon in a matter of hours.

Interestingly, the study predicts the ejected bodies would have had molten surfaces over cooled interiors, consisting of about 60 percent proto-Earth material. That makes the simulated moon a good isotopic match for the real deal. The orbit is no problem, either. The team found that even simulated moons that dip below the Roche limit have high survivability because they are “torqued” into a higher, stable orbit by the large inner blob of ejecta before it falls back to Earth.

As humanity prepares to return to the moon, we may discover evidence that strengthens or weakens this new take on lunar formation. Whatever we learn, it will help us understand not only the moon but also Earth. No matter which version of the story is right, Earth and the moon have a shared cataclysmic history.

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