Earth’s Moon may not have slowly assembled from a debris disk over decades – it could have been finished within just a few hours of the giant impact. That is the conclusion of a new modeling study in the journal „The Astrophysical Journal Letters“.
Simulations with realistic rock strength
A team led by Adeene Denton (Southwest Research Institute) and Erik Asphaug (University of Arizona) re-ran the classic giant impact between the young Earth and the Mars-sized body Theia. Unlike earlier models that treated both bodies as pure fluids, the researchers accounted for the first time for the temperature-dependent strength of the rock – how strongly the material resists being torn apart.
Five hours instead of a long debris phase
In one scenario the Moon formed as an intact body roughly five hours after the impact. When the colliding partners were hotter and therefore softer, the collision shattered Theia completely into a debris disk from which the Moon assembled only gradually. The decisive factor is thus the thermal state of the original bodies – something researchers long assumed to be negligible.
A model, not an observation
Importantly, the results come from computer simulations, not direct measurements. Why Earth and Moon are chemically so similar remains unexplained. Still, the new approach could eventually help pin down exactly when the Moon formed.
Source: The study by Denton, Asphaug et al. appeared in „The Astrophysical Journal Letters“ (DOI 10.3847/2041-8213/ae91e9). Context in the University of Arizona press release: news.arizona.edu.
