Material Strength of Theia and Proto-Earth Enables Intact Moon Formation Hours After Impact

Denton and Asphaug ran smoothed particle hydrodynamics models that incorporated temperature-dependent yield strength and friction, building on the 2001 Canup fluid-only runs. They tested hot versus cold initial states for both bodies, finding that colder, stronger mantles resist full fluidization and permit gravitational reaccumulation of a coherent satellite on orbital timescales of a few hours. The same code framework had previously been validated on the Pluto-Charon system, where strength effects are already accepted as dominant.

This revision connects directly to astrobiology because an intact Moon stabilizes Earth's obliquity within 10,000 years, reducing climate swings that would otherwise hinder early life. It also implies that large moons around rocky exoplanets are more common than fluid-only models predict, altering target selection for future direct-imaging missions. The work further highlights that giant-impact outcomes scale with the thermal state of the colliding bodies, a variable previously treated as secondary.

The principal limitation is that the simulations still omit full vaporization and radiative cooling physics; higher-resolution runs that couple strength with realistic equations of state are required before the hours-scale formation channel can be considered robust. Laboratory impact experiments on analog silicates at 10-100 GPa would provide the needed calibration data within the next five years.