Was the Moon-Forming Impact Squishy or Crunchy?

In the early history of the solar system, a Mars-sized planet called Theia collided with the newborn Earth. This catastrophic impact destroyed Theia and scattered material from both bodies to create the Moon. Although most planetary scientists agree on the general framework of this story, they struggle to reconcile the details of their models with the Earth-Moon system.

A recent study published in Astrophysical Journal Letters investigates whether Theia's material strength during the collision could explain these discrepancies.

Lead author Adeene Denton, a planetary scientist at the Southwest Research Institute, used a more realistic model by treating Theia as a solid body instead of a fluid. This approach produced different outcomes, including the formation of a solid proto-Moon rather than the debris disk typically simulated. Denton's work builds on her previous research on the formation of Pluto's moon Charon, where she considered the impact strength of celestial bodies.

The timing of the collision also plays a crucial role in determining the result. An earlier collision with a warmer Theia (near or below its melting point) would create a different outcome compared to a later collision with a colder, more solid Theia. Moreover, Denton noted that the exact moment of the collision remains unknown. If Theia was cold and strong due to its long existence, it would be less likely to deform compared to a hot, weaker Theia.

While this new model doesn't definitively answer the question of how the Moon formed, it offers a "crunchy" explanation by potentially skipping the debris disk stage and forming the Moon directly from the collision. However, even this solution leaves room for further investigation and debate among experts in the field. The study highlights the importance of considering material strength in planetary impact models and paves the way for future research involving geochemists to refine these simulations.