Caltech study finds internal pressures drop after planetary collisions

A new study out of Caltech has the potential to change how scientists think internal pressures in planets evolve over time. The study has found that massive impacts of patents hitting each other could significantly change the current model of planetary formation. One major impact with the Earth about 4.5 billion years ago is believed to be what caused the formation of the Moon.

Researchers on the study believe that this major collision could explain some of the puzzling geochemical signatures in the mantle of the Earth. The team notes that past studies have incorrectly assumed that the internal pressure of a planet is a function of the mass of the planet and increases continually as the planet grows. The new Caltech study has shown that pressure can temporarily change after a major impact.

A longer-term increase follows the initial pressure reduction after a significant impact in pressure as the post-impact body recovers. The researchers say that planetary systems typically begin as a disk of dust that slowly accretes into rocky bodies. The end of the main stage of this process is characterized by high-energy collisions between planet-sized bodies as they form the final planets.

The shock from the impacts can vaporize significant portions of a planet, temporarily turning the two colliding planets into something known as a "synestia." A synestia is a rotating donut of planetary material that later cools into one of more spherical bodies. The team used computational models in their study.

The models found that with two planets that have masses between 0.9 and 1.1 Earth masses that collide, their internal pressured were much lower than expected immediately after the collision. The team says that the decrease in pressure was due to the rapid rotation caused by the collision generating force that acted against gravity, pushing material away from the Spin axis and the low density of the hot, partially vaporized body. The team thinks their findings might explain the contradiction between the geochemistry of the Earth's mantle and the physical models of planet formation.