Mercury’s Formation: Violent Collision of Protoplanets

New research suggests the unique composition of Mercury may be due to a cataclysmic collision between two protoplanets of similar size in the early solar system.

Collision Scenario

According to planetary scientists, a collision between protoplanets could account for Mercury’s characteristics. “A collision of two planeted embryos, which is about the same size, can reproduce today’s Mercury,” the researchers report. The impact would have had to be forceful enough to strip away much of the mantle while minimizing damage to the core. The simulations indicated that a slower impact speed of approximately 20 kilometers per second, at an angle between 30 and 40 degrees, would best explain Mercury’s formation.

Mantle Stripping

Simulations suggest the collision resulted in the proto-Mercury losing a significant portion of its rocky mantle to the other protoplanet. The remaining debris formed a smaller planet with the mass and core proportion observed in Mercury today after only 12 to 35 hours.

Single Impact Hypothesis

The planetary researchers suggest that this scenario provides the best explanation for Mercury’s unique characteristics compared to other rocky planets in our solar system. Franco and colleagues state, “Our results confirm that a single big collision is the most plausible hypothesis for the formation of Mercury.” They do acknowledge that the simulation does not account for all aspects of the collision’s aftermath. Researchers continue to explore what happened after the collision with the second protoplanet.

Expert Commentary

Luca Maltagliati, senior editor of Nature Astronomy, believes that this scenario is plausible: “While previous suggestions included various types of impacts, this study shows that the simplest and most likely scenario-a foray collision between two similarly large sky bodies-can explain the observed Mercury properties.”

Broader Implications for Exoplanets

The new research has implications for the study of exoplanets, where planets similar to Mercury have been observed in other planetary systems. These exoplanets may have formed through similar collisions. According to NASA, over 5,500 exoplanets have been confirmed in 4,100 systems, offering many opportunities to test this theory (NASA Exoplanet Archive). Franco and his team suggest that, “Our results raise the question of whether planets may have been shaped by other stars by similar collisions.”