'Hit-and-run': Planet Mercury had a weird incident in its youth - Here is what happened
Produced by Tarun Mishra
Produced by Tarun Mishra
New simulations suggest that Mercury's unique density and iron-rich core may be the result of a glancing collision with a similarly sized protoplanet during the early stages of the solar system's development.
Previous models suggested that Mercury formed through a single, massive impact, but this has been questioned due to the planet’s unexpectedly high concentration of volatile elements, which should have been lost during such an event.
The latest study proposes that a more common event — a grazing impact between two similarly sized protoplanets — could have stripped Mercury’s outer layers while leaving volatile elements largely intact.
According to the research, the collision must have taken place tens of millions of years after the formation of the solar system, when Mercury had already developed a distinct core and mantle. This timing allowed selective material loss without full disruption.
The angle of the simulated collision proved important, with specific "hit-and-run" trajectories allowing proto-Mercury to lose just enough rocky mantle to explain its present mass distribution and chemical makeup.
Simulations indicate that the impact likely occurred in a more crowded region of the early solar system — between the orbits of Earth and Venus. This supports the possibility that Mercury later migrated inward to its current orbit.
The ESA-JAXA BepiColombo spacecraft, due to arrive at Mercury in November 2026, is expected to provide new data that could refine or challenge existing theories on the planet’s formation and structural history.