Earth and Mars Grew Through Distinct Planetary Assembly Mechanisms Despite Similar Origins

Research comparing Earth and Mars reveals the neighboring planets accumulated mass through markedly different proportions of two formation processes: while Earth gathered roughly 75 percent of its mass through pebble accretion and 25 percent from planetesimal collisions, Mars developed in the opposite ratio. Scientists reconstructed these divergent formation pathways by analyzing volatile elements such as sodium, zinc, and potassium preserved in each planet's crust and mantle, then tested their findings against computer models of planetary growth. The study demonstrates that planets forming in the same region of the early solar system can follow fundamentally different assembly routes.

Rocky planets in the early solar system had two primary mechanisms for accumulating mass. Pebble accretion involved gravitational capture of smaller particles, while planetesimal collisions occurred when larger bodies crashed together. Earth's composition suggests it benefited heavily from the pebble accretion process, whereas Mars developed predominantly through planetesimal impacts. Researchers reconstructed this history by examining how volatile compounds—elements prone to vaporization at high temperatures—became concentrated in each planet's internal structure over billions of years.

The chemical signature preserved in planetary mantles acts as a geological record of formation conditions. By comparing measured abundances of elements like sodium and potassium against computational models of planetary growth, scientists identified which combination of assembly processes best explained each world's current state. This approach may prove more reliable than previous methods for inferring planetary history, as chemical fingerprints can distinguish between formation scenarios that other evidence alone cannot resolve.