Earth and Mars may have originated from the same rotating cloud of gas and dust that eventually formed the Solar System, but the two planets followed significantly different paths during their formation, according to a new study.
Researchers have reconstructed the early stages of the formation of Earth and Mars and found major differences in how material accumulated to build the two planets. Anders Johansen, a researcher at the Globe Institute at the University of Copenhagen, described the finding as surprising because planets formed side by side within the same Solar System might be expected to have broadly similar formation histories.
Earth and Mars Built From Different Materials
Co-lead researcher Haiyang Wang said at least 75 per cent of Earth's mass came from two young planets, or protoplanets, that grew by accumulating rocks. Planetesimals contributed up to the remaining 25 per cent.
Mars followed a different pattern. Around three-quarters of the planet's mass came from planetesimals, while the remaining quarter was formed through the accumulation of rocks.
The study, published in the journal Nature Astronomy, examined the origins of the two planets about 4.5 billion years ago. Researchers analysed specific elements found in the outer layers and interiors of Earth and Mars to trace their early formation processes.
Chemical Elements Provide Clues
Scientists generally agree that planets can form through collisions between large bodies in space or through the process in which larger rocks gather smaller particles and grow over time.
The latest findings support this hybrid model of planetary formation. Researchers focused on volatile elements such as sodium, zinc and potassium. The presence or absence of these elements can act as a kind of chemical fingerprint, providing clues about the conditions and materials involved in planetary formation.
Using computer models, the researchers were able to reconstruct aspects of the formation process despite the fact that much of the direct evidence from billions of years ago has disappeared.
The study suggests that the composition of Earth's and Mars' layers still preserves distinctive signatures of how the two planets formed. Their shared origin in the same early Solar System environment therefore did not result in identical formation histories.
Different Formation Paths in the Early Solar System
The findings provide further insight into the complex processes that shaped the terrestrial planets. While Earth and Mars emerged from the same broad reservoir of gas and dust, the relative contribution of protoplanets, planetesimals and accumulated rocks differed substantially between the two.
The researchers' analysis offers a clearer picture of how different planetary formation pathways can develop within the same young planetary system.