Earth and Mars Formed Through Different Processes
New modeling suggests the two terrestrial planets grew from distinct ratios of building blocks 4.5 billion years ago.
Updated on Oct. 2, 2026 in Geology
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A study published in Nature Astronomy on October 2, 2026, revealed that Earth and Mars formed 4.5 billion years ago through divergent accretion pathways. While both originated in the same gas and dust cloud, their final compositions reflect markedly different proportions of cosmic building blocks.
Why it matters
Understanding these distinct formation pathways helps clarify how planetary mantles retain chemical imprints of their origin. This finding marks a shift in our understanding of how terrestrial planets in the same neighborhood can evolve through varied mass-accumulation mechanisms.
Earth accumulated 75 percent of its mass through pebble accretion—the gradual growth of protoplanets from small, centimeter-sized pebbles—while Mars drew 75 percent of its mass from planetesimals, which are solid, kilometer-sized building blocks formed from cosmic dust.
The players
University of Copenhagen
An academic institution leading research into planetary science and the chemical history of the solar system.
The details
Researchers utilized computer models to examine the chemical fingerprints of volatile elements, such as sodium, zinc, and potassium, preserved within the planets' mantles. These elements serve as proxies for the accretion history of the celestial bodies, showing that Earth was largely constructed from moon- to Mars-sized planetary embryos, whereas Mars relied heavily on the collision of larger, solid planetesimals. This evidence supports a hybrid model of planet formation that accounts for how the two planets evolved within the same rotating gas and dust cloud.
Timeline
4.5 billion years ago, Earth and Mars formed within the early solar system.
October 2, 2026, the study findings were published in Nature Astronomy.
The Tech Race
This research updates the hybrid model of planet formation by showing how terrestrial planets within the same disk can follow distinct accumulation trajectories. It provides a crucial reference point for future studies analyzing the chemical diversity of rocky planets across the solar system.
This research clarifies the fundamental origin story of our solar system for planetary scientists and astrophysics students. It provides a new chemical benchmark that will influence how future data from Mars exploration missions are interpreted regarding planetary composition.
The takeaway
The study establishes that the distinct mantle compositions of Earth and Mars serve as a long-term record of their initial growth. Readers interested in this process should watch for follow-up isotope analyses that apply these formation ratios to other bodies in the inner solar system.
Further reading
For broader context on how internal structure informs planetary evolution, explore Geology.
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Does understanding the origins of other planets change how you view humanity's place in the universe?
