Researchers at ETH Zurich have published findings that contradict a widely accepted model of planetary formation. The study examined isotope ratios from meteorites and compared them with Earth’s isotopic composition, using statistical analysis methods rarely applied to geochemistry. The analysis revealed that Earth’s material originated entirely from the inner Solar System, with contributions from beyond Jupiter accounting for less than two percent of the planet’s total mass, or possibly none at all. The findings appear in Nature Astronomy.
The research drew on measurements from ten different isotope systems present in meteorites, a significantly broader approach than earlier studies that typically focused on only two systems. Scientists have long used isotopes to determine the origin points of celestial objects within the Solar System. A methodology change in the early 2010s expanded the available tools beyond oxygen isotopes to include chromium and titanium, allowing researchers to categorize meteorites into two groups: non-carbonaceous meteorites from the inner Solar System and carbonaceous meteorites from the outer regions.
According to the new analysis, Earth consists entirely of non-carbonaceous material, indicating no significant exchange occurred between the inner and outer Solar System reservoirs during Earth’s formation. This suggests the planet developed in a relatively stable environment, gradually incorporating nearby planetary bodies. The findings also indicate that volatile substances, including water, must have already existed in the inner Solar System rather than arriving from distant regions.
The research points to Jupiter as a critical factor in the Solar System’s structure. As the gas giant grew, its gravity created a gap in the protoplanetary disc, effectively limiting material movement from the outer regions to the inner zone. The new analysis suggests this barrier was highly effective. The material composition of Earth closely resembles that of Mars and Vesta, and researchers theorize Mercury and Venus may follow the same pattern, though samples from those planets are not currently available for direct testing.
The findings present a new scientific puzzle: if Earth did not receive substantial water-rich material from the outer Solar System, the mechanism by which sufficient water accumulated in the hot inner Solar System to eventually form Earth’s oceans requires explanation. The research team plans to investigate this question further and examine whether comparable planetary formation processes occur in systems around other stars.
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