New Study Suggests Earth Formed Close to the Young Sun

For decades, scientists assumed a meaningful chunk of Earth came from far beyond Jupiter. New research suggests that assumption might be almost entirely wrong.

Comparing Isotopes Across Ten Systems

Planetary scientists Paolo Sossi and Dan Bower of ETH Zurich compared isotope ratios from a wide range of meteorites, including samples linked to Mars and the asteroid Vesta, against Earth’s own isotopic makeup. Earlier studies typically relied on just two isotope systems to trace where meteorites originated. Sossi and Bower instead used ten different systems and applied statistical methods more common in data science than traditional geochemistry.

Almost Nothing From Beyond Jupiter

Their results point to a striking conclusion. Material from the outer Solar System appears to account for less than two percent of Earth’s total mass, and possibly none at all. Sossi says the calculations show Earth’s building material comes from a single reservoir, and Bower described the team as truly astonished to find Earth made entirely of material distinct from any combination of known meteorites. The study appears in Nature Astronomy.

Jupiter as a Gatekeeper

Scientists have long divided meteorites into two broad camps: non-carbonaceous material, which formed in the inner Solar System, and carbonaceous material, which contains more water and carbon and formed farther out. The new analysis finds Earth is made entirely of non-carbonaceous material, with no evidence of exchange between the two reservoirs. Researchers think Jupiter is responsible for that separation. As the gas giant grew, its gravity carved a gap in the disc of gas and dust surrounding the young Sun, acting as a barrier that kept outer material from reaching the inner Solar System far more effectively than previously understood.

A New Mystery About Earth’s Water

If outer Solar System material did not deliver Earth’s water, something else has to explain how enough water existed in the hot inner Solar System to eventually fill our oceans. Sossi and Bower plan to investigate that question next, along with whether similar processes might play out in planetary systems around other stars. The researchers also expect Mercury and Venus to share the same isotopic pattern as Earth, Mars, and Vesta, though no rock samples exist yet to test that prediction directly.

Sources

This report draws on ETH Zurich’s own announcement of research published in Nature Astronomy by Paolo Sossi and Dan Bower.