Water has long been thought to have originated much closer to the Sun than previously supposed, which suggests that the raw materials that built Earth’s water came from a distant source, beyond Jupiter, carried to our planet when the Solar System was young. A new study from ETH Zurich suggests that picture is wrong. Earth’ might have all come from within the inner Solar System.
The Inner Solar System Origin
Paolo Sossi and Dan Bower drew on isotope ratios to compare the makeup of meteorites against that of Earth. Isotopes refer to atoms of the same element carrying a different count of neutrons. After examining ten distinct isotope systems across meteorite samples, including those tied to Mars and the asteroid Vesta, the pair arrived at a striking conclusion.
Their results show that Earth’s material came almost entirely from within the inner Solar System. Material from beyond Jupiter appears to account for less than two percent of Earth’s total mass, and possibly none at all.
“Our calculations make it clear: the building material of the Earth originates from a single material reservoir,” says Sossi. Bower added that the finding was unexpected: “We were truly astonished to find that the Earth is composed entirely of material from the inner Solar System distinct from any combination of existing meteorites.”
Jupiter’s Role in the Early Solar System
Scientists believe Jupiter acted as the barrier that separated the young Solar System into two distinct reservoirs of material, one inner and one outer. As the gas giant grew quickly, its immense gravity cut a gap into the protoplanetary disc surrounding the young Sun — a ring of gas and dust where planets form.
The opening between the two zones may have served as a wall, keeping matter from the outer reaches of our star system from entering the inner region. According to the new research, almost no material from beyond Jupiter’s orbit appears to have made its way into the zone where Earth formed.
“Our calculations are very robust and rely solely on the data itself, not on physical assumptions, as these are not yet fully understood,” Bower emphasizes.
The Water Question Remains
The finding raises a major question about Earth’s oceans. If Earth did not receive large amounts of water-rich material from the outer Solar System, how did enough water exist in the hot inner Solar System to eventually produce Earth’s oceans?
The team led by Sossi intends to examine that question in their next round of work. They also aim to find out if comparable processes might take place in planetary systems orbiting other suns. Until then, the outcome leaves us with a new puzzle about the origins of Earth’s water.
What This Means for Mercury and Venus
The researchers also suspect that Mercury and Venus could fit the same pattern as Earth, Mars, and Vesta. “Based on our analysis, we can theoretically predict the composition of these two planets,” says Sossi.
For now, the prediction remains untestable. No rock samples from Mercury or Venus — the two planets nearest the Sun — have been brought back for the kind of analysis that would settle it.
According to Sossi, the discoveries offer fresh insight into how Earth and the other rocky worlds came to be.
A New Chapter in Planetary Science
The ETH Zurich team’s approach was unusual for the field. “Our studies are actually data science experiments,” says Sossi. “We carried out statistical calculations that are rarely used in geochemistry, even though they are a powerful tool.”
Previous research tended to look at just two isotope systems. The current study compares ten systems across a broad selection of meteorites, which allowed the team to reach conclusions beyond what earlier work could manage.
The findings reveal that Earth shares a similar makeup with Mars and Vesta.
Sossi argues that the debate about the building blocks of Earth remains unsettled, even with the new findings, and “Dan and I will have to engage in many heated debates about the material composition of Earth and its neighboring planets,” is his closing remark on the matter.
The study was published in Nature Astronomy.
| Research Step | What Happened |
|---|---|
| Meteorite analysis | Sossi and Bower examined ten isotope systems across meteorite samples |
| Earth comparison | Data showed Earth’s material came almost entirely from within the inner Solar System |
| Jupiter’s role | Scientists believe Jupiter acted as a barrier separating inner and outer material reservoirs |
| Water question | Team plans to examine origins of Earth’s oceans in next round of work |
The world nearest to us now tells a fresh account of its own origin, and the evidence suggests that the water has been present all along.
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