Earth May Have Formed With Its Water Already Nearby the Young Sun

A study by planetary scientists at ETH Zurich suggests that Earth formed almost entirely from material originating in the inner Solar System, challenging the long-standing idea that a substantial share of Earth’s building material came from beyond Jupiter. The findings also suggest that volatile elements such as water were already present in the inner Solar System during Earth’s formation, raising new questions about how water survived so close to the young Sun.

Earth’s Water May Have Had a Much Closer Beginning

For decades, scientists have debated one of the most fundamental questions in planetary science: where did the material that built Earth come from, and how did our planet acquire its water?

One influential model has suggested that although Earth formed in the inner Solar System, some of its material — potentially between about 6% and 40% — came from the outer Solar System. Because carbon-rich material from the outer Solar System contains considerably more water and other volatile elements, this model provided a possible explanation for how a rocky planet formed close to the Sun ended up with abundant water.

A new analysis by researchers at ETH Zurich challenges that picture.

Published in Nature Astronomy on March 27, 2026, the study by Paolo A. Sossi and Dan J. Bower concludes that Earth’s building material can be explained entirely by material from the inner Solar System. The researchers found no need for a substantial contribution from the outer Solar System when multiple isotope systems are considered simultaneously.

The finding does not simply change where scientists think Earth’s rocks came from. It also raises a deeper question: if Earth formed from inner-Solar-System material, where did its water come from?

Meteorites Carry the Chemical Fingerprints of Planet Formation

The researchers approached the problem through isotopes.

Isotopes are different forms of the same chemical element that contain the same number of protons but different numbers of neutrons. Their proportions can preserve information about where planetary material originated and the processes it experienced during the formation of the Solar System.

Scientists have identified two broad groups of meteorites based on these isotopic signatures. Non-carbonaceous meteorites are associated with the inner Solar System, while carbonaceous meteorites are generally associated with the outer Solar System and contain higher concentrations of carbon and volatile elements.

Earth’s isotopic composition has traditionally been difficult to reconcile with a simple picture of purely local formation.

Sossi and Bower examined ten different nucleosynthetic isotope anomalies rather than relying on just one or two isotope systems. Their statistical analysis showed that Earth’s bulk silicate composition falls on the trend defined by inner-Solar-System material. According to the study, this indicates that Earth formed from a single inner-Solar-System material reservoir whose composition remained relatively consistent during accretion.

That conclusion is substantially different from models requiring a large contribution from material originating beyond Jupiter.

Jupiter May Have Helped Keep the Solar System Divided

The new interpretation also gives Jupiter an important role in the early architecture of the Solar System.

When the Sun was young, it was surrounded by a rotating disc of gas and dust from which planets eventually formed. According to the ETH Zurich researchers, Jupiter’s rapid growth may have created a gravitational barrier within that disc.

The giant planet’s gravity could have helped separate material into two distinct reservoirs: one closer to the Sun and another farther away.

The inner reservoir eventually supplied the material that formed the terrestrial planets, including Earth, while the outer reservoir contained more carbon- and water-rich material.

The ETH Zurich analysis suggests that very little material from beyond Jupiter ultimately crossed this divide and became part of Earth. The researchers estimate that outer-Solar-System material accounts for less than 2% of Earth’s mass, or potentially none at all, according to their model.

This presents a picture of early Earth formation that was more locally contained than many previous models assumed.

So Where Did Earth’s Water Come From?

This is where the study becomes particularly interesting.

If Earth did not need a substantial influx of water-rich material from the outer Solar System, then the volatile elements required to form Earth’s water must have been available within the inner Solar System during Earth’s formation.

The researchers specifically state that their findings imply that most volatile elements, including water, must already have been present in the inner Solar System.

That does not mean the study has identified the exact mechanism that supplied Earth’s oceans. It also does not establish that asteroids or other bodies played no role in delivering water after Earth’s initial formation.

Instead, it changes the starting point of the question.

Rather than assuming that Earth’s water necessarily had to arrive from the distant outer Solar System, scientists now have stronger evidence that at least the ingredients for Earth’s volatile inventory could have existed much closer to the young Sun.

ETH Zurich researchers say their next step is to investigate how sufficient water could have existed in the hot inner Solar System to eventually produce Earth’s oceans.

A Planet That May Have Grown Locally

The implications extend beyond Earth’s water.

The researchers found that Earth’s material composition is closely related to that of Mars and the asteroid Vesta. They interpret this as evidence of a broader compositional trend extending outward from the Sun.

In this scenario, Earth did not need to be assembled through extensive mixing of material from distant regions of the Solar System. Instead, it could have grown largely from its local neighbourhood, accumulating smaller bodies that shared the same broad inner-Solar-System chemical signature.

This could simplify some aspects of planetary formation models while creating new questions about the distribution of volatile elements.

The finding also gives researchers a way to make predictions about the compositions of Venus and Mercury, for which scientists do not currently have returned rock samples. ETH Zurich researchers suggest that these planets could lie along the same compositional trend identified for Earth, Mars and Vesta.

The Young Sun May Have Been Less Dry Than Expected

The question of water becomes especially intriguing because the early inner Solar System was an extremely hostile environment.

The young Sun was surrounded by hot gas and dust, and planets were assembling through violent collisions and accretion. Under such conditions, keeping volatile elements such as water in the inner planetary-building region is not straightforward.

Yet the ETH Zurich findings suggest that the building material itself already carried the chemical characteristics of the inner Solar System and that the outer Solar System contributed little, if anything, to Earth’s bulk composition.

This means planetary scientists now have to explain how water and other volatile elements could have remained available within that inner reservoir.

The challenge is not merely identifying a source of water. It is understanding how water-bearing material could survive, migrate and become incorporated into growing planets in a region close to the young Sun.

That question could become an important area of future research.

The Evidence Comes From Isotopes, Not a Direct Sample of Early Earth

An important limitation is that scientists do not possess physical samples of the original material from which Earth formed.

Instead, the researchers reconstructed Earth’s provenance by comparing the isotopic signatures preserved in meteorites and planetary materials.

Their analysis is therefore a statistical and geochemical reconstruction of the early Solar System. The study’s conclusion is strong within the isotope framework examined, but it does not provide a literal sample of Earth’s original building material.

The researchers themselves describe the work as a data-science-driven analysis of existing geochemical measurements. Their use of ten isotope systems was intended to overcome limitations of earlier studies that considered fewer isotopic signatures.

That distinction matters because planetary formation remains an active field of research, with competing models continuing to be tested against meteorites, planetary samples and increasingly sophisticated simulations.

A New Question for Planetary Science

The ETH Zurich study does not simply replace one explanation for Earth’s formation with another. Instead, it shifts one of the biggest questions in planetary science.

If Earth was built almost entirely from inner-Solar-System material, scientists now have to explain how that same region contained enough volatile material to produce a water-rich planet.

The answer could eventually reshape models of how terrestrial planets form around Sun-like stars.

It may also influence the search for habitable worlds beyond our Solar System. If Earth’s water and other life-relevant ingredients did not necessarily require a late influx of material from a distant icy reservoir, then the conditions for creating a water-rich rocky planet may be possible in more local planetary environments than previously assumed.

For now, the central mystery remains: how did Earth’s water survive the furnace of the young Solar System?

ETH Zurich researchers say answering that question is the next step. The discovery that Earth’s building blocks came from much closer to the Sun may have solved one part of the planetary puzzle — while making the origin of Earth’s oceans even more fascinating.