For many years, scientists believed that Earth was built from a mix of materials coming from both the inner and outer parts of the solar system.
In particular, they thought that some of Earth’s building blocks must have come from beyond Jupiter, helping to deliver important ingredients like water.
However, new research from ETH Zurich is challenging this long-held idea.
Planetary scientists Paolo Sossi and Dan Bower analyzed chemical data from a wide range of meteorites, including samples linked to Mars and the asteroid Vesta.
By comparing these with Earth’s composition, they reached a surprising conclusion: Earth appears to have formed almost entirely from material found in the inner solar system.
Their results suggest that material from the outer solar system contributed less than 2% of Earth’s mass, and possibly none at all.
This finding contradicts earlier theories that suggested a significant mixing of materials from different regions during Earth’s formation.
To reach this conclusion, the researchers studied isotopes, which are different forms of the same chemical element. Isotopes have the same number of protons but different numbers of neutrons, giving them slightly different masses. These differences act like fingerprints, helping scientists trace where materials in the solar system originally came from.
In the past, scientists mainly used oxygen isotopes to study the origins of planets. More recently, they have discovered that isotopes of other elements, such as chromium and titanium, can also provide important clues. These new tools have allowed researchers to divide meteorites into two main groups. One group formed in the inner solar system and contains less water and carbon. The other group formed farther out and is richer in these volatile elements.
Sossi and Bower used data from ten different isotope systems, applying advanced statistical methods to analyze the information. Their results showed that Earth’s composition matches only the inner solar system group. There was no clear evidence that material from beyond Jupiter played a meaningful role.
This raises an important question: if Earth did not receive material from the outer solar system, where did its water come from? The researchers suggest that water and other volatile substances may have already been present in the inner solar system during Earth’s formation.
The study also offers new insights into the structure of the early solar system. Scientists believe that Jupiter, the largest planet, played a key role. As it formed, its strong gravity likely created a gap in the disk of gas and dust surrounding the young Sun. This gap acted as a barrier, preventing most material from the outer solar system from moving inward.
The researchers’ analysis supports the idea that this barrier was very effective. It shows that little to no material from beyond Jupiter reached the region where Earth was forming.
Interestingly, Earth’s composition appears to be similar to that of Mars and Vesta, suggesting that these bodies formed from the same local material. The researchers also think that Venus and Mercury may share this origin, although this cannot yet be confirmed because no samples from those planets are available.
This new study offers a fresh perspective on how Earth and other rocky planets formed. While it answers some questions, it also raises new ones, especially about the origin of Earth’s water. Scientists will continue to explore these mysteries as they refine our understanding of the early solar system.
Source: ETH Zurich.
