Theories around the formation of Earth have just been challenged by researchers from ETH Zurich. For a long time, the general idea saw our planet forming from a mixture of local planetesimals – the larger fraction – and material from the outer Solar System. New work suggests that our planet is made exclusively of local material.
The Earth has a lot of molecules and atoms that are considered volatiles, basically substances that vaporize at low temperatures and can then easily be blown away by the solar wind. A vital example of this class is water. The presence of these volatiles on Earth suggests that between 6 and 40 percent of the material of our planet must have formed away from the Sun, where these volatiles could be incorporated into ices and rocks before getting to the inner Solar System.
This new work looked at a wide range of meteorites. Elements can have different masses (due to more or fewer neutrons in their nuclei). These are known as isotopes, and scientists use isotopic ratios as fingerprints of where things come from. The same isotopic ratios mean the same origin.
Comparing the isotopic ratios of these meteorites, including some from Mars and asteroid Vesta, to Earth suggests that our planet was made of local material. Comparison with meteorites from the outer Solar System suggests that less than 2 percent of our planet came from there.
“Our calculations make it clear: the building material of the Earth originates from a single material reservoir,” co-author Paolo Sossi said in a statement.
“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,” added co-author Dan Bower. They suggest that Jupiter, with its enormous gravity, might have acted as a barrier to the outer Solar System, stopping it from reaching the Earth and the other rocky planets. Even though we do not have rock samples from Mercury or Venus, the assumption there is the same as for Earth and Mars. Though exactly what happened is currently unknown.
“Our calculations are very robust and rely solely on the data itself, not on physical assumptions, as these are not yet fully understood,” Bower explained.
The team now plans to investigate if there was enough water in the inner Solar System to explain what we see today, and even look to see if their scenario could be applied to solar systems beyond our own.
“Until then, however, Dan and I will have to engage in many heated debates about the material composition of Earth and its neighbouring planets, because the scientific discourse over the building blocks of Earth is far from over, despite the new findings,” concluded Sossi.
The study is published in the journal Nature Astronomy.
Context: Researchers from ETH Zurich challenge existing theories about the formation of the Earth. Fact Check: The study is published in the journal Nature Astronomy.
