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New study on space dust strengthens theory that Earth was formed by pebble accretion

Dust, gas and planets in space. Illustration.
Artist’s conception of a young star and a disk of dust and gas. Illustration: NASA, FUSE, Lynette Cook.

Last year, researchers in Lund, Sweden, launched a ground-breaking theory that Earth was formed by pebbles that were sucked together into a celestial body over millions of years. This explanatory model has now been further supported by a new study which shows that cosmic dust also played a crucial role in the creation of our planet.

It has become known as the pebble accretion theory. The radical idea was that Tellus went from a baby planet of rock and ice to reaching its current size and shape thanks to millimetre-sized pebbles being sucked together to form a massive celestial body. The controversial theory, which contradicts the general view that Earth was formed from multiple collisions of gigantic asteroids, was launched last year by the Lund astronomer Anders Johansen and quickly gained a hearing in astronomy circles. In a new study published in the research journal Science Advances, a research team from Sweden, Denmark and China has revealed further details about Earth’s dramatic formation 4 550 million years ago.

“Using advanced computer simulations, we can establish that Earth was formed by a mixture of pebbles and dust from supernova explosions in the outer solar system, as well as dust from the inner solar system, much less of which came from supernovas,” says Anders Johansen, Professor of Astronomy at Lund University.

A man in front of a building. Photo.
Anders Johansen, Professor of Astronomy at Lund University. Photo: Johan Joelsson.

It was previously discovered that meteorites from the outer part of the solar system, called carbonaceous chondrites, contain more dust from supernovas (exploding stars) than meteorites from the inner part of the solar system. This has traditionally been explained by the fact that the planet Jupiter swiftly blocked supernova-rich dust particles from finding their way into the central parts of the solar system. However, the new study indicates that Jupiter's role as a planetary vacuum cleaner is exaggerated.

“Our study shows that Jupiter’s role in the formation of the solar system was not as significant as previously thought. Despite its size, the giant planet would not have been able to block all the dust particles from the outer solar system. A considerable amount of dust continued on and contributed to the formation of the Earth,” says Michiel Lambrechts, astronomy researcher at Lund University.

Landscape. Illustration.
Artist’s conception of the early earth, which according to the researchers was formed by pebbles and dust. Illustration: Don Dixon (used with permission).

The migrating dust particles from the outer solar system that were blocked by Jupiter explain why Earth did not grow larger. Without Jupiter’s help, Earth would most likely have developed into what is known as a super-Earth, with a much greater mass and a hostile atmosphere of hydrogen and helium. The researchers will now continue working on the pebble accretion theory to understand more aspects of how our Earth was formed.

“By learning more about these complex processes we gain an increased understanding of how habitable planets are formed, including around other stars in the universe, places that could potentially support life,” says Anders Johansen.

In addition to Lund University, Zhejiang University and the University of Copenhagen participated in the study.

The study is published in the research journal Science Advances.

Read the study “Natural separation of two primordial planetary reservoirs in an expanding solar protoplanetarium disk” (