The Earth was built from small glass beads

A new study from an international team that includes scientists from the Centre for Star and Planet Formation suggests that clumps of small glassy particules may be responsible for the formation of giant asteroids and the planetary embryos that collided to form rocky planets like Earth.

Asteroid fragments that fall to Earth as meteorites often contain tiny, round pellets known as chondrules that formed when molten droplets quickly cooled in outer space during the solar system's early years. Chondrules are the main constituent of the most primitive meteorites, chondrites.

Previous work had suggested that chrondrules were the building blocks of asteroids, which, in turn, often have been thought to be the building blocks of planets. Now, computer simulations modeling the behavior of more than 150 million particles in space reveal how chondrules might have coalesced into asteroids.

After the sun was born, the rest of the solar system emerged from a giant rotating cloud of gas and dust known as the protoplanetary disk. The researchers found that, as chondrules moved through gas in this disk, the friction between the particles and the gas slowed down the chondrules, allowing them to cluster.

The team calculated that the largest of these clusters of particles could gather enough chondrules within about 3 million years to grow into planetary embryos, the moon- to planet-sized chunks of rock that careened around before planetary formation finished in the solar system.

These planetary embryos might have collided in giant impacts over 30 million to 100 million years to form the rocky planets and moons present in the solar system today.

"Our study shows that protoplanets may have formed very quickly from asteroids, by capturing chondrules in the same way as the asteroids did. Chondrules thus represent the building blocks of rocky planets like Earth", concludes Prof. Martin Bizzarro, coauthor of the new study.

The results are published in the international journal, Science Advances.