“Billiards” instead of “Snowball” .. A new scenario for the emergence of planets

Researchers at the University of Arizona have found that planets were most likely born from hit-and-run collisions, challenging models of planet formation.

The findings challenge the traditional view, which is that collisions between smaller building blocks cause them to stick together, and over time, repeated collisions lead to the accumulation of new material, in a “snowball” position, leading to the formation of planets.

Instead, the authors suggest evidence for a hit-and-run scenario, where they see the pre-planetary bodies collide and bounce off each other, before encountering each other again at a later time. They are more likely to stick together next time, more like a game of pool, rather than the prevailing “snowball” theory.

The researchers published their theory in two studies appearing in Thursday’s issue of “The Planetary Science Journal,” one focused on Venus and Earth and the other on Earth’s moon.

According to the authors’ team, the central point in both publications is the largely unacknowledged one that giant effects are not the efficient mergers that scientists thought they were.

“We found that most giant collisions, even the relatively slow ones, are hit-and-run, meaning that for two planets to merge, you must first slow them down in a hit-and-run collision,” says Eric Asfuge, the study’s lead author.

“Thinking of giant collisions, such as the one that formed the Moon, as a single event would probably be wrong, as it probably took two collisions in a row.”

One implication of that theory, according to Asfuge, is that Venus and Earth had very different experiences of growing up as planets, despite being direct neighbors in the inner solar system.

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