The formation of planets in the inner solar system was messier and complicated than previously thought, according to a new paper.
Planets such as Earth and Venus were previously thought to have formed when smaller rocks, asteroids, and debris, collide and stick together to form a neat, round planet, which further grew as it accumulated more mass from further collisions.
The new research suggests that much of the planets within the inner solar system were likely formed after repeated hit-and-run collisions, potentially upending current models of planet formation.
The paper published in the journal, The Planetary Science focuses on two of the biggest planets within the inner solar system – Earth and Venus and the Earth’s moon. In the paper, the researchers argue that giant impacts are not efficient in merging masses as previously believed by scientists.
They propose a scenario where pre-planetary masses repeatedly crashed into and ricocheted off each other, before colliding with each other again at a later time. Having been slowed down by the first collisions, the objects would be able to stick together better the second time.
According to Erick Asphaug, lead author of the paper and professor at Lunar and Planetary Laboratory, most giant impacts, even relatively “slow” ones, are hit-and-run collisions and won’t lead to colliding masses sticking together. For two planets or rocks to merge, they usually have to slow down first. For instance, it probably took collisions for the moon to form.
The paper suggests that the planets Venus and Earth would have had completely different experiences during their formation, despite being neighbours.
The solar system is a gravity well; the closer a planet is to the sun, the stronger the gravitational pull from the sun experienced by the planet. Hence, when objects move closer to the sun, they are more likely to stay there. Therefore, a young Earth acted as a vanguard to Venus, slowing down and bouncing away bodies colliding with it for the first time, making it more like for them to be absorbed by Venus.
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