Formation Of Earth And Venus Was A Messier Affair Than Previously Thought
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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Ancient impact that formed Earth's moon was likely a one-two punch
Twice the cosmic violence!
By Mike Wall 2 days ago
The gigantic impact that created the moon was actually a one-two punch, a new study suggests.
Scientists think that the moon, our planet's only natural satellite, was born in violence, coalescing from the material blasted into space after a Mars-size body named Theia slammed into the proto-Earth more than 4.4 billion years ago.
But there are some problems with the canonical collision scenario, which invokes a single catastrophic event, the authors of the new study said.
"The standard model for the moon requires a very slow collision, relatively speaking, and it creates a moon that is composed mostly of the impacting planet, not the proto-Earth, which is a major problem since the moon has an isotopic chemistry almost identical to Earth," lead author Erik Asphaug, a professor at the University of Arizona's Lunar and Planetary Laboratory (LPL), said in a statement.
Related: How was the moon formed?
Double whammy made the moon
Asphaug and his colleagues performed computer simulations of the long-ago giant impact and came up with what they believe to be a better fit: Theia and the proto-Earth crashed at faster speeds than previously envisioned, producing an initial "hit and run" collision that set the stage for a slower, accretionary encounter between the two battered bodies about 100,000 to 1 million years down the road.
"The double impact mixes things up much more than a single event, which could explain the isotopic similarity of Earth and moon, and also how the second, slow, merging collision would have happened in the first place," Asphaug said.
Hit-and-run collisions weren't restricted to the nascent Earth-moon system in those early days. Indeed, such bouncing smashups were probably about as common as accretionary mergers in the ancient inner solar system, the same research team reports in a second new study.
In the second paper, the scientists modeled giant impacts in the inner solar system, how those collisions affected planet formation and how the orbits of the involved objects evolved over time. They found that Earth likely acted as a sort of shield for Venus, taking the brunt of hit-and-run first impacts. Those initial collisions slowed the impactors down, setting the stage for accretionary mergers with Venus later.
"The prevailing idea has been that it doesn't really matter if planets collide and don't merge right away, because they are going to run into each other again at some point and merge then," Alexandre Emsenhuber, the lead author of the second study, said in the same statement.
"But that is not what we find," said Emsenhuber, who performed the research during a postdoctoral fellowship in Asphaug's lab at LPL and is now at Ludwig Maximilian University in Munich, Germany. "We find they end up more frequently becoming part of Venus, instead of returning back to Earth. It's easier to go from Earth to Venus than the other way around." (This is because Venus lies closer to the sun, whose powerful gravity draws objects in.)
The results suggest that the compositions of Earth and Venus may differ more than scientists had thought.
"You would think that Earth is made up more of material from the outer system because it is closer to the outer solar system than Venus," Asphaug said. "But actually, with Earth in this vanguard role, it makes it actually more likely for Venus to accrete outer solar system material."
Both new studies — the one led by Asphaug and the one led by Emsenhuber — were published online Thursday (Sept. 24) in The Planetary Science Journal.
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
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