Uranus: 'Cataclysmic Collision' Gave Planet Its Moons, Rings—and Freezing Temperature
Four billion years ago, when the solar system was still forming, a hunk of rock and ice at least twice the size of Earth may have smashed into Uranus and knocked the planet way off-kilter.
This calamitous collision, researchers report in The Astrophysical Journal, may be behind Uranus's extremely cold temperature, its moons and even its rings.
Uranus's tilt is extreme for our solar system. Most planets spin upright like a ballerina as they travel around the sun. But Uranus rolls like a somersaulting gymnast. Researchers used supercomputer simulations to probe how the planet ended up spinning sideways.
"We ran more than 50 different impact scenarios using a high-powered supercomputer to see if we could recreate the conditions that shaped the planet's evolution," study author and researcher Jacob Kegerreis from Durham University, U.K., said in a university statement.
"Our findings confirm that the most likely outcome was that the young Uranus was involved in a cataclysmic collision with an object twice the mass of Earth, if not larger, knocking it on to its side and setting in process the events that helped create the planet we see today."
Although a giant, violent crash isn't a new explanation for Uranus's weird tilt, it's difficult to study. "One of the main challenges for studying collisions like these is getting enough detail from the computer simulations," Kegerreis told Newsweek.
"We have been able to use modern supercomputers and programs to have millions of particles in our high-resolution simulations so we can see many more details."
The team's simulation managed to explain how Uranus clung on to its atmosphere during the violent collision. "For the first time we were able to run a full simulation of the relatively thin atmosphere and see what happens to atmospheres when they suffer such a violent event," Kegerreis said. The team found a vicious graze, rather than a head-on smash, explains the remaining atmosphere.
Studying the collision allowed the researchers to probe why the planet is so cold. Uranus is way beyond freezing, with an estimated upper atmosphere temperature of -357 degrees Fahrenheit.
Researchers think the collision created a thin, insulating layer of debris close to the planet's ice layer. This debris traps in heat from Uranus' core like a blanket and stops it warming up the planet's atmosphere.
The rings and satellites swirling around Uranus, Kegerreis said, may also be relics of the violent crash. "We can… see the details of the debris blasted into orbit by the collision, where it might be able to form some of Uranus' moons and rings," he explained.
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There is only so much scientists can learn from such models, however, as our picture of Uranus is still relatively fuzzy. Research into the planet's interior, for example, could help the team constrain their model further, Kegerreis added.
The research team think their work can help shed light on even less familiar orbs; the exoplanets lying beyond our solar system.
"Giant impacts like this are thought to be quite common in the early solar system," Kegerreis said. "So as well as teaching us about what happened in our planets' histories, we can learn more about what is happening to exoplanets around other stars and better understand how they evolve."
