Twin Asteroids Point to Early Solar System 'Skirmish' Between Jupiter, Saturn, Uranus and Neptune

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Binary asteroid Patroclus-Menoetius is depicted in this image. WM Keck Observatory/Lynette Cook

The existence of a mysterious binary asteroid points to an ancient "skirmish" between giant neighboring planets, scientists have reported in the journal Nature Astronomy. The two space rocks—Patroclus and Menoetius—circle each other as they orbit the Sun in a group of asteroids known as the Trojans.

Researchers think a solar system shake-up sent Uranus and Neptune outwards, and small space rocks like this pair inwards. These cosmic gymnastics, the team suggests, took place within the first 100 million years of the solar system's formation.

Scientists think binaries—pairs of asteroids like Patroclus and Menoetius—formed from collapsing clouds of space "pebbles." The resulting twins are relics of the violent beginnings of our cosmic neighborhood.

"The Trojans were likely captured during a dramatic period of dynamic instability when a skirmish between the solar system's giant planets—Jupiter, Saturn, Uranus and Neptune—occurred," Southwest Research Institute scientist and study author David Nesvorny said in a statement.

As Uranus and Neptune shifted outwards in the burgeoning solar system, they may have encountered early space rocks that eventually became today's Kuiper Belt—an asteroid belt way out at the edge of the solar system. "Many small bodies of this primordial Kuiper Belt were scattered inwards, and a few of those became trapped as Trojan asteroids," Nesvorny explained.

The ruckus probably happened early on, researchers said, because the binary asteroid remained intact amid swarms of Trojans. Two swarms circle the Sun at about the distance of Jupiter's orbit—one in front and one behind.

Researchers think a later shake-up would have resulted in the disruption of delicate binaries like Patroclus and Menoetius. Earlier tussles, on the other hand, may well have allowed the Trojan population to capture the binary.

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This simulation depicts the Patroclus-Menoetius asteroid pair orbiting around each other as they circle the Sun in tandem with Jupiter. Durda/Marchi/SwRI

"Observations of today's Kuiper Belt show that binaries like these were quite common in ancient times," William Bottke, director of the Southwest Research Institute's Space Studies Department and a study co-author, said in a statement. "Only a few of them now exist within the orbit of Neptune. The question is how to interpret the survivors."

The team thinks their work will help unlock the secrets of other relics of solar system violence, such as some of the large ancient craters on the Moon, Mercury and Mars. NASA's Lucy mission, which will probe the binary in 2033, looks set to help scientists understand more about the Trojan bodies.