We May Now Know How The Furthest World We Have Ever Explored Formed

Arrokoth in glorious technicolor. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Roman Tkachenko

The Kuiper Belt Object Arrokoth, formal name 2014 MU69, is the furthest world visited by humanity. Its peculiar shape, like a squished snowman, has intrigued astronomers ever since the close observations of New Horizons on January 1, 2019. Now researchers have developed a simulation that they think explains how the peculiar object came to form.

As reported in the journal Nature, the simulation suggests that the two bodies that came to form Arrokoth and give it its distinctive look started by orbiting quite a distance apart and slowly came together in a highly eccentric elliptical orbit. A faster collision would have shattered the system as the objects are likely made of soft ice, and a circular orbit would have led to a faster rotation on its axis.

The model was constructed not just by considering the mutual gravitational effects of the two lobes of the virtual Arrokoth but by also including the Sun in this simulation. Three-body problems (as they are called) are often very chaotic but using appropriate approximation, the team showed that there was a scenario that explained this peculiar world.

The changes to the orbit of the original two bodies happen on slower timescale than it takes them to go around the Sun, so over 300 years. It is slow but necessary. This approach produces a slowly rotating, highly inclined object, consistent with the properties of Arrokoth.

The results of the researchers' detailed simulations of the Kuiper Belt Objects' collision that formed Arrokoth. Grishin et al., 2020, Nature

Although it might seem weird, it is more likely for two bodies such as this to collide if they start far apart. The team estimates that many more bodies in the Kuiper Belt might have formed like this or evolved from a wide binary system to a close one.

“Our model explains both the high likelihood of collision as well as the unique data of the unified system today, and in fact predict many more objects in the Kuiper Belt,” lead author Evgeni Grishin, a graduate researcher at Technion – Israel Institute of Technology, said in a statement. “In fact, even Pluto’s and Charon’s system might have formed through a similar process, and they appear to play an important role in the evolution of binary and moon systems in the Solar System.”

Arrokoth, which at its widest point is 36 kilometers (22 miles) across, was named for the word for "sky" in the Powhatan language of the Tidewater region of Virginia and Maryland, where the discovery took place.

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