Artist’s impression of the Kuiper belt
IT/M. Harbinger of Korn
The Kuiper Belt, a disk of icy rocks at the edge of the solar system, appears to have more structure than we thought. In 2011, researchers there discovered a group of objects in similar orbits that they dubbed the “core” of the Kuiper Belt. Now another team has spotted an even more compact group of objects that they call the “inner core.”
The original core was discovered by eye using tracings of the orbits of 189 Kuiper Belt Objects (KBOs). It is approximately 44 astronomical units from the sun, an astronomical unit being the distance between the sun and Earth. Since the core’s discovery, no additional structures have been found in the Kuiper Belt.
That is, until Amir Siraj of Princeton University in New Jersey and his colleagues took on the painstaking task of refining the 1,650 KBO orbital data and feeding it into an algorithm that looks for clustering and structure. They trained the algorithm to search for the nucleus, then examined the results to see if there were other structures. “The nucleus was never found alone. Every time the algorithm found the nucleus, it also found another group,” says Siraj.
Researchers called this new cluster the inner core because of its location about 43 astronomical units from the sun. All inner core objects have remarkably circular orbits, almost entirely aligned with the solar system’s disk.
“This kind of orbital quiet is a sign of a very old, intact structure – the kind of structure that can provide clues about the evolution of the solar system, about how the giant planets moved in their orbits, about the kind of interstellar environments the solar system passed through, and about all sorts of things about the early days of the solar system,” Siraj explains.
This could be particularly informative when it comes to learning more about Neptune’s migration from the inner solar system, where it is thought to have formed, to its current position, says David Nesvorný of the Southwest Research Institute in Colorado, one of the discoverers of the original core. Nesvorný says it’s possible that as Neptune moved outward, the KBOs that make up the core and inner core were briefly captured in place by gravitational interactions with the giant planet, causing the clumping we see now, before being released as Neptune continued on its way.
The Vera C. Rubin Observatory in Chile, which began operations this year, is expected to find many more KBOs than we currently know, which should tell us more about the core and inner core, as well as whether there are other, yet undiscovered structures at the edges of the solar system. “The more we learn about the architecture of the Kuiper Belt, the more we learn about the history of the solar system,” says Siraj.
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