Artist's impression of the Kuiper Belt
IT/M. Kornmesser
The Kuiper Belt, a disk of icy rocks on the outermost edges of the solar system, appears to have a more complex structure than we thought. In 2011, researchers discovered a cluster of objects there in similar orbits, which they called “core” of the Kuiper belt — now another team has discovered an even more compact cluster of objects, which they call the “inner core.”
The original nucleus was found by eye using 189 orbital plots Kuiper Belt Objects (KBO). It is approximately 44 astronomical units from the Sun, where one astronomical unit is the distance between the Sun and Earth. Since the discovery of the core, no additional structures have been discovered in the Kuiper Belt.
That is, until Amir Siraj from Princeton University in New Jersey and his colleagues took on the painstaking task of refining the orbital data of 1650 OPCs and feeding it into an algorithm that looks for clustering and structure. They trained an algorithm to find the core and then examined the results to see if there were any other structures. “A core was never found alone—every time the algorithm found a core, it found another group,” Siraj says.
Researchers have named this newfound cluster the inner core due to its location approximately 43 astronomical units from the Sun. All the objects in the inner core have remarkably circular orbits, almost completely coinciding with the disk of the Solar System.
“This kind of orbital quiet is a signal of very old, intact structure—one that may provide clues about the evolution of the solar system, how the giant planets moved in their orbits, what kind of interstellar environments the solar system passed through, and much more about the early days of the solar system,” says Siraj.
“This could be particularly instructive when it comes to Neptune's migration from the inner solar system, where it is believed to have formed, to its current position,” he says. David Nesvorny at the Southwest Research Institute in Colorado, one of the discoverers of the original core. Nesvorny says it's possible that as Neptune moved outward, the OPCs that make up the core and inner core were briefly trapped in place by gravitational interactions with the giant planet, causing the cluster we see now, before they were released as Neptune continued on its way.
Vera K. Rubin Observatory Chile, which began operations this year, is expected to discover many more OPCs than we currently know, which should tell us more about the core and inner core, and whether there are any other as-yet-undiscovered structures at the edge 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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