New Kuiper Belt: Solar System May Be Much Larger Than Previously Thought

A new group of frozen space objects has been identified by the Subaru Telescope in Hawaii, in collaboration with NASA’s New Horizons mission — a spacecraft dedicated to studying the dwarf planet Pluto and the Kuiper Belt, a circumstellar disk previously considered the most extreme in the Solar System.

Eleven celestial bodies have been discovered orbiting the Sun more than 13 billion km away from the star, which, if confirmed, could increase the limits of our neighborhood.

These objects could become targets of investigations by the New Horizons probe, which continues its exploration of deep space after its historic passage by Pluto in 2015.

Fumi Yoshida, from the Chiba Institute of Technology in Japan, co-author of the research (accepted for publication by The Planetary Science Journal and available in the arXiv online repository) highlighted the importance of this finding in a statement, emphasizing that confirmation of the results would be a major achievement for understanding the Solar System.

Density of the Milky Way hampered early observations

Located atop Mauna Kea in Hawaii, the Subaru telescope has been collaborating with the New Horizons mission since its launch in 2006. After its flyby of Pluto, the spacecraft entered the Kuiper Belt, a region beyond Neptune with icy bodies and comets orbiting between 33 and 55 astronomical units (AU) from the Sun.

[One astronomical unit is equivalent to the average distance between Earth and the Sun, which is about 150 million km].

In 2004, before its flyby of Pluto, the Subaru telescope began searching for objects in the Kuiper Belt that could be visited by New Horizons. However, the presence of the dense Milky Way in the background of the constellation Sagittarius made it difficult to identify new targets, and only 24 objects were detected. All of them were too distant for the spacecraft to reach.

One of the few objects found for close study was Arrokoth, which New Horizons flew by in 2019 and was detected by the Hubble Space Telescope.

Over the years, Pluto has moved away from the bright background of the Milky Way, making new observations easier. Since 2020, Subaru’s Hyper Suprime-Cam (HSC) camera has identified 239 new Kuiper Belt objects. Among them, one special group stood out: 11 objects located beyond 55 AU, in a previously unexplored region of the Solar System.

According to the scientists involved in the study, these objects do not belong to the traditional Kuiper Belt. There is a significant gap between 55 and 70 AU, and the new belt, dubbed “Kuiper Belt 2,” appears to extend from 70 to 90 AU, or up to 13.5 billion kilometers from the Sun. For comparison, Neptune is 30 AU away, and New Horizons is currently at 60 AU.

This discovery could provide new insights into the formation and architecture of the Solar System.

Discovery paves the way for finding a possible Planet Nine in the Solar System

The distribution of the Asteroid Belt (between Mars and Jupiter) and Kuiper Belt objects is believed to be the result of events that occurred during the formation of the planets, when Jupiter migrated and scattered smaller bodies throughout the Solar System.

This new population of objects may be connected to the discoveries of cosmic dust made by the particle counter on board New Horizons. Even as the spacecraft moves away from the Kuiper Belt, dust impacts continue to be detected, suggesting the presence of bodies beyond that region.

In addition, stellar occultations observed by New Horizons — when an object passes in front of a distant star — also suggest the existence of unseen bodies in the outer reaches of the Solar System.

Observations of protoplanetary disks around other stars, made by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, indicate that planetary systems may have similar structures with multiple belts.

For Wesley Fraser of the National Research Council of Canada, who led the study, the discovery of Kuiper Belt 2 could challenge the idea that our belt of icy bodies is small compared to other planetary systems. “So perhaps, if this result is confirmed, our Kuiper Belt is not so small and unusual compared to those around other stars.” Astronomers will continue to monitor these 11 newly discovered objects, as they are believed to be just the tip of the iceberg. This suggests the existence of a much larger population, which could include more dwarf planets and even the hypothetical Planet Nine.