The belt of icy debris surrounding the outer Solar System may be much larger than we thought. Data from the New Horizons probe silently moving through the Kuiper Belt points to unexpected levels of particles that must thin out the dust, and suggests that the donut-shaped area extends much farther from the Sun than previously thought.

This is the latest in a growing body of evidence that our understanding of the outer solar system is incomplete; but it may help us better understand our own planetary system and other planetary systems in the wider galaxy.

“New Horizons makes the first direct measurements of interplanetary dust far beyond Neptune and Pluto, so each observation could lead to a discovery,” says physicist Alex Donner of the University of Colorado at Boulder.

“The idea that we may have discovered a vast Kuiper belt, where a whole new population of objects are colliding and producing more dust, offers another clue to unlocking the mysteries of the outermost regions of the solar system.”

The Kuiper belt is characterized by a high density of rocky, icy objects (icy because they are so far from the Sun and so cold). It’s full of big rocks, dwarf planets, and a bunch of objects we can’t see because they’re relatively small and too dark. But dust can tell us what’s going on.

The Kuiper belt was already thought to be quite large. It begins in the orbit of Neptune, about 30 AU from the Sun, and extends outward for an unknown distance. However, the inner main region was thought to disappear at approximately 50 AU.

New Horizons is a NASA probe launched to explore the outer Solar System. In 2015, he continued his journey by visiting Pluto, which is located at an average distance of 39 AU around the Sun. In January 2019, it flew past a strange object called Arrokoth, which orbits the Sun at an average distance of 44.6 AU.

Since then, New Horizons has continued to collect data from a distance of 45 to 55 AU and painstakingly returned them to Earth. And guess what? The student-run Venetia Burney Dust Counter (SDC) detects much more dust than scientists expected at this distance.

High dust density means that additional dust is being produced or that solar radiation forces have unexpectedly pushed dust into this area from denser regions.

The most likely source of additional dust would be interactions between larger objects, such as collisions. This means there needs to be enough ice rocks for them to gather with relative frequency.

Recent telescope observations have begun to suggest that the inner main region of the Kuiper Belt may extend out to 80 AU; This means the discovery is consistent with hints that the Kuiper Belt may be larger than expected.

At the time of this writing, New Horizons was more than 58 AU from the Sun. It’s currently on a second extended mission, running beyond initial expectations and still sending data home. Scientists hope it will last at least 100 AU, and if we’re lucky, more than 120 AU, all the way to the edge of the Solar System.

“These new scientific results from New Horizons may be the first time any spacecraft has discovered a new population of objects in our Solar System,” said New Horizons principal investigator astronomer Alan Stern of the Southwest Research Institute.

“I can’t wait to see how far these high dust levels will travel into the Kuiper Belt.”