Out beyond the orbit of Neptune lies an expansive ring of ancient relics, dynamical enigmas, and possibly a hidden planet—or two.
The Kuiper Belt, a region of frozen debris about 30 to 50 times farther from the sun than the Earth is—and perhaps farther, though nobody knows—has been shrouded in mystery since it first came into view in the 1990s.
Over the past 30 years, astronomers have cataloged about 4,000 Kuiper Belt objects (KBOs), including a smattering of dwarf worlds, icy comets, and leftover planet parts. But that number is expected to increase tenfold in the coming years as observations from more advanced telescopes pour in. In particular, the Vera C. Rubin Observatory in Chile will illuminate this murky region with its flagship project, the Legacy Survey of Space and Time (LSST), which began operating last year. Other next-generation observatories, such as the James Webb Space Telescope (JWST), will also help to bring the belt into focus.
“Beyond Neptune, we have a census of what’s out there in the solar system, but it’s a patchwork of surveys, and it leaves a lot of room for things that might be there that have been missed,” says Renu Malhotra, who serves as Louise Foucar Marshall Science Research Professor and Regents Professor of Planetary Sciences at the University of Arizona.
“I think that’s the big thing that Rubin is going to do—fill out the gaps in our knowledge of the contents of the solar system,” she adds. “It’s going to greatly advance our census and our knowledge of the contents of the solar system.”
As a consequence, astronomers are preparing for a flood of discoveries from this new frontier, which could shed light on a host of outstanding questions. Are there new planets hidden in the belt, or lurking beyond it? How far does this region extend? And are there traces of cataclysmic past encounters between worlds—both homegrown or from interstellar space—imprinted in this largely pristine collection of objects from the deep past?