Just how big is this solar system, anyway?

From Science:

There just doesn’t seem to be enough of the Solar System. Beyond Neptune’s orbit lie thousands of small icy objects in the Kuiper belt, with Pluto its most famous resident. But after 50 astronomical units (AU)—50 times the distance between Earth and the Sun—the belt ends suddenly and the number of objects drops to zero. Meanwhile, in other solar systems, similar belts stretch outward across hundreds of AU. It’s disquieting, says Wesley Fraser, an astronomer at the National Research Council Canada. “One odd thing about the known Solar System is just how bloody small we are.”

A new discovery is challenging that picture. While using ground-based telescopes to hunt for fresh targets for NASA’s New Horizons spacecraft, now past Pluto on a course out of the Solar System, Fraser and his colleagues have made a tantalizing, though preliminary, discovery: about a dozen objects that lie beyond 60 AU—nearly as far from Pluto as Pluto is from the Sun. The finding, if real, could suggest that the Kuiper belt either extends much farther than once thought or—given the seeming 10-AU gap between these bodies and the known Kuiper belt—that a “second” belt exists.

I like this bit of added mystery: 

Just as intriguing as the new objects is the apparent gap between 50 and 60 AU, says Mihály Horányi, a space physicist at the University of Colorado Boulder who oversees New Horizons’s dust counter. “One way or another, something is responsible for maintaining that gap.” In other solar systems, planets orbiting within a dusty disk carve gaps by hoovering up material. But no large planet has been seen in the gap. The gap could also be a relic from the Solar System’s infancy, caused by waves of pressure in the disk.

Hey, I still like the idea that a very small, primordial black hole is rambling around the edge of the solar system.