Beyond what's normally considered to be the outskirts of our solar system, well beyond even Pluto's distant orbit, is a vast orbiting reservoir of icy comets known as the Oort Cloud.

We're talking way out there: up to a fifth of the way to the nearest star.

Despite their incredible distance, the comets of the Oort Cloud still manage to orbit the Sun. The only time we spot one, in fact, is when it zooms into the inner solar system. For some, this might occur once in a million years. For others, it can take 30 times that long to make a single orbit.

Sometimes, on its way around the Sun, an Oort Cloud comet passes close to Earth. Now and then, one slams into our planet. So researchers would like to know how many comets are in the Oort Cloud, how big they are, and how they got there.

The leading theory of Oort Cloud formation holds that the giant planets -- Jupiter, Saturn, Uranus and Neptune -- were the bullies of early solar system, using their immense gravity to push comets off the main playground and then right on out of the neighborhood. The Sun and passing stars weighed in on the side of the bullies.

Scientists have used this theory, along with estimates of how much material was available to be bullied, to predict the total mass of all comets in the Oort Cloud.

Nifty idea. Problem is, it might be totally wrong.

New research, published in the Feb. 1 issue of the journal Nature, suggests that like a bunch of frenetic 97-pound weaklings, the comets themselves tussled frequently in those early years, slamming into each other and shattering into smithereens. Only once they had wiped out a few victims could others be shoved off the playground.

"Comets can't escape until the way is clear, just as a man in a crowd can't easily escape until the crowd thins," explains Alan Stern of Southwest Research Institute in Boulder, Colorado.

Stern told SPACE.com that the new idea, based also on computer models, would not change how many comets are thought to exist in the Oort Cloud. Instead, the results imply that the cloud is less massive overall, because each comet is smaller than thought before.

"The cloud may be 10 times less massive than previously thought," said Paul Weissman of NASA's Jet Propulsion Laboratory, who worked on the study with Stern.

So where did all the debris go, when the comets supposedly destroyed each other?

The large planets would have gobbled up some of the debris, Weissman said. A lot of marble-sized bits would have spiraled inward and eventually been swallowed by the nascent Sun. And the finest dust particles would have been blown clear out of the solar system by the Sun's radiation pressure.