Wandering Star May Have Disrupted Outer Solar System's Order

There's something strange about the outer solar system — and that could be the signature of a long-ago visit to our neighborhood, according to a new study that looked to simulate how the outer solar system might have ended up so oddly arranged.

Astronomers have been wrestling with a few puzzles about the neighborhood for a while now. First, there's just not nearly as much stuff out there, all told, as they would expect. Also, it's odd that Neptune is more massive than the closer-in Uranus. And many of the small objects in the outer swath — like Sedna, a strange dwarf planet — follow extreme, stretched orbits at stark angles to the rest of the solar system's more orderly inhabitants.

Those quirks suggest that something must have stirred up the pot after the planets and large moons clumped together and formed out of the cloud of dust surrounding our sun early in its life. One possible culprit is a star that might have slipped next to our solar system and tugged objects off their original paths, throwing some out of the solar system entirely and skewing the orbits of others. [Planet 10? Another Earth-Size World May Lurk in the Outer Solar System]

That's not a new idea, but astronomers had thought that it was a pretty unlikely scenario. They expected that a close stellar flyby would have been pretty rare, starting about 10 million years after the birth of the Milky Way, when they thought objects would still be busy forming in the outer solar system.

But recently, scientists have been able to study many more young solar systems, and they've realized that, early in their lives, their outer edges can be more developed than expected. That means that an early flyby could still do the trick when it comes to explaining our solar system's oddities.

So, the team behind the new research ran a set of simulations to see how likely it was that a neighboring star might have snuck past our solar system in just such a way that it explains what we see today.

That calculation is pretty promising, and the researchers claim such a model may explain all the weird qualities of the outer solar system. The research is described in a recent paper posted to the preprint server arXiv.org.

Next, the team wants to keep testing the hypothesis, making their models more detailed and exploring more details of how the region could have responded to such a close approach.

Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.