By Kenneth Chang
ABCNEWS.com
Oct. 7 — Astronomers may have found hints of a massive, distant, still unseen object at the edge of the solar system — perhaps a 10th planet, perhaps a failed companion star — that appears to be shoving comets toward the inner solar system from an orbit 3 trillion miles away.
Two teams of scientists — one in England, one at University of Louisiana at Lafayette — independently report this conclusion based on the highly elliptical orbits of so-called "long-period comets" that originate from an icy cloud of debris far, far beyond Pluto.
"We were driven to this by rejecting everything else we could think of," says University of Louisiana physicist Daniel Whitmire.

Clump of Comets
A couple years ago, Whitmire, along fellow physicists John Matese and Patrick Whitman, noticed the farthest points of the comets’ orbits didn’t appear random but bunched together, tracing a path across the sky.
"We accidentally noticed they weren’t uniform," Whitmire says.
First, they tried to explain the clumping from the gravitational pull from a main disk of stars in the Milky Way stars. "That ultimately didn’t work," Whitmire says. "We’ve gone through several other models trying to explain this."
At around the same time, John Murray, a planetary scientist at The Open University in Great Britain, made a similar observation in similar comet data. "I started puzzling what this might could be," he says.
The most obvious but seemingly unlikely explanation would be a planet. "I thought we’d better rule that out," he says. But as he analyzed the orbits, the farthest points appeared to fall on a circular orbital path — "which is exactly what you would expect if there was a planet out there."
As the planet — estimated to have a mass between one and 10 Jupiters — orbits, its gravitational wake disturbs the icy debris of the outer solar system, causing some of it to plunge toward the sun as comets, sort of like an elephant ambling through a china shop.
No one has yet directly observed a 10th planet, and there could still be another cause for the cluster of comets.
The University of Louisiana research will be published in an upcoming issue of the journal Icarus. Murray’s paper will appear in Oct. 11 issue of the Monthly Notices of the Royal Astronomical Society.

Very Distant
What’s surprising is just how far out there this supposed planet is. Both Murray and the University of Louisiana physicists put the planet in an orbit about 3 trillion miles — or half a light-year — from the sun. The nearest star is four light-years away.
To put this distance in perspective, consider a miniaturized version of the solar system in which Earth is one inch from the sun. On this scale, Pluto, the ninth planet would be a bit more than a yard from the sun. The new planet, by contrast, would be a half-mile distant.
At that great distance, the 10th planet would be too dim to see by current telescopes, although there is some hope that if it exists, the next generation of space-based infrared telescopes might be able to pick it up.
Murray hypothesizes the planet may have been wandering through the galaxy before being captured by the solar system’s gravity. Whitmire suggests it is a "brown dwarf," or a failed star, a companion to the sun that was too small to light up.
Although suggestive, the findings are not conclusive. While Murray and the Louisiana physicists agree how distant the new object is, they trace out very different orbits. Murray considers the orbits of 13 comets with the most accurately known orbits; the Louisiana team considers 82.

Too Early to Look for a Name
"It’s possibly suggestive," comments Brian Marsden, associate director for planetary sciences at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "I don’t want to bet on it. We’re certainly not going to name it."
Whitmire agrees it’s too early to say definitely there’s something out there.
"Until it’s found, you can never be overly confident," he says. "We know in science you can be fooled by statistics." But he adds, "If I was betting, it’s better than 50-50 odds that it’s there."