Earth-Sized World Could Lurk in Outer Solar System

Some astronomers say that a planet the size of Mars or Earth could be lurking on the fringes of our solar system. But even the latest space telescopes that launched in 2009 stand little chance of finding such a distant object.

Such a world, if it exists, would probably have an orbit far beyond Pluto or similar dwarf planets in the outer solar system. It would likely resemble a frozen version of Mars or Earth at best, a most unsuitable home for life. And it would not be alone.

"When the solar system's story is finally written, it's much more likely that it will have closer to 900 planets rather than the nine that we grew up with," said Alan Stern, a planetary scientist at the Southwest Research Institute (SwRI) in Boulder, Colo.

Just a handful of those potential discoveries might reach the size of Earth, compared to a swarm of Pluto-sized bodies that Stern and others expect to find.

Each object – be it termed a planet, dwarf planet or otherwise – would serve as a frozen time capsule that could reveal much about the early evolution of the solar system. It could even force scientists to once again rethink the definition of a planet, following the controversial downgrading of Pluto to a dwarf planet.

Beyond the belt

Pluto's downfall came in part because astronomers discovered a number of smaller planetary objects in the outer solar system. Dwarf planets such as Eris occupy a cluttered, icy region beyond Neptune known as the Kuiper Belt. But a planet the size of Mars or Earth has not turned up at such range.

"For the Kuiper Belt we can already say there is nothing Earth or Mars sized, as its dynamical effects would be easily seen," said Mike Brown, an astronomer at Caltech who led teams that discovered Eris (and nicknamed it "Xena" at first) and other dwarf planets.

One of Brown's past dwarf planet discoveries, Sedna, occupies a strange elliptical orbit between the Kuiper Belt and the more distant Oort Cloud — a possible sign of the gravitational influence of another world as big as Earth, one astronomer proposed. But Brown suspects that such a large object would have been spotted already.

Brown and Stern say that the Oort Cloud represents a more likely prospect for worlds the size of Mars or Earth. The Oort Cloud surrounds our solar system with billions of icy bodies at distances as far out as 50,000 times the distance between the sun and Earth.

"Once you go beyond the Kuiper Belt, to the Sedna region or the Oort Cloud, you can always hide things by putting them farther away," Brown told SPACE.com.

How they got there

Brown noted that any future discovery of larger objects in the outer solar system would either suggest that scientists have the wrong idea of how planets form, or might indicate that the early solar system had more material available than previously suspected.

"More interesting to me, though, is that it would be an entirely new class of large body," Brown said. "We don't have any ice rich planetary-sized bodies in the solar system, so we don't really know what they would be like and how they would work."

via Earth-Sized World Could Lurk in Outer Solar System - Yahoo! News.