Earth-Sized World Could Lurk in Outer Solar System

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"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."

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