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Scientists have spotted a new dwarf planet at the outer edge of our solar system. It's a kind of pink ice ball that's way out there, far beyond Pluto. Astronomers used to think this part of the solar system was an empty no-man's land.

But as NPR's Nell Greenfieldboyce reports, this new find suggests it holds many small worlds and perhaps even a planet bigger than Earth.

NELL GREENFIELDBOYCE, BYLINE: Chad Trujillo is an astronomer. He's currently working on a big telescope called the Gemini Observatory, on top of a mountain in Chile. And he says if you were to start at our sun and move out, the first thing you'd see would be...

CHAD TRUJILLO: The inner planets, the rocky planets, you know, which go out to Mars and then the gas giant and ice giant planets which end with Neptune.

GREENFIELDBOYCE: Beyond Neptune would be the Kuiper Belt, a band of tiny ice worlds, including our old friend, Pluto, now known as a dwarf planet. And after that...

TRUJILLO: You know, we used to think there's just not much out there. But it turns out there are some interesting things out there.

GREENFIELDBOYCE: Like, Sedna, a dwarf planet he co-discovered about a decade ago. It's named after an Inuit goddess who lives in the frigid Arctic Ocean. Ever since the surprise discovery of Sedna, scientists have wondered: Is it alone? Maybe there are more. The trouble is looking for them is hard.

These distant things don't emit their own light. Light from the sun has to travel billions of miles out there, reflect off the object, then come billions of miles back. Along the way some light gets lost.

TRUJILLO: As objects get farther and farther away, they get much fainter, and it's a big effect.

GREENFIELDBOYCE: Still, Trujillo has been trying to find other Sednas and now he's got one. He and Scott Sheppard, of the Carnegie Institution for Science, have spotted another dwarf planet that stays even farther out than Sedna. Sheppard says this little world is about 280 miles across.

SCOTT SHEPPARD: The object has like a pinkish hue to it, so it would look a little pink, maybe a little reddish.

GREENFIELDBOYCE: If you were standing on this ball of ice, it would be cold, around minus 400 degrees Fahrenheit, and it would be dark.

SHEPPARD: The sun would just be basically another bright star in the night sky. It wouldn't be much more than that.

GREENFIELDBOYCE: One orbit around the sun takes this dwarf planet around 4,000 years. Sheppard says until it gets a permanent name, it's just called a bunch of letters and numbers that follow a standard format. So it's 2012 VP113.

SHEPPARD: And for short, we've just been calling it VP, or sometimes we even just call it Biden. Affectionately, we call it Biden, just because of the VP.

GREENFIELDBOYCE: He thinks Biden and Sedna probably have plenty of company, thousands of objects out there. In fact, here's something that Sheppard says was mind-blowing: Biden, Sedna and some other bodies at the very edge of the Kuiper Belt all have a strange similarity in their orbits, one that suggests they're being influenced by the presence of something big, perhaps an unseen planet that could be up to 10 times the size of Earth.

SHEPPARD: So we just need to find more of these objects to see really what's happening, but it's definitely a probable thing that there could be a very large object out there.

GREENFIELDBOYCE: The scientists describe their findings in the journal Nature, and other astronomers say it's really exciting.

MIKE BROWN: It shows you that there are large regions of our solar system that we still know next to nothing about.

GREENFIELDBOYCE: Mike Brown at Caltech was part of the team that discovered Sedna. He's relieved that, as he hoped, it's not lonely. And he loves the idea that there might be an even bigger planet lurking around.

BROWN: It's a great idea. I hope it's actually true. It would just be awesome.

GREENFIELDBOYCE: Because if it's true somebody gets to find that planet and name it. Brown says he's going to start looking. Nell Greenfieldboyce, NPR News.

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