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In recent years, scientists have found hundreds of planets orbiting distant stars. Now they've discovered a planet whizzing around a star that's one of our closest neighbors. It's a star known as Alpha Centauri B. And the planet is the nearest ever spotted outside our solar system, as NPR's Nell Greenfieldboyce reports.

NELL GREENFIELDBOYCE, BYLINE: If you are going to imagine interstellar travel, the star system called Alpha Centauri would be your first stop. Its three stars, Alpha Centauri A, B and C, are only around four light-years from our sun. That's far, far away, but it's still closer than everything else beyond our solar system. And that's why imaginary planets in Alpha Centauri are a staple of science fiction.

Now, in the journal Nature, scientists say they've detected the first real planet there. A team of European astronomers used a telescope in Chile to closely observe Alpha Centauri B. They saw it make a telltale wobble that meant a planet's gravity was tugging on the star. Greg Laughlin is an astrophysicist at the University of California, Santa Cruz. He says Alpha Centauri is so well-known, it's practically a household name.

DR. GREGORY LAUGHLIN: And to find out that planet formation did occur there, it's just extraordinarily exciting.

GREENFIELDBOYCE: The newly detected planet has a mass that's similar to Earth, but it zips around its star once every three days. It's so close to its star that its surface might be made of super-hot molten rock, more than 2,000 degrees Fahrenheit. It doesn't seem like a great place to live, but Laughlin says systems with a planet like this one often have more planets orbiting farther away from the star.

LAUGHLIN: I think that the prospects are excellent for finding further planets in this system.

GREENFIELDBOYCE: Perhaps even one in the so-called habitable zone, at a distance from the star where conditions might be right for liquid water and maybe even life.

DR. MARC KUCHNER: I would not be surprised if there were a whole system of planets around Alpha Cen.

GREENFIELDBOYCE: Marc Kuchner is an astrophysicist at NASA's Goddard Space Flight Center. He's most excited about the idea of sending a probe to visit planets found in Alpha Centauri.

KUCHNER: Inside every astronomer is a space cadet and this is the place to go. This is the destination that everyone talks about in the interstellar travel discussions.

GREENFIELDBOYCE: Even though with today's technology, going to this nearby neighbor would take thousands of years. Nell Greenfieldboyce, NPR News.

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