Solar System Reveals a Whole New World

Is there a tenth planet orbiting our sun? Astronomers have found an object at least as big as Pluto that fits the description. But whether it's actually recognized as a planet may be a matter of semantic debate.

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This is WEEKEND EDITION from NPR News. I'm Scott Simon.

Coming up, ever wonder what Saturn sounds like?

But first, astronomers have just found a new planet in our solar system. It's bigger than Pluto. They're calling it the 10th known planet orbiting around our sun, though others would argue that point. Whatever you call it, it's a spectacular find. NPR's Richard Harris has the story.

RICHARD HARRIS reporting:

Pluto lives in a swarming cloud of icy rocks called the Kuiper Belt way out beyond Neptune. Astronomers have never found anything bigger than Pluto out there, but they figured it was simply a matter of time. That time has now come. Pluto, meet your big brother.

Mr. DAVID RABINOWITZ (Yale University): It is called 2003UB313. Everybody has to remember that. Until we give it a new name, an official name, that's what we'll have to call it.

HARRIS: David Rabinowitz at Yale is part of a team that found this object. It turns out it's not where the big planets are. They all lie in the same plane as though they were all drawn on the same sheet of paper. This one has an orbit that carries it far above and far below that plane.

Mr. RABINOWITZ: We thought that we would find fewer objects there, but it turns out the brighter ones seem to be hanging out there.

HARRIS: Rabinowitz and his colleague Mike Brown at Caltech have been keeping an eye on this object for a few months now. It's currently a hundred times farther from the sun than the Earth is, but its elliptical orbit will bring it as close as Pluto in 240 years. A collaborator in Hawaii has even taken a good look at it with a huge telescope.

Mr. RABINOWITZ: Already, Chad Trujillo has gotten observations with the Gemini telescope, and he's found very similar frozen ices as on Pluto: methane, water. So its surface almost looks the same as Pluto.

HARRIS: Most significant, though, is its size. Rabinowitz figures it's at least as big as Pluto and, most likely, half again as big.

Mr. RABINOWITZ: Now that it's bigger than--or as big or bigger than Pluto, I'd call that a major planet, just like Pluto is.

HARRIS: The team announced the discovery at a hastily arranged telephone news conference on Friday night. Rabinowitz says he would rather have gathered more data about it and presented their findings more formally.

Mr. RABINOWITZ: You know, usually we'd like to know what the real reflectivity is, the orbit, rotation, colors, reflectance. All that stuff we like to measure before we announce something just so it's kind of not debated for a long time. But this time, we got beat to the punch with one of our objects, and we figured, well, it's time to make the other ones known.

HARRIS: It turns out that Spanish astronomers have also been scanning these skies for new planets, and they had found one of the same objects Rabinowitz and his colleagues have been observing. So the American team announced findings from three objects, including the one that's bigger than Pluto. Besides, Rabinowitz says, someone had hacked the Web site where they store their data, so they figured the secret was out. The team declared that this new object is the 10th planet in our solar system. Alan Stern at the Southwest Research Institute in Boulder, Colorado, begs to differ.

Mr. ALAN STERN (Southwest Research Institute): I think it's about planet number 20.

HARRIS: Stern says some asteroids are big enough to be considered planets; so are some other objects in the Kuiper Belt. True, they are probably best called dwarf planets, but he says they are planets because they have enough gravitational force to pull their material into a nice round sphere. By that logic, our moon would be a planet if it were orbiting the sun rather than the Earth. So Stern says there are about 20 planets and counting.

Mr. STERN: Richard, hold onto your hat. We're going to find Marses and maybe Earths out in the solar system's attic of the Oort Cloud and the Kuiper Belt. There's just a lot of material--many objects that were scattered out there during the early formation days, and we're now in possession of the technology to find them.

HARRIS: That search is continuing with Rabinowitz's telescope and it's likely to accelerate when a new generation of planet-hunting instruments starts scanning the skies as well. Richard Harris, NPR News.

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