THE SEARCH FOR PLANET NINE IS A NEPTUNE-SIZE WORLD HIDDEN IN OUR SOLAR SYSTEM? BY STEPHANIE WARREN DRIMMER ART BY MONDOLITHIC

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18 MARCH 2017 PLANET NINE ay out in the farthest While observing the belt in 2014, the planet would be roughly the size of reaches of the solar system, Brown and his research partner, Neptune. Like Neptune, it would likely be a mysterious undiscovered Konstantin Batygin, saw something made of gas, and the temperature there Wplanet orbits through space. It’s strange: The orbits of many of the would be a frigid minus 374.8°F. gigantic—almost four times the size of smaller objects in the Kuiper belt were “It’s hard to believe that we could Earth. And it’s so far away that it takes aligned. Weirder still, they never came miss something as big as Neptune!” up to 20,000 years to orbit the sun. closer to the sun than Neptune. It was Brown says. But the planet is really far This planet isn’t science fiction. like something was pulling them away. away, about 56 billion miles from Earth. Astronomers think it really exists. But what? Only a little light would hit it. If it exists, They’ve dubbed it Planet Nine, and only two telescopes in the world are they’re searching the skies to find it. S TRANGE SPACE powerful enough to search vast areas of Brown and Batygin spent over a year the sky for it efficiently—and until now, FAR OUT trying to figure out the objects’ odd they haven’t been looking for the planet. When most people think of our solar behavior. They discussed several system, they think of its eight planets potential answers—but only one seemed THE HUNT IS ON and our sun. But not astronomer Mike to work. “We were convinced another Brown and Batygin are convinced that Brown. Brown is interested in the region planet was out there,” Brown says. their evidence proves that Planet Nine of space beyond these eight planets. To find out if they were right, the pair is hidden somewhere beyond the Kuiper “There’s this huge part of the solar created a computer model illustrating belt. But Brown predicts the search will system that we’re only just beginning to the objects. Then they plugged an take at least a few years. learn about,” he says. imaginary planet into the model. The Soon future telescopes will let us Beyond Neptune is an area known as model showed that the planet’s gravity peer even farther into space. And when the Kuiper (KY-pur) belt, which scientists would pull on these icy objects, making we do, Brown thinks we may discover used to think was empty. But it turns them move in exactly the way they had that Planet Nine isn’t the only thing out out the Kuiper belt is home to icy, rocky moved in space. The model also gave there. “Planet Nine is the planet for my objects; billions of comets; and a few the scientists an idea of the planet’s generation,” he says. “But Planet 10? dwarf planets (objects too small to be size. Because of its strong gravitational That’s what tomorrow’s astronomers— considered planets) such as Pluto. pull, Brown and Batygin inferred that kids growing up today—will look for.”

OUR NEW SOLAR SYSTEM? Scientists aren’t sure of Planet Nine’s exact location, but they think it might lurk in the outer edges of our solar system, somewhere beyond Neptune.

PLANET NINE NEPTUNE URANUS SATURN JUPITER MARS EARTH VENUS MERCURY SUN

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