Its discovery began with Sedna.

Sedna is a dwarf planet smaller than Pluto.

Scientists believe Sedna is in the gravitational pull of a large object, which could be this new planet — aka "Planet 9." (Video via Kurdistan Planetarium)

It has about 10 times the mass of Earth.

It's an average of 600 times farther from the sun than the Earth is and takes 20,000 years to orbit the sun once.

This video includes images from NASA.

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On April 8, 1974, in Atlanta, Hank Aaron smashed baseball’s home run record. Our special coverage celebrating the 50th anniversary of this magical moment has begun online and in our print editions. There’s still more to come as Monday’s historic anniversary arrives.

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