By: Nathan Rousseau Smith, Buzz60
It's been a big year for space exploration. Coming off NASA's discovery of seven Earth-sized planets, scientists may have finally found Planet Nine.
Researchers in Australia led a citizen search for the evasive planet. 60,000 people around the world pitched in, classifying millions of objects in just a few days time.
Now it all comes down to this, four unknown objects in space, any one of them could be Planet Nine. It's up to the Australian National University to figure out those four things actually are.
The idea of a ninth planet captured the imagination of scientists when it was first proposed by CalTech. They say the gravitational pull its exerting on other planets means it would have to be four times the size of Earth.
One of the reasons it's been so hard to find is that it could take Planet Nine upwards of 20,000 years to complete a single rotation around the sun.