The recently discovered dwarf planet 2015 TG387 — aka "The Goblin" — has an extreme orbit. It's far-flung and elongated, and takes the planet a whopping 40,000 years to go around the sun. Because of this anomalous orbit, some astronomers hypothesize that The Goblin is being pulled into the gravitational field of a large planet in our solar system, one of which has never been seen. In this video, Dr. Michelle Thaller dicusses the possibility of a Planet Nine — or "Planet X." | Big Think Science