If Planet Nine Exists, We’ll Find It Soon

Brown and Batygin ruminated on six ETNOs and noticed something weird was going on. Unlike the eight known planets, whose orbits are approximately circular and are oriented along the same flat plane, known as the ecliptic, these six objects—including Sedna—had elliptical orbits and were tilted about 20 degrees with respect to the ecliptic. The six also made their closest approaches to the sun in the same region of space. They were all too far out to be within Neptune’s gravitational reach, but something appeared to have crafted their orbits.

Brown and Batygin’s computer models suggested the only reasonable possibility was a hidden planet with a mass five to 10 times that of Earth orbiting as far as 700 AU away. This world, perhaps one exiled from the warmer confines of the solar system during its chaotic earlier years, managed to cling to the sun’s gravitational ropes. And as it whirled through the distant darkness, it wielded its own gravitational influence on those passing six orbs, herding them into similar, strange new orbits.