For a few years now, the astronomy world has been hard at work searching for a ninth planet of the solar system (no, not Pluto, it’s time to move on). There’s evidence of something massive hanging around in the outer reaches of the solar system—10 times more massive than Earth, big enough to gravitationally warp the orbits of smaller objects in its vicinity, 10 to 20 times farther away than Pluto. And yet it apparently continues to hide in plain sight, eluding our best efforts to observe it directly. If a planet orbits the sun and nobody’s there to see it, is it even real?
The latest tantalizing bit of evidence to back up Planet Nine’s existence is an asteroid called 2015 BP519, first discovered three years ago in the vast reaches of the Kuiper belt (the region of the solar system beyond Neptune). We now know the asteroid possesses a bizarre elliptical orbit that suggests something gigantic is pulling at the little bugger as it tries to make its journey around the sun.