The newly-plotted orbital path of a recently discovered trans-Neptunian object has added new fuel to the growing body of evidence that there is a planet of substantial size orbiting in the far reaches of our solar system. The highly-eccentric orbit of this dwarf planet fits perfectly–and indeed can currently only be explained by–the presence of the mysterious Planet Nine.
Discovered in late 2014, 2015 BP519 (currently nicknamed Caju) has an extreme orbital tilt of 54 degrees from the ecliptic; this is an 8,912-year orbit that cuts between Neptune and Pluto’s orbits at 35 astronomical units (AU), and swings out to a far-flung 825 times farther out than the Earth is from the Sun. Early attempts to plot Caju’s orbit failed to make sense, until parameters for the hypothetical body called Planet Nine were added to the calculations, resulting in a proper resolution of 2015 BP519’s orbital path.
In 2016 CalTech researchers Konstantin Batygin and Mike Brown found that the long axes of the orbits of numerous trans-Neptunian objects pointed in the same direction, indicating that there was a large celestial body in the neighborhood that was affecting their orbits. Subsequent calculations found that the object would need to be massive–10 times the mass of the Earth, at that–fitting perfectly with the otherwise dramatically skewed, and oftentimes backward orbits of these deep-space planetoids.
"It’s not proof that Planet Nine exists," cautions University of Michigan astronomer ans study co-author David Gerdes. "But I would say the presence of an object like this in our solar system bolsters the case for Planet Nine."