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Space Rock Discovery Boosts Evidence for Planet Nine

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I’m sorry, but Pluto sucks and I’m glad it’s not a planet anymore. It’s smaller than our Moon, and it’s about the same size as several other distant, rocky solar system objects. Have you ever seen the way it orbits alongside its partner, Charon? Classifying it as a planet in the first place was a mistake. Can we get a better ninth planet, please?

Thankfully, astronomers have realized that the motions of the objects past the eighth planet, Neptune, imply the existence of the ninth planet we deserve. The theorized planet would be 10 times the mass of the Earth and take a long, eccentric orbit around the Sun. And just this week, scientists reported another strangely moving rock that bolsters the evidence for a ninth planet’s existence.


The new object, called 2015 BP519, takes an elliptical journey around the Sun spanning from 35 to 862 times the radius of Earth’s own orbit. But while the eight known planets orbit the Sun on the same plane, like slot cars on concentric tracks, 2015 BP519 orbits at a 54-degree angle to that plane.

An international team of scientists from the Dark Energy Survey spotted the object and modeled its movement in a new paper published recently on the arXiv physics preprint server. It’s the “most extreme Trans-Neptunian Object found to date,” according to the paper.


After modeling the object’s orbit based on their observations, the team, led by University of Michigan graduate student Juliette Becker, realized that they needed something to explain why its orbit was so cockeyed. If it was formed in the plane of the solar system, it’s unlikely one of the known planets would have been able to provide the kick that knocked it askew. The researchers write that 2015 BP519's strange orbit is readily explained by a ninth planet dragging it along.

This is far from conclusive evidence. As Shannon Hall, who first reported on the paper, writes for Quanta, other astronomers aren’t as certain of this conclusion, since we don’t quite know what things were like in the early solar system. Maybe there were other objects in the early solar system that could have given the initial kick.

But you can bet that Planet Nine enthusiasts, like CalTech astrophysicist Konstantin Batygin, are very excited:


So, is there really a Planet Nine? Unclear. But if there were, we’d finally get a worthy ninth planet, instead of a dud like Pluto.

[arXiv via Quanta]