spaceSpace and Physics

An Unusual Object Found Beyond Neptune Has Strengthened The Case For Planet Nine


Jonathan O'Callaghan

Senior Staff Writer

Artist's impression of Planet Nine. Caltech/R. Hurt (IPAC)

A new paper has found evidence for another dwarf planet in the outer Solar System, which may strengthen the case for the elusive Planet Nine.

As picked up by Shannon Hall for Quanta Magazine, the researchers looked at an object beyond the orbit of Neptune called 2015 BP519. It’s unusual in that its orbit is highly tilted above the Solar System by about 54 degrees.


That orbit takes it from 35 AU from the Sun (1 AU, astronomical unit, is the Earth-Sun distance), which is within the orbit of Pluto, out to a huge 825 AU. It takes more than 8,900 years for it to complete one orbit.

And that massively eccentric orbit is a pretty good indicator for Planet Nine. When that planet was proposed by astronomers Mike Brown and Konstantin Batygin in 2016, we couldn’t actually see it, but we could see its expected effects on other objects. Ones like 2015 BP519, it turns out.

“2015 BP519 adds to the circumstantial evidence for the existence of this proposed new member of the solar system,” the team led by Juliette Becker from the University of Michigan write in their paper, which is available on arXiv and has been submitted to the Astrophysical Journal for publication.

This object, which may be up to 1,400 kilometers (870 miles) across, was first discovered by the Dark Energy Survey (DES) in 2014. Now we know it is likely the most extreme trans-Neptunian object (TNO), a minor planet that orbits beyond Neptune, found to date.


There is a small chance that its extreme orbit was just the result of random processes in the evolution of the Solar System. That seems a bit unlikely at the moment, note the researchers. The team ran a number of simulations to see how it might have reached its orbit, and a hidden planet looks like the best bet.

“The observed orbital elements of 2015 BP519 are readily produced through dynamical interactions if the solar system also contains Planet Nine,” they wrote.

Not everyone is convinced, however. Speaking to Quanta Magazine, Michael Bannister from Queen’s University Belfast – who was not involved in the study – said Planet Nine was just “one of a number of ways that the Solar System could have unfolded.”

But over the past couple of years, there has been a lot of new evidence for Planet Nine. With each extra piece that gets added, the case gets stronger. Now we just need to find it.


(H/T: Quanta Magazine)


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