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Back in March some astronomers were touting a new discovery that hinted at the existence of a ‘Planet X‘ lurking in the outer Solar System, far beyond our ability for direct observation. Now, in a paper on arXiv.org, Carlos and Raul de la Fuente Marcos at the Complutense University of Madrid in Spain have asked whether strange patterns in the orbital alignments of the dwarf planets beyond Pluto suggest the existence of not one, but two giant planets:

Small groups of the objects have very similar orbital paths. Because they are not massive enough to be tugging on each other, the researchers think the objects are being “shepherded” by a larger object in a pattern known as orbital resonance.

For instance, we know that Neptune and Pluto are in orbital resonance – for every two orbits Pluto makes around the sun, Neptune makes three. Similarly, one group of small objects seems to be in lockstep with a much more distant, unseen planet. That world would have a mass between that of Mars and Saturn and would sit about 200 times Earth’s distance from the sun.

Some of the smaller objects have very elongated orbits that would take them out to this distance. It is unusual for a large planet to orbit so close to other bodies unless it is dynamically tied to something else, so the researchers suggest that the large planet is itself in resonance with a more massive world at about 250 times the Earth-sun distance – just like the one predicted in the previous work.

Read more: Two giant planets may cruise unseen beyond Pluto

Paper:Extreme trans-Neptunian objects and the Kozai mechanism: signaling the presence of trans-Plutonian planets?”