The existence of a mysterious ninth planet in the Solar System is still contentious, but the hunt for it has led astronomers to discover more and more objects far beyond the orbit of Neptune.

US astronomers Scott Sheppard, Chadwick Trujillo, and David Tholen have observed several trans-Neptunian objects (TNOs) while conducting the largest, deepest survey of the remote Solar System.

Among the new discoveries, there is 2014 FE72 – the first distant object whose orbit lies completely beyond Neptune. The object stretches very far from the center of the Solar System, 3,000 times the Earth-Sun distance. It is so far away that gravity from other stars and the galactic tides play a role in its movement.

“Objects found far beyond Neptune hold the key to unlocking our Solar System’s origins and evolution,” said Sheppard, from the Carnegie Institution for Science, in a statement.

“Though we believe there are thousands of these small objects, we haven’t found very many of them yet, because they are so far away. The smaller objects can lead us to the much bigger planet we think exists out there. The more we discover, the better we will be able to understand what is going on in the outer Solar System.”

^{The image shows the orbits of the new and previously known extremely distant Solar System objects. The clustering of most of these TNOs' orbits indicates that there could be a very large and very distant undiscovered planet. Robin Dienel}

Most of the TNOs seem to be clustering in a certain direction, which has led researchers to speculate about the existence of a large planet, up to 15 times the mass of Earth, whose gravity is pushing most of the smaller objects discovered in a certain region.

This trend seems so well established that it was quite surprising for the researchers to find one object, 2013 FT28, that doesn’t completely match with the others. It is apparently pointing in the same direction of Planet Nine.

Although the clustering trend seems to be weaker in this paper, accepted for publication in The Astrophysical Journal, the researchers think we still don’t know enough to make confident claims about the existence of Planet Nine.

“Right now we are dealing with very low-number statistics, so we don’t really understand what is happening in the outer Solar System," Sheppard added. "Greater numbers of extreme trans-Neptunian objects must be found to fully determine the structure of our outer Solar System.

“We are now in a similar situation as in the mid-19th century when Alexis Bouvard noticed Uranus’ orbital motion was peculiar, which eventually led to the discovery of Neptune.”