In the race to hunt down the hypothesised ninth planet orbiting our Sun all the way in the outskirts of the Solar System, astronomers have discovered several never-before-seen objects beyond the orbit of Neptune.

The fact that these objects are orbiting the Sun from way out in the fringes of the Solar System makes the existence of Planet Nine all the more likely, the researchers suggest, and say these new finds could actually be the key to locating it.

"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," says astronomer Scott Sheppard from the Carnegie Institution for Science.

"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."

In case you need a bit of a Planet Nine refresher, back in January, astronomer Mike "Pluto killer" Brown from the California Institute of Technology (Caltech) announced that he and his colleagues had found evidence of a massive cosmic body lurking on the edge of the Solar System, just past Neptune.

Nicknamed Planet Nine, it appears to be circling the Sun on a super-elongated orbit that takes an incredible 10,000 to 20,000 years to complete, and could explain why our entire Solar System is tilted.

It's still very much a hypothetical planet at this stage, but evidence suggests that it's about 10 times more massive than Earth and four times the size, and researchers say we've probably missed it this whole time because of how far away it is - about 149 billion km from the Sun, or 75 times more distant than Pluto.

The possible existence of Planet Nine was first hinted at by the strange alignment of rocky objects in the Kuiper belt - a bustling region of space beyond the orbit of Neptune that appears to contain a whole lot of comets, asteroids, and other small chunks of space debris.

"We saw a strange signal in the data that meant something odd was going on in the outer Solar System," Brown told The Guardian earlier this year. "All of these distant objects were lined up in a weird way and that shouldn't happen. We worked through the mundane explanations, but none of them worked out."

Now Sheppard and his team have identified more of these 'extreme trans-Neptunian objects', saying the way they move suggests they're being influenced by the gravitational pull of something extremely massive out past Neptune.

"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," he said in a press statement.

The team is in the middle of conducting the largest, deepest survey for objects beyond Neptune and the Kuiper Belt, using the Dark Energy Camera on the NOAO 4-metre Blanco telescope in Chile, and the Japanese Hyper Suprime Camera on the 8-metre Subaru telescope in Hawaii.

Their newly identified batch of trans-Neptunian objects have been submitted to the International Astronomical Union's (IAU) Minor Planet Centre to receive official designations.

In the meantime, the researchers plan to continue analysing the movements of these new objects to see if they give any more indications for where a hypothetical planet - or whatever else could be exerting such a strong gravitational force - could be lurking.

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

So the Planet Nine plot thickens. 

With all this talk about Earth-like planet candidates at the 'relatively' close distance of 4.2 light-years, it's times like these when you have to remind yourself that space is really freaking huge. We barely even know what's going on in our own cosmic backyard.

But we're getting ever-closer to learning the secrets of the outer Solar System, and what we really want to know is who Pluto has been hanging out with all this time. Who's that heart for, Pluto?

A paper discussing the find has been accepted for publication in an upcoming edition of The Astronomical Journal, and you can read the pre-print version at arXiv.org.