Astronomers around the world are looking for a huge unexplored world dubbed Planet Nine, which could change everything we think we know about the solar system.
They know it's out there, as well as its size – potentially 10 times bigger than the Earth – and its powerful gravitational force.
But Planet Nine is proving impossible to find, demonstrating how much we still don't know what is in the courtyard of our world.
Astronomer Alan Duffy, professor of astrophysics at Swinburne University, said that the theory behind Planet Nine emerged relatively recently after a Brazilian astronomer noticed strange events on the periphery of the solar system.
"The idea is that the outer orbits of our solar system have shown surprising behavior that can be explained by the gravitational attraction of a very large and very distant world," said Professor Duffy.
It was 2012 and Rodney Gomes, an astronomer at the Rio de Janeiro National Observatory, offered his theory that a giant planet that could not be seen was behind the disorder.
But how can you declare the existence of a large planet without being able to see it or even vaguely identify where it is?
"C & # 39; is a historical precedent here because it is exactly as we found Neptune" Professor Duffy He said.
The planet Uranus was discovered using a telescope in 1781 but raised more questions than it answered, he explained.
"Simply put, Uranus was not where it should be," he said. "He wasn't exactly in the position where the calculations indicated he should. With the passing of the years, mathematics has determined that there was an even bigger or farther planet that was pulling its orbit."
That planet was Neptune, which was basically intended to exist before being discovered using mathematics.
"It's a similar situation now where these tiny objects on the outer edges of our solar system in what we call the Kuiper belt have very strange orbits" Professor Duffy He said.
"They all seem to be on one side, stacked in a preferential way, and the way to explain it is with the idea that Planet Nine essentially threw them out there with its gravity."
RELATED: the potential superflare could cause technological blackout on Earth
He estimates that Planet Nine is about 400 times farther from the sun than we are, so finding it is like giving a torch west from Sydney and hoping to see Perth with it.
He estimated that it would be about 100 million times weaker than the weakest star we can see with our eyes.
"The problem is that there is a huge amount of space to look for. Even a very large planet, much larger than the earth, is very small at that distance," said Professor Duffy.
"You're looking for something very weak. Basically it basically looks like a very weak star and there are many of those out there."
And it is so far away that it probably takes about 10,000 years to make a complete orbit of the sun, which means that it moves very slowly.
"It's the slightest of slight movements," he said. "You're actually looking at half the night sky and trying to see if something weak is moving."
RELATED: Jupiter so close to June, its moons visible with binoculars
Professor Duffy equates him to trying to find a needle that looks a lot like hay in a giant haystack.
"The solar system is deceptively big. Most people imagine that the various planets are relatively close and our telescopes have found everything between them.
"Nothing could be further from the truth. The real space in the middle is enormous. Even near our land, the space is littered with huge pieces of rock that we have not yet been able to catalog or even detect.
"The further you get away from the sun, the more difficult it becomes."
To put the solar system into perspective, Professor Duffy uses Australian places and landmarks to express his opinion.
"If the Sun were at the Sydney Opera House, then the Earth would be in the nearest orbit of the airport, while this Planet Nine would turn up to Perth," he said.
"But the outer edges of our solar system, where a graveyard of huge blocks of ice floats giving us long-term comets, would be beyond the moon on this scale."
Why does anyone bother to find a large piece of floating mass that is really far away and uninhabitable?
Professor Duffy said that Planet Nine could test what astronomers know about how planets are formed, particularly in this part of the solar system.
"Something so big so far away will be fascinating. Will it be a cold world? Will it be rocky? Will it potentially be a gas giant? I suspect it is more likely to be a super big version of Pluto, but again we don't know. That's why we look at, to try to better understand our solar system and how these worlds are formed ".