The ninth planet in our solar system has never been observed, but it may have already been photographed at Siding Springs Observatory near Coonabarabran. It is waiting to be discovered.
Australian National University (ANU) has released a collection of images from the SkyMapper telescope, calling on amateur astronomers in the southern hemisphere to help locate the planet and other undiscovered objects in the night sky.
"For young people getting in there, even if they don't find Planet Nine, they are going to find asteroids and comets and all this really cool stuff. And that is what it is all about.” – Donna Burton was a technical support officer and support astronomer at Siding Springs between 2004 and 2013. She now runs her own business near Coonabarabran.
"I think it's important that people are getting out there and doing science. And this is real science,” she said.
The Warrumbungles in central western NSW, where the telescope is pointed into the darkness, is the perfect place for star-gazing.
It is a “dark-sky park”, the first designated in Australia, and the SkyMapper, at the peak of a mountain on the edge of the National Park, 20 kilometres west of the Newell Highway, has captured countless images of the night sky.
No one has observed Planet Nine, but it's out there. And it’s big. If the Earth was a golf ball, the mysterious icy planet lurking far beyond Neptune would be as heavy as a bowling ball, but would fit comfortably in the palm of your hand.
Astronomers are hoping to discover it as it passes Earth and completes part of its orbit closest to the sun. But the discovery could be made by anyone.
"No matter how good our computers are, they still don't have the accuracy of the human eye because we can see differences between the images." Ms Burton said.
During her tenure at Siding Springs, she discovered two comets and collaborated with Australian astronomer Rob McNaught, renowned for his research on near-earth asteroids.
Though there is growing excitement for the discovery of another planet in our solar system, the “real science” is being done by everyone willing to pitch in, Ms Burton said.
"Whether Planet Nine exists or not isn't really important. What is important is that it is getting people out there involved in science and looking."
"SkyMapper hasn't been around that long, and the thing is there is not enough students, PhD students, to sit down and do it. So, by harnessing everybody who is interested in doing it, from the 90-year-old with a computer to a 10 or 11-year-old, it is opened to everybody.
"If you know you are doing it, and you are going to get recognised for it down the track, that's important.”
More than 30,000 volunteers have viewed the images at Zooniverse, a website dedicated to “people-powered” research projects, and more than 430,000 points have already been flagged for further investigation.
The project, at that point, was only five percent complete.
The images are chaotic arrays of blue, red and white dots - a galactic Where's Wally puzzle. But when they are run together, like animations in a flip-book, the differences become clear.
Ms Burton said the project is about spotting the difference. Dots appearing in different colours to the mass of red, blue and white, as well as fast and slow-moving objects could lead to discovery.
Rapid "movers", single dots that appear in all images, careen through the photographs. Others flicker and appear almost stationary.
There will be many moving objects, Ms Burton explained. Some will be satellites, undiscovered comets, and asteroids. Many others, like flickering silver spots, will be useless artifacts – false readings from moments when the telescope moved rather than the stars, or confusing image noise.
Only one can be Planet Nine.
For Ms Burton, the search is about citizen scientists getting their hands in the research. She described it as "buying in" - 1000 eyes are better than two, and they all outmatch the most powerful computer analyses.
"This is the first (project) using SkyMapper and exclusively southern data," she said.
Ms Burton believed the search would eventually lead to a corresponding project in the northern hemisphere.
"And once James Webb, which is the next Hubble, the bigger better Hubble, goes up, then we will have more capability for all this. That is not going to happen for another 10 years or so," she said.
But the mathematics of predicting planets has applications far beyond our little corner of the universe.
"Take it outside of our solar system," Ms Burton said. "This is how we can predict what other planets are there or should not be there. So, it doesn't just work in our solar system; it works on other solar systems.
"It is an application of all that stuff you thought was boring in school."
The mathematics says the planet must be there, but Ms Burton explained there was still a lot of luck needed before discovery.
"If we haven't seen it yet, it means it is at the furthest part of its orbit," she said.
"SkyMapper's data has been taken over the past couple of years, and they are taking more every night, so if it is there, it will be found. But if it isn't found, that doesn't mean it isn't there.
"It just means it is not visible to us yet because it is not in the part of the sky we are looking at."
Behind the story: Search for the missing planet
In 2014, astronomers Chad Trujillo and Scott S Sheppard, in a letter to the journal Nature, proposed that a massive planet could be lurking beyond the Kuiper Belt.
Trujillo was also credited with discovering Eris, a dwarf planet often so far from the sun that its atmosphere collapses.
In January 2016, Konstantin Batygin and Mike Brown, researchers at the California Institute of Technology, supported the prediction that a planet at least 10-times greater than the mass of Earth was influencing the orbits of other distant planets in the solar system, including Sedna.
Their research argued there was only a 0.007 percent chance the strange orbits of planets like Sedna, which takes more than 11,000 years to round the sun, were by chance.
A giant planet, yet undiscovered, was the logical explanation. But it would only be visible during the closest part of its orbit to the sun which, according to Kepler's Laws of planetary movement, are when it is moving fastest.
Similar predictions preceded the discovery of Pluto at the turn of the 20th century, later demoted from the rank of planets largely because of Brown's research, as well as Neptune and Uranus.
"(Predicting planets) has been proven right three times," Ms Burton said.
"The search for (Pluto) was based on the calculations that there had to be something there. And given how small Pluto is, that is pretty incredible."
Brown and Batygin were initially sceptical.
On January 21, 2016, Brown, using the handle @plutokiller and known for his book How I Killed Pluto and Why It Had It Coming, tweeted:
"Ok, ok, I am now willing to admit: I do believe the solar system has nine planets".
OK, OK, I am now willing to admit: I DO believe that the solar system has nine planets.— Mike Brown (@plutokiller) January 20, 2016
He then tweeted a link to the research paper authored with Batygin, titled Evidence for a distant planet in the solar system, published in The Astronomical Journal.
Later, he told the Washington Post his daughter was "still kind of mad" about Pluto's demotion and her father's hand in its demise, despite her barely being born at the time. She said she might forgive him if he discovered the true ninth planet.
"I've been working on this for her," Brown said.
By comparison, there is little question Planet Nine deserves the status. It is predicted to weigh almost 5000-times that of Pluto, is at least 10-times the mass of Earth and is 800-times further from the sun. Its orbit is predicted to take between 10,000 and 20,000 years.