Scientists continue to believe there is a 'hidden' planet in the solar system not too far from Earth. We've just not been able to find it yet.
But that might happen sooner than some think, with experts in the field of astronomy reckoning they have found out the best way to finally catch a glimpse of it.
For years, experts have been searching for the fabled Planet Nine in our solar system.
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The solar system used to have nine planets until 2006 when Pluto was demoted to a dwarf planet. But Pluto aside, there is a real belief a ninth planet does exist that is of the right size. Sorry Pluto.
It's an idea that has been proposed for a number of years, with a belief the planet is a gas or ice giant that orbits the Sun billions of miles further out than the rest of the planets.
Now, things could change with a huge project opening next year.
In 2025, the Vera C. Rubin Observatory will finally open its doors to take stunning images of the universe around us.
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And through the observatory, we may finally discover Planet Nine, which experts believe to be around seven times as big as Earth.
Speaking to Live Science, Mike Brown, an astronomer at Caltech who proposed the Planet Nine hypothesis, revealed how the Vera C. Rubin Observatory could be the key to discovery.
He said: "It's really difficult to explain the solar system without Planet Nine.
"But there's no way to be 100 percent sure [it exists] until you see it."
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How will the observatory find Planet Nine?
It's all to do with the technology inside the Vera C. Rubin Observatory.
Located in Chile and costing $473 million (£374 million), it is home to the largest digital camera ever made by humanity
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Channelling its inner James Webb Space Telescope, it will take pictures of the cosmos from millions and billions of miles away from Earth, allowing us to look further than ever before from our planet.
This is alongside work already taking place at Japan's Subaru Telescope, located in Hawaii.
If successful, Brown reckons we could find Planet Nine within two years of this project being undertaken - while also coyly saying he's been saying that since 2016.
Why haven't we found Planet Nine?
According to Brown, the hidden Planet Nine is 'very, very far away'.
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As a result of this, and how light travels, any light reflecting off of Planet Nine would be incredibly dim by the time it reached Earth. Hence the need for a super advanced piece of kit to view it.
Nevertheless, experts are convinced it is still there. We just have to find it.
Topics: Science, World News, Space, Technology, James Webb Space Telescope