A radical new theory has claimed the mysterious 'Planet Nine' might have knocked every planet in the solar system out of alignment.

Although the eight major planets circle the sun in the original plane of their birth, the sun rotates on an axis tilted 6 degrees relative to a line perpendicular to the plane of the planets.

Experts have been baffled by this - but now say Planet Nine may hold the answer.

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In January, Caltech astronomers Professor Konstantin Batygin and Professor Mike Brown predicted the existence of what they, somewhat controversially, termed 'Planet Nine'. Since the prediction, researchers over the world have been using different instruments to hone in on the planet. Artist's impression pictured

THE SOLAR SYSTEM TILT The eight major planets still circle the sun in the original plane of their birth. The sun rotates on its own axis, but surprisingly, that spin is tilted: the axis lies at an angle of 6 degrees relative to a line perpendicular to the plane of the planets. Advertisement

Theories for this strange tilt range from the temporary tug of a passing star to interactions between the magnetic fields of the sun and the primordial dusty disc that formed the solar system.

Earlier this year, Michael Brown and Konstantin Batygin at the California Institute of Technology in Pasadena argued that this Planet Nine could be responsible for some of the erratic movements of icy worlds in the outer solar system.

Now the idea can be extended to the orbit of all the planets, Elizabeth Bailey, also at Caltech, who did the work together with Brown and Batygin, told New Scientist.

'Because we think Planet Nine has a significant inclination, if it exists, then that means it would tilt things,' Bailey said.

'It's one puzzle piece that seems to fit together, and it really seems to be in support of the Planet Nine hypothesis.'

The planet would have between 5 and 20 times Earth's mass and be in a wildly eccentric orbit, reaching 250 times the sun-Earth distance at its farthest point.

'The six-degree obliquity of the sun suggests that either an asymmetry was present in the solar system's formation environment, or an external torque has misaligned the angular momentum vectors of the sun and the planets,' the researchers wrote in the journal arxiv.

'However, the exact origin of this obliquity remains an open question.

'Using an analytic model for secular interactions between Planet Nine and the remaining giant planets, here we show that a planet with similar parameters can naturally generate the observed obliquity as well as the specific pole position of the sun's spin axis, from a nearly aligned initial state.

'Thus, Planet Nine offers a testable explanation for the otherwise mysterious spin-orbit misalignment of the solar system.'

Planet Nine's tilt, not its mass, is key according to a second study led by Alessandro Morbidelli at Côte d'Azur Observatory in Nice, France.

'We evaluate the effects of a distant planet, commonly known as planet 9, on the dynamics of the giant planets of the Solar System,' his team wrote in the same journal.

'Some of the planet 9 configurations that allow explaining the current solar tilt are compatible with those proposed to explain the orbital confinement of the most distant Kuiper belt objects.

'Thus, this work on the one hand gives an elegant explanation for the current tilt between the invariant plane of the inner giant planets and the solar equator and, on the other hand, adds new constraints to the orbital elements of planet 9.'

Cerro Tololo Inter-American Observatory in Chile, the home of the Dark Energy Camera

HOW THEY 'FOUND' PLANET NINE Researchers inferred Planet Nine's presence from the peculiar clustering of six previously known objects that orbit beyond Neptune. They say there's only a 0.007% chance, or about one in 15,000, that the clustering could be a coincidence. Instead, they say, a planet with the mass of 10 Earths has shepherded the six objects into their strange elliptical orbits, tilted out of the plane of the solar system. Advertisement

Earlier this years experts said The Dark Energy Survey, a Southern Hemisphere observation project designed to probe the acceleration of the universe, by looking at the most distant galaxies, may hold the key to Planet Nine.

The evidence for a ninth planet in our solar system might be hiding in data gathered as part of the survey, and if so it could be found by the end of summer, an expert told MailOnline.

In January, Caltech astronomers Professor Konstantin Batygin and Professor Mike Brown predicted the existence of what they, somewhat controversially, termed 'Planet Nine'.

They used mathematical modelling and computer simulations to find the planet would exactly explain a strange clumping behaviour of a group of dwarf planets in the Kuiper Belt, a field of icy objects and debris beyond Neptune.

The unknown world, dubbed 'Planet X' by others, is thought to be 10 times more massive than Earth and the furthest planet from the sun - but its exact location is unknown.

Since the prediction, researchers over the world have been using different instruments to hone in on the planet.

Great Nebula in Orion as taken by the Dark Energy Camera, pictured. The five year survey is helping astronomers find out exactly what dark energy is made of. They are doing this by analysing very distant galaxies over long periods of time, to watch for objects moving very slowly – which is why the project takes such a long time

And the results pointed to an unexpected part of the sky, the part DES has been inspecting for the last two and a half years.

'I fell into the search for Planet Nine almost by accident,' member of DES Professor David Gerdes, from the University of Michigan, told MailOnline.

Professor Gerdes said he was looking for a project to give his students when Planet Nine was brought to his attention.

THE CONTROVERSIAL PLANET NINE Even the mysterious planet's name causes controversy. Mike Brown is Professor of Planetary Astronomy at Caltech. He is best known for his discovery of Eris, the most massive object found in the solar system in 150 years, and the object which led to the debate and eventual demotion of Pluto from a real planet to a dwarf planet. Alan Stern is an engineer and planetary scientist. He is the principal investigator of Nasa's New Horizons mission to Pluto. He is famously a defender of Pluto's planet title, which was stripped from it in 2006. The two scientists are 'at loggerheads' with each other over the classification of Pluto, according to some astronomers. The mysterious planet has always been termed 'Planet X', X being the roman numeral for ten, suggesting a tenth planet. But when Professor Brown and his team published the paper in January, they controversially named the planet 'Planet Nine' instead of Planet X, as a nod to Professor Brown's work towards declassifying Pluto. 'Calling it Planet Nine is very mischievous,' Professor Monica Grady told MailOnline. Advertisement

A team of French researchers used data from Nasa's Cassini spacecraft orbiting Saturn, looking at the distance between Saturn and Earth, to narrow down where the planet could be in a paper published in March.

The predictions in this, and the original paper published in January, mean DES might have been looking in exactly the right place to spot the mysterious world.

If it was, the planet could be found as soon as by the end of this summer, Professor Gerdes told MailOnline.

At the moment Professor Gerdes and his team are going through a process of cataloging the objects that have been spotted so far.

Most of the area of the sky that will be looked at has been surveyed so far, so if the planet is there and in the right part of its orbit, it should be hiding in the data.

But not finding it does not mean Planet Nine does not exist.

'If we see it, it's a great result and a fun paper to write,' he said. 'If we don't see it, the challenge is working out exactly what that means.'

Not spotting the world would mean a lot more constraints could be placed on the model, helping other searches potentially track the planet down.

But spotting it directly is not the only way to tell if it is there.

The paper published in January made a series of predictions, with consequences that can themselves be observed.

For example, the paper predicted six objects in the solar system that would be perfectly aligned, and one of these has already been found using DES data.

A population of minor planets that cross the orbit of the giant planets in our solar system, which might be found independent of the search for Planet Nine.

The orbit of any of these objects could be used to place more constraints on the place on the location of the planet.

WHAT IS DARK ENERGY? Dark energy is a phrase used by physicists to describe a mysterious 'something' that is causing unusual things to happen in the universe. 'The universe is not only expanding, but it is expanding faster and faster as time goes by,' Dr Kathy Romer, scientist at the Dark Energy Survey told MailOnline. 'What we'd expect is that the expansion would get slower and slower as time goes by, because it has been nearly 14 billion years since the Big Bang.' Coming up with an equation of state would give the researchers clues about what is making up this mysterious force. At the moment the favourite candidate is called the 'cosmological constant' – which has a relatively boring equation of state. 'But, despite its simplicity, the cosmological constant is not the 'something' that scientists are hoping for,' Dr Romer said, 'a cosmological constant then messes up other parts of physics.' 'It's like a table plan at a wedding: you think you've got it all sorted out and then you notice that, because the caterers gave you a round table instead of a long one, your Dad is now going to be sitting next to your Mum's new boyfriend.' Advertisement

The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Such an orbital alignment can only be maintained by some outside force, according to the Caltech researchers who predicted Planet Nine in January

The use of the Dark Energy Survey was by chance, but was not necessarily surprising.

The five year survey is helping astronomers find out exactly what dark energy is made of. They are doing this by analysing very distant galaxies over long periods of time, to watch for objects moving very slowly – which is why the project takes such a long time.

HOW THE SUN STOLE A PLANET It has been one of the biggest mysteries in astronomy - does planet nine exist, and what is it? Now, astronomers at Lund University in Sweden show that it is highly likely that the so-called Planet nine is, in fact, an exoplanet. They believe it was 'stolen' by our sun as it moved past in early in the universe's evolution, and has been a part of our solar system completely undetected ever since. The theory is that our sun, in its youth some 4.5 billion years ago, stole Planet 9 from its original star. According to astronomers in Lund, there is a lot to indicate that Planet 9 was captured by the young sun and has been a part of our solar system completely undetected ever since. Stars are born in clusters and often pass by one another. It is during these encounters that a star can 'steal' one or more planets in orbit around another star. This is probably what happened when our own sun captured Planet 9. Advertisement

This is why the survey is the perfect opportunity for lots of other science to be done at the same time.

The data from survey has led to the discovery of companion galaxies to our Milky Way. Famous companion galaxies like the Large Magellanic Cloud can be seen easily from Earth and are well known because of it, but many more have been spotted by the DES camera.

'DES doesn't just tell us about cosmology. It also tells us about the origins and contents of our own solar system,' Dr Kathy Romer, member of the Dark Energy Survey from the University of Sussex told MailOnline.

'By chance, rather than by design, DES has turned out to be a great way to find new examples of dwarf planets orbiting the sun.'

After starting in 2013, the scientists are now over half way into the five years they set out for the project.

The main aim of the experiment, which involves hundreds of scientists, is to come up with an equation that describes the behaviour of the mysterious force known as dark energy.

Dark energy is a phrase used by physicists to describe a mysterious 'something' that is causing unusual things to happen in the universe.

'The universe is not only expanding, but it is expanding faster and faster as time goes by,' Dr Romer said.

A paper published in March suggests the distance between Earth and Saturn measured by Cassini (artist's impression pictured) could be used to narrow down an area of space where the planet could be

'What we'd expect is that the expansion would get slower and slower as time goes by, because it has been nearly 14 billion years since the Big Bang.'

Coming up with an equation of state would give the researchers clues about what is making up this mysterious force.

At the moment the favourite candidate is called the 'cosmological constant' – which has a relatively boring equation of state.

'But, despite its simplicity, the cosmological constant is not the 'something' that scientists are hoping for,' Dr Romer said, 'a cosmological constant then messes up other parts of physics.'

'It's like a table plan at a wedding: you think you've got it all sorted out and then you notice that, because the caterers gave you a round table instead of a long one, your Dad is now going to be sitting next to your Mum's new boyfriend.'