'Planet Nine' may explain solar system tilt mystery
The hypothesised 'Planet Nine', which is believed to exist beyond Pluto, may have tilted the entire solar system, astronomers believe.
Earlier this year, scientists at the California Institute of Technology (Caltech) announced that a planet 10 times the mass of Earth probably exists around 30 billion kilometres away.
It was shown to exert such a huge influence on its region of space that it was dubbed 'the most planety of all planets'.
Now the same team believes Planet Nine is also responsible for one of the biggest mysteries in astronomy - why the solar system lies on a strange tilt.
All of the planets, including Earth, orbit in a flat plane with respect to the Sun.
But that plane rotates on a six-degree angle with respect to the Sun's equator, a misalignment that has left astronomers scratching their heads for decades.
"It's such a deep-rooted mystery and so difficult to explain that people just don't talk about it," said Prof Mike Brown who made the original discovery about Planet Nine.
The huge planet appears to orbit at about 30 degrees off from the orbital plane of the other planets, which is likely to add a 'wobble' to the solar system.
"Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the solar system has no choice but to slowly twist out of alignment," said Elizabeth Bailey, a graduate student at Caltech and lead author of the study.
Not only does the finding clear up the mystery of the solar system's tilt, it also provides greater evidence that Planet Nine actually exists.
"It continues to amaze us," said Dr Konstantin Batygin, an assistant professor of planetary science at Caltech.
Prof Brown and Dr Batygin discovered Planet Nine after noticing that 13 objects in the Kuiper Belt - an area beyond Pluto - were all moving together as if being 'lassoed' by the gravity of a huge object.
Scientists thought that objects in the belt - a vast region of dwarf planets and icy rocks - were influenced only by the gravitational pull of Saturn, Jupiter, Uranus and Neptune.
But they found some objects were clearly being pulled by another body - Planet Nine.
Pluto used to be regarded as the ninth planet but was downgraded in 2006 to a dwarf-planet or 'plutoid' and is now known unceremoniously as 'asteroid number 134340'. (© Daily Telegraph London)