Extract from ABC News
Updated
Photo:
An artist's impression of 'Planet Nine'. The planet is thought to be gaseous similar to Uranus and Neptune (Caltech/R. Hurt (IPAC))
Our solar system may have a ninth planet about 10 times the mass of Earth far out beyond Neptune, astronomers say.
Key points
- Computer simulations suggest ninth planet is located 20 times farther away from the Sun than Neptune
- Planet is thought to be 10 times mass of Earth, 5,000 times the mass of Pluto
- It takes 10,000 - 20,000 years to orbit the Sun
Although the planet, dubbed Planet Nine, has not been directly observed, computer simulations of the orbits of several distant objects beyond Neptune indicate it exists, scientists from the California Institute of Technology said.
"Although we were initially quite sceptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there," said Konstantin Batygin, an assistant professor of planetary science.
The new findings are reported in the Astronomical Journal.
Dwarf planets Pluto and Ceres were originally classified as planets at the time of their discovery — but were both later demoted.
But Planet Nine's mass — which is at least 5,000 times that of Pluto — and its ability to gravitationally dominate its orbit, means there should not be any debate about whether it is a true planet, Professor Mike Brown from the California Institute of Technology said.
"This would be a real ninth planet," he added.
Professor Brown said the team had been working on the discovery for the last two years.
"We noticed that the very most distant objects in our solar system ... that go out beyond Pluto they all go off in one direction, which is a very strange thing," he told the ABC.
The search is now on to spot the planet, which would take between 10,000 and 20,000 years to orbit the Sun.
Only two planets — Uranus and Neptune — have been discovered in our solar system since ancient times.
"This would be a third," Professor Brown said.
"It's a pretty substantial chunk of our solar system that's still out there to be found, which is pretty exciting."
Missing fifth planet in outer solar system
Professor Brown said astronomers had long suspected a fifth planet formed in the same region as Jupiter, Saturn, Uranus and Neptune, but it got kicked out by Jupiter and Saturn as they moved to their current orbits.
"It looks like it could be that fifth giant planet we once had and now it's hanging out in the outer parts of the neighbourhood," he said.
Planetary Scientist Dr Simon O'Toole of the Australian Astronomical Observatory said it was "perfectly reasonable" to suggest there was a planet that far out in the solar system.
"There's been talk of a planet far out there for quite a while now," said Dr O'Toole, who was not involved in the latest research.
"We don't know it's definitely there until we see it, but it would be pretty cool."
Dr O'Toole said other planets such as Neptune and Pluto were also discovered indirectly.
"Scientists discovered the planet Neptune mathematically rather than observationally when they calculated that a large mass was influencing the orbit of the planet Uranus," Dr O'Toole said.
"And Pluto was later discovered when astronomers noticed unexplained gravitational perturbations influencing the orbit of Neptune."
Eventually they found Pluto was too small to affect Neptune's orbit and have since been able to explain Neptune's orbit without the need for an additional large planet.
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