Researchers say that there is strong evidence of a ninth planet in our solar system. We just do not know where it is. Update: Watch a video explaining the findings about Planet Nine.
Pluto was once called the 9th planet, but it got degraded to a dwarf planet. Now Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system.
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The object, which the scientists have nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits about 20 times farther from the sun on average than does Neptune (which orbits the sun at an average distance of 2.8 billion miles).
It would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun.
Konstantin Batygin and Mike Brown discovered the planet's existence through mathematical modeling and computer simulations. They do not know where it is and have not been able to spot it.
Update: Watch a video by Caltech's scientists explaining their discoveries about Planet Nine.
"This would be a real ninth planet," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy. "There have only been two true planets discovered since ancient times, and this would be a third. It's a pretty substantial chunk of our solar system that's still out there to be found, which is pretty exciting."
Brown says this ninth planet has around 5,000 times the mass of Pluto and all rights to be called a planet. Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the solar system.
"Although we were initially quite skeptical 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," says Batygin, an assistant professor of planetary science. "For the first time in over 150 years, there is solid evidence that the solar system's planetary census is incomplete."
Scientists have long believed that the early solar system began with four planetary cores that went on to grab all of the gas around them, forming the four gas planets: Jupiter, Saturn, Uranus, and Neptune.
Over time, collisions and ejections shaped them and moved them out to their present locations. "But there is no reason that there could not have been five cores, rather than four," says Brown. Planet Nine could represent that fifth core, and if it got too close to Jupiter or Saturn, it could have been ejected into its distant, eccentric orbit.
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The paper is titled "Evidence for a Distant Giant Planet in the Solar System" has been published in Astronomical Journal.