Planet Nine: Researchers Find Evidence of a Giant Planet Beyond Pluto

January 20, 2016 | Joanne Kennell

This artist's conception illustrates a Jupiter-like planet alone in the dark of space, floating freely without a parent star.
Photo credit: NASA/JPL-Caltech

Its orbit is so large it would take nearly 20,000 years to go around the sun once.

This is so exciting!  Researchers from Caltech may have found evidence of a giant planet in the outer region of our solar system.  The last discoveries of real planets orbiting our sun were Pluto (now considered a dwarf planet) back in 1930 and Neptune in 1846.

The object, nicknamed Planet Nine by researchers Konstantin Batygin and Mike Brown, has a very bizarre and extremely elongated orbit, a mass nearly 10 times that of Earth, and orbits the sun about 300 times farther on average than Earth.  In fact, it would take this new planet between 10,000 and 20,000 years to make one full orbit around the sun.

This potential planet was discovered through mathematical modeling and computer simulations — meaning it has not yet been directly observed.  However, the researchers are optimistic.

SEE ALSO: How Pluto Lost it All

“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 is not worried about whether this planet would be considered a true planet — it is 5,000 times the mass of Pluto.  To be considered a planet, the criteria are as follows:

  1. It is in orbit around the sun

  2. It has sufficient mass to form a nearly round shape

  3. It has "cleared the neighborhood" around its orbit

Unfortunately for Pluto, it did not meet the third criterion and was deemed a dwarf planet in August 2006.  Planet Nine, on the other hand, dominates its neighborhood of the solar system.  In fact, it dominates a region larger than all of the other planets in our solar system.  In a press release, Brown calls it “the most planet-y of the planets in the whole solar system.”

Like many discoveries throughout history, Planet Nine was found by accident.  When they ran their simulations with a large planet in an anti-aligned orbit — an orbit in which the planet’s closest approach (perihelion) to the sun is 180 degrees across from the perihelion of all the other objects and known planets — objects in the Kuiper Belt, located between Neptune and Pluto, aligned in the way that is observed.

Not only does Planet Nine help explain the orientation of Kuiper belt objects, it also explains movement of the mysterious objects, Sedna and Biden, which have peculiar orbits around the sun.  Researchers believe the gravity of Planet Nine explains these orbits.

However, the real surprise came when the researchers realized that their simulations also predicted that there would be objects in the Kuiper Belt with orbits inclined perpendicular to the plane of the planets.  In fact, over the last three years, four objects have been observed with this particular orbit — matching their simulations exactly.

“When the simulation aligned the distant Kuiper Belt objects and created objects like Sedna, we thought this is kind of awesome—you kill two birds with one stone,” says Batygin, an assistant professor of planetary science.  “But with the existence of the planet also explaining these perpendicular orbits, not only do you kill two birds, you also take down a bird that you didn't realize was sitting in a nearby tree.”

Brown, well known for the role he played in the demotion of Pluto to a dwarf planet adds, “All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found,” he says.  “Now we can go and find this planet and make the solar system have nine planets once again.”

Okay, maybe we can forgive him.

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