Planet Nine

Planet Nine

Astronomers have proposed a ninth planet for our solar system, and it’s not Pluto. Caltech researchers Michael Brown and Konstantin Batygin believe there is a massive planet orbiting the Sun about 93 million miles away at its furthest point in the orbit.

Brown has previously discovered other significant objects, such as Sedna in 2003 and Eris in 2005, in distant regions of the solar system called the Kuiper Belt and the even more remote Oort Cloud. It was discoveries such as these that prompted the International Astronomical Union (IAU) in 2006 to define planets in a way that expelled Pluto, a demotion favored by Brown.

In 2014 Chadwick Trujillo and Scott Sheppard published a paper regarding an inner Oort Cloud object, 2012 VP113, with its perihelion (the closest point in the orbit) at approximately 80 AU. More significantly, though, in their discussion they suggested a potential super-Earth-mass body to be a gravitational perturber and had mathematically simulated the effects of such at 250 AU (Trujillo & Sheppard, 2014). Brown and Batygin set out to disprove this hypothesis, but instead found evidence that supported Trujillo and Scott. In a January 2016 paper published in The Astronomical Journal, “Evidence for a distant planet in the solar system,” they too proposed a massive gravitational perturber, a new planet, which is responsible for the orbits of numerous other bodies in this region of the solar system (Batygin & Brown, 2016).

These orbits were found to be explainable by the influence of a distant planet with a mass more than 10 times the mass of the Earth.

The orbits of a number of bodies were found to cluster at perihelion, having similar ellipses tilted 30 degrees in the same direction with regard to the eight main planets. This was given only a 0.007% chance of occurring without the gravitational influence of a significantly more massive object. These orbits were found to be explainable by the influence of a distant planet with a mass more than 10 times the mass of the Earth. Such a planet could also give reason for the orbits of certain other Sedna-like objects beyond Neptune in the Kuiper Belt (Batygin & Brown, 2016).

If verified, the IAU will officially name the new planet according to established criteria. For now, though, Batygin and Brown have nick-named the body “Planet Nine” and have set out to find it. Its orbit is roughly known, but not its position on that orbit—an ellipse potentially so large that it could take the planet as many as 20,000 Earth-years to circle the Sun just once. The massive planet would be the 5th largest in our solar system, after Jupiter, Saturn, Uranus and Neptune.  It is thought to be icy, rocky, and it may contain a small gaseous atmosphere (Batygin & Brown, 2016).

Pluto is not massive enough to have the gravitational force necessary to clear its orbit of other objects, one of the primary characteristics necessary to be a planet. Planet Nine, though, at 5000 times the mass of Pluto, will clear its path, changing the orbits of other objects while gravitationally dominating its part of the solar system. When confirmed, this will give us a ninth planet once more.

Brown estimates a 90% chance that Planet Nine exists and states it will definitely meet all planetary criteria. He and Batygin continue their search, but also hope their publication of what they have determined so far will inspire other astronomers at some of the most powerful telescopes to search as well. Brown would like to make the confirmation himself, but even more so he simply wants Planet Nine to be found by someone. He hopes the proof will come soon (Achenbach & Feltman, 2016).


Achenbach, J., & Feltman, R. (2016, January 20). New evidence suggests a ninth planet lurking at the edge of the solar system. The Washington Post.
Batygin, K., & Brown, M. E. (2016). Evidence for a distant giant planet in the solar system. The Astronomical Journal, 151(2), 22.
Trujillo, C. A., & Sheppard, S. S. (2014). A Sedna-like body with a perihelion of 80 astronomical units. Nature, 507(7493), 471-474.

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Steven Gullberg, Ph.D.

Dr. Steve Gullberg is an Assistant Professor of Interdisciplinary Studies and Aviation for the University of Oklahoma College of Professional and Continuing Studies. He is a retired airline captain, a long-time adjunct instructor for the College of Professional and Continuing Studies, and an active member in the International Astronomical Union.