An artist's conception of 2003 UB313
(c)2005 Tony Dunn

The 10th Planet

In July 2005, Caltech astronomer, Mike Brown announced the discovery of our solar system's "10th Planet." The simulation TNO.gsim uses numbers generated by JPL Horizons Ephemeris Computation Service . It shows the "planet" 2003 UB313 orbiting the Sun beyond the orbits of Neptune and Pluto. This simulation also contains two other recently-discovered bodies slightly smaller than Pluto. 2003 EL61 and 2005 FY9 also orbit the Sun in the vicinity of Pluto. For perspective, the outer planets and Quaoar and Sedna, two large Trans-Neptunian Objects slightly smaller than Pluto, are also included.

2003 UB313 has revived the debate about whether Pluto should be considered a planet.


2003 UB313 seems to be in a 17:5 resonance with Neptune. The following screen shot uses a rotating frame to illustrate this resonance.

Unlike the 3:2 resonance that Pluto shares with Neptune, 2003 UB313's resonance appears to be very precise. At any given instant Pluto is orbiting a little too fast or too slow for a perfect 3:2 resonance. But Neptune's influence speeds up Pluto by a small amount at times, and slows it down at other times, ensuring that its resonance averages exactly 3:2 over long periods of time. This helps to ensure that they will never collide.

But 2003 UB313's resonance with Neptune is nearly perfect. Is it a coincidence that 2003 UB313's orbit is in such a perfect resonance with the orbit of Neptune? If an outside influence were to perturb this resonance, would Neptune's influence ensure that the resonance was not broken?

To find out, I perturbed the orbit of 2003 UB313 by boosting its orbital velocity by 1 meter per second at perihelion. This was just enough to destroy the perfect 17:5 resonance. But Neptune provided enough influence to ensure that 2003 UB313's resonance continued to average exactly 17:5 over long periods of time. As 2003 UB313 travels a little too fast and its perihelion begins to advance on Neptune's position, Neptune pulls it into a slightly slower orbit. It's perihelion now recedes from Neptune until its perihelion begins approaching Neptune from the other side. Neptune then pulls it into a slightly faster orbit causing it to retreat once more. This repeats indefinitely. Neptune and 2003 UB313 are locked in their 17:5 resonance.

This animation shows how 2003 UB313 's resonance with Neptune oscilates after being perturbed by only 1 meter per second.

To simulate this resonance yourself, download the simulation NeptuneUB313.gsim.

(You need to have the program Gravity Simulator installed on your computer first. Click Here to download Gravity Simulator.)


2005 FY9 also seems to be in an 11:6 resonance with Neptune. Its repeating pattern also seems to suggest it is locked in this resonance.

To simulate this resonance yourself, download the simulation neptuneFY9.gsim.

Download TNO.gsim

(You need to have the program Gravity Simulator installed on your computer first. Click Here to download Gravity Simulator.)