Is there a ninth planet out there beyond Pluto? Scientists have speculated such a celestial body since the 1850’s. And yet no one can find it.

Unexplained movement of the outer planets Jupiter and Saturn led astronomers to believe more planets were out there. They discovered Uranus and Neptune, and eventually Pluto. But they always thought one was missing even though they had no data to say where it was or why it should be there.

When astronomers started plotting the orbits of planetoids and other objects orbiting the sun beyond Neptune, they started noticing a pattern they could only explain if another planet existed far from the sun and five to ten times the size of Earth. The advent of computers allowed them to start modelling the solar system and run simulations to determine why these objects traveled the orbits they did. The results pointed to the possible existence of a planet orbiting 300-500AU distant.

However, no one has detected a planet where their modelling suggests it might be located. Many astronomers are sceptical of the existence of such a planet and suggest the patterns are the result of observation bias — the observed objects appear to have a pattern but they are just the ones we have identified in a residue belt of objects orbiting the sun in the outer solar system. If all the objects were taken into account the sum would be a random scattering of matter with no pattern.

Still, exciting stuff, and it generates enough interest for astronomers to spend time and money searching for this elusive planet.

And the planet’s name? At present it’s called Planet Nine, or Planet X as Percival Lowell called it in 1906. Other names have been suggested. Personally, I like Planet X. It has some kind of mysterious sci fi  ring to it.

But first we must find it, if it exists.