Earlier this week a schoolgirl from Montana won a National Geographic contest to think of a mnemonic that could be used to memorize the 11 planets of the solar system. Unfortunately for Maryn Smith her fame could be short lived, because it seems that there is yet another mystery planet hiding in the nether reaches of the solar system.

Let’s recap a minute. There used to be nine planets. Everyone was certain about that, but no one actually knew what a “planet” was, because it had never been defined. Then came Eris. The planet named after the goddess of chaos is the astronomical body formerly known as UB313 and Xena. It is a little larger than Pluto, and its discovery led to a massive fuss that even resulted in angry exchanges on the debating floor at the World Science Fiction Society’s Business Meeting during the 2006 Worldcon. Eris, it turned out, was bigger than Pluto, and therefore had to be classified as a planet. But poor old Pluto, tail between his legs, was in danger of being sent to the solar system’s doghouse – planet no more.

After much debate the International Astronomical Union came up with a compromise proposal under which Pluto could stay, but only as a “dwarf planet“. There are now eight proper planets, and three dwarves, Pluto and Eris having been joined by Ceres, the largest body in the asteroid belt. Hence Maryn Smith’s mnemonic: My Very Exciting Magic Carpet Just Sailed Under Nine Palace Elephants (or Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto and Eris.).

But wait! Scientists at Kobe University in Japan believe that they have found compelling evidence for the existence of a twelfth planet, out beyond the orbits of Pluto and Eris. What is more, they believe that it may be up to 70% of the size of Earth, making it a proper planet. They haven’t actually sighted anything yet, but their computer simulations tell them that something massive must be out there. They believe that it is only a matter of time before a new member of our celestial family is welcomed into the fold.

And that, of course, will mean we need to find a name for the new body. It will, if discovered, become the twelfth planet of the solar system. That is a well documented world. Science fiction fans have known that it exists for decades. It was first mentioned in a BBC television program in 1963, and its name is Skaro.

Oh, and while I’m here, there must be another four dwarf planets to be discovered, right? Everyone knows that.