The chance it is just a coincidence, they make one in 15,000, or three sigma - the point where you think there may be something in it.

So, if you had just the one hypothesis ever, and got only a 1 in 15,000 chance that it doesn't exist, that's a near certainty.

But if you have thousands of astronomers searching for things then from time to time some of them are bound to hit on a 1 in 15,000 chance just by chance.

So you are bound to get a few results of similar probability to this from time to time. Though individually they seem very likely if you are the astronomer who came to this conclusion, when you take into account all the other astronomers looking and the number of hypotheses each one considers in a lifetime - it's not so impressive as it seems at first. That's why they are not saying "We have proved it", but are being professionally cautious about it, although it may seem at first like a near certainty. You might think they should just say it exists, with, on the face of it, a 99.993% certainty that it exists, but that's not how it works in science.

In particle physics, where the experiments generate huge amounts of data, 3 sigma results are common and are often just clusters, patterns in the noise. Collect enough data and you are bound to see 3 sigma results from time to time even if the data is random. They aim for 5 sigma for discovery.

Still it's intriguing and they claim it's the most likely planet X to date.

Also, our most sensitive wide field telescope able to search for planets at this distance, the Subaru telescope, has a decent chance of finding it if it exists.

The Subaru telescope, on Mount Kea in Hawaii, with a wide field of view and sensitive to faint sources, probably has best chance of spotting this new Planet X.

They say it will take about five years to search most of the area it could be hiding in see: Astronomers say a Neptune-sized planet lurks beyond Pluto

- This is an extract from my new article on Science20: Why This New "Planet X" Is No Threat To Earth :).