Ninth planet - what else could it be? So recently it was announced that there might be a ninth planet out there.

Some people (from NASA) say the odds are 50% that it is a real planet, since it hasn't been discovered by telescopes yet.

Let's say there is no ninth planet. Is there another explanation for those orbits that require a big mass (8 times earth mass) out there?

Could it even be a very small black hole (a few centimeters in radius) or maybe a clump of dark matter?
What else could it be?  Very simply, it could all be a coincidence...

What they have done is noted that objects in the outer solar system have their orbits grouped in interesting ways. Someone suggested this might indicate there was a heavy planet (or core of a giant protoplanet) that influenced their orbits in this way; the recent announcement is the result of examining this idea in detail.  It is likely to be caused by gravitational influence of such a body.

Of course the TV and newspapers have picked this up and said a planet HAS been discovered. But there might be nothing at all; the loose clustering could all be a coincidence - though that seems, statistically, unlikely at the moment.

Here is the paper for anyone who wants to check.  (Beware, lots of mathematical terminology.)