... Moon . ... solar system . ... Year of Pluto . ... Two Plutos collide in the outer solar system. ... But what are the odds of such a collision happening at the solar system s frontier, where only Pluto and its moon were then known to exist? ... His findings suggested that, given our vast solar system and only two Plutos, the chances of a collision are less than one in a million over all of our solar system s history. ... Only registered members of Astronomy.com are allowed to comment on this article....