Hey Domeman,<br>When I was of single-digit age, our family's 1960's encyclopedia explained how the solar system was laid out and said that the planets would all line up sometime (I forget now) before the end of the century, and how the gravitational pull of all the planets lined up would likely cause all the tectonic plates to shift, causing unprecedented simultaneous earthquakes and volcano eruptions all over the globe. This was our encyclopedia. Well, there was a planetary convergence, sure enough, and absolutely nothing happened.<br>I also, again as a child, read, again in this same encyclopedia, about how scientists had recently discovered a new planet. This planet was called ... Pluto! So, we now knew, as of 1930, that there were nine planets, rather than the eight that science had identified up until then.<br>Of course, Pluto was downgraded, a few years back, from a "planet" to a mere "trans-neptunian object", so we went back to only having eight planets in our solar system. Does that mean that the tenth planet would only then have been the real ninth planet? Except that Pluto was soon then upgraded back to being a real planet again. So, does that mean that if our former tenth planet had now then become the ninth, then Pluto, when it got upgraded again, became our new tenth?<br>Of course not, because we're listing them in order of distance from the sun, not order of discovery.<br>But then, when I was in eighth grade, Pluto and Neptune switched places. Neptune became the farthest planet out. So, Pluto became the eighth planet and Neptune became the ninth. Not that that would have changed the tenth planet's ranking as actually the ninth when Pluto became a trans-neptunian object instead of a planet, but it would have made Neptune the eighth planet again, even though it was supposed to now be the ninth. Boy, I'm sure glad that Pluto and Neptune switched places back to the way they're supposed to be before that whole downgrade/upgrade thing happened with Pluto. Otherwise, it might have gotten confusing...<br>Seriously, there are a whole lot of big chunks of stuff out there. If their orbit is circular enough, we call them asteroids. If their orbits are eliptical enough, we usually prefer to call them comets. You can say that comets are ice and planets are rock, but that's not really true, either, as a lot of moons, asteroids, and possibly a planet or two are actually mostly or all ice, and comets are only mostly ice because they're so far out. If they were closer, they'd be rocks with water, sort of like Earth.<br>We're still learning so much. And the argument over what the definition of a "planet" rages on ... with Pluto's ultimate categorization hanging in the balance. Is it a planet or not? It has a moon, but then, so do some other moons, and even some asteroids have moons...<br>Here's the point: we're still learning so much. For anyone to say, "We've only just now discovered a brand new planet/comet/asteroid/whatever, and we already know that precisely this series of events will occur, at this exact angle and for this number of days and in this specific order" is not possible. We don't begin to know enough to predict that kind of stuff! And as for guessing population casualty rates? That's just not even close to remotely possible! Remember, my encyclopedia told me the late 20th century planetary convergence was going to cause global catastrophe, and what we actually got was a measurable 0% increase in tectonic activity. (Oh well, maybe next time...)<br>For what it's worth, there is more than just one "tenth" something out there. There is a whole bunch of stuff out past Pluto. And we're still learning all sorts of stuff about the fuzzy edges of our solar system all the time. This link has some cool information on hypothetical planets, including the search for trans-neptunian objects (with the resultant finding of Pluto) and trans-plutonian objects (with the current failure to find anything other than asteroids/comets). It may prove helpful, or at least interesting.