Known objects and known impacts can be used in calculating trends, but the goal of the JPL Sentry is to assess existing objects.

As for rogue planets in the Solar System, I'll put it this way. Do you remember me mentioning the YouTube guy who made the wild claims about a nonexistent brown dwarf that was supposed to slam into the Sun last year? Well, as part of the debunking process, another YouTube user ran a gravity simulation (using Gravity 6, I think) of a brown dwarf-type mass hurtling through the neighborhood as described in this particular doomsday movement. Different circumstances yielded different results, of course, but some of them were downright comical. I can't remember exactly what happened, but the one that got used in the refutation showed something along the lines of Earth being flung into a wider orbit and Venus getting ejected from the Solar System.

Mind you, this doomsayer claimed the object had hit Jupiter before skipping on toward the inner system, so it was well within range to cause some seriousness strangeness. (Actually, his initial claim was that it had passed through Jupiter, because "Jupiter is a gas giant, it's not solid," but he changed his claim after being told that Jupiter is the most massive object around other than the Sun). Any way, the point was what it always is when dealing with Nibiru/Planet X weirdos: where is it? Why isn't it doing anything?

Anyway, the moral of the story is that gravity has very clear effects. If something of planetary or brown dwarf mass somehow plunged into our cosmic region, or even if it orbited such that it could affect any of the eight planets, we would notice in no uncertain terms.

There are no discrepancies in planetary orbits that require any significant Trans-Neptunian object to exist, insofar as I'm aware. Neptune caused some calculation oddities for years, but these were resolved by the Voyager II fly-by in 1989, which showed that the mass estimate was off by 0.5%. This doesn't mean there can't be another planet-like body out there (Eris and Pluto, for instance), but one isn't necessary to explain observables like planetary orbits.

• The jovians launched a spacecraft (which would explain why no debris have been observed yet)
• There wasn't really an impact or launch, just Jovians playing with lasers

- These where the most hilarious ones, then came the more "scientific"

• An "unknown" (with subtle hints) object caused asteroids to break loose from the cupier belt
• This same "unknown" object was in fact, which people at ATS (I think) later discovered to be Nibiru
• But, this didn't really compute to the theories of Nibiru already being in the solar system (and visible) so this didn't seem right to many

Well, that was just a few of the ones that was linked to this. Funny how simple minded the doomsayers really are. I mean, nowadays everything is tied to an impedning doomsday. For example, they say that this impact proves that something is wrong in the solar system because Jupiter isn't supposed to get hit this frequentlly.

They do not however, begin to think that perhaps our initial calculations where wrong (which seems likelly due to Jupiters gravitational pull on objects) and these impacts perhaps happen several times a year, just that we aren't able to catch them until fairlly recently. Couldn't it in fact be, just as it is with earthquakes, that we now are able to monitor these events better and thus actually would expect to see more of them? Or is there any truth to the claims that there might be an object residing in the cupier belt (or beyond) that disrupts orbital patterns of asteroids etc? Not Nibiru then, but something other…

I also have an idea about how to unite the Nibiruians on the characteristics. Simply start a forum for them where they can vote on how Nibiru is supposed to look/behave and where it is supposed to be. By doing so, we might finally be able to pinpoint this mysterious planet… Or not=)

But on a more serious note, I found this article: http://www.technologyreview.com/blog/arxiv/25191/ regarding the increased impact probability for Jupiter. I just didn't see how they reached the conclusion that we automatically would be more impact-prone just because Jupiter might be? Wouldn't it be the other way around? If Jupiter "absorbs" objects in a higher rate than previously thought then we would se less close aproaches then we previously thought, right? Finally, isn't the NEA risk assesment based on observations, rather than calculations?