Relax: death by rogue planet kinda unlikely

As it happens, my wife and son were watching 2012 last weekend. (I was moving in and out of the room, but from what I saw, it did look every bit as silly and bad as I expected.)

Of course, I have reassured the son that it's just a silly story and the science in it is just ridiculous. He doesn't seem concerned. Now I can show him a paper by (I think) an astronomer, inspired by some of the apocalyptic theories about what might happen in 2012, with the great title:

Is it plausible to expect a close encounter of the Earth with a yet undiscovered astronomical object in the next few years?

Short answer: no.

Actually, it is interesting to note from the paper that there has been a fair bit of work on what might be lurking around in interstellar space. I was aware of "brown dwarfs" possibly being loose out there, but didn't know (or had forgotten about) the possibility of rogue planets that could unexpected wander into a solar system:

Concerning the existence of free-floating planets of smaller mass, Stevenson (1999)
noted that, under certain circumstances, Earth-sized solid bodies wandering in the
interstellar space after being ejected during the formation of their parent stellar systems may sustain forms of life. Again as a consequence of three-body interactions with Jovian gas giants, Debes & Sigurdsson (2007) have recently shown that during planet formation a non-negligible fraction of terrestrial-sized planets with lunar-sized companions will likely be ejected into interstellar space with the companion bound to the planet. Debes & Sigurdsson (2007) yield a total number of free-floating binary planets in the Galaxy as large as 7×108. At present, no planets like them have yet been detected. Proposed microlensing surveys of next generation will be sensitive to free-floating terrestrial planets (Bennett & Rhie 2002); under certain circumstances, they may be able to yield 10100 detections of Earth-mass free-floating planets (Bennett & Rhie 2002). One to a few detections could be made with all-sky IR surveys (Debes & Sigurdsson 2007).

Anyhow, the paper goes on to list the reasons why we would already know about it if something was about to zoom into the solar system by 2012.

What a relief. :)