Back in 1933 Philip Wylie and Edwin Balmer published a science fiction novel titled When Worlds Collide about a loose planet (actually a pair of them) wandering into our solar system. (George Pal produced a film version in 1951) The existence of freely wandering planets, not associated with any solar system, has long been suspected, and in fact if you’ve ever played with a simple simulation of a multi-planet solar systems you know it’s not unusual to have planets ejected to parts unknown. But as far as I know there’s never been any actual evidence of such planets’ existence.
Until now, that is. Gravity bends light, and even planets can bend it enough to create detectable optical effects. Taking advantage of that, an international team of astronomers has found ten planets, each roughly the size of Jupiter, that appear to be wandering loose in the galaxy. Here’s a report from BBC News.
(Incidentally, the word planet itself comes from a Greek word meaning “wanderer,” because the planets don’t stay in more or less the same relative arrangement in the sky like the stars but rather change positions against the background. The Sun and Moon were classified as “planets” by the ancients.)
None of the planets indirectly observed is anywhere near our region of space, but I’m sure some will take the news as evidence for the fictitious rogue planet popularized by cranks and usually called “Niburu” after a term in Babylonian astronomy, or for an allegedly different crank-promoted non-existent body called Planet X. Here’s a Space.com article on the pseudoscience.