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How much do we really know about other planetary systems? When I last looked into it, most of those planets were discovered via the transit method by the Kepler satellite. That means we're looking at periodic dips in the light from another star. Kepler didn't operate for very long, and so we only have information about very close-orbiting planets.

Also, I think we only called something a planet if the dips could be measured as having a definite period. (Otherwise it could easily be a sunspot or other chaotic event). That by definition restricts our detections to planets that have unvarying orbits (to within the precision of the transit method)!

There are a few weird stars where we see fluctuations that look random, but the "norm" (tongue in cheek given the limitations of our methods) seems to be very closely packed systems around class M stars.


You're quite correct, MadRocketSci. We still don't know much about other planetary systems. As I said above the bear picture, our best methods are biased toward weird systems.

Expanding on your remarks a little: obviously dips in brightness can only be attributed to a planet if they show a regular cycle. This means a strong bias in favor of worlds close to the parent star. You'd have to observe for several centuries to detect Saturn that way. Even Jupiter would take a few decades to nail down.

However I don't think there are many planets with variable periods as you suggest. It's hard to see how that arrangement could last very long on a stellar time scale. I'm sure a physicist could model some system where a planet has a resonant orbit with some other body in the solar system such that it alternates long and short years, but that would likely be an almost unique phenomenon.

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