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Really? Considering how many bodies orbit our Sun, I would have thought 5-10 would be a good average.
by Esau 10y ago
Really? Considering how many bodies orbit our Sun, I would have thought 5-10 would be a good average.
- mortenjorck 10y agoThis Quora answer (https://www.quora.com/What-is-the-average-number-of-planets-per-star https://www.quora.com/What-is-the-average-number-of-planets-...) takes a dataset of 2560 stars and comes out with an average of 1.3 planets per star. As the author caveats, this is an extremely small sample and probably not accurate, but it's something to start from.
- _red 10y agoCaveat+: No one yet knows if we can even reliably count the planets of a distant star, so the figures could be off by some significant amount. Caveat++: That light reaching earth from far away galaxies was then, this is now.
- flukus 10y agoCaveat+++: We're also interested in moons, which I don't think have been detected yet.
- Razengan 10y agoCaveat++++: Factor in rogue planets that don't orbit any stars, or large asteroids drifting through nebulas etc... I'm sure the number of solid bodies — potential habitats for life or artificial constructs — in our universe is magnitudes larger than the number of stars we've detected, and the latter is already a mind boggling quantity.
- Esau 10y agoThanks.
- BurningFrog 10y agoThe way we detect planets only detect some of them. The best method is to notice when a planet passes in front of its star, by how it gets slightly dimmer. That only works if its orbit happens to be directly between us and that star.
- aruss 10y agoWe can also detect them by a Doppler shift of the star, because the planet (if big enough) will move the star as it orbits. This works when the transit method fails, but provides fewer data on the planet itself.
- SAI_Peregrinus 10y agoIt also only works for big enough planets close enough to the star.
- BurningFrog 10y agoDoesn't work when the orbit is perpendicular to our sight line either.
- saiya-jin 10y agothis would not show any planets beyond saturn for solar system, for example
- MPSimmons 10y agoI would tend to agree. The effective gravitational influence of a star would be relative to its mass. We can pretty easily determine the (rough) mass of a star, and ours appears(?) to be somewhere in the middle, so it stands to reason that 8-ish decently sized planets is not an unreasonable number.
- onion2k 10y agoExtrapolating from a single example? There's an XKCD for that: https://xkcd.com/605/ https://xkcd.com/605/