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incarnuim t1_itqkxt6 wrote

Reply to comment by PlaidBastard in If you lived on a planet in the center of the Milky Way would the nighttime be significantly brighter compared to Earth’s nighttime due to the larger concentration of stars? by bad_take_

Why would stars 860 AU away preclude planets? For comparison, Jupiter is 4-6 AU from Earth and 1e-3M(•). Jupiter gives Earth a little bit of a wiggle, but obviously doesn't preclude stable orbits. A body with M=1 M(•) only needs to be ~32 times further out to have the same gravitational effect, so 130 AU or so. Red Dwarf stars with M=0.1 or even 0.05 M(•) could be closer, roughly at the orbit of Neptune, and have little gravitational effect on a planet 1 AU from a parent star (this would technically be a binary star system, but a Far Binary, as opposed to a Close Binary system which would be more like Tatooine....)

A star 860AU away would produce practically no wiggle on a planet 1 AU from a parent star.

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cbusalex t1_itr53i5 wrote

> Why would stars 860 AU away preclude planets?

If 860 AU is the average distance between stars, and the stars are moving relative to each other, then over a long enough timeline most stars will have much closer encounters than that.

Gliese 710 is projected to pass within 0.1663 light-years of the sun within the next couple million years, 30 times closer than the 5 light-year average distance between stars in this neighborhood. If that sort of thing is typical, then you'd expect stars with an average distance of 860 AU to have occasional passes at only a few dozen AU.

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incarnuim t1_itrh0jj wrote

Possibly, but I personally don't know enough to posit the effects of that on planetary systems. Have any other stars passed that close to us over the past several million years? If not, then Gliese 710 may be an atypical event...

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Allarius1 t1_itqmko1 wrote

Isn’t that just considering the impact after planets have formed and stable orbits have already occurred?

How would the presence of the extra stars affect the formation to begin with?

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incarnuim t1_itrhaxo wrote

That's a good question, to which I have no idea.

For that matter, we could talk about capture of rogue planets too. A dense network of stars might act like something of a net for rogue planets...

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