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Astronomy

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    $\begingroup$ On the scale of 0.0002 billion years, movements of stars near the Sun is available. And interaction with siblings since the beginnings of earthly time is only one part of the equation. The other part is how the Sun might have interacted with comets (or spaceships?) from unrelated much older or younger stars, during the 16 or so times the Sun has orbited the Milky Way like once every 0.25 billion years. How frequently should mass exchanging encounters have occured, is really my question. (Wiki's lack of dates makes terms like "recently" mean little in quickly developing fields of astronomy). $\endgroup$
    – LocalFluff
    Commented Jun 2, 2014 at 15:03
  • $\begingroup$ But I think you argue that stars and their comets are most likely to have higher than capture velocity relative to the solarsystem? And for that reason they are unlikely to stick around. $\endgroup$
    – LocalFluff
    Commented Jun 2, 2014 at 15:07
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    $\begingroup$ That's my thinking. Even if perihleion were 1/2 a light year, 14 km/s Vinf would be a hyperbola of very high eccentricity -- the path would look like a straight line. That's how I modeled the paths -- as straight lines. $\endgroup$
    – HopDavid
    Commented Jun 2, 2014 at 15:12
  • $\begingroup$ It's my understanding they get the stars' distance by Parallax -- which is much more error prone as the stars go further. Radial velocity is measured by blue shift. And then distance plus angular velocity are used to get the other velocity components. So estimates are more prone to error with more distant stars. $\endgroup$
    – HopDavid
    Commented Jun 2, 2014 at 15:18
  • $\begingroup$ So distances don't say everything, it's the delta-v that matters for exchanging stuff like comets. It might as well be easier for a more distant star to happen to launch a comet our way that our Sun is more likely to trap. $\endgroup$
    – LocalFluff
    Commented Jun 2, 2014 at 15:20