Binary Star capturing a object.

[fredinno]

Let's just assume a dwarf planet in an elliptical orbit from the galactic core goes into a binary star system. One star is Solar Mass, the other is a red dwarf the size of Proxima Centauri. Could the Dwarf planet go into a Orbit around the larger star by transferring momentum to the smaller star, or the other way around?

 

The stars are binary, which is why this is a problem.

Edited March 24, 2016 by fredinno

[Steel]

In theory, yes, so long as a long list of conditions about the planet's trajectory, relative velocity, mass e.t.c are fulfilled.

It would also depend on the binary system, i.e. is it a "close binary" system or is the smaller star on an orbit further out

[fredinno]

8 hours ago, Steel said:

In theory, yes, so long as a long list of conditions about the planet's trajectory, relative velocity, mass e.t.c are fulfilled.

It would also depend on the binary system, i.e. is it a "close binary" system or is the smaller star on an orbit further out

Farther out.

[HebaruSan]

Sounds a little like this scenario done in the Principia mod. The main difference I see is that your planet presumably starts out on an escape trajectory from the overall system, whereas this craft remains stably in Kerbin's SOI.

 

[fredinno]

9 minutes ago, HebaruSan said:

Sounds a little like this scenario done in the Principia mod. The main difference I see is that your planet presumably starts out on an escape trajectory from the overall system, whereas this craft remains stably in Kerbin's SOI.

 

But the moon is not binary to the Earth...

[HebaruSan]

1 minute ago, fredinno said:

But the moon is not binary to the Earth...

I'm finding conflicting definitions as to whether this is the case or whether it hurts the analogy. On the one hand, a binary planet system seems to require a barycenter outside of either body, so Earth-Moon would not qualify. On the other hand, a binary star system does not have that requirement, so a scaled-up version of the above scenario using stars instead of planets and moons would still count as capturing a body around one member of a binary star system. I think the question of dealing with escape velocity is still the bigger issue.

[fredinno]

36 minutes ago, HebaruSan said:

I'm finding conflicting definitions as to whether this is the case or whether it hurts the analogy. On the one hand, a binary planet system seems to require a barycenter outside of either body, so Earth-Moon would not qualify. On the other hand, a binary star system does not have that requirement, so a scaled-up version of the above scenario using stars instead of planets and moons would still count as capturing a body around one member of a binary star system. I think the question of dealing with escape velocity is still the bigger issue.

I was thinking about a barycenter outside either star. But if the object got closer to the Sun-like star than 0.14 AU, and got enough of a gravity assist, it should be able to get to orbit around the smaller red dwarf? Or is that not how things work?

[Snark]

A binary system could certainly capture a planet, if the velocities work out right.  Doesn't matter whether it's a close binary or far apart, it's the same problem just acted out on a different scale.

However, it would be just as likely to eject the planet, especially considering that it's not like the planet would be captured into a small tight orbit around one of the stars.  Are you looking for a scenario where the planet gets captured "permanently" and sticks around for millions of years?  Or just getting captured for a "while" until an unlucky pass by one of the stars ejects it from the system again?

The former would be unlikely, the latter is plausible.

[Rune]

40 minutes ago, Snark said:

A binary system could certainly capture a planet, if the velocities work out right.  Doesn't matter whether it's a close binary or far apart, it's the same problem just acted out on a different scale.

However, it would be just as likely to eject the planet, especially considering that it's not like the planet would be captured into a small tight orbit around one of the stars.  Are you looking for a scenario where the planet gets captured "permanently" and sticks around for millions of years?  Or just getting captured for a "while" until an unlucky pass by one of the stars ejects it from the system again?

The former would be unlikely, the latter is plausible.

Exactly, when you handle more than one body, pretty much everything is possible with a big enough gravity well.

@fredinno, the trick for gravity assists to exist is to have more than one body, so that an orbit around a primary can be affected by the secondary... any system with two masses would work, and the larger the second mass is, the greater the potential for free dV. If your secondary objet is a freaking star, no matter how small, you dV potential must be on the order of tens or even hundreds of km/s, if you pass close enough to it. I mean, the Sun-Jupiter system can already fling you outside the solar system with escape velocity, as proven by the Voyagers...

 

Rune. Now, the odds of any given final orbit? Tiny, of course, especially around a binary system that already imposes a lot of restrictions on stable orbits.

[fredinno]

52 minutes ago, Snark said:

A binary system could certainly capture a planet, if the velocities work out right.  Doesn't matter whether it's a close binary or far apart, it's the same problem just acted out on a different scale.

However, it would be just as likely to eject the planet, especially considering that it's not like the planet would be captured into a small tight orbit around one of the stars.  Are you looking for a scenario where the planet gets captured "permanently" and sticks around for millions of years?  Or just getting captured for a "while" until an unlucky pass by one of the stars ejects it from the system again?

The former would be unlikely, the latter is plausible.

The former. I would want the planet to end up in the orbit of the smaller star, into an permanent elliptical orbit during the early solar system's formation.

6 minutes ago, Rune said:

Exactly, when you handle more than one body, pretty much everything is possible with a big enough gravity well.

@fredinno, the trick for gravity assists to exist is to have more than one body, so that an orbit around a primary can be affected by the secondary... any system with two masses would work, and the larger the second mass is, the greater the potential for free dV. If your secondary objet is a freaking star, no matter how small, you dV potential must be on the order of tens or even hundreds of km/s, if you pass close enough to it. I mean, the Sun-Jupiter system can already fling you outside the solar system with escape velocity, as proven by the Voyagers...

 

Rune. Now, the odds of any given final orbit? Tiny, of course, especially around a binary system that already imposes a lot of restrictions on stable orbits.

The binarys are supposed to be at least 0.3ly apart at all times. And the object is initially at escape velocity, it needs to go down to an elliptical "short period" comet-esque orbit, like 67P, around the smaller star.

[Rune]

7 minutes ago, fredinno said:

The former. I would want the planet to end up in the orbit of the smaller star, into an permanent elliptical orbit during the early solar system's formation.

The binarys are supposed to be at least 0.3ly apart at all times. And the object is initially at escape velocity, it needs to go down to an elliptical "short period" comet-esque orbit, like 67P, around the smaller star.

That's trickier. I mean, "simple" gravity assists only work on the orbit around the primaries, meaning you could get a low Pe orbit over the primary crossing into the secondary's, and perturbations eventually settle it into a resonant orbit (those are very stable over long periods), but stopping around the secondary means either something very complicated, and therefore unlikely (capture around the primary, but re-captured by the secondary later?), or a third body, so the gravity assist can happen entirely in the secondary's Hill sphere, involving the secondary and a tertiary object. Again, less likely but not impossible I think.

 

Rune. If it's for a story tough, you could always claim "one in a gazillion" and be golden, something like that must have happened somewhere.

[Snark]

34 minutes ago, fredinno said:

The former. I would want the planet to end up in the orbit of the smaller star, into an permanent elliptical orbit during the early solar system's formation.

Yeah, that seems pretty unlikely to happen, especially with a planet coming in at interstellar velocities.

Maybe not impossible, but seems improbable to me.

[YNM]

That depends on the relative velocity during encounter - it could be, but having rogue planets is a more harder thing in the first place. Not to mention the object probably will just end up in a comet-like orbit.

[pincushionman]

35 minutes ago, fredinno said:

The former. I would want the planet to end up in the orbit of the smaller star, into an permanent elliptical orbit during the early solar system's formation…

Key information here. This implies other planets' worth of mass flying around, and giver "early" it is going to be all over the place. Capture chances go up, ejection chances go up, destsbilization chances go up, collision chances go up. Going to be very chaotic.

[fredinno]

4 hours ago, Rune said:

That's trickier. I mean, "simple" gravity assists only work on the orbit around the primaries, meaning you could get a low Pe orbit over the primary crossing into the secondary's, and perturbations eventually settle it into a resonant orbit (those are very stable over long periods), but stopping around the secondary means either something very complicated, and therefore unlikely (capture around the primary, but re-captured by the secondary later?), or a third body, so the gravity assist can happen entirely in the secondary's Hill sphere, involving the secondary and a tertiary object. Again, less likely but not impossible I think.

 

Rune. If it's for a story tough, you could always claim "one in a gazillion" and be golden, something like that must have happened somewhere.

So it would be more reasonable to have the secondary do a gravity assist, then have the resulting orbit the primary?

3 hours ago, pincushionman said:

Key information here. This implies other planets' worth of mass flying around, and giver "early" it is going to be all over the place. Capture chances go up, ejection chances go up, destsbilization chances go up, collision chances go up. Going to be very chaotic.

So do it later in the formation? Seems like that would be a better option.

[pincushionman]

7 hours ago, fredinno said:

So do it later in the formation? Seems like that would be a better option.

Probably earlier. Because you're probably getting some of the capture assist from the other star, you need to get the orbit dragged down in relatively short order to avoid ejection by the same. That means close encounters with the various other protoplanetary objects already in the system which, if there are more, happen more often.

Your rogue body will have to be very lucky  to get most of these interactions to be orbit-closing, but not collisions. You'll have to sacrifice some of your "native" bodies to pull it off.

[fredinno]

6 hours ago, pincushionman said:

Probably earlier. Because you're probably getting some of the capture assist from the other star, you need to get the orbit dragged down in relatively short order to avoid ejection by the same. That means close encounters with the various other protoplanetary objects already in the system which, if there are more, happen more often.

Your rogue body will have to be very lucky  to get most of these interactions to be orbit-closing, but not collisions. You'll have to sacrifice some of your "native" bodies to pull it off.

Why? The Dwarf planet is only 0.3 Lunas. If it was 0.1 Lunas would it be more reasonable? Also, I guess I should put it in the late solar system formation period so that it can get enough gravity assists to get into a stable orbit, but not disturbing the other, already existing planets enough due to the relatively low mass.