[Space] Binary star trojans

[RyanW]

Would there be any reason you couldn't get a planetary sized body orbiting the L4 or L5 points in a binary star system?

Would be an interesting way to get a potentially habitable planet in a binary star system. The seasons would be due to the orbit approaching and receding from the smaller of the two stars.

[lexington]

Physics isn't my strong suit but I'm fairly certain you can't orbit any Lagrange point, given that it isn't exerting a pull on objects near it.

[Agemegos]

Originally Posted by RyanW

Would there be any reason you couldn't get a planetary sized body orbiting the L4 or L5 points in a binary star system?

The L4 and L5 points are only stable if the ratio of the masses of the two stars is greater than about 25. You would need one fairly massively star with a low-mass companion. And since stellar luminosity increases sharply with mass, insolation from the smaller companion will be negligible. What you want is a mid-F star with an M9 or brown dwarf companion in its habitable zone.

Would be an interesting way to get a potentially habitable planet in a binary star system. The seasons would be due to the orbit approaching and receding from the smaller of the two stars.

Well, if the orbit of the two stars about each other is circular then the L points maintain a constant distance from both. Whereas if that orbit is eccentric the L trajectories are similar to the orbits of the stars around the barycentre, which means that the planet will vary in distance from both stars by the same proportion.

[Agemegos]

Originally Posted by lexington

Physics isn't my strong suit but I'm fairly certain you can't orbit any Lagrange point, given that it isn't exerting a pull on objects near it.

Well, it turns out that there are orbits for a test mass in a two-body system that have the same period as the orbit of the two main bodies but which aren't similar to the orbits of the main bodies about the barycentre. In the co-rotating frame of reference these look like loops (often distorted loops) around empty points. There is a family of such "halo orbits" around L1, L2, and L3, which are truly periodic, and there are so-called "Lissajous orbits" around all of the L points, though those are only quasi-periodic and not really stable.

Look up "horseshoe orbit" and "tadpole orbit".

[lexington]

Originally Posted by Brett

Well, it turns out that there are orbits for a test mass in a two-body system that have the same period as the orbit of the two main bodies but which aren't similar to the orbits of the main bodies about the barycentre. In the co-rotating frame of reference these look like loops (often distorted loops) around empty points. There is a family of such "halo orbits" around L1, L2, and L3, which are truly periodic, and there are so-called "Lissajous orbits" around all of the L points, though those are only quasi-periodic and not really stable.

Look up "horseshoe orbit" and "tadpole orbit".

Hey, that's pretty cool. It seems like a designed system (assuming unlimited resources for fun) could put an object in orbit that maintains an certain level of artificial gravity due to the constant acceleration/deceleration of its orbit.

[Agemegos]

Originally Posted by lexington

Hey, that's pretty cool. It seems like a designed system (assuming unlimited resources for fun) could put an object in orbit that maintains an certain level of artificial gravity due to the constant acceleration/deceleration of its orbit.

Well, orbits are free-fall trajectories: an orbiting body accelerates, but only as directed by gravity, and that accelerates all masses equally. The planet and the things on its surface follow the same trajectory (and a good thing too!), so you'll get small effects similar to tides but no gross 'artificial gravity' effects. Unless you wander inside something's Roche limit.

[lexington]

Originally Posted by Brett

Well, orbits are free-fall trajectories: an orbiting body accelerates, but only as directed by gravity, and that accelerates all masses equally. The planet and the things on its surface follow the same trajectory (and a good thing too!), so you'll get small effects similar to tides but no gross 'artificial gravity' effects. Unless you wander inside something's Roche limit.

Ah well, good thing I'm not an engineer.