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Name: Chris
Status: Student
Grade: 9-12
Location: IL
Country: USA
Date: Winter 2011-2912


Question:
Is it possible for a planet to have two stars close enough to it for both of the stars to be considered suns of the planet? If so, what would the planet's orbit look like: would the planet travel in an elliptical orbit around one sun or in a figure eight around both?


Replies:
Dear Chris,

It is possible, and even likely, that planets orbit double stars. However, a figure eight orbit has to involve two suns that are a special distance from one another. Generally the planet will orbit both suns at once in an elliptical orbit. Sun tans!

Sincerely David H. Levy


Chris,

While it is certainly within the realm of possibility, it is highly unlikely. In order to form a stable "figure 8" orbit, several things have to happen exactly: (1) when the planet enters the "gravitational midpoint" between the two stars it must "switch" to the other star, (2) it must do this every single time it enters the gravitational midpoint, (3) when it switches over, the planet must then enter into a stable orbit around that star. Any deviations from this and the planet would either be ejected from the solar system or crash into the star. While it is possible that a 3-body system can form stable orbits with one body doing a figure 8, the initial conditions are so precise that having this happen by chance during the creation of the solar system is very highly unlikely.

Have some fun: go to http://phet.colorado.edu/en/simulation/my-solar-system and play with the simulation. Try different masses, distances, and starting velocities in a 3-body system.

Greg (Roberto Gregorius) Canisius College



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