# Planets around twin stars

1. Oct 23, 2004

### JV

It seems that planets can not exists around twin-stars or even triple-stars. I mean that the planet orbits both stars, and not just one of the two/three.
Why is that? The planet can just circle around the centre of gravity, what is so special about a twin or triple-star system?

2. Oct 23, 2004

Staff Emeritus
The cyclical perturbations from two or more heavy masses in the gravitational system would prevent a stable orbit. Notice that cyclical perturbations from Jupiter shows up in the Asteroid belt; some orbits are empty.

3. Oct 23, 2004

### Mazuz

I wonder if theoretically it could be possible in a highly special circumstance.

4. Oct 23, 2004

### Aphex_Twin

Theoretically, yes, there can be planets doing perfect figure-eights around two stars or performing a very wide orbit around fast and close co-orbiting stars.

5. Oct 23, 2004

### tony873004

Figure 8 orbits are not stable. But a Double Star can have planets that orbit both stars, as well as planets that orbit each star individually. Planets orbiting both stars need to be far enough away from both stars that the center of gravity acts more like a point. Planets orbiting only one star in a binary system must be sufficiently close to that star that the other star won't rip it away.

If Jupiter were more massive, and it were a star, Mars and Saturn would not be able to exist. But Mercury, Venus, & Earth would be planets that belonged to the Sun, Jupiter's moons would be promoted to planetary status, and Uranus, Neptune and Pluto would be planets that orbited both stars.

6. Oct 23, 2004

### turbo

7. Oct 23, 2004

Staff Emeritus
There is a famous solution with five bosies in which the lightest body, through repeated compond slingshots, reaches "infinity" in finite time. In Newtonian physics, that is.

8. Oct 23, 2004

### meteor

Yes, it can. Quoting from David Darling Encyclopedy, one of my favourites, he says
"Two key questions arise when considering whether life could evolve in a binary or multiple star system. They are: (a) is it possible for planetary systems to form around such stars, and (b) if it is, can planets orbit so as to provide tolerable surface conditions for biological activity? On the subject of planet formation, it has been suggested that the gravitational disturbance caused by another nearby star might prevent material from settling into a stable protoplanetary disk. However, evidence is now to hand of such a disk around one of the stars in a young binary system. Assuming then that planets do form, could they support life? Before 1960, it was generally thought not. Then the Chinese-American astronomer Su-Shu Huang showed that there existed various special orbits in which a planet could move in a two-star system and enjoy clement, stable temperatures. Basically, there are three possibilities: a wide, roughly circular path around both stars, a figure-eight orbit around both stars, or a small orbit around just one star . The exact circuits required for habitability would depend on details such as the type of stars involved and their separation distance."

Last edited: Oct 23, 2004