Key Takeaways:
- Planetary systems can exist within binary star systems, with confirmed examples numbering 97 systems containing 143 planets as of July 2019.
- Planets in binary systems can exhibit S-type orbits, where they orbit a single star in the binary pair, largely unaffected by the other star; or P-type orbits, where they orbit both stars collectively.
- A third orbital configuration, termed a T-type orbit, is theoretically possible; in this scenario, a planet would share the orbit of a smaller star around a larger star, situated at a Lagrangian point (L4 or L5).
- No planets have yet been found exhibiting the T-type orbit described.
Q: Can solar systems exist in a binary star system? If so, what kind of orbital patterns would the planets and moons have around the two suns?
A: Yes, planetary systems can exist in binary star systems. As of July 2019, astronomers have found 97 planetary systems containing 143 planets around binary stars. These planets may orbit just one of the stars in the binary system, called an S-type (satellite-type) orbit, or they can orbit both stars together from outside the binary, called a circumbinary or P-type (planet-type) orbit. Most of the known planets in binary systems have S-type orbits, in which they orbit close to one star and essentially ignore the companion star, which is farther away.
There is a third option, although no planets with this type of orbit have been found yet: a T-type orbit. In this configuration, one star in the pair is much smaller than the other. The smaller star orbits the larger star and the planet shares the orbit with the smaller star, gravitationally locked into a position either 60° ahead of or 60° behind the smaller star. These positions are called Lagrangian points. Planets in T-type orbits are sometimes called Trojan planets — just like the Trojan asteroids, for example, that share Jupiter’s orbit around the Sun.
