Planets and
Binary Stars
After years of conflicting claims, there seems to finally be emerging a body of observations supporting the
existence of planets around other stars (extrasolar planets).
Since most star systems are probably binary, this raises the additional
question of whether there are planets in binary star systems.
Extrasolar Planets
We have discussed extrasolar planets in the chapter on the overview of the Solar System
(Chapter 7),
but there
are two interesting considerations concerning planets that are appropriate
to touch on here. The first is that similar astrometric methods as described
for binary stars can also be used to detect the presence of unseen planets around
stars. The adjacent figure summarizes some of the planets that have been discovered
(masses are in units of Jupiter's mass, MJ; this figure is discussed in Chapter 7).
The second is the issue of whether in binary star systems there are
planetary orbits that are stable and conducive to the evolution of life.
Planetary Orbits
Although in principle it is possible to have stable planetary orbits in binary star systems, in practice there are only a few kinds of orbits in such systems that are stable for long periods. In addition, even if an orbit is stable, it is generally more difficult in binary systems to arrange orbits that maintain surface temperatures on the planet in ranges that are required for life as we know it on Earth. Thus, it is a very open question as to how common planets are in binary star systems, and whether any such planets could harbor life.