9 - Types of Planetary System

Summary

Here, I inspect the layout of our own solar system, and consider the extent to which other planetary systems are similar or different. Discoveries so far show that there are many possible layouts, and suggest that quasi-replicates of our system, with four inner rocky planets and four outer giant planets (gaseous or icy) are rare. Every system is different from every other one. This is a consequence of the chaotic process of collisions that leads from a protoplanetary disc to planets. Planets can be found orbiting large, medium, and small stars – with consequences for their maximum lifespans. Some planets are found in binary systems and even in systems with more than two stars. The nearest system to ours – Alpha Centauri – has three stars. This system has at least one planet, which orbits the smallest of the three stars. Planetary systems are also thought to typically contain smaller bodies than planets, as seen in the solar system – moons, minor planets, asteroids, and comets. Life is most likely to occur on planets, but life on moons is also possible. Finally, there are some lone planets that do not orbit a star at all. These are the least probable homes for life.