Building, moving and destroying Planets

To date we have discovered over 300 extrasolar planets and although we are starting to detect some with masses a few times that of the Earth, most have much higher masses and are generally regarded as gas giants, similar to Jupiter or Saturn. Since these planets are predominantly gaseous, we can say—with some confidence—that they must have formed before the dispersal of the gas disc which occurs on a timescale of $∼5 million$ years. What we are still uncertain about is exactly how these planets form. They also have some extremely interesting and unexpected properties. Some, known as hot Jupiters, orbit very close to their parents stars, and although we expect these planets to form from material on circular orbits, the range of eccentricities is extremely high. Some of this can be understood by considering the interaction of planets with the surrounding protoplanetary disc, but this can also introduce new problems such as rapid inward migration of small planetesimals, through gas drag, and planetary cores, through gravitational interaction with the surrounding disc. In this paper I will review the various planet forming models and discuss how these planets evolve through planet‐disc interactions. I will also discuss how recent work is starting to understand how these planets form and is beginning to explain the various properties of the current population of exoplanets.