The way exoplanets form and evolve has a direct impact on the composition and dynamics of their atmospheres. The local conditions at their birth, the accretion mechanism and how they interact with their parent star, disk and potentially other planets, govern the diversity of compositions and atmospheric dynamics seen in exoplanet atmospheres today.
Before the discovery of exoplanets in the 1990’s, our own solar system was the only planetary system able to provide us with observables allowing us to test theories of planetary formation. With space missions exploring the solar system throughout the latter part of the 20th century, an enormous amount of geophysical data describing the chemical composition and internal structure of the giant planets was obtained giving clues to the origin of the solar system. With the subsequent discovery of many new planetary systems, most notably by the Kepler satellite (Borucki et al. 2010), the knowledge of planet formation was complimented by statistical properties of planetary systems with which to test hypotheses, weakening the anthropic bias (Carter 1974) of our planetary system being the only one.
The birthplace of exoplanets is within the predominantly gaseous disk which surrounds protostars. The way they form however, can be divided into two formation mechanisms which all giant planet formation models rely on: disk instability model which best explains giant planets with a large mass on wide orbits, and the core accretion model, which has emerged as the dominant formation mechanism. Each of these mechanisms are described in more detail below.
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