User:Jacobmkrebs13/Magnetospheric Accretion

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(Exo)planet formation remains elusive. Planetary bodies remain hidden within natal circumstellar disks. Recent surveys have added to the amount of known exoplanets bringing the numbers into the thousands. With this large, ever-growing amount, statistical analysis can be performed to aid in synthesis calculations and computations. Of the different types of exoplanet classes (terrestrial/rocky, sub-neptune, ice giant, giant), giant make ideal first targets due to their large radius, mass, and thick atmosphere which all contribute to spectral analysis observed. In recent years, magnetic fields have been indirectly observed of hot Jupiters.

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Gas giants are thought to undergo magnetospheric accretion similarly to low mass T Tauri stars. Magnetospheric accretion occurs when magnetic pressure exceeds the ram pressure of the circumplanetary disk. When this condition is true, ionized gas in the circumplanetary disk follows along the magnetic field lines according to the magnetohydrodynamical fluid evolution equations.

Gas giants can have slower spin rate as young stars thread their magnetic field lines through the their disks. This acts as a braking mechanism from interactions with the proto planets own generated magnetic field, whether it was inherited or produced through a dynamo effect. The braking allows the gas planet to become larger as the angular momentum decreases from a lower spin rate.

The effect of the magnetic field is to both slow down the spin rate, and thus reduce angular momentum, of the planet as well as lead in falling ionized gas to the planet. Two conditions have to be satisfied, in which the angular momentum cannot be too large or shear forces will tear the protoplanet apart. The shock from infalling gas cannot carry a significant amount of kinetic energy or the body will break apart, which is usually only an issue very early on in development of the body. If both of these conditions are not broken, gas can continue to be accreted from the circumplanetary disk so that the planet can form into a giant planet of sufficient mass and radius.