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Giant Planet Formation: “Cold-Start” VS “Hot-Start”

4 Aug 2014, 22:00 UTC
Giant Planet Formation: “Cold-Start” VS “Hot-Start”
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Giant planets are thought to form in two possible ways. The first method involves accreting a solid core and once the solid core attains ~10 Earth masses, it becomes massive enough to accrete hydrogen and helium in a runaway process to form a giant planet. This mode of giant planet formation is known as “core accretion”. In the Solar System, the giant planets Jupiter and Saturn are believed to have formed via core accretion. The second mode of giant planet formation involves a protoplanetary disk becoming gravitationally unstable and collapses directly to form a giant planet. This is known as “disk instability”.Figure 1: Artist’s impression of a giant planet. Giant planets range in mass from a fraction of Jupiter’s mass to tens of Jupiter’s mass.In the core accretion scenario, the solid core accretes gas through an accretion disk. This process cools the gas, causing it to lose much of its initial entropy and forms a giant planet that has low initial entropy (i.e. a “cold-start”). For disk instability, the gas that collapses directly to form a giant planet retains most of it intitial entropy, resulting in high initial entropy (i.e. a “hot-start”). If the age of a giant planet is ...

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