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Pebble accretion may accelerate the formation of planets by a factor of 1000 compared to the accretion of planetesimals, allowing giant planets to form before the dissipation of the gas disk. [ 28 ] [ 29 ] However, core growth via pebble accretion appears incompatible with the final masses and compositions of Uranus and Neptune . [ 30 ]
This process increases the cross section over which the large bodies can accrete material, accelerating their growth. The rapid growth of the planetesimals via pebble accretion allows for the formation of giant planet cores in the outer Solar System before the dispersal of the gas disk.
The various planets are thought to have formed from the solar nebula, the disc-shaped cloud of gas and dust left over from the Sun's formation. [36] The currently accepted method by which the planets formed is accretion, in which the planets began as dust grains in orbit
Gradually, gentle collisions allowed the flakes to stick together and make larger particles which, in turn, attracted more solid particles towards them. This process is known as accretion. The objects formed by accretion are called planetesimals—they act as seeds for planet formation. Initially, planetesimals were closely packed.
Planets start to form within this disk through the process of accretion. As dust and solid materials coalesce to form planetesimals and eventually protoplanets, these bodies begin to exert gravitational forces. The gravity of these growing protoplanets attracts surrounding gases from the protoplanetary disk.
Type I migration in a local isothermal disk was shown to be compatible with the formation and long-term evolution of some of the observed Kepler planets. [9] The rapid accretion of solid material by the planet may also produce a "heating torque" that causes the planet to gain angular momentum. [10]
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The dynamo ceased within 0.5 billion years of the planet's formation. [2] Hf/W isotopes derived from the martian meteorite Zagami, indicate rapid accretion and core differentiation of Mars; i.e. under 10 million years. [23] Potassium-40 could have been a major source of heat powering the early Martian dynamo. [27]