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Grand tack hypothesis
In planetary astronomy, the grand tack hypothesis proposes that Jupiter formed at a distance of 3.5 AU from the Sun, then migrated inward to 1.5 AU, before reversing course due to capturing Saturn in an orbital resonance, eventually halting near its current orbit at 5.2 AU. The reversal of Jupiter's planetary migration is likened to the path of a sailboat changing directions (tacking) as it travels against the wind.
The planetesimal disk is truncated at 1.0 AU by Jupiter's migration, limiting the material available to form Mars. Jupiter twice crosses the asteroid belt, scattering asteroids outward then inward. The resulting asteroid belt has a small mass, a wide range of inclinations and eccentricities, and a population originating from both inside and outside Jupiter's original orbit. Debris produced by collisions among planetesimals swept ahead of Jupiter may have driven an early generation of planets into the Sun.
In the grand tack hypothesis, Jupiter underwent a two-phase migration after its formation, migrating inward to 1.5 AU before reversing course and migrating outward. Jupiter's formation took place near the ice line, at roughly 3.5 AU.
After clearing a gap in the gas disk Jupiter underwent type II migration, moving slowly toward the Sun with the gas disk. If uninterrupted, this migration would have left Jupiter in a close orbit around the Sun, similar to hot Jupiters in other planetary systems. Saturn also migrated toward the Sun, but being smaller it migrated faster, undergoing either type I migration or runaway migration. Saturn converged on Jupiter and was captured in a 2:3 mean-motion resonance with Jupiter during this migration. An overlapping gap in the gas disk then formed around Jupiter and Saturn, altering the balance of forces on these planets which began migrating together. Saturn partially cleared its part of the gap reducing the torque exerted on Jupiter by the outer disk.
The net torque on the planets then became positive, with the torques generated by the inner Lindblad resonances exceeding those from the outer disk, and the planets began to migrate outward. The outward migration was able to continue because interactions between the planets allowed gas to stream through the gap. The gas exchanged angular momentum with the planets during its passage, adding to the positive balance of torques, allowing the planets to migrate outward relative to the disk; the exchange also transferred mass from the outer disk to the inner disk. The transfer of gas to the inner disk also slowed the reduction of the inner disk's mass relative to the outer disk as it accreted onto the Sun, which otherwise would weaken the inner torque, ending the giant planets' outward migration. In the grand tack hypothesis this process is assumed to have reversed the inward migration of the planets when Jupiter was at 1.5 AU. The outward migration of Jupiter and Saturn continued until they reached a zero-torque configuration within a flared disk, or when the gas disk dissipated. The whole process is presumed to end when Jupiter reached its approximate current orbit.
The hypothesis can be applied to multiple phenomena in the Solar System.
The "Mars problem" is a conflict between some simulations of the formation of the terrestrial planets which end with a 0.5–1.0 M🜨 planet in its region, much larger than the actual mass of Mars: 0.107 M🜨, when begun with planetesimals distributed throughout the inner Solar System. Jupiter's grand tack resolves the Mars problem by limiting the material available to form Mars.
Jupiter's inward migration alters this distribution of material, driving planetesimals inward to form a narrow dense band with a mix of materials inside 1.0 AU, and leaves the Mars region largely empty. Planetary embryos quickly form in the narrow band. Most of these embryos collide and merge to form the larger terrestrial planets (Venus and Earth) over a period of 60 to 130 million years. Others are scattered outside the band where they are deprived of additional material, slowing their growth, and form the lower-mass terrestrial planets Mars and Mercury.
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Grand tack hypothesis
In planetary astronomy, the grand tack hypothesis proposes that Jupiter formed at a distance of 3.5 AU from the Sun, then migrated inward to 1.5 AU, before reversing course due to capturing Saturn in an orbital resonance, eventually halting near its current orbit at 5.2 AU. The reversal of Jupiter's planetary migration is likened to the path of a sailboat changing directions (tacking) as it travels against the wind.
The planetesimal disk is truncated at 1.0 AU by Jupiter's migration, limiting the material available to form Mars. Jupiter twice crosses the asteroid belt, scattering asteroids outward then inward. The resulting asteroid belt has a small mass, a wide range of inclinations and eccentricities, and a population originating from both inside and outside Jupiter's original orbit. Debris produced by collisions among planetesimals swept ahead of Jupiter may have driven an early generation of planets into the Sun.
In the grand tack hypothesis, Jupiter underwent a two-phase migration after its formation, migrating inward to 1.5 AU before reversing course and migrating outward. Jupiter's formation took place near the ice line, at roughly 3.5 AU.
After clearing a gap in the gas disk Jupiter underwent type II migration, moving slowly toward the Sun with the gas disk. If uninterrupted, this migration would have left Jupiter in a close orbit around the Sun, similar to hot Jupiters in other planetary systems. Saturn also migrated toward the Sun, but being smaller it migrated faster, undergoing either type I migration or runaway migration. Saturn converged on Jupiter and was captured in a 2:3 mean-motion resonance with Jupiter during this migration. An overlapping gap in the gas disk then formed around Jupiter and Saturn, altering the balance of forces on these planets which began migrating together. Saturn partially cleared its part of the gap reducing the torque exerted on Jupiter by the outer disk.
The net torque on the planets then became positive, with the torques generated by the inner Lindblad resonances exceeding those from the outer disk, and the planets began to migrate outward. The outward migration was able to continue because interactions between the planets allowed gas to stream through the gap. The gas exchanged angular momentum with the planets during its passage, adding to the positive balance of torques, allowing the planets to migrate outward relative to the disk; the exchange also transferred mass from the outer disk to the inner disk. The transfer of gas to the inner disk also slowed the reduction of the inner disk's mass relative to the outer disk as it accreted onto the Sun, which otherwise would weaken the inner torque, ending the giant planets' outward migration. In the grand tack hypothesis this process is assumed to have reversed the inward migration of the planets when Jupiter was at 1.5 AU. The outward migration of Jupiter and Saturn continued until they reached a zero-torque configuration within a flared disk, or when the gas disk dissipated. The whole process is presumed to end when Jupiter reached its approximate current orbit.
The hypothesis can be applied to multiple phenomena in the Solar System.
The "Mars problem" is a conflict between some simulations of the formation of the terrestrial planets which end with a 0.5–1.0 M🜨 planet in its region, much larger than the actual mass of Mars: 0.107 M🜨, when begun with planetesimals distributed throughout the inner Solar System. Jupiter's grand tack resolves the Mars problem by limiting the material available to form Mars.
Jupiter's inward migration alters this distribution of material, driving planetesimals inward to form a narrow dense band with a mix of materials inside 1.0 AU, and leaves the Mars region largely empty. Planetary embryos quickly form in the narrow band. Most of these embryos collide and merge to form the larger terrestrial planets (Venus and Earth) over a period of 60 to 130 million years. Others are scattered outside the band where they are deprived of additional material, slowing their growth, and form the lower-mass terrestrial planets Mars and Mercury.