Grand Tack hypothesis

The Grand Tack hypothesis proposes that Jupiter migrated inward through the early Solar System, then reversed direction as Saturn caught up and migrated outward with it.

Type II migration: The inward or outward drift of a planet embedded in a protoplanetary disk, shaped by the gap it opens. Disk torques drive the giant planets’ migration in the model.
Grand Tack model of terrestrial planet formation: An application of the Grand Tack scenario in which Jupiter’s migration truncates the material available to build terrestrial planets. The inward sweep can restrict the feeding zone that produces Mars and the inner planets.
Alessandro Morbidelli: An Italian planetary scientist known for research on Solar System formation and planetary dynamics. Morbidelli co-developed the Grand Tack scenario with collaborators.
Planetary migration: A change in a planet’s orbit caused by interactions with a disk, other bodies, or tides. The Grand Tack is a specific, large-scale episode of planetary migration.
Mean-motion resonance: An orbital configuration in which bodies’ orbital periods have a ratio close to a ratio of small integers. Jupiter and Saturn enter resonance before their migration reverses.
Mars: The fourth planet from the Sun, a terrestrial planet substantially smaller than Earth. The model links Mars’s small mass to a depleted region of the planet-forming disk.
Kevin J. Walsh: An American planetary scientist who studies the formation and evolution of planets and small bodies. Walsh led the study that introduced the Grand Tack model in 2011.
Disk-planet interaction: The exchange of angular momentum between a planet and the gas or dust disk surrounding a star. Uncertainties in disk structure affect whether the proposed reversal occurs.
Jupiter–Saturn resonance: A commensurability between Jupiter’s and Saturn’s orbital periods that changes their gravitational interaction with the surrounding disk. Their resonant configuration helps create the outward-migration phase.
Asteroid belt: The region between Mars and Jupiter containing most of the Solar System’s known asteroids. Jupiter’s migration can scatter material into the belt from distinct source regions.

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