The Sun formed 4.6 billion years ago roughly 10,000 light-years closer to the center of the Milky Way than it currently sits. It didn't drift outward alone. Using data from ESA's Gaia satellite, researchers identified 6,594 “solar twins” — stars with similar mass and metallicity — within 1,000 light-years of Earth, many of which share the same migration history. The Sun was part of a mass exodus, not a lone wanderer.
The mechanism was the Milky Way's central bar. Between 4 and 6 billion years ago, the bar strengthened, boosting star formation in the inner disk and launching large-scale radial migrations. Stars didn't scatter randomly — gravitational resonances, where orbital periods align with the bar's rotation or spiral arm patterns, funneled them outward in coherent groups. Angular momentum diffusion across resonance boundaries moved entire populations of stars to larger orbits without requiring violent encounters.
The migration mattered for habitability. The inner disk, where the Sun formed, had vigorous star formation — abundant material for building planets, but also frequent supernovae, intense radiation, and gravitational disruption. The outer disk, where the Sun ended up, is quieter. The migration took a young solar system out of an environment that encouraged planet formation but was likely lethal to planets on long timescales, and delivered it to one where a planet could remain habitable for billions of years.
The general principle is that the condition for forming a system and the condition for sustaining it can be different locations. The inner galaxy assembles planetary systems. The outer galaxy preserves them. The transition between assembly and preservation requires physical relocation — and that relocation happened not by chance but by a galaxy-scale dynamical process that moved thousands of similar stars together. The Sun's position in the galaxy isn't arbitrary. It's the result of a selection process where only stars that migrated outward kept their planets long enough for complexity to develop.