  The Local arm of the Milky Way, a short spiral feature near the Sun whose
existence is known for decades, was recently observed in detail with different
tracers. Many efforts have been dedicated to elaborate plausible hypotheses
concerning the origin of the main spiral arms of the Galaxy; however, up to
now, no specific mechanism for the origin of the Local arm was proposed. Here
we explain, for the first time, the Local arm as an outcome of the spiral
corotation resonance, which traps arm tracers and the Sun inside it. We show
that the majority of maser sources belonging to the Local arm, together with
the Sun, evolve inside the corotation resonance, never crossing the main spiral
arms but instead oscillating in the region between them. This peculiar behavior
of the Sun could have numerous consequences to our understanding of the local
kinematics of stars, the Galactic Habitable Zone, and the Solar System
evolution.
