Origin and sustainability of the population of asteroids captured in the exterior resonance 1:2 with Mars

► Yarkovsky effect generates captures and losses from the resonance 1:2 with Mars. ► A fraction of asteroids remains captured generating an observed excess of 20%. ► Yarkovsky effect generates an excess of small asteroids inside the resonance. ► Resonant asteroids experience diffusion in eccentricity and inclination. ► This diffusion explains misidentifications of asteroids from families Vesta and Nysa.