Close encounters: How stellar flybys shape planet-forming discs

We review the role of stellar flybys and encounters in shaping planet-forming discs around young stars, based on published literature this topic last 30 years. Since most stars $$\le ~2$$ Myr old harbour protoplanetary discs, tidal perturbations affect planet formation. First, we examine probability experiencing or encounters: More than 50% with a typical star-forming environment should experience close encounter flyby within 1000 au. Second, detail dynamical effects discs. Prograde, parabolic, disc-penetrating are destructive. Grazing penetrating particular lead to capture disc material by secondary form highly misaligned circumsecondary respect primary. One both may undergo extreme accretion outburst events, similar ones observed FU Orionis-type stars. Warps broken distinct signatures retrograde flybys. Third, some recently systems where an is suspected—including UX Tau, RW Aur, AS 205, Z CMa, Ori. Finally, discuss implications for formation exoplanet demographics, including possible imprints Solar System orbits trans-Neptunian objects Sun’s obliquity.