2025AJ....170..299K

Two leading hypotheses for hot Jupiter migration are disk migration and high-eccentricity migration (HEM). Stellar obliquity is commonly used to distinguish them, as high obliquity often accompanies HEM. However, low obliquity does not guarantee disk migration, due to possible spin-orbit realignment or coplanar HEM. Seeking a proxy for disk migration, we investigate the idea that when the circularization timescale of a planet on circular orbit is longer than its age (τ_cir > τ_age), HEM would not have had sufficient time to complete, favoring disk migration. We empirically calibrate the reduced planetary tidal quality factor to be ${Q}_{{\rm{p}}}=4.{9}_{-2.5}^{+3.5}\times 1{0}^{5}$ using the eccentricity distribution of 500+ Jovian mass (0.2M_J < M_p < 13M_J) planets with measured masses and radii, a value consistent with solar system Jupiter. We then calculate τ_cir and identify dozens of disk migration candidates (τ_cir > τ_age, e < 0.1). These planets show three notable trends. We first find a clear cutoff of obliquity at τ_cir ∼ τ_age, suggesting the primordial alignment of protoplanetary disks. Second, we find that among hot Jupiters (a < 0.1 au), nearby companions are preferentially found around disk migration candidates, suggesting that either HEM dominates hot Jupiter formation, or disk migration also disrupts nearby companions at short separations. Finally, we find a possible dearth of disk migration candidates around mass ratio ${\mathrm{log}}q\sim -3.2$, consistent with a similar dip suggested at longer orbits from microlensing. The lack of planets across different orbital distance, if true, could be interpreted as a hint of runaway migration.