Unified Formation Channel of Hot and Warm Jupiters via Planet–Planet Scattering

Abstract Recent observations show distinct orbital architectures for hot and warm Jupiters: hot Jupiters span a wide range of stellar obliquities and tend to host distant companions without close-by companions, whereas warm Jupiters are often aligned and accompanied by both close-by and distant companions. In this Letter, we revisit planet–planet scattering and demonstrate that it provides a unified framework for both populations. Using N -body simulations with tides, we explore three regimes: hot ( a 1 < 0.1 au), warm (0.1 < a 1 < 1 au), and cold (1 < a 1 < 10 au) scattering. Hot scattering predominantly produces compact hot Jupiter pairs, which are rarely observed, implying this channel is rare. Cold scattering readily produces retrograde hot Jupiters and likely constitutes a main reservoir feeding the hot Jupiter population. However, cold scattering produces few inner warm Jupiters at a ≃ 0.1–0.3 au. We show that warm scattering naturally fills this gap: high-inclination inner warm Jupiters produced by warm scattering are preferentially removed through further eccentricity excitation followed by tidal circularization into hot Jupiters. As a result, the surviving inner warm Jupiters are biased toward a broad range of eccentricities but modest inclinations, producing the observed “eccentric-but-aligned” population. This theory makes testable predictions: (i) warm Jupiters, especially at a ≳ 0.3 au, should not be exclusively aligned; and (ii) warm Jupiters should often host nearby companions with nonnegligible mutual inclinations up to ≲30°.