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Abstract Observations suggest that the hot Neptune desert contains the remnants of destroyed gas giants. Recent theoretical work has shown that gas giant destruction via Roche lobe overflow (RLO) can indeed populate the desert with remnant planets, but only if mass transfer removes most of the planet’s orbital angular momentum (“lossy” RLO). Motivated by the fact that stellar accretion naturally gives rise to such lossy RLO, in this Letter we examine how planet-to-star mass and angular momentum transfer manifests in the distribution of stellar obliquities. We find that RLO tilts host stars into spin–orbit alignment (within a few ∼tens of degrees) regardless of initial conditions. Obliquity damping by RLO can only be reversed by the presence of misaligned companion planets within ≲2 au. While tides and mass transfer usually produce stellar spin-up, host stars can also emerge from RLO slowly rotating if systems begin strongly retrograde; retrograde RLO reconciles theory with the anomalously slow rotation of the desert-dweller host, LTT 9779. Predicted spin–orbit alignment may differentiate RLO from alternative giant planet destruction mechanisms, in particular hot Jupiter disruption during high-eccentricity migration (which tends to produce broadly distributed stellar obliquities). We summarize other population-level predictions that can further distinguish RLO from high-eccentricity migration. Our work suggests that follow-up obliquity measurements may reveal the formation pathways of desert dwellers and potentially open a window into gas giants’ exposed interiors. 

Abstract Recent observational and theoretical work suggests that the sub-Jovian desert (periods ≲3 days, masses ∼10–100M_⊕) hosts the remains of destroyed hot Jupiters (“desert dwellers”). In this work, we explore how differing hot Jupiter destruction mechanisms—Roche lobe overflow (RLO) versus tidal disruption during high-eccentricity migration (HEM)—may be discerned observationally based on the presence of companion planets to desert dwellers. We show that gas giant destruction via RLO clears out the desert of any companions inside orbital periods ≲4 days; desert dwellers should sit alone in the desert if they form through this mechanism. Numerically mapping the instability threshold in planet mass and orbital distance, we find that the majority of observed companions to desert dwellers are safely in the stability region. RLO therefore does not preclude the existence of nearby companions beyond the desert, in contrast to gas giant tidal disruption during HEM. Further characterization of desert dweller systems may therefore elucidate the fates of hot Jupiters. 

Abstract Recent observations have revealed an intriguing abundance of polar-orbiting Neptune-sized planets, many of which exhibit unusually inflated radii. While such misaligned orbits point to a complex dynamical history, the connection between their orbital orientations and planetary structures remains poorly understood. In this study, we analyze a sample of 12 misaligned and 12 aligned planets using structure models that incorporate tidal heating. We use various statistical tests to demonstrate—with at least 90% confidence—that misaligned planets experience more tidally induced radius inflation compared to aligned planets. This inflation likely stems from their dynamically active histories, which often place them in close-in, eccentric, and highly inclined orbits. We further present a case study of WASP-107 b, an exceptionally inflated polar Neptune, and model its history using a simple coupled orbital and radius evolution approach. Our results place constraints on the planet’s tidal quality factor that agree with recent JWST observations. 

Abstract We present an updated characterization of the TOI-1685 planetary system, which consists of aP_b= 0.69 day ultra-short-period super-Earth planet orbiting a nearby (d= 37.6 pc) M2.5V star (TIC 28900646, 2MASS J04342248+4302148). This planet was previously featured in two contemporaneous discovery papers, but the best-fit planet mass, radius, and bulk density values were discrepant, allowing it to be interpreted either as a hot, bare rock or a 50% H₂O/50% MgSiO₃water world. TOI-1685 b will be observed in three independent JWST Cycle 2 programs, two of which assume the planet is a water world, while the third assumes that it is a hot rocky planet. Here we include a refined stellar classification with a focus on addressing the host star’s metallicity, an updated planet radius measurement that includes two sectors of TESS data and multicolor photometry from a variety of ground-based facilities, and a more accurate dynamical mass measurement from a combined CARMENES, InfraRed Doppler, and MAROON-X radial velocity data set. We find that the star is very metal-rich ([Fe/H] ≃ +0.3) and that the planet is systematically smaller, lower mass, and higher density than initially reported, with new best-fit parameters ofR_pl= 1.468 ${}_{-0.051}^{+0.050}$ R_⊕andM_pl= ${3.03}_{-0.32}^{+0.33}$ M_⊕. These results fall in between the previously derived values and suggest that TOI-1685 b is a hot rocky planet with an Earth-like density (ρ_pl= 5.3 ± 0.8 g cm⁻³, or 0.96ρ_⊕), high equilibrium temperature (T_eq= 1062 ± 27 K), and negligible volatiles, rather than a water world. 

A planet’s orbital alignment places important constraints on how a planet formed and consequently evolved. The dominant formation pathway of ultra-short-period planets (P < 1 day) is particularly mysterious as such planets most likely formed further out, and it is not well understood what drove their migration inwards to their current positions. Measuring the orbital alignment is difficult for smaller super-Earth/sub-Neptune planets, which give rise to smaller amplitude signals. Here we present radial velocities across two transits of 55 Cancri (Cnc) e, an ultra-short-period super-Earth, observed with the Extreme Precision Spectrograph. Using the classical Rossiter–McLaughlin method, we measure 55 Cnc e’s sky-projected stellar spin–orbit alignment (that is, the projected angle between the The star 55 Cancri (Cnc) A hosts five known exoplanets with minimum mass estimates ranging from approximately 8M⊕ to 3MJup and periods less than one day to nearly 20 years1–4. Of particular interest has been 55 Cnc e, one of the most massive known ultra-short-period planets (USPs) and the only planet around 55 Cnc found to transit5,6. It has an star’s spin axis and the planet’s orbit normal—will shed light on the formation and evolution of USPs, especially in the case of compact, multiplanet systems. It has been shown that USPs form a statistically distinct popula- tion of planets9 that tend to be misaligned with other planetary orbits in their system10. This suggests that USPs experience a unique migra- tion pathway that brings them close in to their host stars. This inward migration is most likely driven by dissipation due to star–planet tidal interactions that result from either non-zero eccentricities11,12 or plan- etary spin-axis tilts13. orbital period of 0.7365474 +1.3 × 10−6 days, a mass of 7.99 ± 0.33M −1.4 × 10−6 ⊕ and a radius of 1.853 +0.026 R⊕ (refs. 7,8). A precise measure of the −0.027 stellar spin–orbit alignment of 55 Cnc e—the angle between the host planet’s orbital axis and its host star’s spin axis) to be λ = 10 +17∘ with an +14∘ −20∘ unprojected angle of ψ = 23 −12∘. The best-fit Rossiter–McLaughlin model to the Extreme Precision Spectrograph data has a radial velocity semi- amplitude of just 0.41 +0.09 m s−1. The spin–orbit alignment of 55 Cnc e −0.10 favours dynamically gentle migration theories for ultra-short-period planets, namely tidal dissipation through low-eccentricity planet–planet interactions and/or planetary obliquity tides.