Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2611.04544

The Survival Paradox of Close-In Planets Orbiting Red Clump Giants

Wen-Xu Lin·Sheng-Bang Qian·Qi-Bin Sun·Li-Ying Zhu·Wen-Ping Liao·Ting Li·Fu-Xing Li·Xiang-Dong Shi·Tao Wang·Ergang Zhao·Huiting Zhang·Ping Li
View original source ↗Read source document ↗Export metadata ↓

Abstract

Close-in planets orbiting core-helium-burning red-clump (RC) giants directly challenge tidal-engulfment theory, which predicts that planets within about 1 au of Sun-like stars should be engulfed during red-giant-branch (RGB) expansion. The existence of such survivors would imply missing physical processes in the late stages of stellar and planetary evolution. Yet only one such "forbidden" planet had been identified to date. Here we report three systems-24 Boo b, HD 12648 b, and TYC 4282-605-1 b-whose host stars are confirmed red-clump giants through asteroseismology, showing that each has already undergone dramatic expansion and contraction following helium ignition. Their planets now reside at orbital separations smaller than the maximum stellar radii attained during the RGB phase, implying that they should not have survived. Among them, 24 Boo b orbits at only 0.183 au with a 30-day period, making it the closest planet known around a red-clump giant. These discoveries demonstrate that this paradox is not an isolated anomaly but signals the emergence of a new class of evolved planetary systems. Their survival defies current models of stellar-planetary coevolution and points to unexplored physics shaping planetary architectures around post-RGB stars.

Explore related subjects

astro-ph.EPastro-ph.SR

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Wen-Xu Lin, Sheng-Bang Qian, Qi-Bin Sun, Li-Ying Zhu, Wen-Ping Liao, Ting Li, Fu-Xing Li, Xiang-Dong Shi, Tao Wang, Ergang Zhao, Huiting Zhang, Ping Li. 2026-11-03. The Survival Paradox of Close-In Planets Orbiting Red Clump Giants. https://doi.org/10.1073/pnas.2603847123

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Calibration of CNEOS Fireball Velocities and the Robustness of Nominally Hyperbolic Events

The NASA/JPL CNEOS Fireball Data catalogue provides a near-global record of bright atmospheric entries but does not report per-event velocity covariance. We calibrate its kinematic accuracy using 19 events with independent reference trajectories and use optical, satellite, radar, and infrasound catalogues as source-specific controls. For nine modern high-quality comparisons, the CNEOS-minus-reference speed residual has mean -1.00 km s$^{-1}$ and standard deviation 0.86 km s$^{-1}$; variance decomposition assigns 0.77 km s$^{-1}$ to the CNEOS component. The radiant residuals have a 0.74 degree per-axis core plus one 16.3 degree outlier, so the extreme tail remains poorly determined. Seven of 354 complete CNEOS states are nominally hyperbolic without correction. A +0.9935 km s$^{-1}$ atmospheric-stage shift produces five additional crossings, but these are treated only as sensitivity cases. Polar-IM (2026 April 1) is the strongest post-2018 CNEOS anomaly, whereas independent GLM-LI stereo solutions yield 57.3 +/- 2.0 and 56.7 +/- 3.0 km s$^{-1}$, close to their direction-specific parabolic thresholds. We conclude that CNEOS can identify priority candidates, but secure interstellar classification requires an independent, uncertainty-bearing three-dimensional trajectory for the same event.

astro-ph.EP↗
arXiv2026

Fitting Resonant Exoplanets Orbits. I. Properties and Applications of Fixed-Point Orbits

Intact chains of mean-motion resonances may preserve information about the formation and early dynamical evolution of multiplanet systems. Although most mature multiplanet systems are non-resonant, the resonant fraction may have been substantially higher at young ages. Establishing whether exoplanet data are consistent with a resonant configuration is often challenging because the planetary orbits must be sufficiently well constrained. Moreover, while resonance configurations promote stability, standard orbital fitting methods do not impose such a dynamical constraint, with stability tested only a posteriori. As the first step in a series of papers aimed at favoring stable orbital solutions during the fitting process, we develop a method that restricts solutions to stable fixed-point orbits (fPOs)---coplanar, exactly periodic configurations associated with resonant dynamics. We show that dissipative evolution drive resonant systems toward an fPO state, motivating for fPO-constrained fitting for those planet systems that have avoided large-scale dynamical rearrangements since formation. The fPO model greatly reduces the number of free parameters and yields stable solutions by construction. We determine the best-fitting fPos through $χ^2$ minimization and apply the method to astrometric data for the directly imaged PDS 70 and HR 8799 systems and to radial-velocity data for GJ 876. For HR 8799 we independently recover a previously reported resonant solution, illustrating the fidelity of our method. For PDS 70 we find solutions fall in two groups, with the group where the outer planet c mass exceeds planet b more aligned with previous measurements. Finally, For GJ 876 our fPO fit is on par with previous unconstrained fitting, which strengthens the case that its planets reside deep in resonance.

astro-ph.EP↗
arXiv2026

Outer pressure bumps beyond the dust disc: Missing Outer Rings in the exoALMA Sample: Physical Mechanisms Suppressing Dust Ring Formation Despite Strong Pressure Bumps

The exoALMA survey has revealed candidate gas pressure bumps at radii beyond the observed millimetre continuum discs in several protoplanetary systems, raising the question of whether these regions could host undetected dust structures. We investigate this for nine of the exoALMA discs by reconstructing gas surface density profiles from midplane pressure gradient measurements derived from $^{12}$CO and $^{13}$CO ALMA Band 7 observations. We evolve the dust using DustPy across a grid of turbulence and fragmentation parameters ($α\in \{10^{-4}, 10^{-3}\}$; $v_\mathrm{frag} \in \{1, 10\}\,\mathrm{m\,s^{-1}}$), followed by radiative transfer calculations with RADMC-3D to give predictions for the continuum emission. We find that the dominant outcome across the explored parameter space is efficient outer dust trapping, leading to prominent outer continuum rings that should be detectable at ALMA Band 7, in tension with the observations. The $^{13}$CO-based reconstructions almost universally produce detectable outer rings, whereas the $^{12}$CO-based reconstructions show more variation. We further test delayed formation of the outer pressure bump and enhanced outer-disc turbulence as possible suppression mechanisms of ring formation. Enhanced turbulence weakens the predicted outer continuum emission most effectively, although the efficiency of the mechanism depends on the system explored and on where the turbulence transition is placed. Delayed bump formation generally does not prevent rapid outer dust accumulation.

astro-ph.EP↗