The planetary system v1298 Tauri can be considered a landmark in our current theories of planetary formation: It harbors four near-resonant super-earths orbiting its host star, whose age is estimated to be 20Myr. Recent analysis of  Transiting Time Variations (TTV) data allowed to precisely characterize the dynamical architecture of the system and to pinpoint it in the early stages of it's formation and evolution, shortly after the dispersal of it's protoplanetary gas disk and after the break-up of the resonant chain 6:4:2:1.

The efforts to characterize the dynamical architecture of v1298 Tauri system allowed for tight constrains on the orbital elements of the three inner planets (c, d and b), but planet e's eccentricities e_e are not as sharply determined as those of the inner planets. Additionaly, its longitude of periapsis ϖ_e display an essentially uniform distribution, whereas it was clearly defined for the other planets of the system.

In this context, we propose to better understand how the different possible apsidal configurations of planet e could impact the dynamical stability and the domains of different regimes of motion in v1298 Tauri planetary system.

For this, we mapped the distinct regimes of motion in the (e_e,ϖ_e) plane, which allowed us to observe apsidal corotation for a range of longitudes and eccentricities. After understanding which ϖ_e give rise to apsidal corotation, we dynamically probed stability of the phase space of planets b and e in the (P,e) plane for selected apsidal configurations by making use of the Spectral Number, which calculates through a Fast Fourier Transform (FFT) how many dominant frequencies dominate the motion of the planets. We also mapped the regions in which the secular and the resonant angles (Δϖ = ϖ_b-ϖ_e and σ_be=2λ_b-1λ_e-ϖ_b,e, respectively) were librating for the b-e planet pair. The stability maps are shown in Figure 1.

Figure 1: Stability maps of the phase space of planet e for an anti-aligned apsidal orientation (left panel) and aligned (right panel). Darker blue regions are considered dynamically stable due to being subject to few identifiable frequencies, whereas yellow ones are considered highly chaotic, with motions composed of a high number of noise-like frequencies in the FFT spectra. Greener regions are related to dynamical structures related to the  separatrix of the Mean Motion Resonance. The red dot represents the mean value of P_e, e_e and its errorbars.

We observed that systems that are initially in apsidal alignment (ϖ_e=ϖ_b) allow for persistent apsidal corotation for larger values of e_e, while shrinking the instability region associated with the 2:1 Mean Motion Resonance (MMR) between planets b and e. On the other hand, in the case of anti-aligned apsis (ϖ_e=ϖ_b-π), the instability strip related to the MMR increases around the MMR location, giving rise to regions where the resonant angle λ¹_be librates rather than circulates. We also observed an extended region in low eccentricity regime where λ¹_be librates for different orientations of ϖ_e, hinting for a low-eccentricity resonant regime.

We further investigated sections of the phase space for fixed values of e_e, in which we applied the Frequency Map Analysis, so as to understand the behaviour of the independent frequencies associated with the MMR and with the secular angle, which allowed us to better understand in detail the dynamical mechanisms acting in this system.

Considering how young this planetary system is, better characterizing the possible regimes of motion it can be subject to is fundamental in pointing possible formation and evolutionary pathways.

How to cite: Guimarães, G. and Kokubo, E.: Dynamical Characterization of v1298 b-e planetary pair, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-205, https://doi.org/10.5194/epsc2026-205, 2026.

Giant planets are fundamental to the dynamical evolution of planetary systems. In our solar system, Jupiter and Saturn act as key architects in shaping the asteroid belt and promoting terrestrial planet formation. Among extrasolar planets many similar systems exist such as the system of GJ 876 where three cold giants created an empty inner region analogous to our asteroid belt while driving a super-Earth into a 2-day orbit. To identify the specific mechanisms through which giant planets affect their systems, we performed over 1,200 numerical simulations of planet formation across diverse protoplanetary disks. We found that secular resonances induced by giant planets are, by far, the most dominant factors in the subsequent formation, long-term stability, and final architecture of their systems. For instance, in our solar system, it is the secular resonance of Saturn that limits our terrestrial planets to within 1.9 (au) and inhibits the formation of super-Earths. In contrast, in GJ 876 system, a super-Earth did in fact form, but it was the sweeping secular resonances due to the migration of giant planets that created the system’s asteroid belt-analog and caused the inward scattering of the super-Earth into its close-in and stable orbit. Furthermore, our results demonstrate that secular resonances are crucial to the scattering of planetesimals to large distances, especially during the formation of planets. These scattered bodies are the primary sources of the exo-Oort cloud comets and serve as the origin of the interstellar objects. In this talk, we present a detailed analysis of these implications and highlight how secular resonances dictate system architecture and stability, and also drive the formation of interstellar bodies.

How to cite: Haghighipour, N., Sudol, J., and Honarbakhsh, L.: The Dominant Role of Secular Resonance in Shaping Planetary Architecture, Stability, and the Origin of Interstellar Objects, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-733, https://doi.org/10.5194/epsc2026-733, 2026.

In this work we investigate the problem of orbital stability of planetary orbits in stellar binaries. We carry out  a large number of numerical simulations of  planets on circumbinary (p-type) and circumstellar (s-type) orbits over long timescales.  We cover the whole parameter space by considering three dimensional and eccentric orbits for all bodies in the system, while exploring a wide range of mass ratios.  The results of the numerical integrations provide us with two critical borders: i) for the p-type case, an outer border beyond which all planetary orbits are stable and an inner border closer to the binary below which all planetary orbits are unstable. In between the two borders, a mixture of stable and unstable planetary orbits is observed.  ii) For the s-type case, an inner border closer to the planet hosting star below which all planetary orbits are stable and an outer border beyond which all planetary orbits are unstable. Again, between the two borders, a mixture of stable and unstable planetary orbits is observed. We provide empirical expressions in the form of easy to use fits for these two critical borders. Application of our results to known planetary systems are presented and comparison is made with past results on the subject.

How to cite: Georgakarakos, N., Eggl, S., Ali-Dib, M., and Dobbs-Dixon, I.: Stability of planets in double star systems, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-820, https://doi.org/10.5194/epsc2026-820, 2026.

Circumbinary planets are commonly observed close to the dynamical stability limit of their host binaries, although planet formation is expected to be inefficient in the regions where these planets are currently found. A widely accepted scenario therefore suggests that circumbinary planets formed farther out in a circumbinary disk and migrated inward through planet–disk interactions. During this migration phase, resonant multi-planet configurations may naturally emerge. However, only two multi-planet circumbinary systems orbiting main-sequence binaries have been detected so far, and observational biases are unlikely to fully account for this apparent scarcity. This suggests that the dynamical environment induced by the central binary may strongly affect the long-term stability of such systems.
    
    In this presentation, we investigate the conditions required for the formation of stable circumbinary multi-planet systems through more than 1,000 N-body simulations of migrating super-Earth pairs. We explore the impact of a broad range of binary and migration parameters on the resulting planetary architectures. We first show that planets can be trapped in mean-motion resonance with the central binary, providing the starting point for potential resonant multi-planet chains. We further show that the binary mass ratio and eccentricity strongly influence the long-term stability of these systems, with distinct regions of parameter space leading either to stable configurations or to strong dynamical instability. In addition, for a given binary configuration, the final system architecture can still depend on the adopted migration timescales, related to disk and planet properties. Overall, these results help identify which binary configurations are most favourable for hosting stable circumbinary multi-planet systems. They also provide guidance for future observational surveys and constitute a first step toward studying the stability of circumbinary multi-planet systems in higher-order stellar systems.

How to cite: Grane, R., Cuello, N., Sucerquia, M., Gianuzzi, E., Ávila-Bravo, M., Charalambous, C., and Triaud, A. H. M. J.: Stability of circumbinary multi-planet systems, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-1072, https://doi.org/10.5194/epsc2026-1072, 2026.

Long-period transiting planets provide important constraints on planet formation and evolution, but remain difficult to characterize because their transits are rare and require extended photometric follow-up. Thanks to its unique Antarctic location, ASTEP (Antarctic Search for Transiting ExoPlanets) is particularly well suited to the monitoring of such systems, enabling continuous observations over long time baselines and contributing to the characterization of planets on orbits of several tens to hundreds of days. For long-period planets in multi-planet systems, mutual gravitational perturbations can generate detectable transit timing variations, providing a valuable route to measuring planetary masses and characterizing the architecture of systems that are otherwise difficult to constrain.

Several of these long-period TTV planets appear to have unusually low densities and inflated radii. The origin of these properties remains unclear, especially in systems where stellar irradiation alone cannot easily account for the observed inflation. These planets therefore represent important benchmarks for testing our understanding of formation pathways, interior composition, atmospheric evolution, and cooling histories. In this contribution, I will present the analysis of long-period TTV systems observed with ASTEP, with a focus on their photometric follow-up and physical characterization. I will also discuss preliminary interior and evolution models computed with the stellar evolution code Cesam2k20, recently extended to model exoplanets through updated equations of state, opacity tables, and planetary atmosphere prescriptions. Finally, I will discuss how these results fit into the perspective of PLATO, which is expected to uncover new long-period transiting planets for which dedicated ground-based follow-up will be essential.

How to cite: Gauvrit, L., Petit, A., Guillot, T., Suarez, O., Mekarnia, D., Abe, L., Dransfield, G., H.M.J Triaud, A., and Almenara, J. M.: Long-period TTV planets observed with ASTEP: analysis and modelling with Cesam2k20 in preparation for PLATO, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-1030, https://doi.org/10.5194/epsc2026-1030, 2026.

Over the past decade, advances in high-contrast imaging and extreme adaptive optics have enabled the discovery of planets and brown dwarfs orbiting at wide separations from their host stars, challenging current planet-formation paradigms. We present SaNDi-SHoP, a VLT/SPHERE star-hopping survey aimed at the search for satellites and circumplanetary disks around direct imaged companions. Our sample comprises thirteen planetary-mass and brown dwarf companions observed between June 2023 and July 2025. The survey also provides updated near-infrared photometry, new high-precision astrometry, and low-resolution IFS spectra for GQ Lup B, PZ Tel B, and HD 984 B.  We identify extended residuals around TYC 8047-232-1 B consistent with a possible 3-6 Jupiter masses satellite companion, and marginal residuals at the location of the previously proposed candidate around DH Tau b, compatible with a 1 Jupiter mass satellite. Our analysis generally excludes companions more massive than a few Jupiter masses beyond 1-5 au. Combining our astrometry with literature measurements, we derive updated orbital solutions for all systems, including the first orbital fits for CT Cha b, HIP 78530 B, HIP 64892 B, and RX J1609.5–2105 b. The updated orbital constraints favor eccentric, non-circular orbits for most companions, supporting formation scenarios involving gravitational instability or molecular cloud fragmentation. Alternatively, the observed eccentricities may result from dynamical interactions and planet–planet scattering. 

How to cite: Bernardi, A.: SaNDi-SHoP: Searching for Satellites’N’Disks with a Star-Hopping Program, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-283, https://doi.org/10.5194/epsc2026-283, 2026.

Atmospheric escape and orbital evolution play a central role in shaping the observed exoplanet population, particularly the structure of the radius–period diagram. Features like the Neptunian desert raise fundamental questions about formation, long-term evolution and survivability. Yet, dynamical and atmospheric evolutions are usually treated separately. To address this need, we developed JADE (Joining Atmosphere and Dynamics for Exoplanets), a framework that self-consistently models the coupled evolution of secular orbital migration and atmospheric escape over billion-year timescales. JADE has successfully reproduced the misaligned orbit of the warm Neptune GJ 436 b, demonstrating how late-stage high-eccentricity migration driven by a massive outer companion can delay atmospheric loss. It is now routinely used to study the evolution of Jupiter- to Neptune-mass planets with H/He-dominated envelopes.
To study the potential erosion of gas giants into sub-Neptunes, we expanded JADE to include metal-enriched and water-dominated atmospheres. By refining atmospheric opacities and equations of state, and by implementing fractionated mass loss of hydrogen and oxygen, we enable more realistic simulations of envelope erosion and internal structure evolution. JADE is an open-source and versatile tool, and we welcome collaborations to broaden its applicability across diverse exoplanetary systems. JADE, constrained by atmospheric escape signatures from near-IR spectrographs, high-precision constraints from transit (e.g., PLATO) and radial-velocity (e.g., ESPRESSO, ANDES) surveys, as well as compositional constraints from atmospheric measurements (e.g., JWST, ARIEL), will enable population-level studies across the entire close-in planets landscape.

How to cite: Wong, E., Bourrier, V., Alibert, Y., Eggenberger, P., Egger, J., Dorn, C., Leconte, J., Mordasini, C., Owen, J., and Valatsou, M.: Long-Term Evolution of Gas Giants and Sub-Neptunes with the JADE Code, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-1402, https://doi.org/10.5194/epsc2026-1402, 2026.