The population of over six thousand detected exoplanets demonstrates remarkable diversity, spanning rocky planets, ocean worlds, and gas giants. The astrophysical mechanisms driving this broad spectrum of planetary outcomes are not yet fully constrained. Here, we systematically analyze the interplay between protoplanetary disc lifetime, host star mass, and the resulting planet type to elucidate the underlying physical processes.

The evolution and dispersal timescale of protoplanetary discs constitutes a pivotal constraint on the planet formation process. While the mean disc lifetime offers a first-order estimate for the temporal window available for planet assembly, it fails to account for the considerable star-to-star scatter and the systematic dependence on stellar mass. To overcome these limitations, we quantify the full disc lifetime probability distribution as a function of stellar mass. Our analysis uncovers a strong mass dependence: fitting the distributions with a Weibull profile, we identify maxima at t_max^H = 3. 7 Myr for higher-mass stars (~1—3 M_Sun) and t_max^L = 7.2 Myr for low-mass stars (~0.01—0.2 M_Sun), assuming an initial disc fraction of f_init = 80%. All distributions are intrinsically broad (typically 3.2 Myr < s < 4.7 Myr), with the low-mass star sample showing a somewhat greater width.

Our results further indicate that a significant fraction of stars are not initially encircled by a protoplanetary disc (60% < f_init < 90% at cluster zero age), with the initial disc fraction dropping to approximately f_init ≈ 40% for higher-mass stars. Potential mechanisms—such as external photoevaporation, stellar encounters, and variations in core accretion efficiency—may account for the observed dispersion and the mass dependence in disc lifetime distributions and initial disc fractions.

To probe the link between disc lifetime diversity and the architecture of planetary systems, we utilize planetary bulk densities as diagnostics for planet classification. Our findings reveal three distinct host star mass regimes associated with planet type: (1) For M_s < 0.3 M_Sun, the formation of rocky planets is strongly favoured; (2) in the range 0.3 M_Sun < M_s < 1.2 M_Sun, all planet types are present but ocean worlds predominate; and (3) for M_s > 1.2 M_Sun, gas giants emerge as the dominant population.

The corresponding disc lifetimes for different planet types vary substantially: giant planet formation predominantly occurs within 1–4 Myr, ocean worlds assemble within 5–10 Myr, and rocky planets may require disc survival beyond 10 Myr. Planet formation efficiency declines sharply with increasing stellar mass and decreasing mean disc lifetime; fewer than 6–13% of stars in the 1.5–3 M_Sun range host giant planets, while rocky planets are prevalent (>60%) around low-mass stars. We discuss the critical role of disc lifetime in setting the overall efficiency of planet formation.

How to cite: Pfalzner, S., Wagner, F. W., and Dincer, F.:  Stellar Mass, Disc Lifetimes, and the Origins of Exoplanet Diversity , Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-35, https://doi.org/10.5194/epsc2026-35, 2026.

A key question in astronomy is how ubiquitous Earth-like rocky planets are. The formation of terrestrial planets in our Solar System was strongly influenced by the radioactive decay heat of short-lived radionuclides (SLRs), particularly 26Al (aluminum-26), likely delivered from nearby supernovae. However, current models struggle to reproduce the abundance of SLRs inferred from meteorite analysis without destroying the protosolar disk. We propose the "immersion" mechanism, where cosmic-ray nucleosynthesis in a supernova shockwave reproduces estimated SLR abundances at a supernova distance (~1 parsec), preserving the disk. We estimate that solar mass stars in star clusters typically experience at least one such supernova within 1 parsec, supporting the feasibility of this scenario. This suggests that Solar System─like SLR abundances and terrestrial planet formation are more common than previously thought.

How to cite: Sawada, R., Kurokawa, H., Suwa, Y., Taki, T., Lee, S.-H., and Tanikawa, A.: Cosmic-ray bath in a past supernova gives birth to Earth-like planets, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-590, https://doi.org/10.5194/epsc2026-590, 2026.

A longstanding assumption is that planetary growth commences after the infall of gas and solids to a circumstellar disk ends, with disk infall and planet accretion traditionally modeled as two separate phases.  While conceptually and computationally convenient, this division may not always be physically valid: indeed, there is substantial observational evidence that accretion commences early and even during infall in some systems. 

We are developing a first generation of simulations to assess the effects of planet accretion during late disk infall on resulting system properties.  In Rufu & Canup (2025), we focused on compact systems, whose short orbital timescales imply that once > km-sized planetesimals form, full planet accretion proceeds rapidly on timescales shorter than or comparable to infall timescales.  We simulated planet growth within a disk supplied by an infall with small centrifugal radius, r_c ~ 0.1 to 0.5 au.   In disk regions undergoing infall (i.e., for r < r_c,), planet masses are set by a balance between accretion of infalling solids and Type I migration.  This produces a similar planet size within each system, consistent with the observed “peas-in-a-pod’’ structure, which can also be explained by prior, post-infall formation models.    

Figure 1:  Estimated total mass of transiting compact systems, M_tot, scaled to the stellar mass, M_*, for compact systems having ≥3 known planets that orbit a single star within a<0.5 au (circle markers, blue box).  Points are ordered left-to-right by ascending stellar mass. For cases without mass estimates, we use the observed planet radius, increase the estimated radius uncertainty by a factor of 2, and then apply a radius vs. mass relation.  Light [medium] blue circles are systems with all [some] planetary masses estimated from this relation, while dark blue circles are systems with measured planetary masses.   Over a wide range of stellar masses, compact multi-planet systems display a common mass ratio, with 90% of systems having 3 x10^-5 < (M_tot/M_*) < 3 x 10^-4.  This mass ratio is more similar to that of the gas giant satellite systems (square markers, yellow box) than to the inner or outer planets in our Solar System (triangle markers, red box).

More notably, Rufu & Canup (2025) find that accretion during infall explains two traits of compact systems that are not easily explained by standard, post-infall models.  First, compact systems display a remarkably consistent ratio between the total planetary mass and the stellar mass, with this ratio being few times 10^-5 to 10^-4 across systems whose stellar masses vary by an order-of-magnitude (Figure 1).  Why such a preferred mass ratio would exist for varied stellar masses and disk evolutions has been a mystery.  We show that accretion during infall regulates a compact system to have this common mass ratio for a wide range of disk and infall conditions (Figure 2).  Second, the mass of compact system planets shows an unusually weak dependence on stellar metallicity, in contrast to, e.g., gas giants.  For a standard post-infall model, planet masses would generally be proportional to metallicity, in contrast to the observational trend.  We find that accretion during infall yields planet and planet system masses that have only a weak dependence on metallicity, providing an explanation to this long-standing problem.      

We will discuss observational implications of planet accretion during infall and key areas for further advancement.  The latter include a better understanding of where and when early planetesimals may form, particularly during the late stages of infall.

Figure 2:  Results of compact planet system accretion simulations with varied disk and infall properties. Final planetary system mass scaled to the stellar mass as a function of (ae/f) (a is the viscosity parameter, e is the fraction of infalling solids incorporated into planets, and f is the infall gas-to-solids ratio). The infall rate decays with timescale t_in = 5 x 10⁵ yr, while the gas disk disperses over a longer timescale, t_g= 1.3 to 2t_in (colors, legend). The simulations assume either an inner disk cavity (triangles) or no cavity (circles). Grey region shows range for 90% of observed compact systems shown in Figure 1.  Dashed lines show analytical predictions for the no-cavity case.  Horizontal bars show plausible viscosity ranges, assuming (f/e) = 100.

Rufu, R. and R. M. Canup (2025)  “Origin of compact exoplanetary systems during disk infall” Nature Communications, 16, 4853.

How to cite: Canup, R. and Rufu, R.: Accretion of compact system planets during late infall to a circumstellar disk, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-724, https://doi.org/10.5194/epsc2026-724, 2026.

Rocky planets on short-period orbits are the most common planets found around late M dwarfs. Around these small, cool stars, such planets can range from potentially temperate worlds to highly irradiated lava planets with molten surfaces. While many formation pathways have been proposed for such close-in rocky planets, the origin of the most extreme cases, ultra-short-period (USP) planets with orbital periods shorter than one day, is still not fully understood. In this talk, I will discuss whether the formation and survival of USP planets can be linked to the location of the inner edge of the protoplanetary disk. To test this, we performed N-body simulations that include planet-disk interactions, star-planet tidal interactions, and relativistic corrections. The simulations start from lunar-mass planetary seeds growing by pebble accretion in a low-viscosity disk. We compared three different prescriptions for the inner disk edge: a fixed close-in edge, an outward-moving edge set by the magnetospheric truncation radius, and an inward-moving edge associated with the corotation radius. The results show that the formation of USP planets appears to be strongly controlled by the location of the disk’s inner edge. USP planets are produced only when the disk edge either remains close to the star or evolves inward, because migrating planets tend to follow the motion of the disk edge. These findings suggest that USP planet formation around late M dwarfs is favored when the inner edge of the disk stays near the corotation radius of a rapidly rotating star.

How to cite: Brandenberger, S. N., Sanchez, M., Van der Marel, N., Vidotto, A. A., and Miguel, Y.: Following the Edge: How Inner Disk Edges Shape Ultra-Short-Period Planet Formation, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-639, https://doi.org/10.5194/epsc2026-639, 2026.

Since the first detection of an exoplanet orbiting a Sun-like star more than thirty years ago, exoplanet science has advanced at an extraordinary pace. More than 6,000 exoplanets have now been confirmed, and this number is expected to grow rapidly in the coming years. Advances in detection and characterisation techniques, supported by a wide range of ground- and space-based observatories, have greatly expanded our ability to study planets beyond the Solar System.

In parallel, theoretical modelling has progressed dramatically. Modern simulations can now model protoplanetary discs on global scales while including radiation and magnetic fields. Yet a fundamental challenge remains: planet formation itself is rarely observable directly. Constraining formation models therefore requires large ensembles of simulations whose outcomes can be compared statistically with the observed exoplanet population. Owing to their low computational cost, 1D models remain the preferred tool for such studies.

This computational efficiency, however, comes at the cost of physical simplifications, particularly in the treatment of planet–disc interactions. Existing models often rely on simplified prescriptions for orbital migration and gap formation, especially in multi-planet systems. These approximations can significantly affect predictions for planetary masses and orbital distributions.

Here, we present a novel framework for modelling planet–disc interactions in 1D simulations. Our approach includes a detailed treatment of angular momentum exchange between planets and the disc and accurately reproduces gap structures seen in hydrodynamic simulations.

How to cite: Schib, O.: Towards a comprehensive model for planet-disc interaction in 1D models, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-1046, https://doi.org/10.5194/epsc2026-1046, 2026.

Context. Much like the Sun, measurements of radius and temperature of starspots in young solar-like stars are key parameters to quantify the level of magnetic activity in such stars. The magnetic activity can be particularly impactful in stars hosting transiting exoplanets, because it induces brightness variations that negatively impact the accuracy of exoplanet transit measurements. In particular, these variations can affect the transit depth estimates, having the potential to alter planetary transmission spectra, that could undermine the interpretation of results in exoplanet atmospheric characterizations. 

Aims. Our objective is to study the magnetic activity of solar-like stars to be inferred by studying the starspots transited by hot-Jupiter exoplanets. For that, we used the planetary transit mapping method to probe for occulted spots by the exoplanets, in order to map the physical characteristics of the individual spots. Specifically, our main objective is to break the degeneracy between the radius and intensity (contrast) of stellar spots inferred from planetary transit mapping, using chromatic photometric observations in multiple bands.

Methods. Continuing the previous study of the stellar activity done by our research group, we propose a new non-parametric variation of the transit model incorporating the contamination from occulted starspots, using the ECLIPSE tool. For this purpose, differently from previous studies of targets from the CoRoT and Kepler missions, chromatic data provided by instruments in space and ground-based telescopes will be used, among the combined monochromatic signal and usually denomined as ‘white light’, by the sum of the individual channels. Based on the results from the model fitting of the exoplanet transits with starspots contamination, physical characteristics will be used to estimate the temperature and the intensity of the magnetic field of the spots. Moreover, a possible differential rotation may also be estimated, assuming the persistence of spots among subsequent transits of the exoplanet. 

Results. We employed the transit mapping method to probe starspot-crossing events of the solar-like star CoRoT-2, in transit observations of the exoplanet CoRoT-2 b, using archival observations from the CoRoT space mission, using its three colors (blue, green, and red) from the exoplanet channel. From the intensities of these spots, we estimated the temperatures assuming a blackbody emission and employing a PHOENIX stellar atmospheric model, as well as the relative sizes for the spots. Our results show spots up to about 200 K cooler than the stellar photosphere (5529 K) and having radii of 0.31 stellar radii, or 196 Mm, and both larger than values from previous studies for CoRoT-2 in white light, corresponding to solar penumbra temperatures for spots much larger than typical sunspots. So, we can conclude that the degeneracy between the radius and the intensity of the spots, present in the analysis in "white light", can underestimate the size and intensity of the starspots. We also compare the results from CoRoT to the results from ground-based observations using the multi-channel instruments SPARC4 and MuSCAT3.

How to cite: O. Kovacs, A. and Valio, A.: Analysis of stellar magnetic activity through non-parametric modeling of transits in chromatic light curves: mapping of starspots with the ECLIPSE algorithm, Europlanet Science Congress 2026, The Hague, The Netherlands, 6–11 Sep 2026, EPSC2026-163, https://doi.org/10.5194/epsc2026-163, 2026.