Embedded Files
Planetary Science with the
Stellar properties shape the global architecture of multi-planet systems (Ramler et al., 2026)
Stellar properties shape the global architecture of multi-planet systems (Ramler et al., 2026)
Ramler et al 2026 explored how planetary mass is distributed within different Ariel multi-planets systems by measuring the fraction of the total system mass contained in the largest planet. Most systems were found to have their largest planet containing between 25% and 75% of the total planetary mass, ranging from systems with relatively equal-sized planets to systems similar to our Solar System, where Jupiter dominates the mass budget. Systems with very high mass concentration (more than 75% of the total mass in one planet) almost always contain only two planets and are generally among the most massive systems observed. This suggests that these systems likely experienced strong accretion onto a single dominant planet or underwent chaotic dynamical evolution, such as planet–planet scattering, collisions, or ejections.
Total planetary mass available in each planetary system, as a function of the stellar mass, colour-coded by the ML metric (see main text). The grey dots represents the mass of planets in single planet systems. Dashed lines are plotted to provide a visual range of masses in terms of MJ. (Ramler et al, 2026)
To better understand these patterns, the systems were divided into low-, mid-, and high-mass categories. High-mass systems typically contain only two planets and show signs of violent dynamical histories, including highly eccentric orbits (eccentricity greater than 0.5) and planets spread across a broad range of orbital distances. These features strongly indicate past gravitational instabilities and scattering events. Mid-mass systems display mixed characteristics, with some appearing dynamically evolved and others retaining more primordial structures. In contrast, low-mass systems tend to host a larger number of planets, sometimes up to six, with masses distributed more evenly among them. Their eccentricities are generally lower and their orbital spacing more regular, suggesting calmer evolutionary histories with only moderate gravitational interactions. Overall, the results imply that the most massive planetary systems evolve through chaotic dynamical processes, while lower-mass systems maintain more stable and orderly architectures.
Multiplicity and eccentricity distributions. Dashed line marks e = 0.1 (Ramler et al, 2026)
Semi-major axis of the largest body in the system, as a function of the host stellar mass, and colour-coded by the total mass in each system. The dashed regression lines are plotted for trend identification purposes. Labels indicate the multiplicity, N, and the eccentricity for each planet (Ramler et al, 2026).
Planets in the Galactic framework (Tsantaki et al, 2025)
Planets in the Galactic framework (Tsantaki et al, 2025)
Cumulative distribution functions for the three planetary mass populations hosted by the stars in the Ariel Stellar Catalogue. The gray dashed line shows the limit of 0.2 Mj to separate between low mass and giant planets. In the currently analysed Ariel sample of transiting planets, the smallest planets orbit mostly thick disc stars.
(Tsantaki et al., 2025)
The study explored how the chemical differences between the Milky Way’s thin and thick galactic discs influence planet formation. Thick-disc stars are generally older, iron-poor, and α-enhanced, while thin-disc stars are younger and richer in metals. The results show a clear difference in the types of planets hosted by these stellar populations: low-mass planets are more commonly found around thick-disc stars, whereas giant, high-mass planets are much more abundant around the younger and more metal-rich thin-disc stars. Statistical analysis confirmed that the planet mass distributions in the two discs are significantly different.
In the sample studied, around 74–75% of planets orbiting thin-disc and transition-disc stars are high-mass planets, while only about 47% of planets around thick-disc stars fall into this category. This suggests that giant planets form more efficiently around stars with solar or super-solar metallicities because these stars possess larger reservoirs of solid material needed to build massive planetary cores. The findings also indicate a possible link between giant planets and stellar age, since thin-disc stars are typically younger and metal-rich. These results are consistent with recent theoretical simulations predicting that giant planets should be common in the thin disc but rare in the thick disc, while low-mass planets can form across the Galaxy with much less dependence on metallicity.
Although observational biases and the lack of a volume-limited sample make it difficult to fully separate evolutionary effects from detection limitations, the study still strongly supports the well-known correlation between stellar iron abundance and the presence of giant planets. Overall, the results suggest that the chemical evolution of the Galaxy has played a major role in shaping planetary populations in different regions of the Milky Way.
Correlations between stellar metallicity and the stellar C, N, O elemental ratios (da Silva et al., 2024)
Correlations between stellar metallicity and the stellar C, N, O elemental ratios (da Silva et al., 2024)
Stellar [C/O] (left) and [N/O] (right) as function of the stellar [Fe/H] for the sample of 60 host stars with all three C, N and O determined. Markers are colour-coded with [N/O] and [C/N] values, respectively. All elemental ratios are normalised to the solar values. The black cross represents the Sun. Dashed line mark the linear regression line.
(da Silva et al., 2024)
What does this mean for the planet characterisation, and in particular for inferring the planetary formation location ?
What does this mean for the planet characterisation, and in particular for inferring the planetary formation location ?
Since the stellar C/N systematically decreases with respect to the solar one for increasing stellar metallicities (left plot), while N/O and C/O systematically increase (right plot), the adoption of solar values (for the host star of the planet you are analysing) means that we systematically underestimate (overestimate) the planetary C/N (N/O and C/O) values for stars of supersolar metallicity, the opposite being true for stars of subsolar metallicity. This leads to incorrect constraints on the formation region of the giant planets from their deviations from the stellar values, for instance, causing giant planets around supersolar metallicity stars to appear to have formed closer to their host stars than they actually have (see e.g. Figs. 7 and 8 in Turrini et al. 2021 or Figs. 4–7 in Pacetti et al. 2022).
[extracted from da Silva et al,. 2024]Page updated
Report abuse