Introduction
Understanding how outer giant planets (OGPs) shape the architecture of planetary systems is crucial for theories of planet formation and evolution. The interplay between OGPs and inner light planets (ILPs) remains debated, with models predicting correlations or anticorrelations between these populations. Observationally, results have been varied due to limited samples and heterogeneous methods. This article breaks new ground by detailing an ongoing, homogeneous survey designed to probe ILP occurrence in systems with and without OGPs, using the CORALIE, HARPS, and ESPRESSO spectrographs.
Survey Design and Homogeneity
The project adopts a rigorous approach to ensure sample uniformity across stellar properties and observing strategies. By selecting sun-like stars with carefully matched metallicities, ages, and activity indicators, the team minimizes biases that could masquerade as planetary signals. The observational cadence is standardized across targets, enabling consistent sensitivity to short-period, low-mass planets. This consistency is essential when comparing ILP occurrence in OGP hosts versus non-OGP systems, allowing the study to test competing formation scenarios with greater statistical power.
First Detections: ILPs in OGP Systems
In the present work, three inner planets have been detected in systems known to host outer giants, marking the first concrete ILP discoveries within the OGP host sample. The signals are robust and span short orbital periods, highlighting the ability of high-precision spectrographs to uncover low-mass planets in these dynamic environments.
- HD 23079: an 8.3 Earth-mass (m_E) planet in a 5.75-day orbit, demonstrating a compact inner companion to an outer giant host.
- HD 196067: a 10.4 m_E planet with a 4.6-day period, adding to the growing catalog of ILPs around mature, Sun-like stars.
- HD 86226: a confirmed 7.5 m_E planet in a 3.98-day orbit, reinforcing the presence of close-in, low-mass planets in OGP systems.
Although these discoveries contribute valuable data points, the current sample richness remains modest. A rigorous, formal statistical analysis will follow in subsequent studies, but the preliminary results already challenge some earlier findings that suggested a strong link between the existence of OGPs and ILP frequency. The observed number of ILP detections in OGP systems appears comparatively small, inviting further investigation into selection effects and dynamical histories that shape planetary systems.
Implications for Planet Formation Theories
The emergence of ILPs within OGP-host systems informs competing formation models. A correlation would favor scenarios in which gas giants influence the accretion efficiency or migration paths of inner planets. Conversely, an anticorrelation or a lack of a clear trend could imply that inner planet formation proceeds largely independently of distant giants, or that dynamic interactions erase primordial configurations over time. The current results, while preliminary, underscore the importance of homogeneous samples and long-term monitoring to disentangle these effects.
Next Steps
The team plans to extend the sample, refine activity diagnostics, and apply uniform statistical techniques to quantify ILP occurrence as a function of host star properties and OGP characteristics. Longer time baselines will improve sensitivity to longer-period inner planets, and continued collaboration across CORALIE, HARPS, and ESPRESSO will enhance overall measurement precision. Through this ongoing effort, the study aims to clarify whether a universal link exists between outer giants and inner, low-mass planets or whether the relationship is more nuanced and system-specific.
Conclusion
This first article in a series documents the careful design and early ILP detections in systems with outer giant planets. While the initial detections suggest a modest ILP yield compared with some prior studies, the emphasis on sample homogeneity and long-term data collection sets the stage for a clearer understanding of planetary system architecture. The coming analyses will test theoretical predictions and improve our comprehension of how the grand architecture of planets is assembled around Sun-like stars.
