Understanding the Link Between Outer Giant Planets and Inner Light Planets
Planetary systems come in a dazzling variety, but a central question persists: do outer giant planets (OGPs) influence the presence and properties of inner light planets (ILPs)? Theoretical models offer contrasting predictions. Some scenarios anticipate a positive correlation, where giant planets shepherd or promote the formation of close-in, rocky worlds, while others suggest an anticorrelation, where OGPs disrupt inner planet formation or stability. Observationally, the picture remains murky due to small samples, heterogeneous methods, and limited statistics. The present study outlines a long-term observational program designed to test these ideas with a homogeneous approach across targets.
The Observational Program and Sample Homogeneity
Using a coordinated effort with CORALIE, HARPS, and ESPRESSO, the project seeks to quantify the occurrence of ILPs in systems with and without OGPs. A key strength of the program is its emphasis on sample homogeneity—careful matching of stellar properties (mass, metallicity, age) and a uniform observing strategy—to minimize biases in detection efficiency. By controlling these variables, the team aims to reveal genuine trends in planetary architecture rather than artifacts of sample selection.
First Detections of ILPs in OGP-hosting Systems
In this first article of a series, three inner planets have emerged in systems known to host outer giants. The detections come from high-precision radial-velocity measurements, enabling the confirmation of low-mass, short-period planets that complete the inner architecture picture in their respective systems:
- HD 23079: a planet with a minimum mass of 8.3 Earth masses (mE) in a 5.75-day orbit.
- HD 196067: a planet with a minimum mass of 10.4 mE in a 4.6-day orbit.
- HD 86226: confirmation of a 7.5 mE planet in a 3.98-day orbit.
These planets are compact, short-period ILPs that lie well inside the orbits of any known outer giants in their systems. Their existence adds important data points to the ongoing debate about how outer and inner planets coexist and evolve.
What the Detections Tell Us About Planetary Architecture
Although a rigorous statistical comparison is reserved for subsequent analyses in this program, the initial results hint at a nuanced landscape. The relatively small number of detected ILPs in this OGP-host sample contrasts with some previous studies that reported a strong correlation between outer giants and inner planets. Several factors could explain this discrepancy, including the diversity of stellar environments, the diversity of giant-planet configurations, and the sensitivity limits of different surveys. The current work emphasizes controlling these variables to allow a fair assessment of whether ILP occurrence is enhanced, hindered, or unchanged by the presence of OGPs.
Future Prospects and Implications for Planet Formation
As the survey continues, the team will expand the sample and perform formal statistical analyses that account for detection biases and observational completeness. The results will feed into broader theories of planet formation, including core accretion and migration pathways, and will help clarify whether OGPs play a constructive role in shaping inner planetary systems or whether their influence is limited or even detrimental to ILP formation and survival.
Authors across several institutions emphasize that this is an ongoing, collaborative effort. The findings to date—detections of three ILPs around HD 23079, HD 196067, and HD 86226—highlight the value of uniform, long-term monitoring in resolving questions about planetary system architecture and the interconnected fates of inner and outer planets.
