The multi-planetary systems we have discovered so far (around 850 at the beginning of 2023) exhibit a great variety of architectures. In a pair of papers, Lokesh Mishra and colleagues look at the ensemble of these systems to find common trends that could inform us on the existence of global rules shaping their structure.
The first paper presents a model-independent framework to classify the systems according to the distribution of their planetary masses using two parameters: a coefficient of similarity (CS) that quantifies how much the mass changes from one planet to another, and a coefficient of variation (CV) defined as the ratio of the standard deviation of the masses in a system with their mean. Four classes of system architectures emerge: ‘similar’, where the planets in a system are similar to each other, like in the ‘peas-in-a-pod’ configuration found in many Kepler systems; ‘ordered/anti-ordered’, where the planetary masses increase/decrease with the astrocentric distance; and ‘mixed’. The ‘similar’ class is the most populated one.
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