Planets similar in size are often dissimilar in interior

• Published in: Astronomy and astrophysics (Berlin) 2024-05, Vol.685, p.A143
• Main Authors: Mamonova, E., Shan, Y., Hatalova, P., Werner, S. C.
• Format: Article
• Language: English
• Subjects: Bulk density; Correlation; Data points; Extrasolar planets; Metallicity; Peas; Planet detection; Planet formation; Planetary composition; Planetary evolution; Planetary systems; Similarity; Statistical analysis; Trends
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202347049

The number of discovered exoplanets now exceeds 5500 allowing statistical analyses of planetary systems. Multi-planet systems are mini-laboratories of planet formation and evolution, and analysing their system architectures can help us to constrain the physics of these processes. Recent works have found evidence of significant intrasystem uniformity in planet properties such as radius, mass, and orbital spacing, collectively termed ‘peas in a pod’ trends. In particular, correlations in radius and mass have been interpreted as implying uniformity in planet bulk density and composition within a system. However, the samples used to assess trends in mass tend to be small and biased. In this paper, we re-evaluate correlations in planet properties in a large sample of systems with at least two planets for which mass and radius have been directly measured, and therefore bulk density can be calculated. Our sample was assembled using the most up-to-date exoplanet catalogue data, and we compute the relevant statistics while using a procedure to ‘weight’ the data points according to measurement precision. We find a moderate correlation in radius and a weak correlation in the densities of adjacent planets. However, masses of neighbouring planets show no overall correlation in our main sample and a weak correlation among pairs of planets similar in size or pairs restricted to M p