Comparing the Architectures of Multiplanet Systems from Kepler, K2, and TESS Data

TL;DR

The paper investigates multiplanet system architectures across Kepler, K2, and TESS by analyzing adjacent planet period ratios with kernel density estimation, focusing on resonant and near-resonant structures. It constructs consistent samples from Kepler DR25/Lissauer catalogs and TESS/K2 data, identifies robust features at mean-motion resonances (notably $ rac{3}{2}$ and $ rac{2}{1}$) and a secondary $2.19$-ratio peak, and assesses their significance with Monte Carlo simulations and KS/AD tests. The results show Kepler’s distribution is dominated by the $ rac{3}{2}$ MMR peak and a persistent $ rac{2}{1}$ feature, while TESS exhibits a strong exterior-to-2:1 excess and a nearby $ rac{3}{2}$ peak with a significant $2.19$ signal; K2 displays weaker resonant structure, though the vetted Zink K2 catalog aligns better with Kepler. The study demonstrates that many observed peaks have an astrophysical origin, while survey-specific biases influence the detectability of certain features, informing formation and migration models and guiding cross-survey demographic comparisons.

Abstract

Exoplanet surveys like Kepler, TESS, and K2 have shown that planetary systems are common in our galaxy. These surveys, along with several others, have identified thousands of planetary candidates, with more than five thousand having already been confirmed. Many of these planetary systems host multiple planets. As we discover more multiplanet systems, notable trends begin to appear in the data. We use kernel density estimation (KDE) to analyze the period ratios of adjacent planet pairs in multiplanet systems in the most recent Kepler, TESS and K2 data, paying particular attention to pairs in first order mean motion resonance (MMR). We compare a recent Kepler catalog with the DR25 data release. We also compare TESS and K2 against this recently released Kepler data. To verify the significance of our findings against selection bias, we perform Monte Carlo simulations of multiplanet systems in the TESS catalog, finding an excess of planet pairs near the 2 (2:1), and 1.5 (3:2) period ratios, both exceeding the 99\% confidence interval. We also find a significant peak at the 2.19 period ratio, which exceeds the 90\% confidence interval. Using a lower limit for period ratios determined by the period of the inner planet proposed in Steffen & Farr (2013), we identify two planet pairs orbiting M dwarf stars in a very tight ratio. We also note a likely misidentified planet pair orbiting an FGK type star, which if further study proves to be true, would indicate that only planets orbiting M dwarf stars may violate this limit.

Figures (4)

• Figure 1: Scatter plot showing the period ratio as a function of the inner planet period, in days, for Kepler (blue), TESS (green), and K2 (red). The solid blue line in the lower left corner indicates a lower limit to observed period ratios (\ref{['eq:1']}) as discussed in Section \ref{['sec:close in']}.
• Figure 2: Kernel Density Estimation using the normal distribution of Kepler (top), TESS (middle), and K2 (bottom) for period ratios of adjacent planet pairs. The vertical dashed lines denote the locations of the 5/4, 4/3, 3/2, 2/1, and 2.19 period ratios. Top figure compares adjacent planet pairs between the Lissauer and DR25 catalogs.
• Figure 3: P-value results for Kolmgorov-Smirnov (a) and Anderson-Darling (b) tests comparing the orbital periods of the TESS and K2 catalogs against the Kepler catalog. For each maximum period value, planets with larger orbital periods are removed from consideration.
• Figure 4: Significance estimates for the peaks of the KDE of the period ratio distribution for TESS multiplanet systems using 1000 realizations of the nominal (unimodal) distribution. The 90th (green), 95th (blue), and 99th (red) intervals are indicated.