ExoNAMD: Leveraging the spin-orbit angle to constrain the dynamics of multiplanetary systems

TL;DR

ExoNAMD is a new open-source tool that uses the normalized angular momentum deficit metric, incorporating spin-orbit angles, to evaluate and compare the dynamical states of multiplanetary systems, aiding future exoplanet research.

Contribution

The paper introduces ExoNAMD, a novel tool that enhances dynamical state assessment of exoplanet systems by integrating spin-orbit angles into the NAMD metric.

Findings

Inclusion of spin-orbit angle improves dynamical state description.

A-NAMD provides better insights than R-NAMD.

Tool facilitates target selection for future observations.

Abstract

Multiplanetary systems are excellent laboratories for studying the formation and evolution of exoplanets inside the same stellar environment. The number of known multiplanetary systems is expected to skyrocket with the advent of PLATO and the Roman space telescope. The spin-orbit angle is a key context information for the systems' dynamical history, and in recent years a growing number of planets had their spin-orbit angle measured, revealing a large diversity in orbital configurations, from well-aligned to polar, and even retrograde, orbits. Still, observers lack a robust tool to compare the dynamical state of different systems and to select the most suitable ones for future avenues of exploration, such as investigating the evolutionary pathways and their links to the atmospheric composition. Here, we present ExoNAMD, an open source code aimed at evaluating the dynamical state of multiplanetary systems via the Normalized Angular Momentum Deficit (NAMD) metric. The NAMD measures the deficit in angular momentum with respect to circular, co-planar orbits. It is normalized to compare systems with different architectures and provides a lower limit on the past dynamical excitation of the system. We find that using the spin-orbit angle parameter in the NAMD calculation (A-NAMD) improves the dynamical state's description, compared to using only the relative inclinations (R-NAMD). Comparison of A-NAMD and R-NAMD also yields powerful insights into the interplay between eccentricity and spin-orbit angle. ExoNAMD is a timely tool for easy and fast comparison of the myriad of exoplanetary systems to be discovered by PLATO and Roman, and to optimize the target selection and scientific output for future atmospheric characterization using ELTs, JWST, and Ariel.