How eccentric orbital solutions can hide planetary systems in 2:1 resonant orbits

TL;DR

This paper investigates how two planets in 2:1 resonance can mimic a single eccentric planet in radial velocity data, revealing potential misinterpretations in exoplanet detection.

Contribution

It quantifies the degeneracy between single eccentric planets and resonant planetary systems, highlighting that many reported eccentric exoplanets may actually be multiple planets in resonance.

Findings

35% of reported eccentric single-planet solutions are indistinguishable from resonant systems

40% of solutions cannot be distinguished from circular orbits

Earth-mass planets could be hidden in known eccentric super-Earths and Neptune-like planets

Abstract

The Doppler technique measures the reflex radial motion of a star induced by the presence of companions and is the most successful method to detect exoplanets. If several planets are present, their signals will appear combined in the radial motion of the star, leading to potential misinterpretations of the data. Specifically, two planets in 2:1 resonant orbits can mimic the signal of a single planet in an eccentric orbit. We quantify the implications of this statistical degeneracy for a representative sample of the reported single exoplanets with available datasets, finding that 1) around 35 percent of the published eccentric one-planet solutions are statistically indistinguishable from planetary systems in 2:1 orbital resonance, 2) another 40 percent cannot be statistically distinguished from a circular orbital solution and 3) planets with masses comparable to Earth could be hidden in known orbital solutions of eccentric super-Earths and Neptune mass planets.