How Eccentric Orbital Solutions Can Hide Planetary Systems in 2:1 Resonant Orbits

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 resonant orbits can mimic very efficiently the signal of a single planet in an eccentric orbit. We quantify the physical implications of this solution degeneracy using the well known harmonic expressions of keplerian motion. We find that a significant fraction of the published eccentric one-planet solutions might instead be multiple planet systems in near circular orbits , and that several planets with masses comparable to Earth could have already been detected. Subject headings: Exoplanets – Orbital dynamics – Planet detection