Top: phase space of the co-orbital resonance valid for small eccentricities and inclinations. The x axis displays the resonant angle ζ = λ₁ − λ₂ while the y axis is its normalised angular frequency, which is proportional to . Bottom: value of the normalised fundamental frequency ν for initial conditions along the line (ζ,) of the top graph. Both graphs were obtained by integrating Eq. (1).