Couples of period ratio and Love number of the planet that solve Equations (8) and (9). The blue and light blue points correspond to a combination of (F_p, k_2,p) that satisfies the observed periastron precession rate within its 1σ, 2σ, and 3σ error bars (red, green, and blue areas, respectively). The red horizontal line represents the physical limit where the body is homogeneous. From left to right, the three vertical lines highlight a non-rotation planet (P_orb/P_rot,p →0), synchronous rotation (P_rot,p = P_orb), and the break-up limit (P_rot,p ≃ 8.95 P_orb, corresponding to P_rot,p ≃ 2.18 hours). The grey shaded regions are unphysical.