Top: transit probability for a planet in a circular orbit around GJ 1214 as a function of the orbital period, assuming σ_disk = 0 (black), 1.1 (green), 2.2 (red) and 4.4 deg (blue), and neglecting the transiting nature of the known planet (dashed line). Middle: transit depth of a planet orbiting around GJ 1214 as a function of the planetary radius. Bottom: RV semi-amplitude above which a planet could be detected in the HARPS data. See text for details.