Lyman-α light curve of 55 Cnc b from Fig. 5 (top panel) compared to a best-fit model transit light curve (thick line) with an impact parameter of 1.03 and an optically thick radius of 0.35 times the size of the Roche lobe. Inset: Sketch of the system at inferior conjunction. The Roche radius of the planet is represented by the dotted circle, while the shaded region corresponds to the optically thick hydrogen envelope.