Simulated CC detections of molecular oxygen in a temperate rocky planet orbiting an M4V star, 12 pc from Earth, using the 39 m E-ELT. This is the same as Figure 6, but for the case of molecular oxygen. In the absence of unocculted star spots (blue curve) and with photon noise turned off, the S/N for the detection is 43, limited by overlap between the template and other molecules present in the exoplanetary atmosphere. With 10% unocculted spot area, the S/N is 9, and when considering only photon noise for 200 transits (lower panel) the S/N for the detection is 4.