Broadband light curve fits for both JWST observations. Left: combined NIRSpec NRS1 and NRS2 broadband light curve fit of the overlapping transits of TOI-270 b and TOI-270 d. JWST ETC calculations predict noise levels of ≈85 ppm, which is roughly 12% below the standard deviation of our residuals. Right: NIRISS first order broadband light curve fit of the transit of TOI-270 d. From S/N calculations with the ETC one would expect a noise level of ≈69 ppm, much lower than we find to be the case for the broadband light curve. This could partially be caused by stellar activity, see Appendix B.