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Kepler-9 was the first case where transit timing variations have been used toconfirm the planets in this system. Following predictions of dramatic TTVs -larger than a week - we re-analyse the system based on the full Kepler dataset. We re-processed all available data for Kepler-9 removing short and longterm trends, measured the times of mid-transit and used those for dynamicalanalysis of the system. The newly determined masses and radii of Kepler-9b and-9c change the nature of these planets relative to the one described in Holmanet al. 2010 (hereafter H10) with very low, but relatively well charcterised (tobetter than 7%), bulk densities of 0.18 and 0.14 g cm$^3$ (about 1/3 of the H10value). We constrain the masses (45.1 and 31.0 M$_\oplus$, for Kepler-9b and-9c respectively) from photometry alone, allowing us to see possibleindications for an outer non-transiting planet in the radial velocity data. At$2R_\oplus$ Kepler-9d is determined to be larger than suggested before -suggesting that it is a low-mass low-density planet. The comparison between theH10 analysis and our new analysis suggests that small formal error in the TTVinversion may be misleading if the data does not cover a significant fractionof the interaction time scale.

Kepler-9 revisited 60% the mass with six times more data