enhanced during the previous 1:2 MMR crossing. Our understanding of planet formation is too limited to assess with confidence where Saturn formed. However, there is an emerging view that Saturn might have accreted its atmosphere (and therefore acquired the bulk of its mass) when it was already quite close to Jupiter. In fact, the immediate neighborhood of Jupiter’s gap, being a local maximum of the disk’s surface density, acts as an accumulation point of dust and small planetesimals (Haghighipour and Boss, 2003), and thus appears as a sweet spot for the growth of Saturn’s core. Moreover, Saturn’s core, independently of its formation location, might have suffered Type I migration until it was halted at the edge of Jupiter’s gap, which acts as a planet trap (Masset et al., 2006), or in a mean motion resonance with Jupiter (Thommes, 2005). Thus, we believe that it is important to verify whether the MS01 mechanism can still work if Saturn is released in the proximity of Jupiter.

Fig. \[MS-proches\] shows the result of a simulation that differs from the previous one only for the initial location of Saturn (now at $r=1.4$). As one sees, after a short range migration, the planet is trapped 