Maximal outflow length observed projected on the plane of the sky, L_max, vs. the mass of the launching core, M_core (a) and the visual extinction of the cloud background crossed by the outflow, A_V (b). For the longest outflows, measurements at their tip (in parenthesis in Table 2) are used instead of that averaged over their complete extent. Filled and empty squares pinpoint outflow lobes developing in the central and south-western parts of W43-MM1, respectively. Blue and red colors show theblue- and red-shifted lobes, respectively. The anti-correlation found in (b) (best fit line with α = −0.5 ± 0.1) suggests that molecular outflows are shorter in denser environments.