Neutron star (NS) merger ejecta offer a viable site for the production of heavy r-process elements with nuclear mass numbers A > ∼ 140. The crucial role of fission recycling is responsible for the robustness of this site against many astrophysical uncertainties, but calculations sensitively depend on nuclear physics. In particular the fission fragment yields determine the creation of 110 < ∼ A < ∼ 170 nuclei. Here we apply a new scission-point model, called SPY, to derive the fission fragment distribution (FFD) of all relevant neutron-rich, fissioning nuclei. The model predicts a doubly asymmetric FFD in the abundant A 278 mass region that is responsible for the final recycling of the fissioning material. Using ejecta conditions based on relativistic NS merger calculations we show that this specific FFD leads to a production of the A 165 rare-earth peak that is nicely compatible with the abundance patterns in the Sun and metal-poor stars. This new finding further strengthens the case of NS mergers as possible dominant origin of r-nuclei with A > ∼ 140.PACS numbers: 26.30. Hj,24.75.+i,26.60.Gj Introduction.-The rapid neutron-capture process (rprocess) of stellar nucleosynthesis explains the production of the stable (and some long-lived radioactive) neutron-rich nuclides heavier than iron that are observed in stars of various metallicities and in the solar system (see review of [1]). While r-process theory has made progress in understanding possible mechanisms that could be at the origin of the solar-system composition, the cosmic site(s) of the r-process has (have) not been identified yet and the astrophysical sources and specific conditions in which the r-process takes place are still among the most longstanding mysteries of nuclear astrophysics.

International audienceUntil now, the mass asymmetry in the nuclear fission process has been understood in terms of the strong influence of the nuclear structure of the nascent fragments. Recently, a surprising asymmetric fission has been discovered in the light mercury region and has been interpreted as the result of the influence of the nuclear structure of the parent nucleus, totally discarding the influence of the fragments' structure. To assess the role of the fragment shell effects in the mass asymmetry in this particular region, a scission-point model, based on a full energy balance between the two nascent fragments, has been developed using one of the best theoretical descriptions of microscopic nuclear structure. As for actinides, this approach shows that the asymmetric splitting of the 180Hg nucleus and the symmetric one of 198Hg can be understood on the basis of only the microscopic nuclear structure of the fragments at scission