In the frame of the Europlanet-RI-2020 program, the VESPA (Virtual European Solar and Planetary Access) team has developed a metadata dictionary dedicated to data discovery in solar system sciences. The dictionary is called EPNcore and includes metadata for data coverage (temporal, spatial, spectral…), data content (target, measured parameter…), data origin (instrument, publisher…) and data access (format, URL…). In order to interoperate with the NASA/PDS4, the main archive information model in planetary sciences, it is first necessary to implement the EPNcore dictionary into the PDS4 information model. This is done with setting up a Local Data Dictionary (LDD). The second step deals with the mapping between terms already defined in the PDS4 information model and the EPNcore dictionary. We present the EPNcore LDD and a first version of the term mapping, as well as a prototype interface to query PDS4 from the VESPA portal. The Europlanet H2020 Research Infrastructure project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654208.