I am finished with the new planet structure. Check my latest pull request esa/pykep#27 . You will find there also a new object deriving from planets::base and interfacing with the JPL SPICE toolbox. This allows to compute precise ephemerides for all planets and moons in the solar system, at the cost of downloading first some files (kernels) needed by SPICE. I am now working on some examples and tutorials for the new structure.