has part has part has_part astronomical body part biosphere Whether this class should be grouped with classes such as "hydrosphere" and "cryosphere" requires some discussion. The gravitational sphere of influence referenced in this class' definition is the Hill sphere: a region in which an object dominates the attraction of satellites despite gravitational perturbations. An astronomical body part which includes all the living entities within the gravitational sphere of influence of that body, as well as the non-living and dead entities with which they interact. envoPolar envoAstro collection of organisms