Neptune is one of the Solar system’s planets that are still unexplored, and mankind needs to be prepared for these new engineering challenges. For now, a lot of similarities are assumed between the atmospheres of Neptune and Jupiter. Specifically, both planets’ main components are believed to be molecular hydrogen and helium (in an approximate proportion of 80%/20%). However, Neptune’s atmosphere is also believed to have a small methane’s (CH4) percentage (1.5%). This work aims to evaluate the exact Neptune chemical composition (including CH4) influence in the aerothermal environment of a capsule entering this atmosphere. Different capsule’s shapes are considered (60◦ and 45◦ sphere-cones), and two trajectory points for two different mission types are studied: a ballistic entry trajectory point (around 80km altitude at 18 km/s) an and aerocapture trajectory point (around 130km altitude at 29 km/s).