Possible sources for methane and C2-C5 organics in the plume of Enceladus

► Enceladus could have formed with organics from comets or Titan-like tholin. ► Internal processes include the Fisher-Tropsch synthesis, water-rock reactions, or biology. ► Acetylene provides an important constraint and could only be of cometary origin. ► CO is expected from cometary origin, but could be consumed by internal processes. ► C2H4 could come from comet and could be produced by internal processes.