Pioneer plaque Coloured version of a pictorial plaque attached to the exterior of the Pioneer and spacecrafts indicating their origin in case an intelligent alien species one day examines it The dumbbell symbol at top left represents a hydrogen atom the most common element in the Universe Below lines radiate from our Sun to the relative positions of Pulsars cosmic sources of radio energy Human figures the mans hand raised in goodwill are set against the spacecraft to give scale At bottom is a plan of the Solar System showing the route of a Pioneer spacecraft from Earth Pioneer and left Earth in and respectively The frequency of each Pulsar at the time of launch is quoted in binary relative to that of the Hydrogen atom with its unity symbol