There have been many unmanned ORGANIZATION@1 space missions as well , including at least one that visited each of the other seven planets in the Solar System , and four missions -LRB- Pioneer NUMBER@1 , ORGANIZATION@2 NUMBER@2 , Voyager NUMBER@3 , and Voyager NUMBER@4 -RRB- that have left the Solar System .

Four ORGANIZATION@1 spacecraft have left the Solar System , Voyager NUMBER@3 , Voyager NUMBER@4 , ORGANIZATION@2 NUMBER@1 and ORGANIZATION@2 NUMBER@2 .
