section_path: Targets of exploration
section_name: Targets of exploration
paragraph_text: Targets of exploration
  
  Starting in the mid-20th century probes and then human mission were sent into Earth orbit, and then on to the Moon. Also, probes were sent throughout the known Solar System, and into Solar orbit. Uncrewed spacecraft have been sent into orbit around Saturn, Jupiter, Mars, Venus, and Mercury by the 21st century, and the most distance active spacecraft, Voyager 1 and 2 traveled beyond 100 times the Earth-Sun distance. The instruments were enough though that it is thought they have left the Sun's heliosphere, a sort of bubble of particles made in the Galaxy by the Sun's solar wind.