In all of history, human beings have set foot on only two worlds: our home planet Earth, and its solitary moon. But we've explored far beyond our Earthly bounds with the help of orbiters, landers, and probes that sail through the solar system and report back what they find. Since NASA's Mariner 2 flew by Venus in 1962, every planet in the solar system has been visited by at least one spacecraft, in addition to missions studying asteroids, dwarf planets, the sun, and even the unknown world of interstellar space.
These hardy robots have shown our solar system to be full of dynamic and complex worlds. The much-celebrated Cassini mission, which came to an end in September, revolutionized our understanding of Saturn and discovered a hidden ocean on its moon Enceladus. A stream of missions to Mars has revealed flowing water, making the red planet a tantalizing place to search for life. And NASA and Japan's space agency both have missions to rendezvous with asteroids and bring pieces back to Earth for study.
Here's a helpful infographic highlighting the active missions exploring new worlds: