Short answers, pulled from the story.
The Mariner program was a NASA initiative conducted between 1962 and late 1973 that sent ten robotic probes to explore the inner Solar System. The spacecraft visited Venus, Mars, and Mercury, achieving the first flyby, the first orbital insertion, and the first gravity assist maneuver in planetary exploration history.
The total cost of the Mariner program was approximately $554 million. Seven of the ten spacecraft succeeded; three were lost during launch or shortly after liftoff.
Mariner 2 flew by Venus on the 14th of December 1962 and found that the planet's clouds were cool while the surface beneath them was extremely hot. It also made the first direct measurement of the solar wind and detected cosmic rays originating from outside the Solar System.
Mariner 4 flew past Mars on the 14th of July 1965 and returned the first close-up photographs of another planet. The images showed a heavily cratered surface, with some craters touched with frost, and no sign of the canals long observed from Earth.
Mariner 9 became the first artificial satellite of Mars when it entered orbit on the 14th of November 1971. It waited out a global dust storm before compiling a complete mosaic of Mars's surface and returning the first close-up images of the Martian moons Phobos and Deimos. It operated for 516 days.
The Mariner Jupiter-Saturn program, approved in 1972, used Mariner-derived spacecraft and was renamed Voyager just before its 1977 launch. The Viking program's Mars orbiters were enlarged versions of the Mariner 9 spacecraft. Later probes including Galileo, Magellan, and Cassini-Huygens also traced their design heritage to the Mariner series.