There have been a total of 57 missions launched to Mars before the 2020 Launches. Of those missions, 20 have been successful and 8 are still operational. Lets take a look at some of the more notable missions to the Red Plant, as a more complete look at currently operational missions can be seen here.
Mariner 4 provided the first TV images of Mars during the first ever FlyBy of the planet on July 15th, 1965. We talked more about this in here as scientists from NASA JPL bought pastels to color in the image, which was later hung on the wall of JPL. Science done by Mariner 4 included finding that there was no magnetic field or Martian radiation belts or surface water detected on the surface. Images of craters and measurements of a thin atmosphere., which indicates a relatively inactive planet exposed to the harshness of space. This thin atmosphere was thinner than expected by scientists at the time.
Mariner 6 and 7 were two unmanned NASA space probes that completed the first dual mission to Mars in 1969 as part of NASA’s wider Mariner program. This included flying over the equator and south polar regions, analyzing the atmosphere and the surface with remote sensors, and recording and relaying hundreds of pictures. The mission’s goals were to study the surface and atmosphere of Mars during close flybys, in order to establish the basis for future investigations, particularly those relevant to the search for extraterrestrial life, and to demonstrate and develop technologies required for future missions to the Red Planet. The spacecrafts were able to image 20% of the surface of the planet and the infrared radiometers showed that the atmosphere of Mars is composed mostly of carbon dioxide (CO2), and they were also able to detect trace amounts of water on the surface of Mars.
Mariner 9 was the first orbiter of Mars, narrowly beating Mars 2 and 3 from the USSR to the title. When it arrived, there was a huge dust storm, which meant scientists had to wait until after the dust storms ended to capture data. After 349 days in orbit, Mariner 9 had transmitted 7,329 images, covering 85% of Mars’ surface, whereas previous flyby missions had returned less than one thousand images covering only a small portion of the planetary surface. The images revealed river beds, craters, massive extinct volcanoes, such as Olympus Mons, the largest known volcano in the Solar System; Mariner 9 led directly to its reclassification from Nix Olympica, canyons, including the Valles Marineris, a system of canyons over about 2,500 miles long, evidence of wind and water erosion and deposition, weather fronts, fogs, and more. Mars’ small moons, Phobos and Deimos, were also photographed.
The Soviet Mars 3 spacecraft was an orbiter and had a lander, which became the first lander on Mars. This soft landing occurred on December 2nd, 1971. The first partial image was transmitted, which was in grey, and not in color, before contact was lost.
Viking 1 was the first US spacecraft to land on the red planet, with the designation of studying the Martian surface and atmosphere, plus take high resolution photos. “Operating on Mars’ Chryse Planitia for more than six years, Viking 1 performed the first Martian soil sample using its robotic arm and a special biological laboratory. While it found no traces of life, Viking 1 did help better characterize Mars as a cold planet with volcanic soil, a thin, dry carbon dioxide atmosphere and striking evidence for ancient river beds and vast flooding.”
Viking 2 immediately followed the success of Voyager 1, consisting of a lander and an orbiter designed to take high-resolution images, and study the Martian surface and atmosphere. Voyager 2 did help investigate for signs of life, but although the spacecraft did not find traces of life, it did find all the elements essential to life on Earth: carbon, nitrogen, hydrogen, oxygen and phosphorus.
The Mars Orbiter Mission is India’s first mission to the red planet, which has provided a test bed of what technology India can send. Moreover, notable scientific achievements include providing a global photographic view of Mars, and providing a 120 page atlas of the surface. This has been a resounding success for India and there have been reports that a follow up mission and other future Mars missions are planned.
“The Mars Global Surveyor orbiter, which operated on Mars for more than nine years, was designed to study the composition of Mars, map its topography and monitor weather patterns. The orbiter made a number of discoveries about the Red Planet, including evidence of liquid water at or near the Martian surface. Observations from the Mars Global Surveyor, especially its identifications of water-related minerals, were used to determine drive routes for the Mars Exploration Rover Opportunity in 2010.” 
Launched in December 1996, and landing in Mars’ Ares Vallis on July 4th, 1997, Mars Pathfinder was designed as a technology demonstration of a new way to deliver an instrumented lander and the first-ever robotic rover to the surface of the red planet. In addition to testing the new landing methods, Pathfinder was able to analyze the Martian atmosphere, climate, geology and the composition of its rocks and soil. Notable finding included proof of previous running water in the past, proof of early mornin water ice clouds in the lower atmosphere, and temperature changes indicating the atmosphere is warmed by the planet’s surface.
As part of the Pathfinder Mission, there was a rover landed, named Sojourner, on the surface of Mars using an air bag landing system and innovative petal design, which have been used since in various incarnations to land other rovers on the Red Planet. Sojourner spent 83 days of a planned seven-day mission exploring the Martian terrain, snapping photographs and taking chemical, atmospheric and other measurements.
Mars Odyssey is a spacecraft designed to find out what the planet is made of, detect water and shallow buried ice and study the radiation environment. It currently holds the record for the longest continually active spacecraft in orbit around a planet other than Earth. It’s been in orbit since Oct. 24, 2001. The spacecraft has made many discoveries including the discoveries of hydrogen and salts in the planets soil.
MAVEN mission was designed to explore the Red Planet’s upper atmosphere, ionosphere and interactions with the sun and solar wind. Launched November 18th, 2013 and performed a Mars orbital insertion on September 21st, 2014, MAVEN became the first mission dedicated to studying Mars’ upper atmosphere. Maven is still providing valuable data on the structure and composition of the Martian upper atmosphere. MAVEN’s mission was designed for two years, but the spacecraft has enough fuel to operate through 2030. Moreover, MAVEN was shifted to a lower orbit to prepare it to take on additional responsibility as a data-relay satellite for NASA’s Mars 2020 rover.
The ExoMars Trace Gas Orbiter is a collaborative project between the European Space Agency and Roscosmos that sent an atmospheric research orbiter and the Schiaparelli demonstration lander. This has a goal to better understand methanols Martian atmosphere that could be evidence for possible biological activity. This orbiter will be filled by future missions by the ExaMars project lander and the Rosalind Franklin rover in 2020. These future missions will search for biomolecules and biosignatures, at which time Trace Gas Orbiter will operate as the communication link between the rover and Earth communication.
Launched in 2018, “The InSight mission seeks to uncover how a rocky body forms and evolves to become a planet by investigating the interior structure and composition of Mars. The mission will also determine the rate of Martian tectonic activity and meteorite impacts.”
Built by NASA JPL, the MarCo mission included 2 cubesats with the Insight lander to really data to Earth as Insight landed.
Check out the Planetary Bodies Category for previous and upcoming articles on the solar system planets.
To learn more about the Mars missions that NASA has sent, check out their website on the subject.
Sources And Further Reading
 = http://solarsystem.nasa.gov/missions/profile.cfm?Sort=Target&Target=Mars&MCode=Mariner_09&Display=ReadMore
 = http://www.space.com/18439-mariner-9.html
 = http://mars.jpl.nasa.gov/programmissions/missions/past/mariner89/
 = https://www.jpl.nasa.gov/missions/viking-1/
 = https://www.jpl.nasa.gov/missions/viking-2/
 = https://www.jpl.nasa.gov/missions/mars-global-surveyor/
 = https://mars.nasa.gov/mars-exploration/missions/pathfinder/
 = https://www.jpl.nasa.gov/missions/mars-pathfinder-sojourner-rover/
 = https://mars.nasa.gov/odyssey/files/odyssey/Odyssey0302.pdf
 = https://solarsystem.nasa.gov/missions/mars-odyssey/in-depth/
 = https://solarsystem.nasa.gov/missions/maven/in-depth/
 = https://mars.nasa.gov/insight/mission/overview/
 = https://www.jpl.nasa.gov/cubesat/missions/marco.php