The Viking and Pathfinder were two different names given to unmanned spacecraft launched from the United States that landed on the planet Mars and gathered data. Approximately two decades separated the Viking and Pathfinder missions. The Viking Program took place in the 1970s, while the Pathfinder wouldn't fly until the 1990s. Although these spacecraft were not the first to land on the Red Planet, they were far more successful.
Back in 1971, what was then known as the Soviet Union launched two spacecraft dubbed Mars 2 and Mars 3. Mars 2 was destroyed when the lander crashed on the planet's surface, but Mars 3 managed to make a soft landing. (That is, if you consider a 50 mph impact to be soft.) Once it landed, the probe took about 90 seconds to start transmitting photographic data to the orbiting module, but after just 20 seconds, no further signals were received. What resulted was all of one dark and distorted image that was for all intents and purposes useless. Later, in 1973 and 1974, the Soviets attempted to send four more probes to Mars. Mars 4 and Mars 5 were intended to orbit the planet, but only Mars 5 managed to do so. Mars 6 was supposed to land, but like Mars 2, it crashed. As for Mars 7? It missed the planet and was lost in space! To say the Russians had a streak of bad luck would be an understatement.
As hinted at above, the Americans fared better. On September 9, 1975, Viking 1 was launched and landed on June 19, 1976. Viking 2 was actually launched a bit earlier, on August 20, 1975, and landed on Mars August 7, 1976. In case this doesn't make sense, Mars and Earth were closer together after Viking 2 was launched, and thus it was known that Viking 1 would arrive sooner. Otherwise, the Viking 1 and 2 designations would have been reversed.
Viking 1 took 26,000 pictures of Mars and its moons, Phobos and Deimos. On board were a weather station, a seismometer, and an instrument to analyze the Martian soil. Unfortunately, the seismometer didn't work, but the photographic images are awesome to this day. Save for a pinkish-looking sky, one could easily mistake the landscape with some remote area of Utah. Viking 1 conducted the first-ever measurements of Mars' atmospheric and surface weather conditions. Temperatures were on the chilly side, ranging from -120 degrees to 20 degrees Fahrenheit. Winds typically blew at around 30 mph. The atmosphere was found to be made of 95% carbon dioxide, 2-3% nitrogen, 1-2% argon, and just a trace of water vapor and oxygen. Ozone was virtually non-existent.
Viking 2 also took 26,000 photos of Mars and its moons. This sister craft landed in a rockier area and had better luck with its seismometer. As such, minor "Marsquakes" were recorded from time to time, but the overall seismic activity was minuscule when compared with Earth's. Unlike Viking 1, Viking 2 found nearly three times as much water vapor at its landing site. Thus, the rocks held small traces of water.
Fast-forward some 21 years, and the Pathfinder Program was underway. On July 4, 1997, the Pathfinder spacecraft landed on Mars with cameras, a weather station, and for the first time, a robotic rover filled with instruments called Sojourner. The rover weighed 22 pounds. The Pathfinder was the first spacecraft to land on another world without orbiting it. It also deployed a parachute while still descending at a speed of 1000 mph and hit the surface at about 35 mph. It was also the first spacecraft to employ airbags to soften the landing. Conversely, the Viking made use of retro-rockets to slow the landing down to about 5 mph.
The Pathfinder sent back 2.6 billion bits of data to the Jet Propulsion Laboratory, which included 16,000 lander photos and another 550 from the rover. The images from this mission contained much greater resolution than what the cameras from the earlier Viking spacecraft had provided. Pathfinder's lander was built to last for a month while the rover was expected to last a week or so. However, they both lasted for over three months. A short time after the Pathfinder landed on Mars, the site was renamed the Sagan Memorial Station after noted astronomer and writer Carl Sagan, who died in December, 1996.
Sadly, the current state of the US Space Program is quite poor. Thanks to budget cuts, the nation's efforts at space exploration have for all intents and purposes been placed in a suspended animation of sorts. If society is to progress and expand, it is imperative that humans continue to acquire knowledge of the limitless frontiers that await beyond this sole speck of the universe known as Earth. This can only be accomplished by continuing to explore what lies beyond. The very survival of Homo Sapiens depends on it.