According to experts, Mars is one of the few places in the universe that could sustain life with its thin atmostphere—and where traces of life and water could be found soon! As a result, this terrestrial planet is being constantly studied by scientists in several countries. In fact, many unmanned missions have also been sent to the red planet to increase our understanding of it.
So far, the United States, Japan, Europe and the Soviet Union have sent various probes to Mars since the 1960s. Their missions have included orbiters, landers and rovers meant to collect data in order to possible send a human mission to the planet some day.
However, until now, out of all the missions to Mars, only a few have been successful. A few missions have even failed before they began! This has led to scientists jokingly coining the term 'Mars Curse.' This so-called curse is also, at times, referred to as The Galactic Ghoul—a ghoul that devours Mars probes!
There are several variables that go into sending a probe to Mars. One of the most important one is the Launch-window, which is the precise period when it's ideal to send a robotic mission to the planet. This window appears once in 2.135 years or 708 days.The idea behind this window is that it results in minimum-enegry interplanetary transfer, making the probe more feasible. The same principle applies for earth bound missions returning form Mars.
In October 1960 the Soviet Union launched two flyby probes under the Mars 1M program, but this and many subsequent attempt failed. However, this marked the first time a Mars bound probe was launched form earth.
In the mid-60s NASA's Mariner program was launched, and the Mariner 4 managed to take the first close-up images of the planet. Mariner 9 was the first successful Mars orbiter. Since then, there have been several successful surface missions as well. The most notable of these are Viking 1, which was the first to successfully land and transmit data; Mars Pathfinder and Dawn, which is the most recent one.
Thanks to the many missions to this planet, scientists and researchers have quite a lot of data and pictures to try and simulate Martian conditions, and one day send a manned mission to the planet!