For hundreds of years our observations of Mars were restricted by the vast distance separating Earth from the red planet. About once every two years, at its closest approach (called opposition), Mars passes within about 55 million km of Earth and it is then that we are able to capture pictures of maximum resolution with earth-based telescopes. The Hubble Space Telescope now provides us with excellent views from earth-orbit, but until the launching of probes to Mars to collect and relay data back to Earth, much of what was "known" about Mars was based on fuzzy pictures which showed only large scale planetary features and events. Some of the earth-based observations were: orbital and rotational dynamics, atmospheric phenomena, seasonal variations in the polar caps, variations in surface color (which were explained by theories ranging from the presence of vegetation, to water bodies linked by martian-made canals, to variations in surface composition); all of which resulted in a variety of interpretations. Atmospheric pressure and composition, as well as surface temperature, was studied using spectroscopy, but there was much debate about the varied results obtained by different studies.
The earth-based observations of Mars paved the way for spacecraft exploration of the planet. So many questions had been raised about Mars and there were so few answers. Did life exist on Mars in the past or present? Was water present on the planet? If so, what form was it in? What was the atmosphere composed of and what were its dynamics? Could Mars be used to tell us more about the evolution of both Earth and our solar system? These were some of the questions which captured the imaginations of scientists from many disciplines, and the answers could only be found by direct observation. Judging by the reaction to the H.G. Wells "War of the Worlds" radio broadcast, the public was not immune to the mysteries of Mars either. Fueled by the curiosities of both the scientific community and the public, on November 28, 1964 at 9:22 EST Mariner 4 was launched and 228 days later it would become the first spacecraft ever to visit the red planet.
SUCCESSFUL NASA MARS MISSIONS TO DATE
Chronology of Mars Exploration
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