In the 1960s, the Mariner probes were built to scout the inner planets of the solar system: Mercury, Venus, and Mars. The Mariners were large -- even the smallest weighed over 440 pounds. And they were costly. Each craft had a shield to protect it during launch as it traveled up through the Earth's atmosphere. Later, the shield was jettisoned to allow the probe to perform its experiments. The Mariners came equipped with instruments to analyze a planet's atmospheric temperature and density and to beam back to Earth low-resolution photographs.
In 1965, Mariner 4 passed within 6,118 miles of Mars and beamed back twenty-two images that gave scientists their first good look at the planet. The images revealed a few surface features that were more clearly shown in later photos taken by Mariner 6 and Mariner 7 ,when they raced within 2,120 and 2,190 miles, respectively, of the planet.
The views that the Mariner craft provided brought scientists one step closer to unlocking some of the secrets of the fourth planet from the sun.
