There were two major events in Mars exploration history on this date. In 1965, Mariner 7 became the third spacecraft to return pictures of the Red Planet, flying past at an altitude of 3,430 kilometers above the planet’s surface. It was a close thing, too, since less than a week before, JPL had lost contact with the probe, believed to be due to gasses leaking from its battery interfering with the signal from the high-gain antenna; JPL managed to regain contact using the low-gain antenna and were able to sort things out with the high-gain antenna just in time for the pass. They were even able to mark targeted observations based on the data returned by its twin Mariner 6, just a few days ahead.
Then, on August 4, 2007, a Delta II 7925 rocket blasted off from Cape Canaveral carrying the Mars Phoenix Lander, constructed largely of flight spare components from the ill-fated Mars Polar Lander mission. Phoenix would complete its nine-month cruise and land successfully on Mars on May 25 of the following year. Amongst its many discoveries was the first observation of liquid water on the Martian surface — water droplets that briefly persisted on the lander’s legs shortly after touchdown, and then rapidly boiled away in the tenuous atmosphere. Its surface mission lasted 157 sols, 67 past the mission objective, before the Martian arctic winter claimed it forever.