Mariner 4 was a robotic spacecraft launched by NASA on November 28, 1964. It was the first spacecraft to successfully fly by Mars, providing the first close-up images of the planet's surface. The mission aimed to gather data about Mars' atmosphere, surface features, and temperature. On July 14, 1965, Mariner 4 transmitted 21 images back to Earth, revealing a cratered landscape similar to that of the Moon. The mission helped scientists understand that Mars had a dry and cold environment, paving the way for future exploration of the planet.