21 Photos, and a Big First
Decades before Spirit and Opportunity were launched, a probe named Mariner 4 lifted off from Cape Canaveral, Fla.
On July 14, 1965, it reached the planet Mars and took the first photos humans had ever seen of another world: 21 grainy black and white images, sent back through the distances of space.
Mariner 4 was among 10 spacecraft designed by the Jet Propulsion Laboratory to explore the three nearest planets: Mercury, Venus and Mars.
The first launch of the series, Mariner 1, went off course during launch. But its counterpart, Mariner 2, went on to Venus and took scientific readings as it coasted past the planet. Mariner 4 captured 21 photos of the red planet as it flew past in July of 1965. The probe passed as close as 6118 miles from the surface.
Next to liftoff were Mariner 3 and 4, designed identically, with the goal of reaching Mars and sending back readings of the planet's atmosphere and magnetic field, and the first close-up photos of the red planet.
Mariner 3's launch vehicle failed to release the spacecraft after launch and it never made it to Mars. Three weeks later, Mariner 4 took off successfully and began its eight month journey.
In July 1965, Mariner 4 flew past Mars, took its observations and claimed its place in history.
The spacecraft told us news about Mars we might not have expected: the planet had no magnetic field and its atmospheric pressure was a fraction of what is found on Earth.
The pictures sent back from Mariner 4 showed a martian surface densely covered in impact craters. But later missions, such as Mariner 9, would photograph volcanoes, canyons and features which pointed to a unique geological history of the planet. Mariner 4 could transmit information back to Earth at a speed of up to 33.3 bits per second through its high-gain antenna. In comparison, the Spirit and Opportunity Rovers currently on the martian surface are capable of communicating at over 11,000 bits per second.
After the Mars flyby, Mariner 4 coasted into solar orbit. The spacecraft continued to return data to Earth for another three years, and was used by scientists to study the solar wind environment.
For more pictures of the martian surface from Mariner 4, visit the
National Space Science Data Center's image gallery
NASA's John F. Kennedy Space Center and Jet Propulsion Laboratory