Mariner 4

8:00:57 p.m. EDT, 14 July 1965

NASA's Mariner 4 made the first successful spacecraft flyby of Mars on 14 July 1965, passing 6,118 miles above the surface at 8:00:57 p.m. EDT — already 15 July in Universal Time.

Beginning about 40 minutes before closest approach, its television camera recorded 21 complete images plus 22 lines of a 22nd, through red and green filters.

About 1.25 hours after closest approach the spacecraft passed behind Mars as seen from Earth. Refraction of its radio signal through the atmosphere gave a direct measurement of very low surface pressure, initially estimated at roughly 4 to 7 millibars.

A narrow strip of very old ground

The photographs covered a narrow swath and revealed heavily cratered, ancient-looking terrain rather than the detailed Earth-like landscape some observers had expected.

They were not a representative global survey. Later missions showed that Mariner 4 had happened to photograph unusually ancient cratered terrain, and that Mars also has volcanoes, canyons, channels and younger surfaces.

The pictures arrived the next day

The pictures did not come back live. The image data were stored on an onboard tape recorder for slow transmission, and the first picture elements reached Earth the following day; full playback continued for days.

While waiting for normal computer processing, JPL staff printed the numerical picture data, cut the paper into strips and coloured the values by hand. That is the origin of the often-reproduced hand-coloured image — not a colour photograph taken at Mars.