Mariner 4 Results
The total data returned by the mission was 5.2 million bits. All experiments operated successfully with the exception of the ionization chamber/Geiger counter which failed in February, 1965 and the plasma probe, which had its performance degraded by a resistor failure on 6 December 1964. The images returned showed a Moon-like cratered terrain (which later missions showed was not typical for Mars, but only for the more ancient region imaged by Mariner 4). A surface atmospheric pressure of 4.1 to 7.0 mb was estimated and no magnetic field was detected.