Mariner 4 flyby

Mariner 4 · 1965 CE · Mars

Mariner 4 flyby — Mariner 4 · 1965 CE · Mars — Recorded expedition route · schematic map

Photograph Mars from close range and measure its atmosphere and magnetic field.

Historical context

Before 1965 no telescope could settle what the markings of Mars were, and maps still carried the straight lines called canals. Mariner 4 travelled some 525 million kilometres in seven and a half months to fly past the planet, take twenty-one pictures and part of a twenty-second of a cratered surface, and measure, by radio, a surface pressure less than a hundredth of Earth’s.

The voyage, step by step

  1. The first frame

    15 July 1965

    At 00:18 Universal Time on 15 July 1965, by the spacecraft's clock, the camera took its first frame: the edge of the planet near 37 degrees north, between Elysium and Arcadia Planitia.

  2. Where the canals should have been

    1965 CE

    The swath crossed the equator over Amazonis, where telescopic maps had ruled straight dark lines, the canals drawn by Percival Lowell and others. The frames showed no trace of them.

  3. A cratered ground

    1965 CE

    From frame seven onward the pictures showed a heavily cratered landscape, and frame eleven caught a crater about 150 km across.

  4. The last frames

    1965 CE

    The swath ended at the terminator near 51 degrees south, beyond Phaethontis, with a twenty-second frame cut short after twenty-one lines.

  5. An air too thin

    1965 CE

    At 02:19 Universal Time, by the spacecraft's clock, the probe passed behind the planet; its radio signal, bent through the atmosphere, gave a surface pressure of four to seven millibars.

Outcome

Twenty-one pictures and part of a twenty-second across about one per cent of the planet, showing craters, a surface pressure of four to seven millibars and no detectable magnetic field.

Mariner 4

First spacecraft to return close-up photographs of Mars, in July 1965; NASA counts it the first successful Mars flyby.

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