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

For a century Mars had been the one world where educated people could still argue about inhabitants, and telescopes were too weak to settle it. Mariner 4 crossed 216 million kilometres to take twenty-one pictures of a cratered plain and measure an air a hundred times thinner than ours. Both answers arrived in a single July night.

The voyage, step by step

  1. The first frame

    15 July 1965

    At 00:18 on 15 July 1965 the camera opened over Amazonis, near 40 degrees north, and began the swath.

  2. Where the canals should have been

    1965 CE

    The swath crossed the equator over ground that Lowell's maps had ruled with straight dark lines. The frames showed nothing of the kind.

  3. A cratered ground

    1965 CE

    Frames eleven to fifteen showed a heavily cratered landscape that looked, to everyone who saw it, exactly like the Moon.

  4. An air too thin

    1965 CE

    As the probe passed behind the planet its radio signal bent through the atmosphere and gave a surface pressure of four to seven millibars.

  5. The last frames

    1965 CE

    The swath ended at the terminator near 50 degrees south, in Phaethontis, with a twenty-second frame cut short after twenty-one lines.

Outcome

Twenty-one pictures across about one per cent of the planet, showing craters and a very thin air.

Mariner 4

First spacecraft to fly past Mars and send back close-up photographs, in July 1965.

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