Mariner 4 — first close-ups of Mars
On 15 July 1965 Mariner 4 flew past Mars and returned about twenty grainy pictures, the first close views of the planet. They showed a dry, cratered world with no canals and no civilisation.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
Launched on 28 November 1964, the American spacecraft Mariner 4 travelled for about seven and a half months before passing about 9,846 km above the surface of Mars on 15 July 1965. As it went by it photographed the planet: 21 pictures and part of a 22nd, according to NASA’s records. These were the first close-up pictures ever taken of another planet.
Sending the pictures home was very slow. They were first stored on magnetic tape inside the spacecraft and then sent back a little at a time at just 8.33 bits per second, so each picture took hours to arrive. Compared with a modern phone, which exchanges millions of bits every second, it was as slow as copying out a text by hand, letter by letter.
The team could not wait for the first picture to be processed by computer. So they printed the incoming numbers on paper, cut the printout into strips and coloured each number by hand with pastels, using a set colour for each value. Made like a colour-by-numbers picture, this hand-drawn version of the first digital image sent from space is still a famous piece of history.
The Mars in the pictures was nothing like what many people had imagined. There were no canals and no cities, only dry ground full of craters, much like the Moon. The orbit view reproduces Mariner 4’s route of about seven and a half months as it left Earth, flew outward towards the orbit of Mars and met the planet.
Mission goals
Mariner 4 greatly changed how people thought about Mars. Streaks seen through telescopes, and markings that changed with the seasons, had once led some to claim that intelligent beings had built canals there. The close-up pictures, however, showed only cratered ground much like the Moon’s. For some years after these pictures, Mars was thought of as a ‘dead planet’.
Mariner 4 also learned something important about the Martian air. By studying how its radio signal changed as it passed through the Martian atmosphere, scientists found that the air pressure at the surface was less than one percent of Earth’s. In air that thin, water has a hard time staying liquid for long. No clear magnetic field like Earth’s was found at Mars either.
This finding later shaped the design of Mars landers. In air so thin, a parachute alone cannot slow a lander down enough. So in 1976 the Viking landers used parachutes together with retro-rockets, engines firing downward, to settle onto the ground. Later Mars landers have also used other ways of slowing down besides parachutes.
Mission chronology and background
Mariner 4 had a twin that went before it. Mariner 3, launched on 5 November 1964, failed because the protective cover around the spacecraft did not come away properly. Engineers redesigned the cover in about three weeks, and Mariner 4 was launched before the best period for reaching Mars came to an end. In the same period the Soviet Zond 2 also set off for Mars but lost contact on the way.
The story of Martian canals began with a translation mistake. In 1877 the Italian astronomer Schiaparelli described streaks he saw on Mars as ‘canali’, meaning channels, and in English this became ‘canals’, suggesting something dug by builders. Between 1895 and 1908 the American Percival Lowell published three books arguing that Martians had built canals, and together with the 1898 novel The War of the Worlds, the idea spread widely among the public.
Mariner 4’s pictures covered only about one percent of the Martian surface, and by chance they showed the heavily cratered southern highlands. That left the impression that Mars was a dead world like the Moon. Only in 1971, when Mariner 9 orbited Mars and photographed the whole planet, did giant volcanoes, canyons and dry channels that look as if water once flowed through them come into view. It is a good example of how judging a whole from a small part can go wrong.
Other milestones of this mission
Where to see it — sky and simulator
Contact with Mariner 4 ended in December 1967. It is thought to be still circling the Sun, but it cannot be seen from the ground. The replay in the orbit view follows its route instead, from the launch in November 1964 to passing Mars on 15 July 1965, slowing down at the moment of closest approach.
About every two years and two months, Mars comes closest to Earth. Around that time it rises after sunset and shines all night like a bright, reddish star. Choosing Mars in the sky view works out when it rises from your location, how high it climbs and in which direction it stands. Moving the time to July 1965 reproduces where Mars was in the sky when Mariner 4 flew past.
Mariner 4’s pictures are available in NASA’s archives. Placing the hand-coloured first image and these grainy frames beside the sharp pictures sent by today’s Mars orbiters and rovers shows at a glance how much pictures of Mars have changed in sixty years. Pictures that once took hours each now arrive far sharper and faster.
See this for yourself — replay the moment in the orbit view
FAQ
How many pictures were there?
According to NASA, 21 pictures and part of a 22nd; sources count them slightly differently. Each picture took hours to send.
How close did it pass?
On 15 July 1965 it passed about 9,846 km above the surface of Mars.
What did it discover?
Cratered ground, air less than one percent as thick as Earth’s, and no clear magnetic field. There was no sign of canals or civilisation.
What is the hand-coloured picture?
A picture of Mars the team made before the first image was processed by computer, by printing the incoming numbers on paper and colouring them one by one with pastels.
Related
- Viking 1 — to the surface of Mars
- Curiosity launch
- Mariner 2 — first planetary probe
- Mars — object index
- Perseverance — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.