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Mariner 4

Flyby mission

Mariner 4 was a flyby orbiter designed with three main objectives in mind. It was launched on November 28, 1964.
Mariner 4 is prepared for a weight test before launch to Mars. Image: NASA/JPL-Caltech
Engineers designed the spacecraft to conduct field and particle experiments in interplanetary space. These experiments included measuring the Martian magnetic field, cosmic dust and cosmic rays, as well as the solar wind. If Mars had a magnetic field (as we do on Earth), it would protect the planet from potentially life-threatening cosmic radiation and solar radiation. Here is a short video on how we measure magnetic fields in space:
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For more information on the interaction between solar particles and the earth's magnetic field, check out this short video:
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Most importantly, scientists wanted Mariner 4 to provide close-range images of Mars in order to provide us with the most detailed surface pictures ever obtained of the planet, hopefully revealing geologic and atmospheric processes.


Mariner 4 would not enter the Martian orbit. Instead, engineers designed it as a flyby mission that would pass as closely as possible in order to take pictures and measurements. Mariner 4 had only one chance to perform its scientific work,  since the probe could not return to Mars again.
Mariner 4 trajectory. Image: NASA/JPL-Caltech

First picture

On July 15, 1965,  the camera began snapping pictures. Here is the first close-up picture of Mars ever taken:
The first close-up image ever taken of Mars.
Mars scientists hypothesized  that the hazy area barely visible above the limb on the left side of the image might be clouds. This close-up image was the first visual evidence of a Martian atmosphere!

A rocky surface

The relayed surface images revealed a cratered and moon-like surface, findings that were contrary to even conservative estimates of the Martian topography. This image was taken from 13,400 km and covers an area of 255 km by 296 km. The two craters at the center of the image are about 32 km in diameter.
Rocky surface of Mars. Image: NASA/JPL-Caltech
Roughly 1% of the surface was photographed, leaving many questions unanswered...

Atmosphere & Temperature

One of the great achievements of the Mariner 4 mission was the modification of mission plans while the spacecraft was in transit in order to accommodate the radio-occultation experiment. The experiment took advantage of radio waves from the spacecraft passing through the Martian atmosphere. Variations in the amplitude, frequency, and phase of the returned signal allowed rough calculations of atmospheric density & temperature.
Diagram showing radio waves passing through a planets atmosphere.
The results of the experiment suggested that Mars generates surface pressures of around 4.1 to 7.0 mbar (for comparison Earth has a surface pressure of 1013 mbar). This would mean that the Martian atmosphere is less than 1% the density of Earth. These findings led to surface temperature estimates of -100 degrees celsius.

Magnetic field:

The spacecraft did not detect a magnetic field around Mars, meaning the surface is not protected from solar wind as compared to Earth.

Want to join the conversation?

  • aqualine ultimate style avatar for user Shawn
    One of the videos mentioned that Mars doesn't have a global magnetosphere, but instead has local magnetic fields. How strong are these fields and are they possible locations for a colony?
    (31 votes)
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  • aqualine ultimate style avatar for user Bayla Ward
    how did they find out that mars did not have a magnetic fleid?
    (13 votes)
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  • aqualine ultimate style avatar for user Janae
    why does earth get more heat than mars
    (4 votes)
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    • piceratops tree style avatar for user Justin
      Actually, mars is simultaneously hotter and colder than earth. The side of mars facing the sun is scorching hot because there is no atmosphere to dissipate the heat, and the side facing away from the sun is freezing cold because there is no atmosphere to contain the heat from the day side.
      (5 votes)
  • purple pi teal style avatar for user Tyler Jang
    Why is the Earth's magnetosphere not symmetrical like the bar magnet? Why is one side larger than the other (see NASA THEMIS Discovers Biggest Breach of Earth's Magnetosphere )?
    (3 votes)
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  • winston baby style avatar for user Anand Shankar
    meaning that mars does not have any magnetic field?
    (2 votes)
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    • male robot johnny style avatar for user Theodoric
      Short answer: Yes.
      Long answer: Kind of. Mars has no planetary magnetic field, but it has small local pockets magnetic fields, which are basically magnetic fields around large objects on a planet. So It doesn't have A magnetic field, it has lots of small ones.
      (3 votes)
  • starky tree style avatar for user Toad Latifa
    How feasible is it to use high powered electro-magnets in place of a molten core? Would the energy required to make a powerful enough shield from solar wind make this impossible?
    (3 votes)
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  • leafers seed style avatar for user Jillian Pressnall
    Did Mariner 4 come back to Earth, float away, crash land on Mars, or crash land on a different planet
    (3 votes)
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  • piceratops seed style avatar for user kal0016
    if we send a satellite to the jupiter will it land on jupiter or not ?
    ( because there are 62 moons revolving around it. there may be a crash with the satellite )
    (0 votes)
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    • piceratops ultimate style avatar for user AegonTargaryen
      We are sending a satellite to Jupiter! The Juno probe will arrive at Jupiter on July 4th. It will complete about 38 orbits around Jupiter, measuring its gravitational and magnetic field. At the end of those orbits, it will be intentionally crashed into Jupiter.

      But the thing is, you can't actually land on Jupiter. Jupiter has no surface, its essentially a planet made of sky. We have sent a probe into Jupiter's atmosphere before to measure it. The Galileo probe entered the atmosphere and floated down for around 40 minutes before the heat and pressure destroyed it. Landing isn't an option, this is also true for Saturn, Uranus and Neptune.

      Jupiter does have a lot of moons (and a faint dust ring) but collisions are unlikely to be a problem. Space is big and you usually have to try to collide with something in order to actually collide with it. That being said, Jupiter does have a lot of moons and some of them have water. Given enough time (hundreds or thousands of years perhaps) a satellite could collide with a moon and perhaps seed it with Earth life that might survive in the water. To avoid this, Every satellite sent to Jupiter (only 1 so far) has been crashed into Jupiter at the end of its mission. This happened with the Galileo spacecraft in 2003 and it will happen with Juno when its mission is done.

      There is however one hazard associated with the moons. One of Jupiter's moons, Io, is extremely volcanic and it often launches dust and debris into space. Jupiter's magnetic field sometimes latches onto these particles and ionizes them making them into a ring of extremely high radiation called the Io plasma torus. This radiation field will rapidly degrade electronic equipment so Juno's orbit was carefully selected to try to avoid this ring as much as possible. Juno however will eventually succumb to this and its more sensitive scientific instruments (including the camera) will be destroyed as the mission progresses.
      (7 votes)
  • mr pants teal style avatar for user psweeney13
    Is it true that a big solar storm occurs every century or so? If so would a big solar storm from the sun knock out all the electronics and modern technology on earth like what happened in 1859? If a solar storm knocked out technology on earth how long would it take to get it back?
    (2 votes)
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  • aqualine ultimate style avatar for user 0402478
    If there we're only parts of mars in lumps of magnetic field, wouldn't those parts be shielded?
    (2 votes)
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