Mariner 7

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An Atlas-Centaur rocket launched Mariner on March 27, 1969. On August 5, 1969, it made its closest approach to the Red Planet.[1] It made a close flyby of Mars just five days after Mariner 6. After examining the images from Mariner 6, scientists changed picture taking program so that Mariner 7 could take additional images of the Martian south pole.[2] Although Mariner 7 was launched 31 days after Mariner 6, it arrived at Mars only 5 days behind Mariner 6 because its path was shorter.[3] Mariner 6 and 7 were twin spacecraft. They were identical, but they took pictures of mostly different parts of Mars. The spacecraft was 3.35 m high and had 17,472 solar cells which provided 800 W of power near Earth and 449 W at Mars. It used a 1200 W-hr rechargeable silver-zinc battery. Mariner found its way around by tracking the sun and the star Canopus.[4] Canopus is a brightest star in the constellation Carina (the old ship Argo). Carina is visible in the southern hemisphere and is near the Small Cloud of Magellan.[5]

Scientific instruments

Ultraviolet spectroscope Infrared spectroscope Infrared Radiometer Wide-angle television camera Narrow-angle television camera[6]

  • As with most spacecraft Mariner 6 had solar panels and a high-gain antenna Mariner 6 and 7 were identical.

Cameras

The best resolution was about 900 feet. This compares to the best resolution from Earth at the time of about 100 miles. Mariner IV pictures taken in 1965 had a resolution of two miles.[7] Images were converted to 704 lines with 935 pixels per line for a total of 658,240 pixels per image. At the time, regular television used 400 pixels per line and 525 lines. The brightness for each pixel was measured in 256 brightness levels. Camera A, the wide-angle camera, had a 52 millimeter vocal length. It covered an area with sides 10 times larger than Camera B. Camera B, the close-up camera, had a focal length of 508 millimeters, and covered an area measuring 72 by 84 km. It was able to resolve craters as small as 300 meters in diameter. Pictures were first recorded on two tape recorders. The sending of the whole set of pictures took over eight hours.[8]

Accomplishments

Mariner 7 took a total of 93 far-encounter pictures from a distance of between 1,716,000 to 127,000 Km. It also took 33 close-encounter pictures.[9] Mariner 7 took pictures of the edge of the polar cap at 60 degrees S, 0 degrees W as well as a band from 10 degrees N to 30 degrees S, spanning 20 degrees W to 105 degrees W.[10]

Approach view of Mars from Mariner 7 The southern ice cap and Nix Olympica (circle in northern hemisphere) are visible.

Approach view of Mars from Mariner 7 The southern ice cap and Nix Olympica (circle in northern hemisphere) are visible.


The far off pictures from Mariner 7 showed large numbers of craters were found in the dark (called maria) areas.[11] The scientific measurements from the two craft were similar. The surprising discovery of Mariner 4 about a very thin atmosphere was confirmed by Mariner’s radio-occultation experiment. An ionosphere was also found with this device. The atmospheric pressure was measured to be between 6 and 7 mb.[12] That was very low as compared to roughly 1000 mb on the Earth. So, the air pressure on Mars is similar to that of the Earth at 100000 to 115 000 ft) above sea level on the Earth. The south polar cap was found to be made up of mostly frozen carbon dioxide (dry ice). The Infrared radiometer found temperatures in the daytime hemisphere close to those expected from Earth-based studies--about 62 ° F at noon at the equator and -45 ° F at the polar-cap edge. But temperatures as low as -100 ° F were detected at night at the equator.[13] Both Mariner 6 and Mariner 7 took pictures across the dark area of Meridiani Sinus, but at different times of the day. Nix Olympica, later named Olympus Mons, was clearly visible in the far encounter pictures.[14] [15] Neither Mariner 6 or 7 took pictures of volcanoes or of Valles Marineris, the giant canyon on Mars.[16] One photo even showed Mars' irregularly shaped moon, Phobos.[17] [18] At the time of this mission, some still wondered about the famous “canals” observed by some from ground-based telescopes. Images of some places that should have displayed canals instead had semi-alignments of dark patches including craters with dark floors.[19] The Mariner missions of 1969 basically killed the idea about canals on Mars.[20]

Meteoroid Strike?

For 7 hours, late in the mission, Mariner 7 went intermittently dead. It was first thought that it had been hit by a meteoroid flying through space. Later, it was determined that it was an explosive failure of a battery. The gas from the battery changed the spacecraft’s path.[21] [22]

References

  1. ↑ https://mars.nasa.gov/programmissions/missions/past/mariner67/
  2. ↑ https://www.jpl.nasa.gov/missions/mariner-7/
  3. ↑ Leighton, R. 1970. The Surface of Mars. Scientific American: 222 (number 5 May), 26-41
  4. ↑ https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1969-014A
  5. ↑ Bernhard, H., et al. 1948. New Handbook of the Heavens. The New American Library. N.Y.
  6. ↑ https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1969-014A
  7. ↑ https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690007929.pdf
  8. ↑ Leighton, R. 1970. The Surface of Mars. Scientific American: 222 (number 5 May), 26-41
  9. ↑ Leighton, R. 1970. The Surface of Mars. Scientific American: 222 (number 5 May), 26-41
  10. ↑ https://nssdc.gsfc.nasa.gov/planetary/mars/mariner.html
  11. ↑ Leighton, R. 1970. The Surface of Mars. Scientific American: 222 (number 5 May), 26-41
  12. ↑ https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1969-014A
  13. ↑ https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700009038.pdf
  14. ↑ http://science.sciencemag.org/content/165/3894/685
  15. ↑ Leighton, R., et al. 1969. Mariner 6 Television Pictures: First Report. Science: 165, 685-690.
  16. ↑ https://www.jpl.nasa.gov/news/fact_sheets/mariner.pdf
  17. ↑ http://www.planetary.org/multimedia/space-images/mars/first-spacecraft-photo-of-phobos.html
  18. ↑ https://www.jpl.nasa.gov/missions/mariner-7/
  19. ↑ https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700009038.pdf
  20. ↑ https://nssdc.gsfc.nasa.gov/planetary/mars/mariner.html
  21. ↑ https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1969-030A
  22. ↑ Leighton, R. 1970. The Surface of Mars. Scientific American: 222 (number 5 May), 26-41

See Also

External links

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