text: Viking Orbiter 1 - Valles Marineris | The Planetary Society
  Viking Orbiter 1 - Valles Marineris Color image of a cloudy afternoon over the Valles Marineris canyon system, taken by Viking Orbiter 1 during its 701st orbit of Mars, on September 29, 1979. This image was constructed using pairs of red and violet filter images that were taken by the spacecraft, with the green channel of this image formed by a 40/60 blend of the two images, respectively. NASA / JPL / USGS / Justin Cowart