Meridiani Planum in 1969 – Our First Closeup View of Opportunity’s 2004 Landing Site

On January 25, 2004, NASA’s MER B (Mars Exploration Rover B) named Opportunity successfully landed at 1.95° S, 354.47° W on Meridiani Planum. After moving out of the small crater it had come down in during its bouncing airbag landing, Opportunity found this region of Mars to be a fairly flat plain covered with hematite and other mineral deposits indicative of a long history of water interacting with the eroding sedimentary strata of the area.

This approximate true-color panorama taken by Opportunity, dubbed “Lion King,” shows Eagle Crater (where the rover landed on January 25, 2004) and the surrounding plains of Meridiani Planum. Click on image to enlarge. (NASA/JPL/Cornell)

Originally designed for a 90-Sol mission exploring the Martian surface, Opportunity instead lasted over 14 years covering a record-setting distance of 45.16 kilometers. The hardy solar-powered rover finally succumb to a dust storm which blocked out the Sun for months in the summer of 2018 as it was exploring the rim of the 22-kilometer Endeavour crater. Because of its flatness and lack of large rocks and other hazards, Meridiani Planum was chosen by ESA and Roscosmos (the European and Russian space agencies, respectively) as the target of the Schiaparelli EDM (Entry, Descent and Landing Demonstrator Module) for its unsuccessful landing attempt on October 19, 2016.

A map showing Opportunity’s 14-year traverse across Meridiani Planum. The image covers an area of about 56×47 kilometers. Click on image to enlarge. (NASA/JPL-Caltech/MSSS)

While a succession of NASA Mars orbiters has been able to provide high-resolution images of Opportunity’s landing site and tracked its progress over the years to come, the first closeup images of Meridiani Planum were actually acquired 34½ years before the long-lived rover’s arrival by NASA’s second and third spacecraft to reach Mars, Mariner 6 and 7.

The Mariner 6 & 7 Images

Mariner 6 and 7 were launched on February 25 and March 27, 1969, respectively, on flyby missions to Mars. This was a follow up the JPL’s earlier Mariner 4 mission which reached the Red Planet on July 15, 1965 (see “Mariner 4 to Mars”) and a needed precursor for a planned Mariner Mars orbiter mission in 1971 as well as the Viking lander then planned for 1973. Although based on the basic design of Mariner 4, the Mariner 6 and 7 spacecraft were much more massive than their predecessor (412 kilograms versus 261 kilograms) owing to the availability of the powerful Atlas-Centaur launch vehicle. In addition to the increased mass, the performance of the new spacecraft’s systems was significantly enhanced owing to years of cumulative operating experience with Mariner 4 and its Venus-bound sister, Mariner 5 (see “The Return to Venus: The Mission of Mariner 5”), as well as four years of advances in space technology.

This is a view of the Mariner 6 and 7 spacecraft built by JPL. (NASA/JPL)

The plan for the Mariner 6 and 7 missions was to flyby Mars at a distance of about 3,400 kilometers (compared to the closest approach of 9,846 kilometers for Mariner 4) to provide medium-resolution image swaths covering about 10% of the Martian surface (compared to the 1% figure for Mariner 4) as well as secure observations with a significantly enlarged suite of multispectral instruments. The new Mariner Mars spacecraft was equipped with a significantly larger scan platform fitted with an Ultraviolet Spectrometer and Infrared Spectrometer to study the Martian atmosphere, an Infrared Radiometer to measure temperatures and a pair of new vidicon-based cameras. Camera A was a wide-angle imager fitted with red, green and blue filters with a field of view covering about 1,000 kilometers on a side at closest approach while Camera B, fitted with a fixed “minus blue” filter to help reduce the effects of atmospheric scattering, had a narrower field of view covering an area of about 100 kilometers on a side. Images from these cameras were broken up into a 945×704 pixel image digitized to 8 bits – a significant improvement over the 256×256 pixel, 6-bit digital imaging system employed by Mariner 4.

Closeup of the scan platform and its instruments carried by Mariner 6 and 7. Click on image to enlarge. (NASA/JPL)

During the close encounter with Mars, Camera A would create a continuous swath of medium resolution images with pixel footprints of about 1 to 2 kilometers from the limb to the terminator as the color filters were cycled while Camera B would provide a sample high-resolution view with a 100 to 200 meter pixel footprint nested inside the wider angle images. Using a hybrid digital/analog magnetic tape system, up to 33 images could be recorded during the close encounter with Mars for subsequent playback at a data rate up to 2,000 times that of Mariner 4. Camera B would also be used to record sequences of far encounter images in the days preceding closest approach with pixel scales ranging from a few to a few tens of kilometers covering most of Mars as it rotated – one to two orders better resolution than Earth-based Mars images of the time. As luck would have it, both spacecraft would take images during their close approaches of the albedo feature known by the classic name Meridiani Sinus which would latter be renamed Terra Meridiani after it had be imaged and its geology mapped (with Meridiani Planum being the plains on the west side of this feature). Meridiani Sinus was specifically targeted so that both spacecraft could provide views of the region during slightly different times of day.

Mars globes (sporting albedo features observed from Earth) illustrating the image coverage for Mariner 6 (a) and 7 (b). Click on image to enlarge. (NASA/JPL)

At 05:03 GMT on July 31, 1969, Mariner 6 started the close encounter phase of its mission acquiring a swath of two dozen images total (alternating between Camera A and B) across Mars’ equatorial region as it zoomed in to its closest approach of 3,431 kilometers at 05:19:07 GMT. The close encounter images of Sinus Meridiani showed it to be covered with eroded, flat-bottomed craters partially filled with light-colored windblown dust with no rays or secondary craters evident (suggesting an ancient surface). The best wide-angle image of Opportunity’s eventual landing site taken by Mariner 6, designated 6N11, had a pixel scale of about 1.4 kilometers revealing no difference in crater density between the light and dark albedo regions. The highly eroded Endeavour crater (the largest feature to be visited by Opportunity decades later) is visible as not much more than a dark spot several pixels across in this image.

This is a mosaic of photometrically corrected images centered on Sinus Meridiani acquired by Mariner 6 during its flyby of Mars on July 31, 1969. It was created by Ted Stryk using modern digital image processing techniques. Click on image to enlarge. (NASA/JPL/Ted Stryk)

A finder chart showing the mosaic of Mariner 6 “maximum definition” images (processed to enhance the visibility of small scale details) with a grid of latitude and longitude overlaid on it. Also indicated are the locations of the near encounter narrow angle images. Click on image to enlarge. (NASA/JPL)

A “maximum definition” version of Mariner 6 image 6N11 roughly centered on Endeavour crater (dark smudge indicated by the yellow arrow). It covers an area of about 1,177×1,124 kilometers. Click on image to enlarge. (NASA/JPL)

Mariner 7 was next up with its close encounter on August 5, 1969. Mariner 7 followed a more inclined trajectory past Mars allowing it to take a swath of images from Sinus Meridiani southeastward towards Hellas as well as separate swath showing the southern polar cap for a total of 33 images before reaching its closest point from Mars of 3,430 kilometers at 05:00:49 GMT. Because of the oblique viewing geometry for this encounter, the Mariner 7 images only had about half the resolution of its predecessor’s best images but, despite being taken about 3½ hours earlier in the Martian day, there were no noticeable difference in the visibility of features. Because of the overlapping images taken through red, green and blue filters, it was possible to create a color mosaic of the region (although it would be decades before this was done as improved digital image processing techniques and computers became available). Little did anyone realize a half century ago that these would be our first close up views of the eventual landing site of the longest-living rover (so far) in the history of lunar and planetary exploration.

A color mosaic of Mariner 7 near encounter images from August 5, 1969 centered on Sinus Meridiani. It was created by Ted Stryk using modern digital image processing techniques. Click on image to enlarge. (NASA/JPL/Ted Stryk)

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Related Video

Here is a NASA documentary about the Mariner 6 & 7 mission, “Mariner-Mars ‘69”:

Related Reading

“Mariner 4 to Mars”, Drew Ex Machina, July 14, 2015 [Post]

General References

Stuart A. Collins, The Mariner 6 and 7 Pictures of Mars, NASA SP-263, 1971

R.B. Leighton et al., “Mariner 6 & 7 Television Pictures: Preliminary Analysis”, Science, Vol. 166, No. 3901, pp 49-67, October 3, 1969