On Mars: Exploration of the Red Planet. 1958-1978

 
 
CANDIDATE SITES
 
 
 
[297] With money problems temporarily set aside, the landing site working group turned once again to site selection. The "Viking `75 Project Landing Site Selection Plan,'' distributed the second week of February 1972, spelled out the entire process the Viking teams would follow in finding sites. The plan carefully delineated responsibility distributed among the groups within the Viking organization. 29
 
At the top of the pyramid, John Naugle's Office of Space Science at NASA Headquarters would have overall responsibility for reviewing the project's proposed landing areas and approving final selections. Jim Martin's Viking Project Office at Langley would oversee the six groups whose activities influenced the selection process. Martin Marietta Corporation's Denver Division, in its role as mission planning coordinator, would have to keep track of all flight and engineering considerations that might influence [298] or be influenced by the landing spots ultimately chosen. Jet Propulsion Laboratory, supervising the design of the orbiter, would ensure that the craft could actually perform the tasks required of it. The United States Geological Survey was charged with making a series of Mars maps (regional, area, topographic, and geologic) to support the site selection process and with analyzing the terrain in the territory mapped. 30 The landing site working group, which established science criteria for landing areas, applied those criteria to candidate spots and recommended the best sites to the Science Steering Group. And the Science Steering Group, after reviewing recommendations, formulated its own site selections for Martin's project office-a simple format for a complex task.
 
Twenty-five members of the landing site working group met for their fifth meeting, at JPL on 25 April 1972, to discuss a wide variety of topics. James D. Porter of Martin Marietta, Viking mission analysis and design program engineer, brought the working group up to date on the engineering constraints that impinged on the site selection process. One was obvious: north or south of 25° latitude, the spacecraft in orbit would not receive adequate solar radiation on its solar panels to keep its batteries charged. Without that power, the orbiter could not relay messages to Earth. Other problems concerned the surface the lander encountered: slopes it touched down on had to he less than 19°, free of rocks and other hazards greater than 22 centimeters in height. Porter was also worried about winds during descent. A landing area that had winds greater than 70 meters per second was automatically eliminated. Porter's presentation was a status report, and he would be keeping the landing site working group informed as new restrictions were discovered.
 
As the day's discussions progressed, a lively debate developed over the nature of the processes that had shaped the Martian terrain. Areology, the scientific study of the planet Mars, was still less than a precise enterprise. Tim Mutch, in considering the terrain map (1:25 000 000 scale) that the Viking data analysis team had developed, questioned how the working group could extrapolate terrain information from such a map to determine topographical features as small as 22 centimeters. Several men present believed that rock sizes in the centimeter range could be determined from ground-based radar, since it would supposedly provide information on Martian features that small. Combining radar data with high-resolution images similar to the Mariner B-frame pictures had worked well in selecting landing sites on the moon. Others suggested that the radar-photo analysis approach would not be as simple on Mars; the varying kinds of terrain created by different processes would make interpretation of radar data more difficult. At this meeting, the rift between believers in radar and believer, in photography first appeared. That division would widen and characterize many of the discussions held, right up to the time of the Viking landings. 31
 
After additional consideration of physical characteristics for landing sites, Howard Robins turned the meeting's attention toward the 35 sites that had been proposed for Mariner 9 photographic coverage. Mariner 9 had [299] taken 6876 photos covering 85 percent of the planet. At the time of the meeting, the spacecraft was powered down and would remain so until June, because its position relative to Mars and the sun no longer gave its solar cells adequate exposure. Apollo 16 was a second factor leading to the suspension of the Mariner mission; during mid-April the Goldstone, California, 64-meter deep space antenna was being used to return Apollo's color television pictures. On 4 June 1972, Mariner 9 would begin its "extended mission"-to complete the mapping of the planet and take landing site photographs for Viking.
 
After a rather lengthy discussion, the landing site working group recommended that all 35 sites be photographed. 32 With a dual purpose in mind, I. George Recant, Viking science data manager, decided it would be useful to rank the 35 sites. The information would be valuable "in the inevitable tradeoffs which have to be made in the negotiations with the Mariner Project in targeting areas for photography." And he thought that the evaluation exercise would identify "many of the considerations which may be required by the [working group] in the landing site selection process." 33 The next two working group meetings, previously scheduled for June and July, were slipped to August and September, at which time the group would have to determine six 30° by 45° regions that would be topographically mapped by Hal Masursky's Branch of Astrogeological Studies of the U.S, Geological Survey at Flagstaff, Arizona. 34
 
During May, George Recant, Tim Mutch, Bob Schmitz, and Travis Slocumb evaluated the 35 areas according to engineering safety and scientific interest, with safety considerations outweighing science by more than five times. After much juggling, which Recant noted was subjective in many ways because "no quantitative methods were used in evaluating most of the criteria,'' they came up with a "relative rating'' of the candidates. 35 Schmitz took the target preferences and worked out a photography schedule with the Mariner team, and on 6 June he advised Martin that three narrow- angle, close-up B-frames and one wide-angle A-frame coverage would be attempted for each target. The B-frames would be large enough to cover an entire landing ellipse. He noted further that sites with a relative score between 90 and 75 would be covered first, 74 to 60 second, and below 60 last. Finally, 24 of the 32 sites-3 sites were dropped from consideration-would be photographed during the first nine weeks of work that summer. 36
 
Typical of the complexities brought on by continuous evaluation of data was the proposal to add 4 more targets to the list of 32. On 9 June, Hal Masursky, Al Binder, and James Gliozzi, representing the Viking data analysis team, wrote a memo to Bob Schmitz. The 4 additional sites "are in areas which have become accessible on the basis of Binder's recent revision of the Mars Topography map and updated Viking Lander capability.'' Masursky and his colleagues pointed out that "these sites are typical of some of the most striking geomorphologic features of the Martian surface which have not been considered in previous targeting exercises" They also presented alternate choices for landing sites should engineering constraints [300] continue to change. If these areas were not established as candidates soon, they feared that these particular kinds of terrain would never be considered if no B-frame pictures were taken, even though upgraded lander capability might warrant selection of such spots. Looking back at their experience with Project Apollo, the data analysis experts realized that no pictures of a location meant its immediate rejection from consideration as a landing site. They hoped to forestall that kind of decisions. 37
 
It quickly became clear that the Viking planners might be asking for too many photographs. The Mariner team had to divide the attitude control gases aboard the spacecraft between Viking's requests and Mariner's experiments. One investigation in particular, the relativity experiment scheduled for September during solar conjunction, would require a major expenditure of control gases. Since early spacecraft maneuvers had consumed more propellant than anticipated, the total number of Viking target sites to be photographed had been reduced to 24. As of early July, 15 areas had been photographed with the wide-angle A-frame camera and three times with the high-resolution B-frame camera. Tim Mutch complained about this cut to Naugle, who while sympathetic could only note that although the Mariner pictures would be an important factor in the Viking landing site selection "Viking Orbiter capability for reconnaissance and site certification can also be used as needed." 38
 
 

 
A mosaic (at rigth) of photos taken by Mariner 9's high resolution camera B of a Mars feature about 130 km long by 64 reveals dunelike ridges in what shows as a dark patch in a large crater in the photo (at left) taken by wide-angle camera A. Highest resolution of camera B at lowest planned point in orbit could reveal features as small as 60 m and cover an area 16.4 by 20.8 km, while a camera A frame covered 164 by 108 km with a resolution of 800 m.

 
 
[301] On 19 July, Tom Young distributed copies of the 19 Viking target photographs taken by Mariner 9 to date, in an attempt to accelerate the site selection process so that operational mission design could begin as early as possible. On 13 July, he told the landing site working group that he hoped it would choose regions of primary interest during its 4-5 August session. At a meeting to be held late in September or early in October, Young expected the working group to identify and debate candidate landing sites. Everyone would have his say, but in two months the group would pick primary and backup sites for each lander. A review by the Science Steering Group and the Office of Space Science would follow immediately. It was a tight, busy schedule, but Young believed it was necessary to make the best use of the project's resources and give the scientists time to participate in the mission design process. 39
 
When Young met with the landing site working group at Langley Research Center in August 1972, he summarized the many preliminary steps already taken to finding landing areas for Viking l and 2 on Mars. All this had been necessary and useful training for the actual selection process. "I want to be sure we understand the seriousness of the actions we'll be taking. Consider[able] design effort will be expended on designing the mission starting in December and changes will be costly and have schedule impacts," Young emphasized. Therefore, "the sites we are selecting will be the landing sites unless we learn something significant from future analysis of our data or [from] a Soviet landing in 1973." He meant that no site changes would be made for minor reasons; they could react only to important findings or new safety considerations. ``I want us to select the best sites to December that our collective wisdom will permit." 40
 
The debate that followed Young's statements demonstrated just how divergent opinions were among the 33 specialists present. Jim Porter, who kept the minutes of the meeting, noted that during a discussion of the Mars atmosphere each investigator appeared "to have his own technique for determining atmospheres'' and total correlation was not achieved. There were similar debates over radar analysis, the fate of the Soviet Mars landers, and other topics, Hal Masursky gave the group additional cause for concern when he pointed out that the visual impressions of Mars had been constantly changing from the beginning of the mapping mission. For example, features were just now becoming visible on the floor of the region called Hellas as the dust in the atmosphere dissipated. He expected his whole outlook on landing sites to alter by February when the skies would be clearer and orbital photographs more revealing. Jerry Soffen ranked the experiments proposed for Viking, giving the search for life the highest priority, which meant that water or evidence of water in the past would give a region good marks as a landing spot. And there were other considerations:
 
 
Regardless of their interests, the specialists all had to work within an established "landing site strategy": The Viking sites would be selected using Mariner and Earth-based data, with primary and a backup site for each lander. The preselected Mission A primary site would be examined by the Viking orbiter's Science instruments before the first landing, to make sure there were no surface changes or atmospheric hazards. If the site was certified, the lander would be committed to it; if not, the backup site would be the next choice. If results from the Mission A orbiter and lander supported the preselected Mission B sites, certification would be made in the same way as for Mission A, but spacecraft B could be retargeted to a new area if data indicated the need. A new site would be certified by orbiter instruments, although certification would be more complicated because the site would not have been studied intensively beforehand.
 
On 5 August, "with maps, overlays, theories and opinions abounding, each interest group was given an hour to indicate its primary choices for landing regions. Two stood out-15°N, and 0° to 10°S longitude. Viking 1 would be targeted for the north; Viking 2 would be sent south. Before the end of September, the eight regions chosen would be examined in detail. 41
 
Before the working group adjourned that day, it placed a conference telephone call to Joshua Lederberg of the biology team. Professor of genetics at the Stanford University School of Medicine, Nobel Laureate, and long-term supporter of Mars exploration, Lederberg carried considerable influence. He restated the biologists' desire to land at low, wet places, preferably near river basin deltas, but he raised another possibility. Why couldn't Viking land far north, 65° or higher, touching down where the polar cap had recently retreated? He had originally expressed the desire to go north in a handwritten memo to Howie Robins in June, believing the zone between 30°S and 30°N to be too restrictive. "I am about to leave the U.S. for about a week; but on my return will prepare a statement of dismay (for the record). Biology is assertedly a prime goal of Viking, The [Mariner] 71 data surprised us by indicating that Mars' H2O is principally poleward. Yet here is the box we are in for Viking '75: to be choosing 'optimal' landing sites within the least promising zone." 42 Since many members of the working group responded favorably to Lederherg's proposal to go farther north, Tom Young had his mission planners look into the engineering constraints. Jim Martin subsequently authorized Martin Marietta and JPL to make a limited study to determine what would be involved in landing between 65° and 80°N, but Young advised the landing site working group they would "approach this subject with caution and much reservation." 43
 
[304] The 28 September 1972 landing site working group session at Langley was well attended. After Soffen introduced new member Noel Hinners of the Apollo Lunar Explorations Office at NASA Headquarters and Jim Porter briefed the group on engineering constraints, Young addressed the key topic: Should they try to land a craft near the north polar region of Mars? His answer was no. It could be done, but the risks to the landing craft did not seem to justify the potential gains. Equally significant, not only would it cost between $2 million and $20 million more depending on hardware changes, it would also slow the project's schedule. Young believed the combined increase in money and time was bad news, but he was ready with a detailed reply to the scientists' grumblings. First, landing in the north polar region was technically feasible, an important consideration for future missions. And second, the Viking Project Office understood the high scientific interest in the far north. But third, studies indicated high- risk or high-cost schedule impact because additional communications equipment would have to be developed to ensure adequate links between the orbiter and the lander. With a fixed launch date, the risk was just too high. Because of a November 1976 solar conjunction-Mars would be out of view from Earth-a delay in launching the spacecraft would cut into the prime cycle of science data gathering. All factors considered, Viking 75 would not try to land closer to the northern polar region. John Naugle also restated the budget limitations, firmly reminding the scientists that no additional money would be made available. Information gathered by Mariner 9 regarding the polar regions would have to be filed away for use on some future mission to Mars. Considerably more discussion ensued about sites in the 30°S to 30°N latitude range, as each member of the working group had the opportunity to indicate his preferences. At the conclusion of the meeting, they recommended 10 sites.
 
 

 

Table 48

Candidate Landing Sites Selected August 1972

Mission A

Mission B

No.

Latitude

Longitude

No.

Latitude

Longitude

1

20°N

158°

7

2°S

148°

2*

20°N

77°

8

2°S

186°

3

19.5°N

34°

9

9°S

144°

4

12°N

158°

10

9°S

181°

5

12°N

77°

6

12°n

267°

 
* Denotes lower priority.
 

 
[304] The group's next step was to review these candidates and select one primary and one backup site for each mission at the next meeting, scheduled for 4 December 1972 at Orlando, Florida. 44 But it was not that simple. On 19 October, Tom Young telexed 20 members of the landing site working group; Hal Masursky and William Baum of the Planetary Research Center, Lowell Observatory, had recommended changes in the 10 sites.
 
 

 

Table 49

Changes in Candidate Landing Sites, October 1972

28 September Locations

Masursky Recommendations

Site No.

Latitude

Longitude

Latitude

Longitude

1

20.°N

158°

21°N

157°

2

20.°N

77°

19°N

65°

3

19.5°N

34°

No Change

4

12.0°N

158°

8°N

163°

5

12.0°N

77°

10°N

80°

6

12.0°N

267°

10°N

269°

7

2.0°S

148°

No Change

8

2.0°S

186°

No Change

9

9.0°S

144°

9°S

141°

10

9.0°S

181°

No Change
 

 
The alterations had been proposed so the Viking team could get maximum Mariner B-frame high-resolution pictures. Tom Young polled the working group by telephone on the 20th-15 had no objections; Barney Farmer, Richard Goldstein, Jim Porter, and Toby Owen had specific comments; and Al Binder could not be reached. Changes like these would become part of the routine process of landing a spacecraft on the surface of another -planet, and this was just the beginning. 45
 
 
Polar Option Revisited
 
 
By the time the landing site working group next met, in December 1972, Mariner 9 had completed its mission and Joshua Lederberg had thumped on the desk of NASA Administrator James C. Fletcher. On 27 October when Mariner 9 used the last of its attitude control propellant, a command was Sent from JPL's Mariner Mission Control that shutdown the spacecraft's transmitters. Despite initial setbacks, the mission had mapped the entire planet, permitting Viking scientists to gather far more images of candidate landing zones than they had originally anticipated. The infrared and ultraviolet instruments aboard Mariner had also observed large portions of the planet. As the data were being analyzed in November, Lederberg met with Fletcher and Naugle to express the scientists' concern that the [305] polar region was not being given a fair chance because the "engineers" - Lederberg's shorthand for the project management- had not done their homework earlier and examined polar regions for possible landing zones. The upshot of his argument was the decision by Fletcher, in consultation with George M. Low, his deputy, and Naugle, to hold in abeyance any final action on a polar region landing until they had heard from all the science team leaders. 46
 
Armed with the latest in a growing series of maps based on Mariner 9 data, the landing site team met 4-5 December at Martin Marietta's Orlando facility to pick the primary and secondary landing sites for Viking l and 2 . When Tom Young opened the session, he admitted that the question of a polar landing site had not yet been resolved, but the working group would go ahead with the original task of naming the landing sites in the equatorial band. In turn, John Naugle commented briefly on the strategy for a polar landing mission: "Send Mission A to the equatorial zone and target Mission B for the polar regions. Then if A succeeds, allow B to continue to the polar landing site, but if A fails, retarget B to an equatorial site,'' The Viking Project Office would provide a work plan and cost estimate to NASA Headquarters by 15 January 1973. Young responded that the ground rules would be kept open but no hardware changes would be made yet. If a decision was made to go to the pole, a fifth and sixth site should be selected; that is, a primary and secondary site in the polar region. NASA intended to hold a press conference in late December to announce the landing targets, and Young wanted any decisions reached by the working group before then withheld until the briefing.
 
The December 1972 announcement was not made; it was 7 May before any decision was made public. Between the December 1972 and the April 1973 sessions of the landing site working group, there was a great deal of argument, debate, or spinning of wheels-depending on one's perspective. Unanimity over where to land was difficult to achieve. During the 4 December dialogue, which lasted some 12 hours, only one site was selected. The group agreed that the primary site for the first lander would be at Chryse, 19.5°N longitude, 34° latitude. On the fifth, after another lengthy discussion, site 10 from the list, Apollinares, 9°S, 181°, was picked as the prime target for the second lander; site 9, Memnonia, 9°S,144°, would be the backup. A secondary target for the first lander was not selected, because of concern over the strength of the surface at site l (21°N, 157°) and because site 2 (19°N, 65°) had undesirable elevation characteristics. 47
 
A backup target for Viking 1 and the question of going further north continued to be nagging problems into the early months of 1973. An ad hoc group* for identifying north polar region sites for review by the working group met 14 December at Stanford University. Five sites were proposed.
 
 

[306] Table 50
Polar Landing Sites Proposed December 1972

Site No.

Latitude

Longitude

12

73°N

350°

13

74°N

225°

14

63°N

15

63°N

85°

16

63°N

160°

 

 
 
During the next several weeks, each of the science team leaders indicated his group's thoughts on the polar landing, as Jerry Soffen had requested during a December Science Steering Group meeting. 48
 
Mike Carr was one of the first scientists to express his opinion: "In general the Orbiter Imaging Team has conflicting responses." On one hand, team members were enthusiastic about a polar landing coupled with a successful equatorial touchdown, because of the potential benefits to lander science. But on the other, they were apprehensive about the impact of such a landing on the orbiter imaging experiment. If the orbiter was used to support a lander in the polar regions, the craft could not be employed to photograph other areas of the planet as planned, because the orbiter's path would have to he altered considerably to accommodate a polar site. Carr said, "We are unable at this time to adequately, confidently assess some of the implications of a polar landing because of inadequate study of the problem."
 
Carr was also concerned that landing one spacecraft so far north would curtail the two "walks" around the planet, during which the orbiter would photograph Martian features at higher resolution. Four years would have passed since Mariner 9 did the same; to lose this comparative photography would reduce measurably the understanding of the processes at work shaping the planet's features. If there were great pressure to go north, "the disadvantages could be tolerated if the Lander were to go to a site that exhibits uniquely polar phenomena ie one that is at least as far north as 75°. We would be very reluctant to accept these substantial disadvantages for a site at 65°N, which is not likely to be significantly different geologically from an equatorial site." 49
 
Physical properties investigator Richard W. Shorthill said that he had discussed the "north polar site' with his team, and it had not favored the proposal. From the start, this group had considered safety to be the prime requirement for a Viking landing site. "Considering the present state of knowledge we cannot support a North polar landing.'' There was no radar coverage of the polar regions-"no information on surface roughness at the scale of the spacecraft, no information on the mechanical properties of the surface materials.'' Mariner imagery of the polar regions had been either ambiguous or too obscured by dust for a reliable evaluation. He went on:
 
[307] We believe that soils with excessive amounts of water or ice are incompatible with the Viking lander surface sampler system as well as the GCMS [gas chromatograph mass spectrometer] experiment. The behavior of soil with intersticial ice in a Martian environment [is] poorly understood. One could visualize a sublimation process that yields a porous under dense surface material more than 40 cm thick. On the other hand the surface could be wind swept yielding a rock like surface composed of soil and ice.
 
Furthermore, the safe landing of the first spacecraft at the equator would not ensure that vehicle's longevity on the surface. The team believed that the second lander should also be sent to a relatively safe place. Shorthill also looked at the question of money. He was strongly opposed to cutting back on science funding to provide changes in the lander and orbiter so that they might operate to the polar region. "Any new funds NASA might make available for design changes required for polar operations could better be used to increase mission success in areas where previous cutbacks have reduced the chances of success" -areas such as testing, mission planning, team activities, and continued assessment of the surface properties of the equatorial landing sites.
 
After first evaluating the polar proposal on its scientific merits, Seymour L. Hess of the meteorology team had subsequently developed reservations. He found it "incredible that a project with such severe financial problems has accepted the addition of a thirteenth experiment and now seems to be about to swallow an additional major cost for the polar option." He also believed that the polar site proposal would be bad for the entire project. "One of the major sources of our troubles is that NASA has been extremely ambitious in the total amount of science it is scheduling in comparison to its fiscal resources. To add this new ambition is, in my opinion, fiscal recklessness." 50
 
Harold P. Klein, biology team leader, had another point of view. Klein told Soffen that the biology team had once again reviewed the polar versus equatorial site question at its 11 December meeting and regarded the presence of water as ``the most critical parameter in the search for life on Mars.'' After listening to all the facts and opinions, the team believed that liquid water would be less likely on the equatorial regions than in areas closer to the poles. ``We are not, of course, assured that the polar regions will afford opportunities for the production of Water under or near the ice caps, but we feel that these regions afford a significantly better prospect for this than the more equatorial zones." Therefore, Klein reported that his team strongly supported the proposition that at least one landing be made in the polar region. 51
 
Tim Mutch made a personal response. He had written one letter to Soffen that was a "dispassionate, scientific-engineering analysis," which came to a slightly negative to neutral conclusion on the polar landing proposal. After thinking about what he had written, Mutch concluded that he had probably missed the real issue: "The point is that Viking is an [308] exciting journey of exploration. The fact that it survives NASA's budget cuts is partly attribute to its wide appeal. Scientific skepticism not withstanding, laymen are intrigued by this bold search for life on another planet." Looking at Viking in this framework, Mutch had asked himself what all the talk about a polar landing really meant. "We are maintaining that we should keep open the possibility-only the possibility-of going to a northern latitude after the first lander has been on the surface almost two weeks and has been working perfectly for that period." A second successful landing did not guarantee a doubling of the scientific knowledge gained about the planet. Indeed, exploring near the poles might yield less information than gained at the equator. The Lederberg scenario was only a "long shot," which may or may not be worthwhile, but to Mutch, the single, most important aspect of the mission was exploration. If the lander is a success, then Viking as a project will be a success. Keeping the polar option open permitted them to continue playing the role of bonafide explorers. "The public will appreciate this (and ultimately we're responsible to those tax-payers who foot the bill). In essence we've identified the two most disparate areas on the planet and we're considering going to both. It's not that different from any polar journey. You equip yourself as best you can. You equip yourself as best you can. You set some intermediate reasonable goals, and if all goes well you make a dash for the pole."
 
Although the polar option would increase the cost by at least $2 million to $3 million, Mutch felt that it should be preserved. He thought that Administrator Fletcher should award the additional money. "Failing that, it does not seem unreasonable to absorb it within existing Viking budgets-even though there will be associated pain." 52
 
Not all of colleagues agreed with him, and Young and Soffen continued to receive letters concerning the matter as late as the day of the next landing site working group session, 8 February, Robert Hargraves of the magnetic properties team seemed to favor trying a polar landing. "If `A' is successful, the prospects of a 77 or 79 Viking Mission are dim, and the engineering risk is not horrendous, I'd say let's try.'' Hugh Kieffer, representing the infrared thermal mapping team, said that it "moderately opposed" north polar landing site considering only the infrared thermal standpoint of lander science, they noted that it was a proper objective for Viking; however, it would be difficult to validate such a site for safety. Kieffer, therefore, Was "hesitantly in favor of a polar site." C. Barney Farmer, leader of the Mars atmospheric water detector experiment team, was also somewhat ambivalent in his analysis. A polar landing would not be good for his group's experiment, but from the overall science strategy it seemed to be the thing to do. He favored "a polar B-site strategy. " The molecular analysis team, led by Klaus Biemann, had met on 10 January at JPL, deciding unanimously in favor of trying a polar landing. It had not considered the funding and risk problems, assuming that the final decision-makers [309] at the Viking Project Office and NASA Headquarters would take them into account. 53
 
When the landing site team met at Langley in February, it began to tackle its two problems-a backup site for the first lander and a possible site in the polar latitudes. All aspects of the polar problem were reviewed again, as Carl Sagan outlined the positive and the negative. Sagan had come to the side of the those who favored safety. In a 12 January letter to Young, he had said, "When I total up the pros and cons I find that the scientific advantage of a polar landing site, while real, is far outweighed by the risks." He believed the successful landing of the second spacecraft in the polar region was actually much less than 50-50. When he equated that to losing $200 million-the total projected cost of a future Mariner-Jupiter-Saturn probe-he considered the risk unjustified, but Sagan had other worries on his mind. He was still concerned about the possibility of the first lander's disappearing in quicksand at one of the equatorial sites and favored further study of the meaning of the radar data, expressed in terms of dielectric constants, so the surface-bearing properties of Martian soil could be better evaluated. Generally, he believed too much stress was being placed on visual images at the 100-meter scale and not enough on radar, which could indicate surface irregularities at the 10-centimeter scale. He pointed out:
 
It is perfectly possible for a candidate landing site to be smooth at 100 meters and rough at 10 cm. or vice versa. Cases of both sort of anticorrelation are common enough on Earth. It has been alleged that at least in studies of the Moon there is an excellent connection between roughness at 15 cm and roughness at 150 meters. A detailed statistical study of such correlation should be prepared and subjected to critical scrutiny. The [U.S. Geological Survey] seems to be the obvious organization to prepare such a study. . . .However even if such correlations exist for the Moon, it is by no means clear that they exist for Mars. A similar study should be performed for the Earth. This can readily he done by cross-correlating Apollo and Gemini photography of the Earth with radar studies.... Until such a connection is clearly shown for the Earth-and I have grave doubts that such a strong correlation exists-we would be foolhardy to attach very much weight to the 100 meter appearance of candidate landing sites on Mars. Unfortunately visual appearance has been given high weight in (working group] deliberations. 54
 
Arguments and debate over, the majority of the working group favored northern sites 12 and l3 as primary and backup targets for a polar landing. Tom Young forwarded the group's recommendations to the Science Steering Group that
 
1. The Mission "A" landing sites with all factors considered be:

Latitude
Longitude
Primary
Site 3
19.5°N
34.0°W
Backup
Site 11

20.0°N

252.0°W
 

[whole page 310] The landing site working group on 8 February 1973 debates the choice of targets on Mars for Viking landers. In a voting process on one proposal are (above, left to right) Richard Young, Harold Klein, Henry Moore, William Baum, Noel Hinners, Harold Masursky, and Walter Jakobowski. At left, Norman Crabill and Masursky discuss pros and cons. From left below, Carl Sagan, Tobias Owen, Terry Gamber of Martin Marietta, and Barney Farmer consider arguments for a proposed site.

 

 

 
 
[311] 2. The Mission "B" landing sites, if NASA decides that the sites will be in the North Polar Region, be:

Primary

Site 12

73.0°N

350.0°W

Backup

Site 13

73.5°N

221.5°W

3. The Mission "B" landing sites, if the sites are in the equatorial region, be:

Primary

Site 10

9.0°S

181.0°W

Backup

Site 9

9.0°S

144.0°W

 
 
While approving the A sites for the first lander, the Science Steering Group could not come to an agreement over the second lander's destination. Several members of the group still wanted additional information regarding which areas had the highest probability of containing water in liquid form. In a joint memo to the steering group, Soffen and Young noted that any additional delays would have "a significant impact on the Viking mission design schedule and other Viking planning''; completion of the recommendation by l April was extremely important. 55
 
As the delays mounted, the Viking management grew restive. Some unknown person suggested that when ultimately chosen the Mission B site should he called "Crisis Continuum," but at higher levels that sense of levity was not shared. On 20 February, John Naugle reported to Administrator Fletcher that the polar latitude site issue had still not been resolved. In reviewing the problem, Naugle went over the " presence of water" issue that was dividing the scientists, "It appears that the regions most recently studied by the Viking Landing Site Working Group may not be good sites from the point of view of availability of liquid water because of low temperatures, even though large amounts of water ice are known to exist." Furthermore, Mariner 9 data being analyzed suggested that the optimum....
 
 

 
Viking landing site working group discussions continue on 8 February 1973, with (left to right) Michael Carr, Gerald Soffen and Thomas Young at the table, Robert Hargraves, Burt Lightner, Arlen Carter, and Priestley Toulmin (back to the camera).

 
 
[312].....sites for water availability might be around 55° north. Naugle added that this region had not yet been studied in detail by the landing site specialists. The possibility of water and the geographical differences between the polar and equatorial zones were the two reasons some of the scientists favored landing in the northern latitudes. Naugle said that the Office of Space Science saw sufficient justification, in recommendations from a majority of the landing site working group to plan for a polar landing. "If we do decide to do a polar mission. We have a majority decision....to recommend a site at 73°N to you." Liquid water was the nagging question. Where were they most likely to find it? Naugle promised the administrator a recommendation by early April. On the following day, 22 February, Fletcher returned a copy of Naugle's memo with a terse, handwritten message in the margin. 56
 
John N-
I have two questions.
(l) Does Lederberg (& his committee) agree that the chances of life are best at 73°?
(2) Does liquid water have to exist now or could it have existed once, for life "signatures" to be detected?
From my own point of view, the main reason to consider polar landings was to increase the probability of finding life, not to study vastly different geological regions.

 

JCF
 
 
The biologist, would commit themselves only to the statement that the chances of finding life "are highest wherever liquid water is present for at least transient periods." As for Fletcher's second question, Naugle reported:
 
For an active biota to exist, liquid water must exist at least transiently. Biological "signatures" (eg., organic molecules) can exist if liquid water was ever present and life existed in the distant (millions of years) past. The difficulty here will be in determining whether the organic molecules detected are the product of biological processes or nonbiological (or prebiological) processes. Viking will detect organic matter, but may not be able to clearly distinguish between biological and nonbiological types. We have newly developed techniques available in the laboratory now.....but such sophisticated analyses will have to wait for post-Viking or return sample missions.
 
A special meeting had been held 28 February to consider the question of possible locations for liquid water on the Red Planet. Naugle summarized the results of the "water hole tiger team's" session for Fletcher. No one could say positively that there was any locale on Mars where liquid water could be found. "This does not preclude the possibility for liquid water; it simply means that based on what we know now about the surface of Mars, we cannot determine where liquid water may exist even in transient form.'' Therefore, it was not realistic to select any site using only the liquid water argument. In the absence of a firm consensus among the biologists, Naugle had to report that he was not much closer to a recommendation than before. [313]  He told Fletcher that he would have the necessary information following the next meeting of the landing site working group. 57
 
 
Destinations Determined
 
 
The big day was 2 April, and Tom Young wasted no time in laying down the ground rules for this important meeting of the landing site working group. Selection of Viking targets "should be based upon the best knowledge that we have today." In choosing a backup for the second lander, Young wanted the group to assume that the first one had made a successful touchdown. Finally. site selection should be based only on scientific, cost, schedule, and risk considerations-not on policy constraints. 58
 
While Naugle and Fletcher were puzzling over a polar landing site, the Viking scientists were changing their minds about the north. The more they talked about liquid water at higher latitudes, the more they thought about the low temperatures they would find there. Could they expect living organisms to survive during the transient appearance of liquid water as that compound passed from the solid to the vapor form or vice versa? Biologist Wolf Vishniac had looked into that question during February but had not turned up any evidence to support the belief that bacteria could grow or survive at temperatures much below -12°C. 59 Studies made with the Mariner 9 infrared interferometer spectrometer had disclosed surface temperatures ranging from -123°C at the north polar region to +2°C near the equator. 60 The search for unfrozen, active life forms in the northern latitudes on Mars seemed unrealistic.
 
On 2 April, Lederberg conceded that 73°N no longer appeared to be a rational goal. Now the biologists were seeking a region where condensation might be anticipated that reached a temperature as high as -13°C - they wanted to land between 40° and 55°N. Long hours of discussion followed, during which the working group voted not once but several times on where to send the Viking spacecraft. Site 3 (19.5°N, 34°) was selected as the primary target for the first lander, and site 11 (20°N, 252°) was chosen as the backup. The group narrowed the second mission to two candidates, 16 and 17, but remained undecided over which should be the primary target. The Science Steering Group subsequently made that decision, recommending number 16 (44.3°N, 10°) as the Mission B primary site and number 17 (44.2°N, 110°) as the backup. 61
 
Looking back on the ordeal of choosing sites for Viking, Tom Young used the word "traumatic" to describe the process. "We really thought that we were embarking on a reasonably simple task....."But it had been very difficult to focus all the engineering and scientific issues on each specific site; "everytime we thought we [had] it, we would find another problem...." One of the complicating factors had been the continuous stream of new knowledge about Mars. Their immediate need for information had forced them to take a quicker and harder look at the recent Mariner 9 and Earth-based data than they would have under normal conditions. And each [314] new piece of data changed the Martian picture as the specialists tried to select their targets. 62
 
Hal Masursky, who had worked with Lunar Orbiter, Surveyor, Apollo, and earlier Mariner missions, thought the lengthy debate over landing sites had been not only useful but essential. However, he thought that the biologists and organic chemists had not thought through the landing site question; they had to be educated about the nature of the planet and the spacecraft's capabilities. According to Masursky, some of the scientists developed many of their ideas as the debates went along, and they were forced to analyze quickly new facts at the table. The photogeologist recalled that while Tom Young and Jim Martin had kept pressing the working group for timely decisions, the managers had obviously understood the need for extended debate and had never tried to stifle interchange of ideas. Young and Martin, despite all kinds of external pressure, had managed to protect the scientific integrity of the landing site working group. 63
 
Results of the landing site search were made public on 7 May 1973. John Naugle announced that a valley near the mouth of the six-kilometer- deep "Martian Grand Canyon" was the target for the first lander. Known as Chryse, the region had been named for the classical land of gold or saffron of which the Greeks had written. If all went well, Naugle told the assembled press corps, the first Viking would be set down on or about the Fourth of July 1976. The backup to the Chryse site was Tritonis Lacus, Lake of Triton named for the legendary river in Tunisia visited by Jason and the Argonauts. The second Viking was targeted for Cydonia, named for a town in Crete, with Alba, the White Region, as backup. Soffen told the press that NASA hoped Viking 1 would be heading for a very safe but interesting target. The scientists had decided early that the first site should be sought in the northern hemisphere (because it would be Martian summer there), at the lowest elevation possible (higher atmospheric pressure and better chance of water in some form), on the flattest, least obstructed region they could find (for landing safety and weather observations). But the second mission had been a different story. The biologists wanted water, and after much debate and study they hoped to find it in the 40° to 55° north latitudes. Their Mission B sites were just above 44°.
 
But what about these specific sites? What were they really like? Hal Masursky spoke to this point. From the Mariner 9 photographs, he could demonstrate that about 50 percent of the planet was pockmarked with large craters not unlike the southern highlands of the moon. "We think this is the ancient crust of Mars that was differentiated very earlyŠand continued to be bombarded by cosmic debris...." Large basins on the planet recorded that epoch. The largest basin, Hellas, was nearly twice the size of the Mare Imbrium, a giant lunar crater 676 kilometers in diameter. To the north, the planet appeared to be smoother and younger, and scientifically more interesting. Chryse was at the point where a number of "stream" channels appeared to empty onto a plain (Chryse Planitia). Essentially featureless in the Mariner A-frame photographs, there was reason to believe that the area [315] was covered by fine wind-borne materials. The photogeologists believed that there was a likelihood of finding fossil water ** in this region, since highland materials would have been deposited here during earlier epochs of water-caused erosion. According to Masursky, "It looks like....the Mars environment has been different enough so that there was surface flowage of enormous amount of water....into this great northern basin, and our landing site is at the mouth of that great channel system." The B site, Cydonia, combined the greatest chance of atmospheric water with a low, smooth plain. Masursky thought that this was an optimal landing target. Whereas the first area saw the drainage of the highlands materials, the second site, near a large volcanic complex, was covered with basalt flows partly blanketed by wind-blown debris. "We think this combination of sites gives us the best possibility of fossil and present water, and our best samples to test the evolution of the planet." 64
 
Selection of the Viking landing sites based on the data available in 1973 was only a first step toward ensuring safe havens for the spacecraft on Mars, and the Viking scientists recognized that additional data should be obtained from Earth-based radar observations and Viking orbital photography. Still, the work of the landing site working group provided the foundation for subsequent debate about the safety of the two Viking landers. The second phase of the landing site story focuses on the certification of the chosen sites, a process that started in May 1973 and was still going on hours before the landers were released for descent to the Red Planet. As is so often true of first steps, site selection was the initiation to a more bewildering process-landing site certification.
 

* N. L. Crabill, J. A. Cutts, C. B. Farmer, J. Lederbery, H. Masursky, L. Soderblom, G. A. Soffen, and A. T. Young.
 
** Stream channels are equivalent to fossils in that they are evidence that water once existed.