Viking Science

1. Introduction

On that fateful day more than half a century ago, the first Viking lander began sending out the first-ever picture taken on the surface of Mars. As breathless crowds gathered around television sets and watched, the picture built up with painstakingly slow progress. One vertical line after another swept across a field of view that was, by design, not of the horizon, but directed down, at the nearest footpad. “Oh my, all those rocks” the narrating scientist exclaimed. The engineers were elated—Viking had not sunk into the fabled foo-foo dust that supposedly threatened to allow the lander to sink and damage its underbelly on some sharp rock. Mars, rather, was just what we wanted it to be, and the lander was dutifully performing exactly as the pre-programmed sequence of events (SOE) intended.

The landing by the first Viking lander (VL-1) was an unmitigated success! Having been ejected from its sister orbiter, it had modified its own trajectory with small rockets to re-aim toward the surface for what would be either a humiliating crash or the planned soft landing. Aided by orientation maneuvers, the lander’s aeroshell had slowed, followed by a parachute deployment while still at supersonic speed. This was followed further by the lander measuring altitude with its radar, dropping out of the aeroshell, extending landing legs, orienting precisely toward north, firing the descent engines, and then turning them back off as a footpad switch detected touchdown. The entire series of events was far more intricate than the most spectacular possible play on a football field.

Over the next several “sols” (Martian days), the lander began performing a pre-planned SOE that included a full mission of multiple sampling and analysis by the various instruments it carried. This “canned” SOE had been meticulously planned as a precaution for a possible communication failure that would prevent updates to operations. However, both telecommunications links worked perfectly, one directly to Earth by pointing the dish antenna and the other transmitted to the orbiter as it passed overhead each sol. With quick action, it was possible to update an arm deployment sequence, and the first sample was taken a week after landing.

2. The Science

Viking-1 landed at Chryse Planitia after topographical data from orbital imagery necessitated a delay from the planned July 4, 1976, Bicentennial date. The site proved rugged, a characteristic later navigated by the Mars Pathfinder’s airbag system. Beyond meteorological data and imaging, the mission’s primary objective involved soil analysis via the Biology Team’s instrument and the Inorganic Chemical Analysis Team’s (ICAT) X-ray Fluorescence Spectrometer (XRFS).

Geochemical characterization by XRFS analysis confirmed high iron concentrations, consistent with long-held hypotheses regarding Martian hematite and similar iron oxides. However, the data also revealed unexpectedly high concentrations of sulfur and chlorine. These were identified as sulfate and chloride salts, and they indicated a pervasive “salty” regolith. While these salts were not visually apparent as white veins—features only confirmed by subsequent missions—they suggested a history of liquid water.

Current Martian conditions restrict water primarily to ice at the poles, frost at higher latitudes (as seen at the Viking lander 2 [VL-2] site), and subsurface deposits (as proven by the later Phoenix mission). At the surface, the triple point of water is a critical constraint: While equatorial midday temperatures may reach melting, the tenuous atmospheric pressure causes water to boil below +15°C. This promotes “cold trapping,” where water vapor migrates and condenses toward and at the poles, which effectively desiccates mid-to-low-latitude soils.

Searching for life was the primary goal of the missions. The biology suite comprised three experiments—Gas Exchange (GEX), Labeled Release (LR), and Pyrolytic Release (PR)—which included incubation chambers maintained at only 10°C–20°C above freezing to prevent overheating potential microbes while ensuring any indigenous ice was melted.

1.

GEX evaluated metabolic gas flux by adding a high-nutrient medium (“Chicken Soup”) to the soil.

2.

LR injected seven nutrients labeled with a radioactive carbon-14.

3.

PR exposed soil to carbon-14-labeled carbon dioxide gas under a xenon lamp (to simulate solar radiation) to detect carbon fixation.

Only the LR experiment yielded a strong positive signal. However, several factors led to skepticism about whether it indicated life. First, a second injection of nutrients failed to produce additional metabolic signatures; a biological colony would typically show growth or sustained activity. Second, the GEX experiment produced a sudden release of oxygen upon exposure to water vapor before contact with nutrient, suggesting a purely chemical reaction with powerful soil oxidants (e.g., peroxides or superoxides). Publications by leading biologists quickly questioned the life detection results on these grounds (Ponnamperuma et al., 1977) as well as overviews of the results (Mazur et al., 1978; Margulis et al., 1979).

The most significant contradiction came from the gas chromatograph–mass spectrometer (GCMS). Despite exquisite sensitivity (ppb range), the GCMS detected no organic molecules. Given that all known life is carbon-based, the absence of organics suggested that the LR results were likely the product of nonbiological surface chemistry, such as UV-irradiated minerals mimicking metabolic processes.

The negative GCMS results especially contributed to a global consensus that Mars was sterile. This reversed the early 20th-century public fascination with “Martian canals.” These canals, once championed by the New York Times and early astronomers, were eventually debunked as optical illusions by higher-resolution telescopes (Baron, 2025).

A surprising discovery was the near-identical elemental composition of soil at the VL-1 and VL-2 sites, despite their being on opposite sides of the planet. This uniformity is attributed to global dust storms that homogenize surface material. To investigate vertical stratigraphy, VL-1 excavated a 23 cm trench. Geologists anticipated a decrease in sulfate salts with depth; however, concentrations remained constant. Conversely, an ICAT “pebble” sampling experiment provided evidence of aqueous transport. Using the sampler arm to sift coarse material, the team analyzed gravel-sized “peds”—soil consolidated by salt cementation. These peds showed marked increases in sulfur and chlorine, likely in the form of chloride and magnesium sulfate.

Subsequent missions have confirmed that these salts, along with clays, are ubiquitous, often appearing as veins in rock formations across the planet. This indicates that while Mars is currently a desiccated, oxidizing environment, it was once characterized by active brines. These findings remain foundational to Martian geobiology and the ongoing search for halophilic or primitive life in the planet’s aqueous past (Icarus, 1972).

While the Viking landers were performing their research on the surface, the orbiters were also busy taking thousands of pictures and measurements over the majority of the planet’s surface. Besides the camera, each orbiter had instruments for mapping surface temperatures and atmospheric water vapor. Although Mars is quite dry, relative to Earth, it nonetheless has some moisture in its atmosphere everywhere, and these levels of humidity vary with the seasons.

At the time of Viking, planetary science was still in its infancy. Likewise, many technologies that we today take for granted were also in their infancy—some not yet even born. An issue of the journal Icarus published descriptions of each Viking lander investigation (Icarus, 1972), and a description of the actual final Biology Instrument was published in Reviews of Scientific Instruments (Brown et al., 1978). Overall, the scientific results of Viking were mostly reported in the journals Science and various special issues of the Journal of Geophysical Research.

3. The Scientists

The Viking mission was essentially an all-US science endeavor. All but one of the 72 members of the Steering Group and 13 Science Teams (3 Orbiter Teams; 10 Lander Teams) were associated with US institutions, mostly but not exclusively with universities. In contrast, NASA’s two current Mars rover science teams have included approximately 400 participants each, about one-fourth of whom are contributed via international partnerships with France, Spain, Canada, Finland, and many other countries, including even Russia.

Not well known, however, is that several important members of the Viking science teams were US immigrants: Biemann from Austria, McElroy from Ireland, Oro from Spain, Orgel and Carr from England, Hargraves from South Africa, and Keil from Germany. Many others were first-generation descendants of immigrants: From Japan/Hawaii (Oyama), from Hungary (Klein), from Germany (Soffen), from Russia/Ukraine (Sagan), and from Russia (Masursky).

Unlike the Mars rover missions, whose scientists now generally participate by remote connection from their home institutions, the Viking lander scientists mostly relocated to the Pasadena area for the summer of 1976 when mission operations began. It was a heady time.

More than 80% of all Viking scientists never again participated in another space mission. Even more had never before been involved in any NASA mission. But many had already established major scientific credentials as researchers on their own. Two had won Nobel Prizes (Lederberg and Urey), and several were so illustrious as to be considered strong candidates to become Nobelists (e.g., Nier, Rich, Horowitz, Oro, and Orgel). As a result, some seemed to be more inclined to “pontificate” than to “participate.” This was quite unlike modern Mars missions, where there is often a high percentage of repeat scientists who are instrument specialists, and the newest members often include a broad cadre of post-docs and advanced graduate students, who are nonetheless accepted as full-fledged team members because of their dedication to the work effort and their familiarity with advanced methods of analysis (including, now, machine learning and AI).

The fact that extremophiles are dominated by microbes, which are also different in various biochemical ways from most other bacteria, was just being revealed. Woese and Fox proposed the third domain of life in 1977, as the Viking mission unfolded. What we now recognize as the domain Archaea happens to include those organisms most adaptable to more extreme environments, such as Mars.

Also in 1977 was the first discovery of hydrothermal vents in the deep seafloor, populated with organisms, from unique bacteria to exotic “tube worms” (Corliss et al., 1979). So while Viking was seeking life on Mars (and not necessarily finding it), ocean scientists seeking geologic “hot spots” were incidentally discovering new forms of life (where they didn’t expect to find it).

4. The Public

The public response to the Viking search for life was enthusiastic. Most major newspapers covered the successful landing as a front-page news event. Some followed the results of the attempts at life detection with multiple articles. There were more than 1000 daily newspapers in the United States at the time, and many had correspondents who specialized in science.

Also, newspapers in major cities employed artists who created daily cartoons that often lampooned various political figures or their proposals. The Viking mission attracted the best of the best, and dozens of cartoons were drawn. Some simply mimicked the mission; others were comical or satirical. One had a script balloon rising out of the ground, which said, “Don’t move. They’ll think we’re rocks.”

5. The Project

NASA’s Langley Research Center, which was also the original field center of NASA and its forerunner the National Advisory Committee for Aeronautics (NACA), had responsibility for the Viking mission. They selected Martin Marietta Corporation (MMC) for design, development, fabrication, test, and launch support for the landers. The NASA Jet Propulsion Laboratory (JPL) was selected for the complementary orbiters and hosted mission operations because of their ties to the Deep Space Network telecommunications system.

At NASA/Langley, Project Manager Jim Martin operated with strict discipline. When the development costs for the Biology Instrument continued to spiral upwards, it was decided that one of the four experiments would be deleted. The scientists reluctantly chose to eliminate the “Wolf Trap” experiment, which used turbidity assays of particles suspended in nutrient solution to monitor growth. Little did scientists know, at that time, that Martian dust is extraordinarily fine-grained (3 microns and less) and likely would have confounded any results.

At the same time, pressure from NASA headquarters (Steve Dwornik) and CalTech (Prof. Gerry Wasserburg) for Viking to also include geologically oriented science resulted in the addition of the XRFS and seismometer instrument.

From initiation through launch, the Viking Project at Headquarters was led by seasoned engineering managers, not all of whom had worked with scientists. However, leadership then transitioned to Dr. Noel Hinners, a scientist with geological credentials from Princeton and CalTech who, along with Dr. James Head at Brown University, among others, had provided training for the Apollo astronauts (one of whom was Dr. Harrison Schmidt, the only geologist who actually flew to the Moon).

Building 264 at NASA JPL needed to be expanded by adding six more floors to support the influx of engineers and scientists for the Viking mission. Congress, however, refused to approve NASA’s facilities budget. It seemed that Viking operations would originate from some rented facility in Pasadena. Just in time for the mission, the construction was finally approved.

6. The Hardware

The Viking Project set up Mandatory Parts and Materials Lists. Materials were screened for outgassing, and Viking developed a whole new database on such properties, used to this day.

Electronic parts were highly limited because of susceptibility to damage from the required sterilization by heat (the entire lander was encapsulated and baked for more than 24 h at a temperature above 100°C). Integrated circuits were still new, and those approved were quite primitive. The only CPU was in the VLBI and not in the spacecraft main computer (GCSC). The latter had only 18 K words (24 bit) and had to be programmed in machine language, as spaghetti code, yet had to autonomously control the entire complex landing sequence. Flash memory did not yet exist, and the working memory was a special array of plated wires (magnetically programmed) plus a tape recorder. The latter required the development of a metal tape for recording to survive heat sterilization.

There were no desktop computers, and therefore, no CAD, and no significant amount of CAM for fabricating parts. Designs were hand-drawn in pencil on velum sheets at arrays of drafting tables, using motor-driven erasers when a complex drawing needed to undergo modification and revision.

The Viking program was hardware-rich. Four identical Flight Units (FUs) were built for each “black box” in the landers. Prior to that, there was a Qualification Test Unit, essentially identical to the FUs but subjected to all of the prelaunch tests and, in some cases, to excessive levels to determine its ruggedness to adversity. Before these, there was a Development Test Unit, which was “form, fit, and function” but not necessarily constructed with all the exact flight components. And, of course, before that, there was a Breadboard, which demonstrated that the sensors could perform with the accuracy and efficiencies expected.

Despite apprehensions by virtually all of the engineers who designed, developed, tested, and baby-sat their individual subsystem, virtually everything worked either to perfection or adequately for overall success. The planned lander missions of 90 sols stretched to 3.5 years for VL-2 (until battery failure) and nearly 6.5 years for VL-1 (until an incorrect uplink overwrote software code with data, which no longer enabled the high-gain antenna to properly point to Earth). The orbiter missions unfortunately ran out of fuel much sooner. Subsequent Mars orbiters plumbed together fuel for the attitude control engines and propulsive engines. Thus, the Mars Odyssey orbiter has operated for 25 years and the Mars Reconnaissance Orbiter for two decades.

The only Viking instrument that did not work properly was one of the two seismometers, which failed to uncage its launch lock. A subsequent Mars mission, the InSight lander, took an ultrasensitive seismometer to Mars and used lessons learned from Viking to perform exquisite measurements of Mars quakes and meteoroid impacts. These have revealed much about not only the relatively sparse Martian seismic activity but also the current rate of meteoroid impacts and the internal structure of the planet.

7. The Software

Viking lander software was written for a full mission, from sampling to data downlink. Progress in S/W development was strictly monitored and documented and was completed before launch. For example, for analyzing data from the XRFS instrument, three of us developed 20,000 lines of code in Fortran IV, including team-restricted passcodes and plots of spectra using the line printers since computer-friendly x–y plotters were rare. Only a few mainframe computers were available, and qualified desktop computers did not yet exist.

8. The “Then versus Now”

Unlike today’s world, connectivity between remote institutions was mostly by telephone, fax, and very low data rate “modems” that converted digital signals into sounds over telephone lines, which then had to be demodulated by the receiving modem. There was no e-mail. No internet. No Zoom, Webex, Teams, or other collaborative tools for video conferencing. Cell phones were not yet available, but “pagers” were available so that the few key personnel who were entitled to one could be “paged” when needed.

Documentation occurred as follows: A technical person writes some text by hand. The paper is given to a supporting secretary who has a typewriter (in those days, the IBM Selectric typewriter with its spherical “typeball” had come into existence and was the top of the line). For graphs, the technical person plots points by hand on pre-printed graph paper (linear, log-lin, or log-log). For polished reports, an artist (or the technical person) prepares finished artwork versions of plots in ink.

For project documents, the typewritten input could be provided to a central group that had a team of individuals who were able to retype the information into a computer as an early form of word processing. Turnaround was typically overnight or longer. Once initiated, updates could be made from “red-lined” hardcopy.

Thermal analysis codes were just being written. The Viking lander program actually helped spur their development and adoption because of its challenges: designing a lander to operate in a cold-biased environment with wild swings in air temperature amid a relatively significant solar component and two nuclear power sources that created an enormous heat load. To verify calculations, a full-scale thermal mockup of the lander was constructed and tested.

There were, of course, no personal computers. No GUI. Computer monitor screens typically had green characters on an otherwise black screen.

In addition to punch cards, there was punched-paper tape. And with the mainframe computers came large magnetic tapes, which could be loaded on any of several tape machines to read and write data. Such tapes could sometimes be damaged, so it was prudent to make one or more copies of all critical data. Users were not allowed inside the computer room, so it was necessary to send a message asking for a specific tape to be located in storage and then loaded before it would become accessible to the computer. Accidental writing new data over old, but critical, data could occur—and too often did.

Software lines of code were handwritten and then provided to a support person who key-punched them into “IBM Cards.” The resulting stack of many tens or hundreds of cards was then loaded as a deck into a reader, which fed the information into the mainframe computer. Dropping such a set of cards could be disastrous. Printouts of the lines of code and of the output were accomplished by large, noisy, high-speed, very expensive impact-based line printers, which could print up to 132 characters simultaneously.

The Viking orbiter cameras used vidicon tubes (similar to studio TV cameras at that time). Solid-state arrays for cameras were not yet available. However, for the Viking lander, a facsimile camera with a single-pixel concept using multiple solid-state detectors was invented, with six wavelengths covering 400–1100 nm (Vis-near-IR). To create an image, the single pixel element had to be mechanically scanned up-down to create a line image, combined with the cylindrical camera body rotating slightly to create the next line to form an x–y image.

9. The Legacy

The next Mars mission opportunity was originally expected to be Viking-3. Fortunately, conservatism had caused the project management to plan construction of three identical flight landers so that, in the event there was a problem on the launch pad, a substitute would be available. The two launches had to occur within a 6 week “window” in order to reach Mars, flying their “conjunction class” trajectories. The original third lander had been halted during its final assembly as a matter of cost avoidance, and the hardware was safely placed in “Bonded Reserves.”

Just prior to the launches, Hal Masursky and I were part of a presentation to top management, led by Project Manager Jim Martin at a meeting at MIT in Cambridge, Massachusetts. The company that had designed and developed all the hardware and software, Martin Marietta, had completed an internal study, which showed that the third lander could be completed and outfitted with treaded tracks replacing the footpads. These tracks had originally been developed at NASA Marshall Space Flight Center for possible use on a lunar rover. This would enable placement of a roving vehicle on Mars as early as 1981 or 1983. Masursky, Carr, and other geologists had recognized the need for mobility and a capability for analyzing rocks as keys to the future exploration of Mars. Although the Viking rover was never funded, the subsequent rover missions on Mars have more than proved the importance of mobility, for we now know that, although the soil is monotonously similar everywhere, the rocks on Mars are amazingly diverse in their composition and significance. NASA could have begun roving Mars two decades before the Mars Exploration Rovers (MERs) landed and discovered the diversity that was all but hidden. However, the null results from the life detection experiments and NASA’s pivot to development of the space shuttle and a new space station precluded any follow-up of the first two Viking missions, in spite of the original concept of a series of Mars missions.

What we got, instead, was the abandonment of Mars exploration for the next two decades, until a “tech-demo” named Mars Pathfinder “broke the ice.” Its purpose was to demonstrate a presumably cheaper method of landing, using airbags. It also demonstrated a micro-rover, built at extremely low cost. A few years later, the MER mission was formally proposed, but accepted only if two separate landing attempts were made, as with Viking. Like Viking, both missions were fully successful. The MERs discovered that although the soils are monotonously similar and almost identical (due to the violence of dust storms), there is considerable diversity in the rocks of Mars.

Mars remains the best possible analog for conditions on early Earth, because much of the earliest history of the solar system is still evident on its surface, as exhibited by the presence of craters of all ages, as well as the streams and canyons carved by flowing water. In comparison, the history of our own planet is confounded by Earth’s much more dynamic history of tectonics, volcanism, and earthquakes, plus erosion and depositions by wind and water. To understand how life may have arisen, Mars may be the best analog of suitable environments for the origin of life. We are not yet finished with the red planet, in spite of amazing progress in just a few decades from the subsequent missions to Mars. Now that we have nearly three dozen amazing samples carefully extracted from Martian rocks and soil, we await with keen anticipation their return to Earth, where a variety of specialty laboratories can use their finely tuned sample preparation skills to unlock secrets no future space mission will ever be able to achieve.

Perhaps there are indeed signs of life hidden in samples from Mars. The Martian meteorites are not the answer because they come from deep-seated, highly competent rocks rather than soils and the mudstones that preserve the sedimentary history when water perfused Martian materials. The next major leap in Mars science awaits us, although it is currently marooned in the innards of the Perseverance rover.

And although there are many hurdles to overcome, the Martian environment is far and away the most likely place where we human beings could manage to survive, should we desire to become a “multi-planet species.” At the same time, it is by far the most likely place where earliest life may at one time have gained a foothold, other than our own planet Earth.

Author’s Contributions

The author was the sole contributor to all aspects of this article.