The Vikings Reach Mars

On July 20, 1976, a small spacecraft emerged from a cloudless, apricot-colored Martian sky and fell toward the western Chryse Planitia, the “Golden Plain.” Its heat shield glowed as it buffeted through the tenuous atmosphere.27 About four miles up, the para­chutes deployed, the heat shield was jettisoned, and three landing legs unfolded like a claw. At one mile up, the retrorockets fired, and less than a minute later the Viking 1 lander decelerated to six miles per hour, reaching the surface with a slight jolt.28 It was a landmark of technological prowess, the first time humans had ever soft-landed an emissary on another planet.

The twin Viking missions were the most complex planetary probes ever designed. Their total price tag was around $1 billion, equivalent to $4 billion today after adjusting for inflation. That can be compared to the $80 million cost of Mariner 4. Mission plan­ners were well aware of the challenges; the Soviets had previously failed four times to soft land on Mars.29 Each Viking consisted of an orbiter designed to image the planet and a lander equipped to carry out detailed experiments on the surface.30 For the most part, the hardware worked flawlessly, but there were tense moments for the engineers and scientists on the team. After ten months and 100 million miles of traveling, the Vikings reached Mars two weeks apart. The first landing had been planned for July 4, 1976, the na­tion’s bicentennial, and the landing sites were selected after years of deliberation. But as the twin orbiters started mapping the planet with ten times sharper images than had ever been taken before, mission planners were shocked to see that the planned Viking 1 landing site was not the benign plain they’d expected, but the rock – strewn bottom of what appeared to be a riverbed.

The landing site was abandoned. Gentry Lee, the director of Sci­ence Analysis and Mission Planning for Viking, vividly recalled the turmoil the new images caused: “For almost three weeks the Viking Flight Team operated at an unbelievable pace and intensity. Many of the key members of the team, including not just the engineers, but also [Jim] Martin and [Tom] Young and many of the world’s foremost planetary scientists, worked fourteen or more hours a day for the entire period. Landing Site Staff meetings, to synthesize the results and look at all the logical options, were held every day. Carl Sagan, Mike Carr, Hal Masursky, and other famous Viking scientists argued eloquently about the safety of each of the candi­date landing sites. Finally, the exhausted operations team managed to reach a consensus.”31 A new site at Chryse Planitia was selected. Once the lander separated from the orbiter, it would not be pos­sible to redirect the lander with any additional commands. The die was cast. Few team members slept much that night.

Media coverage and public interest were intense. Viking 1 and 2 marked the first close-up glimpse of the red rocky soil of Mars. “Despite the early hour, the von Karman Auditorium [at NASA’s

Jet Propulsion Laboratory] was packed. In addition to 400 jour­nalists from around the world, there were 1,800 invited guests watching a closed-circuit television view showing the control room, with Albert Hibbs, one of the mission planners, provid­ing the commentary.”32 For nineteen agonizing minutes, everyone waited—that was how long it took for telemetry to reach the Earth saying the lander was safe. Its first picture was of its own foot, to see how far it had sunk into the Martian soil. When, on its sec­ond day on Mars, Viking 1 sent back the first color panoramic views of the Martian terrain, scientists and public audiences alike recognized a kind of reddish, iron-rich soil familiar to them from the deserts of the American southwest (plate 2).33 In fact, among the first panoramic photos released to the press was a view of the Martian landscape under blue skies, though JPL scientists quickly realized the sky should be salmon colored. As Paolo Ulivi and David Harland note, “Initially, the image-processing laboratory combined the red, green and blue frames to produce the dark blue – black sky that the thin atmosphere had been expected to yield, but after [the images] had been recalibrated the sky was found to be pinkish-orange.”34

The missions galvanized global fascination with the stark Mar­tian landscape, and they continue to provide a compelling story of discovery and of the sheer difficulty of trying to do science so far from a conventional laboratory. The feelings were best described by NASA’s Gentry Lee: “The Viking team didn’t know the Martian at­mosphere very well, we had almost no idea about the terrain or the rocks, and yet we had the temerity to try to soft land on the surface. We were both terrified and exhilarated. All of us exploded with joy and pride when we saw that we had indeed landed safely.”35