PASADENA, Calif — In the early summer of 1976, the engineers and scientists of NASA's Viking mission hoped to do something no one had ever done before: land a fully operational spacecraft on Mars.
They had placed three science experiments on board the Viking 1 lander, each of which would analyze Martian soil for signs of microbes. The lander also featured two cameras, which were life-detection instruments in their own right. A single image might solve the ancient mystery of extraterrestrial life. No one could completely rule out the possibility that a Martian creature might go hopping by.
“There was almost hanging in the air the possibility of people becoming famous overnight if we did discover life,” says Ben Clark, who worked for Martin Marietta, the company that built Viking under a NASA contract. “There could have been Nobel Prizes.”
Forty years later, the Viking mission remains legendary — both for its triumphs and disappointments — and continues to cast a shadow over Mars exploration.
When rovers trundle across Mars today, they do not carry any life-detection instruments. That’s not because of a presumption that Mars is sterile, but because Viking showed that scientific questions have to be framed carefully. Viking’s error might be described as scientific overreach.
Forty years ago, the scientists and engineers tried to do too much too fast. But it was such a heady time, when so many boundaries had already been crossed, so many rules broken, so many truths shattered. If you weren’t overreaching, you weren’t really trying.
Landing on Mars
1976 was not only the nation’s 200th birthday, it was also an election year. Gerald R. Ford, an accidental president, occupied the White House, facing a stiff challenge on his right flank from Ronald Reagan. The Democrats were poised to nominate a peanut farmer and one-term Georgia governor named Jimmy Carter. Watergate and Vietnam were fresh, painful memories.
Space travel was in a lull. The last Apollo landing had been four years earlier, and the space shuttle was still years from its inaugural flight. But Viking had the potential to inject new life into the space program.
The Viking mission launched two spacecraft, one trailing the other. Viking 1 went into orbit around Mars on June 19; Viking 2 was due to arrive in early August. Each carried a robotic lander.
Gentry Lee was one of the young, brash, long-haired engineers dedicated to the mission. He would later gain fame as a science fiction writer. First, he had to help land two spacecraft on Mars.
“I spent seven years of my life averaging 60 hours a week working on Viking,” Lee said recently at NASA’s Jet Propulsion Laboratory in Pasadena. “I had no life.”
He remembers how astronomer Carl Sagan, another Viking team member, would “filibuster” during planning sessions. Sagan, a Cornell astronomer, had already gained fame for his appearances on Johnny Carson’s “Tonight Show.” It was Sagan who thought Viking should be outfitted with an external light because Martian creatures might be attracted to it.
Lee, exasperated by Sagan’s loquaciousness, cut a deal with him: Come to my office any time and talk to me as much as you want, but let other people talk in the meetings. Sagan agreed.
Relatively little was known at the time about the surface of Mars. Long gone was the imaginary Mars of Percival Lowell, the influential astronomer who in the late 19th and early 20th centuries had insisted that he could see, through his telescope, canals on the surface — built, no doubt, by a Martian civilization.
Sagan had been among those who figured out that seasonal variations on the Martian surface — which some scientists thought were signs of vegetation — were caused by dust storms.
The first clear view of the surface had arrived in 1965, when NASA’s Mariner 4 probe flew by and captured images of craters — a surface much like Earth’s moon. A later Mariner mission revealed huge volcanoes and a canyon that could eat Earth’s Grand Canyon for breakfast.
The Viking team had picked out a landing site, but Viking 1 relayed images showing the site to be rough, probably covered with boulders. The July 4 date was scrapped. The team spent 17 days, working around the clock, trying to figure out where to land.
They finally chose a location called Chryse Planitia (the Chryse plain), not because it looked optimal but because Viking 2 was rapidly approaching Mars and they knew they couldn’t actively manage both spacecraft.
“We were exhausted,” Lee said. His wife was due to have their first child at the end of July, and Lee recalls her saying, “Can you get the thing to land so I can bring the baby into the world?”
The feat of landing on Mars would have to be achieved through preprogrammed, computer-controlled maneuvers, for Mars was millions of miles away from the control center here in Pasadena. A spacecraft cannot be joysticked at such a distance.
Landing on the planet is tricky because of the atmosphere, which is too thin to be of much help in braking a vehicle with parachutes but thick enough to cause turbulence or overheating. The Soviets had tried three times to land a robotic vehicle on Mars; only one landed intact. It transmitted meaningless data for a few seconds before going silent forever.
On July 20, 1976 — the seventh anniversary of the first moonwalk — the Viking lander separated from the mother ship and began its descent toward the surface. Thrusters fired briefly. Parachutes deployed, then were discarded. Thrusters fired again. The journey to the surface took more than three hours, and the JPL flight team could do nothing but wait and hope.
And then: “Touchdown!”
The signal arrived at mission control indicating that Viking had landed safely, settling on three legs with footings shaped like lily pads.
In The Washington Post, reporter Tom O’Toole wrote, “Tears ran down the face of Mission Planning Director B. Gentry Lee, who pulled at his hair, which had grown to his shoulders since Viking left Earth 11 months ago.”
The search for life
Then came the first image from the surface. It showed . . . rocks. And on the right side of the frame, one of the Viking footpads. It was a spectacularly boring image, except that it was Mars. Mars! Everyone now knew: That’s what Mars looks like.
Lee said recently: “I still get goose bumps just thinking about it. All of a sudden, humanity had done something that would have been considered preposterous just 20 years earlier.”
Lee explained why the first image showed the footpad: to see how far Viking might sink into the surface. “One-third of the scientists thought the consistency of Mars might be like that of shaving cream,” he said.
The next big event was the search for life. But something went wrong. A robotic arm was supposed to reach out and scoop up some soil. But the arm wouldn’t budge. Viking couldn’t do a thing! Lee remembers uttering an exclamation that cannot be published in a family-friendly article.
Eventually the team realized that they had forgotten to load the software code for unlocking the arm. They beamed the instructions to the computer of the spaceship on Mars.
Over the course of many days, Viking performed the science experiments. The spacecraft had been baked at high temperature before leaving Earth to kill any stray microbes that might contaminate the results. All three experiments essentially looked for Earth-like life, by adding organic material to Mars soil that could potentially be gobbled up by microbes.
The results, which would be repeated later by the second Viking lander after it touched down in September, were confusing. The most promising result came from what was called the Labeled Release experiment, designed by Rockville, Md.-based scientist Gilbert Levin. Radioactive nutrients were added to the Martian soil. A large amount of radioactive gas quickly erupted — as if organisms had metabolized the nutrients.
Then duplicate soil samples were heated to kill these (hypothetical) microbes. Nutrients were then applied, and this time no gas emerged — as if the heating had killed the micro-Martians.
Levin's conclusion: Mars was teeming with life.
But there were contrary indicators. The “biological” reaction was suspiciously pronounced, spiking way too high too fast. The most damning evidence came from a device called a gas chromatograph mass spectrometer, which looked for organic molecules — the kind of complex molecules necessary for life on Earth. It found none.
“Mars Soil Activity: Does It Signal Presence of Life?” read a hedged, but very large, headline on the front page of the Aug. 1, 1976 Post.
“Life may have been found today in the red sands of Mars, but scientists cautioned that the responses they are getting from the first Viking soil samples may be the result of a totally strange soil chemistry on the Red Planet,” O’Toole wrote.
The most influential scientists on the team, including Norman Horowitz of the California Institute of Technology, leaned toward a non-biological explanation. Horowitz saw a planet without any obvious liquid water, or organic molecules, or an ozone layer to protect the surface from radiation. He concluded that Mars was covered with oxidizing molecules that sterilized the surface in the same way that hydrogen peroxide can disinfect a cut in your skin.
In his book, “To Utopia and Back,” Horowitz gave a grim assessment of life beyond Earth: “Since Mars offered by far the most promising habitat for extraterrestrial life in the solar system, it is now virtually certain that the Earth is the only life-bearing planet in our region of the galaxy. We have waked from a dream. We are alone, we and the other species, actually our relatives, with whom we share the earth.”
Bad things on good planets
Viking had been a screaming success at the technological level, but the scientific results landed with a thud. Life roots for life. No one fantasizes about sterile planets. Not until 1997 did NASA land another probe on Mars.
“It kind of went from riches to rags,” Ben Clark, the former Martin Marietta employee, says of Viking. “The science community was left with this kind of bland picture of a uniform planet.”
John Grunsfeld, until recently the head of NASA’s science directorate, said, “I think for 20 years that put the damper on the Mars program.”
Levin, however, hasn’t changed his assessment of his Labeled Release experiment. “I’ve been working on that for 40 years. We are completely confident we detected life,” Levin said last week.
Most of the Viking scientific team found Levin’s case unpersuasive. In the years since, new evidence has periodically nudged the debate one way or the other.
The Phoenix lander in 2008 found the chemical perchlorate, an oxidant that might explain the sterile surface. The Curiosity rover, however, found organic molecules when it drilled a few inches into the soil. And last year, NASA produced tentative evidence of ephemeral liquid water seeping along sandy, sun-warmed slopes. Optimists hold out hope for "cryptic" life beneath the surface.
Mars could have hosted life a few billion years ago, when the planet was warmer and had seas and rivers. That was a different Mars, before it lost most of its atmosphere and became parched and rusty. One lesson from Mars exploration is that bad things can happen to good planets.
Sagan famously declared that extraordinary claims require extraordinary evidence. Life on Mars is an extraordinary claim. Viking’s evidence was ambiguous at best.
Since Viking, NASA has not tried to detect life on Mars directly. Cynics would say that’s a case of don’t ask if you don’t want to know the answer. But it’s also a reflection of post-Viking scientific modesty.
NASA’s strategy has been to take a step back and look for potentially habitable environments, places where water can remain in a liquid state.
The next rover, scheduled to be launched in 2020, will cache soil samples and leave them on the surface. That’s in anticipation of a future sample-return mission, but such a mission, though high on the wish list of scientists, remains unfunded.
There is one other unresolved issue about Viking: Whatever happened to the two orbiters?
They functioned for several years before going silent. But they were in a high orbit, where Mars’s thin atmosphere would provide very little drag. The engineers at JPL, who have done calculations, think they may still be in orbit.
Dead satellites.
Artificial moons, built by Earthlings, circling a desert world.
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