NASA’s twin Viking landers landed on Mars in 1976 to search for signs of life on the Red Planet. Forty years later, scientists are still arguing about what the landers’ observations mean.
In 1976, NASA’s twin Viking landers landed on Mars in an attempt to answer an important question: Is there life on the Red Planet?
Gilbert Levin was the principal investigator of the Vikings’ Labeled Release (LR) life-detection experiment. The tool received positive comments on both the landing locale. However, scientists have not reached a consensus on the question of whether his results were evidence of life.
In 1997, Levin concluded that the experiment had, indeed, discovered life on Mars — and he has defended that position ever since. [The Search for Life on Mars: A Photo Timeline]
Call for follow-up
More Of Space.com
The Viking landers
The Search for Life on Mars: A Photo Timeline
Ancient Mars Could Have Supported Life (Photos)
Now, more than four decades after the Viking landings — and with much more information about the Mars in the hand — Levin is of the opinion that NASA is still not well-followed on the Viking landers’ results.
“I am sure that NASA knows that there is life on Mars,” he said last July on David Livingston’s popular online program “The Space Show.”
Levin called for a re-evaluation of the Viking LR data by an objective panel. But there is more.
In the past 40 years, a succession of probes, landers and rovers has gathered evidence that there is life on Mars, Levin said.
There is a “substantial indirect evidence of existing microbial life on Mars,” he said on “The Space Show.”
As an example, Levin noted that NASA’s Curiosity rover has found cyclical and seasonal peaks in the Mars methane. More than 90 percent of the methane in the atmosphere of the Earth is generated by bacteria and other organisms.
“This is really difficult to ignore as evidence for life,” Levin said.
However, water-rock chemistry can also produce methane, so it is not a convincing evidence of life, Curiosity mission team members, and other scientists have said.
Curiosity has discovered organic molecules in 3 billion year old rocks in the vicinity of the surface. Organics are the carbon-containing building blocks of life as we know it. But again, they are not persuasive evidence of the life itself, from naturally occurring organic have also been spotted on asteroids, for example.
Water, water and more water
Liquid water on Mars
Researchers believe they have discovered that there is a persistent body of water beneath the south polar ice cap on Mars. What does this mean for life on the Red Planet?
Then there is the July 2018 news of the European space agency esa’s Mars Express mission: The orbiter apparently saw an underground lake, under a mile of ice near the Red Planet’s south pole.
Different spacecraft have found evidence of water on Mars over the years, Levin said, and now “we are overwhelmed with an underground lake … so the water is no longer the problem.”
Levin also pointed to the Curiosity of images that can be interpreted as the image of fossil stromatolites, structures built by the colonial microbes here on Earth. There are intriguing similarities between ancient sedimentary rocks on Mars and structures shaped by microbes on Earth, ” he said.
Everything we have learned about the environmental conditions on Mars, Levin said, would allow terrestrial micro-organisms to survive — and that includes the hard radiation, the low pressure and the cold temperatures.
As for the contemporary life on the Red Planet, “it is at the point where the shoe on the other foot,” Levin said. “It is very difficult to get the image of a sterile Mars.” [Ancient Mars Could Have Supported Life (Photos)]
Viking veteran Ben Clark, now a senior research scientist at the Space Science Institute in Boulder, Colorado, said: “it is time to start with a sincere look for signs of [Mars] life.”
Clark developed a Viking-borne instrument that measured composition of the Mars soil.
“From what we have learned since the Viking on the history of Mars, it was eminently suitable for the origin of life, than we knew when the quest began,” said Clark. “A Viking lesson learned, is that you gain a better understanding of the environment and for the design of tests for the biological activity.”
Astrobiologist Dirk Schulze-Makuch, a professor at the Technical University Berliny, also said the Viking life-detection experiments have been performed before scientists really understood the Red Planet.
“Life is inextricably linked with its environment,” Schulze-Makuch told Space.com. Not that that information in hand, we can’t home in on the optimal search-and-life-detection strategies, and “that, of course, is also applicable on the icy moons,” he added, referring to the ocean-harboring worlds such as Jupiter’s moon Europa and the Saturn satellite Enceladus.
“If it would have been at the time of the Viking mission on Mars what is known today, they probably would come up with the conclusion that microbial life likely exists on Mars,” Schulze-Makuch said.
“I think the consensus is a shift in the direction that the extraordinary claim would be that ‘Mars’ is and always was a stillborn,'” he added, referring to the astronomer Carl Sagan’s famous saying, that “extraordinary claims need extraordinary evidence.”
However, Schulze-Makuch says that a declaration of life on Mars still requires overwhelming evidence for scientific regards. “Just think about how long it took before it was accepted that there was and still is liquid water on Mars!”, he said.
A better-informed instruments
John Rummel is familiar with Levin’s steadfast, life-on-Mars-position.
“The Mars science community would have benefited if Gil Levin had aspired to a leading position in science after the Viking lander missions had completed their life-detection experiments,” said Rummel, who twice served as NASA’s planetary protection officer and is a former chairman of the planetary protection for the agency’s Committee on Space Research.
New missions with a better-informed instruments, in search of life is possible, Rummel said, but they’d need a strong advocate who had the kind of data that Levin possessed.
“In fact, there is nothing new under the Mars, that was not possible with the Viking, but it’s a long way from Chryse or Utopia [the two Viking landing sites on Mars in 1976] to the sub-polar cap is now more claimed by the Italians,” Rummel, who is now based at the SETI (Search for Extraterrestrial Intelligence) Institute, told Space.com. “If Levin was busy, perhaps we have already tried to go there.”
Outside of the scientific debate
Astrobiologist Chris McKay, of NASA’s Ames Research Center in Silicon Valley, is an old Mars researcher.
The science is generally accepted, McKay said, that the Viking LR experiment did not detect life. The reactions pointed out by that instrument, and the other results from Viking can be explained by reactive chemicals called perchlorates, he said.
Perchlorates were first discovered in the Martian soil by NASA’s Phoenix lander in 2008, at the Red Planet’s north pole. Further observations by other spacecraft suggest that perchlorates are widespread on Mars.
That perchlorate explanation, however, for the time, McKay said. “We cannot exclude the possibility that Gil Levin is correct and that there are dormant life-forms in the Martian soil,” he said.
If that is the case, that the finding has implications beyond the science discussed. “We are confident that the Martian soil is lifeless send astronauts … and then to get those astronauts back to Earth? I say no,” McKay said. “It seems to me that the burden of proof should be higher for these activities, which we have not yet reached that standard yet.”
But He thinks Levin is right to continue to insist that the possibility of life are considered.
“Life may not be the scientifically recommended explanation, but it still cannot be refuted,” McKay concluded.
This version of the story published on Space.com.