The Search for Life on Mars

The Greatest Scientific Detective Story of All Time

Elizabeth Howell, Nicholas Booth

• Publisher: Arcade
• Year: 2020
• ISBN:
  9781950691661
• Topic: Physical Sciences
• Subtopic: Space Science

With a focus of the Perseverance rover mission, here is the "Quintessential account of one of humanity's most intriguing quests" (Pail Halpern, Medium ), "A remarkable, timely, and up-to-date account of Mars exploration" (Leonard David, "Space Insider, " Space.com ). From The War of the Worlds to The Martian and to the amazing photographs sent back by the robotic rovers Curiosity and Opportunity, Mars has excited our imaginations as the most likely other habitat for life in the solar system. Now the Red Planet is coming under scrutiny as never before. As new missions are scheduled to launch this year from the United States and China, and with the European Space Agency's ExoMars mission now scheduled for 2022, this book recounts in full the greatest scientific detective story ever. For the first time in forty years, the missions heading to Mars will look for signs of ancient life on the world next door. It is the latest chapter in an age?old quest that encompasses myth, false starts, red herrings, and bizarre coincidences—as well as triumphs and heartbreaking failures. This book, by two journalists with deep experience covering space exploration, is the definitive story of how life's discovery has eluded us to date, and how it will be found somewhere and sometime this century. The Search for Life on Mars is based on more than a hundred interviews with experts at NASA's Jet Propulsion Laboratory and elsewhere, who share their insights and stories. While it looks back to the early Mars missions such as Viking 1 and 2, the book's focus is on the experiments and revelations from the most recent ones—including Curiosity, which continues to explore potentially habitable sites where water was once present, and the Mars Insight lander, which has recorded more than 450 marsquakes since its deployment in late 2018—as well as on the Perseverance and ExoMars rover missions ahead. And the book looks forward to the newest, most exciting frontier of all: the day, not too far away, when humans will land, make the Red Planet their home, and look for life directly.

1

FROZEN IN TIME

“To understand how life would evolve on Mars, you have to go to Antarctica,” says Dr. Christopher McKay. “There is no other place like it.”

Widely seen as the most eloquent spokesman for the tantalizing possibilities of life on Mars, Chris McKay has spent decades studying life in Antarctica to gain a greater understanding of how microbes could exist on the Red Planet. Working out of NASA’s Ames Research Center, south of San Francisco in the suburb of Mountain View, McKay is a leading astrobiologist. Tall, genial, and with a voice so basso profundo it seems to emanate from somewhere below the floor and boom in empty spaces, McKay made his first journey down to “the ice” in 1980. “Antarctica is like a second home to me,” he says today.

McKay is acknowledged as a voice of reason in a field of research that has sometimes split into contentious factions, especially where life on Mars is concerned. “That question would be easier to answer if we could understand the evolution of life on Earth,” he says, “or even if there was a consensus on the origins of life. Mars is going to help us with this riddle.”

Though he has also investigated life in Siberia and in the Atacama Desert in Chile, McKay believes that the high, dry valleys of Antarctica are the only place on Earth where conditions are sufficiently extreme to mimic the Red Planet. The key ingredient is water. “People often say how amazingly robust life is,” McKay says. “My reaction is the opposite. It always needs water. If we had the trick of learning to live without water, life would be hardier.”

If we can’t look for life directly, then searching out water is the next best thing. That has informed the scientific rationale behind the most recent and the next missions to the Red Planet. Without liquid water, life would have been unthinkable on Earth as it would have been on Mars. Given the fact that most water on Mars is concentrated in the form of ice at its poles, McKay believes that is where life is most likely to be found.

The polar ice caps of Mars have beguiled and enticed astronomers since their discovery in the eighteenth century. Their waxing and waning showed that, like Earth, the Red Planet undergoes seasons as it alternately tilts away from and toward the Sun. The seasonal ice caps grow and retract with the passage of the seasons. It was later found that the Martian tilt is 25˚, similar to the 23.5˚ value for Earth.

However, it is very difficult to reach the Martian poles. Tricky maneuvers would be required to touch down far from the easier-to-reach equator of the planet, requiring greater amounts of fuel at the expense of scientific instruments. Any attempt would be severely constrained by weight limitations and the extreme temperatures. Actually landing a probe amid the ice there is even more hazardous than exploring the poles of our own world.

NASA’s first attempt to do so, in 1999, failed. The Mars Polar Lander crashed somewhere in the southern polar regions, likely as a consequence of a software error that affected its landing system. Nine years later, the Phoenix lander, named for the ancient bird that rises from the ashes, successfully made it all the way down at 67˚N (“which is like Iceland on Earth,” says one observer).

Over the northern winter of 2008–2009, Phoenix found evidence that snow accumulates on the surface and detected what are known as perchlorates (a possible “food” for some microbes) in the soils. It also showed beyond doubt that there is a solid ice layer immediately underneath where Phoenix landed. “Nobody really knew how much ice was lurking just below the surface,” says Professor Jack Holt, a glaciologist at the University of Arizona. “So that was kind of a surprise to a number of people.”

That discovery has, he says, opened the door to discovering that there are much more extensive icy deposits below the surface, which have been remotely detected across whole swaths of the Red Planet. Ice on Mars, the result of changes to the planet’s climate over geological time, is no longer confined to the poles. Have these icy deposits always been so prevalent, or are they, as some believe, more of a recent phenomenon?

* * *

Antarctica is as alien as it gets on Earth.

Conditions are scored for extremes. During the summer, the average temperature in coastal regions hovers around freezing point, while it varies between –15˚C to –30˚C (–5˚F to –22˚F) inland. In the central plateau, temperatures range from –40˚C to –70˚C (–40˚F to –95˚F). The lowest temperature ever recorded on Earth was –89.6˚C (–130˚F) in the winter of 1983 at the Soviet Vostok research center there. Small wonder it has been referred to as “the Gulag of the South” by those who have willingly stayed at the center in the name of scientific duty.

Though it only covers about 10 percent of the total landmass on Earth, the South Pole contains about 90 percent of the world’s supply of ice. The Antarctic continent is shaped like a squat, lopsided letter Q, with the lower squiggle forming the Antarctic Peninsula. It points like a crooked finger toward South America, five hundred miles (some thousand kilometers) distant. Antarctica’s ice lies on a foundation of rock, most of which is hidden from view.

Ice flows in strange ways on this southern continent. Around the edge of Antarctica is a ring of mountains through which continental ice is forced to pass. Eventually, it falls into the sea, but first the frozen hulk tends to form ice shelves that are glued to the landmass by the freezing cold. Some ice chunks are as large as small countries. At times these massive sheets break off to form large icebergs; this process has accelerated with recent climate change, which is warming Earth’s poles rapidly.

The climate of Antarctica is unique: its air is trapped for most of the year under a giant anticyclone. As a result, winds descend around its outer extremities and flatten as the air flows outward. The winds, immortalized by mariners as the Screaming Sixties, whip up sudden storms and squalls. Thankfully, on the shelf-like coast of the continent around the main ice sheet, a thousand miles from New Zealand, the weather is distinctly better.

It was both the clement conditions and the sheltered inlet of this area that commended it as a stopping-off point for one of the most important voyages of discovery of the nineteenth century. James Clark Ross, a dashing officer in the British Royal Navy, had already discovered the magnetic north pole when he set off to find its southern equivalent in the late 1830s. In the large sailing ships Erebus and Terror, his expedition ventured farther south than anyone had ever done before.

They happened upon the Antarctic coastline after “a magical journey of towering mountains and shining glaciers,” in the memorable phrase of one chronicler of their travels. Ross’s own diary records that on January 28, 1841, the sea that now bears his name appeared like a sheet of frozen silver in the uncharacteristically good weather and blue skies. His crew were openmouthed upon finding “a perpendicular cliff of ice between 150 and 200 feet above the level of the sea, perfectly flat and level at the top and without any fissures or promontories on its seaward face.”

Because the ice cleared faster here than anywhere else they had happened upon in Antarctica, it became an obvious point of contact for future explorers. Scientists today head for this sheltered sound, which was named after the senior lieutenant of the Terror, Archibald McMurdo. Now visitors have the luxury of flying in on modified Hercules transport aircraft on flights from New Zealand. Once they’re deposited, the plane often doesn’t stick around in case its delicate engine parts freeze over.

Only in the direst of circumstances will the authorities ever attempt a Win-Fly, as the flights in during the dead cold of winter are known. One such situation took place in the austral winter of 2017 to rescue an eighty-seven-year-old man who was experiencing breathing difficulties at the geographical South Pole. Later shown recuperating in a hospital in Christchurch, he smiled for the cameras after his ordeal. That he wore a T-shirt with the phrase GET YOUR ASS TO MARS, made famous in the original Total Recall movie, and that he was the second human being to walk on another world had a lot to do with the impression of sangfroid he gave.

But then, Buzz Aldrin has always dreamed of an encore: walking on Mars. “I think we can all say with confidence that we are closer to Mars today than we have ever been,” Aldrin had said earlier that same year.

* * *

Antarctica is tough to explore, but it has nothing on Mars.

The Red Planet is roughly 1.5 times farther from the Sun than we are. Mars orbits the Sun at an average distance of 142 million miles (228 million kilometers), compared to 93 million miles (150 million kilometers) for Earth. Its orbit is much more elliptical than Earth’s. The Red Planet takes twenty-three of our months—nearly two years—to complete one orbit. It also receives much less heat than Earth. Conditions on Mars would make Vostok station look positively balmy. The average temperature on Mars is about –60˚C (–76˚F), and though there are places where it can fleetingly hover around the freezing point of water, temperatures can plunge down to –150˚C (–240˚F) during the polar night.

Atmospheric pressure distinguishes Mars from Antarctica, even though our own southern continent is one of the highest regions on Earth. (The thinner atmosphere there caused the problems with Buzz Aldrin’s breathing.) Because of Antarctica’s altitude, one Soviet researcher at the same Vostok station where the coldest temperature was measured was astounded to find that potatoes took three hours to cook through. They boiled at 88˚C (190˚F). On the Red Planet, the average atmospheric pressure is less than a hundredth of that on Earth. There is so little atmosphere on Mars that water molecules would rush out in a mass exodus. If you took a pan of water outside, it would burst outward in a freezing explosion.

Mars has a lower atmospheric pressure because it is roughly half the size of Earth and a tenth of its mass, so its gravitational influence is smaller, roughly 40 percent of ours. Throughout its history, Mars was not able to hold on to its primordial reserves of water, which evaporated or were lost to space. Today, this also means that the Red Planet cannot hold on to as thick an atmosphere as Earth. The average atmospheric pressure on Mars is 6.1 millibars, compared to 1013 millibars at sea level on Earth. The range of pressures on the Red Planet varies, running from nearly 9 millibars at the bottom of the largest basin to 2 millibars at the top of the highest volcanoes.

The atmosphere of Mars is composed almost entirely—95 percent—of carbon dioxide. The gas traps sunlight on the planet’s surface, lifting the average temperature there some 5˚C (41˚F), compared to 35˚C (95˚F) on Earth. Mars is also almost completely dry. Even more so than Antarctica, it lives up to the nickname of “freezing desert.”

* * *

The most Mars-like places in Antarctica are the remarkable Dry Valleys, close by McMurdo Sound. Here the temperature averages –20˚C (–4˚F) and rarely rises above the freezing point of water. The Dry Valleys receive less annual precipitation than the Gobi Desert. They were discovered by Captain Robert Falcon Scott on one of his first journeys to the South Pole, in a region known as Victoria Land in honor of the monarch of the time. The Dry Valleys are separated from the remorseless encroachment of Antarctic glaciers by the Transantarctic Mountains.

When Scott and his team happened upon them, they were astounded. “The hillsides were covered with a coarse granitic sand strewn with numerous boulders,” he recorded in his diaries. “It was curious to observe that these boulders, from being rounded and sub-angular below, gradually grew to be sharper in outline as they rose in level.”

Scott later investigated this area during his more famous, ultimately tragic expedition in 1912. Two of the valleys are named after scientists attached to his expedition, Thomas Griffith Taylor and Charles Wright. The valleys receive at most four inches (ten centimeters) of snow per year, precipitation that is blown away by the harsh winds whistling through the region. They are the coldest and driest places on Earth.

Until the 2000s, scientists had found no trace of life in these harsh valleys. In the early 1970s, when NASA was preparing its first missions to land on Mars, the Viking spacecraft, the Dry Valleys were chosen as a test site for some of the life-detecting instruments. If they could find microbes in the Dry Valleys, they would be able to find them on Mars. However, their findings in Antarctica were ambiguous. What resulted was an almighty row between factions within the Viking biology teams, with some claiming that the valleys were entirely sterile and others that they weren’t.

Today, cooler heads have prevailed. The original argument was based on biologists’ ability to culture any living material from samples of the soil. The greater truth is that nothing could be cultured from the soils in the Dry Valleys, hardly surprising given that 90 percent of organisms in any soil cannot be grown in this way. With a sensitive enough probe, though, biologists have subsequently found plenty of evidence for microorganisms throughout the Dry Valleys. Whether that life resulted from material blown in from elsewhere or was indigenous and actually growing there remained a matter of debate until more recent times.

Closer examination reveals thriving microbial ecosystems in the Dry Valleys. Rocks act like little greenhouses and often trap water. Just below the surface of Sun-facing sandstone rocks are layers of lichen and algae that can survive because the dark surface of the rocks is warmed above air temperature. Pores within the rock trap whatever liquid water is available from the occasional snow flurries. The organisms are cocooned from the cold and receive enough sunlight to allow photosynthesis to take place.

At the bottom of the valleys are lakes and ponds, which were also discovered in Scott’s time. Some are replete with thick, salty waters that are fed by the annual buildup of snow. Uniquely, they do not drain away. Rather, their liquid content evaporates due to the fearsome winds that constantly blow through the valleys. Around the shorelines of the lakes may be found microbial life in the form of algae, upon which populations of yeast and molds may feed. These microbes support microscopic protozoa, rotifers, and tardigrades, all tiny organisms that congregate at the very base of the food chain.

Whatever their origin, the microorganisms in the Dry Valleys provide clues to ones we may ultimately find on Mars. If we can better understand how such life originally formed here, biologists will be able to get a much better handle on what may have happened on the planet next door. In 2011, when the most powerful camera ever sent to the Red Planet detected what looked like fresh flows of water from orbit, one scientist’s comment to the press was especially pertinent: “Mars looks more like the Dry Valleys of Antarctica every day.”

* * *

Chris McKay was in graduate school when the Viking missions landed on Mars in 1976. Though they found no evidence for microbial life, he was more intrigued about the absence of organic molecules in the Martian soil. These complex chains of carbon are crucial in the evolution of life as we know it. The singular fact of their complete absence led to an absolute change in scientific opinion about the possibilities for life on Mars. Taken at face value, the lack of organics implied it would be pointless looking for life there. In very simple terms, there was no biochemical backbone on which life could have formed.

“After Viking, there was a general lack of interest in the scientific community,” he says. “Viking immediately suggested to many people that there isn’t life on Mars, nor could there have ever been. I don’t think there was a really objective scientific assessment of the results. The initial disappointment was too much.”

Now, in the twenty-first century, the pendulum is swinging back the other way. Over the last eight years, NASA’s Curiosity rover has uncovered organics on several occasions on the Martian surface; the latest, in the summer of 2018, were tough organic molecules—“tough” in the sense the...

Table of contents

• Front Cover
• Half-Title Page
• Title Page
• Copyright Page
• Dedication
• Contents
• Authors’ Note
• Preface
• 1 Frozen in Time
• 2 Inside Out
• 3 Curiosity
• 4 The Road to Utopia
• 5 The Measure of Mars
• 6 The Pathfinder
• 7 Waterworld
• 8 Claims
• 9 Reactions
• 10 Signatures
• 11 Return to Sender
• Acknowledgments
• Notes
• Sources
• Illustration Credits
• Index
• Plates