The Quest for Mars: NASA scientists and Their Search for Life Beyond Earth

In 1980, Tim Mutch led an expedition to the Himalayas. He made a successful ascent accompanied by two graduate students, but the weather turned foul during their descent. One of his crampons broke, and it was impossible for him to continue. The students wanted to carry him down, but he told them, “No way. Strap me in here. Go back to base camp and get help and come back for me.” By then, he might have been delirious from lack of oxygen. The students went down to base camp, and he probably thought they’d return in an hour to rescue him, but they had a rough time getting through the storm, and by the time they made it back, eight hours had passed, and there was no sign of Tim. His body was never found. The best guess is that the storm blew him off the mountain.

About a year later, Tim’s widow, Madeline, held a memorial gathering to which Jim was invited. She showed slides taken during her husband’s fatal descent. It was unbearably moving, especially for Jim, who had been Tim Mutch’s last graduate student. In an obscure but deeply felt way, Jim believed that as Mutch’s disciple, he was supposed to carry the torch – but where? He didn’t know, and even today, he still doesn’t know where, exactly, but he always hears Mutch’s voice in his ear, pointing the way to the Red Planet. And NASA was the only way to get there.

During Jim’s early career at the agency, an unofficial Mars Underground developed within NASA’s bureaucracy. This was a loosely-knit affiliation of scientists and engineers who maintained a keen interest in Mars, despite the agency’s lack of Mars programs, and who also maintained a fervent desire to return to the Red Planet, first with robotic spacecraft, and later, with people, if the money and the motivation could somehow be found. The Mars Underground published papers, held symposia, and tended the flame through difficult times.

These were not easy years for Jim. An instrument he’d proposed, a radar altimeter, was initially selected for a Mars mission, but later deselected, or dropped. Soon after, in January 1986, the Space Shuttle Challenger disaster threw the agency into crisis. A period of soul-searching ensued within NASA. He worked for Sally Ride, the astronaut, on a project designed to renew the agency. Out of copious discussions, the Ride committee produced a grand new vision for NASA: the United States must return to the moon, and, beyond that, establish a permanent lunar base. Their recommendations were never acted on. After the group disbanded, Jim’s laser altimeter was selected for the Mars Observer mission, which ended in catastrophe in September 1993.

Finally, in 1996, Mars’s time came round again. First, there was NASA’s announcement of the discovery of nano-fossils in a meteorite from Mars. Suddenly, as one scientist put it, NASA was bitten by the life-on-Mars bug. The discovery, by a team of NASA scientists, gave the agency a focus it had been lacking since the Challenger disaster a decade earlier. The following year, the Pathfinder spacecraft settled on Mars on the Fourth of July, and its miniature rover rolled down a ramp and inched across the surface of the Red Planet, acting as a robotic geologist. “We can now get to the Red Planet for the price of a big-budget Hollywood movie,” NASA claimed. Jim puts it even more simply: “Mars is back.” It’s his mantra.

The Keflavik Naval Air Station, where Jim and I are billeted in Iceland, is a sprawling NATO base that once served as an essential Cold War outpost. These days, it’s mostly a stopover for young European pilots who bring their planes in from France or Italy; they drink a lot, sleep a little, and depart at first light. Although Jim is a civil servant, his quasi-military status becomes evident the moment he enters the base. He salutes everybody, and they salute back – at least, some do. “My civil service status grade is equivalent to a Colonel’s,” he says, “but no one here is aware of that.”

We’re assigned to the Bachelor Officers Quarters, cement barracks strongly reminiscent of college dormitories. The penetrating odor of burned pizza crust wafts through the halls; the walls reverberate with blasts of heavy metal music. Occasionally, you hear squeals and shouts from girls who may or may not belong here. When you look out the window, you see a landscape so flat and featureless it could be Nebraska. There are schools, playgrounds, pickup trucks, a movie theater, a bowling alley, and a Wendy’s where they play “God Bless America,” country-style, over the PA system. The unofficial motto of the base might be: “Keflavik, a Nice Place to Raise a Family.”

In July, it’s light all the time, and the only way you can tell it’s late in Keflavik is that it gets very quiet. For a few hours, there are no cars zipping around the roads, no fighter jets streaking overhead. Around midnight, there’s a sort of dusk, a suggestion of darkness like a shadow across the sky, but it soon passes, and brightness returns by 2 AM or so.

A few days after our Surtsey expedition, Jim goes forth in search of glaciers to measure. We head out in a Land Rover Discovery across the treeless, craggy, doom-laden landscape, in which people, or, for that matter, all life forms, even grass, seem out of place. Mars on Earth. “You have to remember, Iceland, except in the highlands, looks like the ocean floor,” Jim says. “Now, what if I were Spock in ‘Star Trek,’ looking at the Earth from the Starship Enterprise? Captain Kirk says, ‘Spock, what do you see? Put the scanners on.’ I’d say, ‘I see a watery planet. It’s a planet dominated by oceans.’ The land is an insignificant fraction of what makes up this planet. If we could peel away the water and look at the Earth from space, planetary scientists would say, ‘I see what the Earth does. It has a large system of very thin crustal blocks that are moving and being eaten up in some places and being regenerated in others.’”

Jim catches his breath and swerves to avoid a small herd of scrawny Icelandic sheep. “Now we are starting to add a tapestry of new measurements from Mars Global Surveyor, as we try to understand all these different surface units on Mars. Scientists want to find hot pits, if there are any, just like the ones you saw on Surtsey. Now, how big were they on Surtsey?”

Just a few inches wide, I remind him, and he points out that it would be very difficult to see such tiny formations from space, even at high resolution. “You would need an extremely sensitive thermal scanner in orbit.” Such a device actually exists, but it would not, on its own, be able to detect alien life. Scientists also look for biomarkers, that is, distinctive signatures of life. And they seek signs of an energy or nutrient system capable of sustaining life. “On Mars, we want to find playas, dried up sea-beds, where there might have been standing bodies of water. We see playas on Earth, in the dried lake beds of the western United States, the dry lakes of Australia. On Mars, these playas may be even bigger. The topography measured by the laser going around Mars can find those areas for us.” So playas may hold clues to life on Mars, and volcanoes may also lead scientists to Martian gardens of Eden. It may just be Garvin’s bias, because he is crater expert, but he thinks volcanoes are an important component in the design for living – another reason that Iceland appeals to him. “Iceland has volcanoes that are active, with ice, certainly something that happened on Mars. We have volcanoes interacting with ground water, very important, because there may be ground water on Mars. We don’t know. And we have volcanoes here producing new lava at great rates. Some of the volcanoes on Mars have sustained high eruption rates for hundreds or even thousands of years. That’s what it takes to make an Olympus Mons” – and Olympus Mons is so big that it couldn’t exist on Earth. “There’s too much gravity here, and anything aspiring to Olympus Mons-like grandeur would collapse under its own weight.” He likens its shape to the much smaller lava shield volcanoes of Iceland. The term is meant to suggest a Viking shield turned on its side; a lava shield volcano slopes very gently. “It’s the most common landform made by volcanism in the Solar System. Mother Nature does not know how to do it any simpler.”

Later, we coast past an immense, dry lake bed studded with pebbles. We get out and walk across its dusty surface. It would not be surprising to see a pterodactyl soar overhead, or a spacecraft descend from the skies. This is Nature’s rough draft, a land of possibilities. It’s not as polished as later versions, but the crude landscape yields its secrets and intentions to geologists. “When the water dries up, it leaves behind a lag deposit of rocks,” Jim remarks. The rocks range in size from small cobbles up to large boulders. “And anything bigger,” he announces, “is called a real big boulder! The bright stuff you see here is a layer of desiccated, cemented dust made of clay. That is what comes out of suspension when water evaporates. We expect to see signatures of that kind of stuff on Mars.” He points to a fissure in the soil. “See this desiccation crack? This is what we hope to see on Mars.”

We head north until we reach an enormous glacier: Langjökull. On the other side, its summit obscured by cloud cover, is the great volcano known as Ok. The stony, dusty ground, reddish brown, contrasts with the huge wall of ice. I slowly become aware of the landscape’s resemblance to images of the Martian icecaps, those vast dull white fields rising out of the reddish Martian desert. The more we look, the more striking the resemblance to the northern latitudes of Mars. Our isolation feels complete. No birds or cars disturb the pure silence. No airplanes streak by overhead; the atmosphere is untarnished by plumes of smoke. The spectral glacier rises impressively from the dark red rock, its façade reaching into the clouds and mist, massive, gloomy, impersonal, hypnotic. Nearly everything looks alien and supremely indifferent to the two tiny human figures in the midst of this vast, primeval sanctuary. Take all the measurements you want of Mars, but walking through this strange and unnerving place suggests, as nothing else can, what it would be like to traverse the surface of the Red Planet.

Suddenly a pair of bicyclists disturbs us, a man and a woman, en route to a distant town or campsite. It’s a relief to share the oppressively majestic Martian landscape with others, even briefly. And then they’re gone, gliding into the distance on their bicycles, and we’re alone again. For once, Jim is speechless. We return to the car in silence.

When we reach Keflavik, Jim drives us over to the tarmac, saluting smartly whenever he passes a military guard. At last, the afflicted P-3 aircraft is here. It looks all right from a distance, but a closer inspection reveals oil leaking from the nose, creating an embarrassing, 125-foot long stain on the ground, beginning directly beneath the aircraft. There’s talk that the Keflavik Naval Air Station may insist the P-3 leave immediately so that it does not foul the runway.

Jim trots to the base’s weather station, where the latest satellite data are available. The weather station glitters with state-of-the art equipment; the place is so big and solid it looks like the bridge on an aircraft carrier. Although it’s sunny here in Keflavik today, the instruments reveal there is a weather front moving in, and steel gray clouds are visible on the horizon. It’s now about 3:30 in the afternoon, and sometime after 5:00, the plane is supposed to be in the air, on a six-hour mapping mission. Right away Jim sees it will likely be too cloudy to take data over Surtsey, so instead they’ll survey a floodplain known as the Sandur, located in the Eastern portion of Iceland. Given the weather and mechanical constraints, this will likely be the only day they will be able to take measurements.

Jim sits at a computer terminal in the Weather Station and begins composing a report to the base commander about his activities here in Iceland; at the same time, he chatters with me and an affable young naval attaché. He types rapidly, never making a mistake – “…As part of NASA’s continuing research interests in Iceland as a microcosm for global Earth environmental change and as a natural analogy for landscapes on Mars, an aircraft remote sensing campaign was conducted during the period from 20 July to 26 July, 1998. A NASA P-3 aircraft, outfitted with two scanning airborne laser altimeters, an ice penetrating radar, a nadir-viewing digital video imaging system, and multiple GPS receivers, was deployed to Iceland …” – and when he’s done, he rips his report from the typewriter, drops it off at the base commander’s office, and trots back to the P-3.

He bounds up the ladder to the cabin, which looks like the inside of an Eyewitness News van, crammed with television monitors and wires, strewn with Styrofoam coffee cups, and devoid of creature comforts. Within this funky hi-tech cave, he confers with the navigator, Jon Sonntag, and the two pilots. They plot coordinates. They discuss backup plans. They propose flight paths. “Here’s the game plan,” Jim says, tracing the route on the map with his finger. “Take off, come around … here … and then straight to the Sandur. Surtsey looks really good. Now come over here and do this middle line. That’s the number one priority. If that looks good, see if we can do the north line. At that point, we call the option for doing the south line. If it looks like there are no clouds over this icecap, we might be able to sneak up and come around. In the past we always went way up here and came down. I’m afraid that, unless we can throw a real sharp turn, we can’t do it. We fly at eighteen hundred feet.”

All they need is a working airplane. José’ is the mechanic responsible for maintaining the leaky P-3. He stands about five foot three or maybe four, stocky, with a scruffy, uncertain beard, and a good-natured grin. Jose’, who’s American, likes his wine, and he likes his beer. In the evenings, he’s the first to hit the strip bars of Reykjavik, such as they are. The fate of the P-3 now rests in his hands. Even as they tell me stories of his wild doings, everyone about to fly on this plane expresses confidence in him. (Frankly, I wouldn’t let him near my car.) He works slowly and methodically on the plane, and when he’s done, declares it good to go. The engines roar to life.

The white P-3, with Jim inside, taxis far out onto the tarmac and ascends to the skies over Iceland. While they’re in the air, the pilots do most of the work, for they have to maintain alignment not only with the surface of the planet below but with the Global Positioning System satellite above. This means the plane can’t wander more than six feet off course. They map the Sandur, and, weather predictions to the contrary, they do Surtsey, as well. They do their mapping with reference not to the Earth’s surface, which is always shifting, but to Earth’s center, which is about as close to an absolute, fixed point as you can get.

Mission accomplished, the P-3 returns to Keflavik after midnight. To everyone’s surprise, the aircraft has performed flawlessly that evening, laying down precise tracks over Surtsey and a glacier to the north. “We laid down fourteen lines!” Jim announces. “It was fantastic. Staggered just the way we wanted them. And the weather was great. It was sunny and clear on the island. I’ve got digital video, nose cone video. We’re going to have the best map of Surtsey ever made, no question. The flight was as tranquil as bath water. Even the leak stopped by the time we landed.”

To celebrate, Jim and Jon Sonntag and I go out for a beer. After a long day’s work in the field, no self-respecting NASA scientist thinks of anything but a beer. The drinking etiquette is to avoid brand names and even recognizable microbreweries in favor of obscure local product. Eventually, we find a little place overlooking the large bay, where they serve frosted glass tankards of Viking, an Icelandic beer. We sit in front of a picture window overlooking the steel gray expanse of Keflavik Bay. A few lights flicker across the water, but not many.

Having just spent the last five hours in geological nirvana, Jim talks on and on about what a great mission it’s been, while Jon brings up a slightly different subject: the kind of woman he’d like to meet and settle down with. He’s from Houston, but he wants to meet a different kind of girl from the ones he’s known in Texas. Maybe here, in Iceland. Maybe even in New York City. He asks me about the women in New York, where I live, and I tell him the best thing to do is visit and see for himself. He pauses and smiles shyly, contemplating the prospect. He just might do that.

This type of talk makes Jim uncomfortable. Throughout our time in Iceland, a lot of stray remarks have escaped his lips about power tools, about the power washer he was using just the other day with his son Zack (“That thing was so powerful,” he said with genuine conviction, “that it could take the paint right off a car”), about the Ford F-150 pickup truck he’d like to own, and about a Hummer (“How much do those things cost?”), but nothing about women. Which doesn’t mean that women don’t look at him. They do, indeed. His handsome dark Irish looks, his snappy NASA flight jacket, and his politeness combined with an occasional air of confusion tend to attract women.

He met his wife Cindy by accident in 1990 when she was working at NASA for a contractor. It seems there was another J.B. Garvin with whom she was doing business, and Jim kept getting e-mails intended for the other one. So he got in touch with her to clear up the confusion. He found himself talking on the phone with her, and she coaxed him gently into asking her on a date. “I often get too focused on my work. I wished I didn’t, but that’s the way it is,” he confides. Cindy was determined to change all that.

When they came face to face, Cindy already knew what he looked like; to this day, Jim is not sure how she knew. They went to a hockey game, and not long after that, moved in together. Cindy recognized that his interests were a little unusual. Here’s a Phi Beta Kappa from Brown, a Ph.D., who says his most valuable possession in the world is a complete set of Jim Bunning baseball cards. He owns practically every Bunning card ever issued, tracing his pitching career from 1954 through the 1980s. Cindy liked shopping, dining out, and other normal activities. That was fine with Jim, he wanted to be with someone normal, someone who would keep him in touch with daily life. They married in 1992. We sit drinking and talking until the sky begins to brighten almost to daytime intensity, and we return to base a little after two in the morning.

The next day, while packing to leave, Jim ponders what to do with the data he’s collected during the week in Iceland. He must get it out – in the new NASA, nothing is secret – so he will post it on various Internet sites, for starters. He will write multiple papers, some of which will appear in scientific journals. He will give lectures. He will share the information with Icelandic scientists. “It’s my job as a research scientist at NASA to publish the results in Science, Nature, and other journals. That’s my job, to disseminate.” He will have plenty to discuss, for a crowded schedule of Mars exploration lies ahead. “We’re launching again in December and sending a small probe to the south polar ice cap on Mars, which we think is all frozen carbon dioxide. It’s so cold, one hundred to two hundred and fifty degrees centigrade below zero. We’re also asking other, very fundamental questions: Did life start on Mars? If it did, is it dormant, frozen, fossilized? Is it still there? Is it all microbial? What can it tell us about extremophile life on Earth?” Jim asks, savoring each question.

“I think the potential for Mars is totally untapped, and that’s something of a surprise,” he continues. “When we first got there in the sixties with the Mariner spacecraft, we thought, ‘Oh, my God, there are going to be Martians, canals, it’s going to be great.’ But when we got there, it looked like the moon. Mars puzzled us. We returned with Viking in the mid-seventies, looking for life, and instead we found the great arctic desert of Mars. We saw frost form in the winter, and we saw snow. We saw rocks and pits that reminded us of gas bubbles in the volcanic rocks you see here in Iceland, but we didn’t see the obvious signatures of life. We’ve got to go back. We’ve got to understand this place. We’ll have a series of robotic voyages to set the stage for bringing back samples of Mars to Earth to investigate the chemistry and – maybe – signs of life. And then someday we’ll put human beings there, God and the great American economy willing.”

The taxi cab heading home from JFK Airport feels as cramped as Oscar’s co-pilot seat. I’m probably in more danger barreling along the Grand Central Parkway than I was aloft in Oscar’s little Aerospatiale. Night falls for the first time in a week; how strange the darkness seems. After experiencing Iceland’s white nights and thinking intensely about what it’s like to walk across the surface of Mars, I find that nothing on Earth looks quite the same. The initiation is over, and back home, I reflect on a whimsical passage from Ray Bradbury’s sci-fi novel, The Martian Chronicles, published in 1950:

The ship came down from space. It came from the stars and the black velocities, and the shining movements, and the silent gulfs of space. It was a new ship; it had fire in its body and men in its metal cells, and it moved with a clean silence, fiery and warm. In it were seventeen men, including a captain … Now it was decelerating with metal efficiency in the upper Martian atmospheres. It was still a thing of beauty and strength. It had moved in the midnight waters of space like a pale sea leviathan; it had passed the ancient moon and thrown itself onward into one nothingness following another. The men within had been battered, thrown about, sickened, made well again, each in his turn. One man had died, but now the remaining sixteen, with their eyes clear in their heads and their faces pressed to the thick glass ports, watched Mars swing up under them.

“Mars!” cried Navigator Lustig.

“Good old Mars!” said Samuel Hinkston, archeologist.

According to Bradbury, this landing, the third human expedition to Mars, was supposed to occur in April 2000. NASA is running a little behind schedule, but sends spacecraft to Mars as often as budgets and planetary orbits allow. For now, they are robotic missions; in time, they will bring people to the Red Planet.

Welcome to the new Martian chronicles.

2 MESSAGE IN A BOTTLE (#ulink_dfa6ed39-e414-52ec-8daf-cbd488ac9866)

Jim Garvin’s collection of Jim Bunning baseball cards got me to thinking about what is perhaps the most famous baseball card of all – the 1909 portrait of Honus Wagner in a Pittsburgh Pirates uniform. When I gaze at the face of this young man, who seems to be staring into space, I find myself asking, “What was it like to be alive in 1909?” I have little idea, although it was just the other day, in geological terms. All I have to go on are artifacts, such as this famous baseball card. I can’t watch Wagner play baseball, and I can’t hear his voice; all I can see is a fuzzy image of the athlete in a uniform, a trick of light and shadow, an impression of life as it once was. To fill in the gaps, I would have to look beyond the card, but if I’m relying on the card, and only the card, I have precious little data.

The card, and its limitations, call to mind the tantalizing images of fossilized bacteria in a 3.9 billion year-old meteorite from Mars – images that may be the first scientific evidence of life beyond Earth. Fossilization occurs when minerals replace organic elements in once living things. The morphology remains, although the chemistry is different. Still, scientists can learn a lot from fossils. They can detect the approximate age, which is crucial, and, by studying fossils in their natural setting – in situ – they can extrapolate a great deal about the geological, chemical, and biological circumstances surrounding them. “Fossils are the autographs of time,” wrote the American astronomer Maria Mitchell. For these reasons, fossilized bacteria from Mars – if that’s what they are – have great appeal; they are our best indication of life beyond Earth. Like the antique baseball card, they offer only a very narrow glimpse into the past. 1909, the year of the Honus Wagner card, wasn’t very long ago, but it’s long enough past to seem quite mysterious. How much more difficult it is, then, to construct a scenario for the existence of life on Mars several billion years ago from the evidence contained in a meteorite.

If the fossilized bacteria are genuine artifacts of Martian life, they raise more questions than they answer. If life started on Mars, how did it begin? Is it still there? If not, when did it end, and why? If it’s on Mars, where else in the universe might it be, and what form does it take? Did it originate on Mars, on Earth, or somewhere else? All these Genesis Questions point up how much scientists have yet to learn about how life began. In the course of asking questions of various scientists who study these problems for a living, almost every reply I received began this way: “No one knows, but …” That’s followed closely by, “There are several possible scenarios,” and “Well, current speculation has it that …” The answers are all variations on the theme that no one knows, yet. But scientists have hypotheses. They have scenarios. The meteorite from Mars has inspired a widely accepted scenario – I’ll call it the Best Guess Scenario – concerning the origins of life on the Red Planet, and how it came to be transported to Earth.

Four and a half billion years ago, the Solar System was in its infancy, and the planets were new. In its first billion years of existence, Mars was a warmer and wetter place than it is now. Water flowed freely over its surface and pooled underground, in reservoirs. The flood channels carved into the surface of Mars, some of them many miles in width, left an eloquent record of catastrophic outpourings of water. In all likelihood, the water on Mars was quite salty. (Fresh water on Earth is due to evaporation and rainfall.) Eventually, the floods subsided, and the water drained into Mars’ vast northern plains, where it might have frozen. In the process, it reshaped the Martian terrain until it resembled a desert that had once been flooded, but became bone dry. Nevertheless, its contours preserved geological memories of rivers and oceans and lakes.

The large Martian pools of standing water were subject to peculiar tides caused by the planet’s two small moons, Phobos and Demos. And they were subject to the Martian winds; when they blew, reaching speeds of hundreds of miles an hour, they generated waves with peculiar shapes, higher and steeper, with more pronounced peaks than exist on Earth. The lower Martian gravity, less than half of Earth’s, allowed the slender waves to tower until they resembled the watery shapes in a drawing by Dr. Seuss; they would flop over and spatter, as if in slow motion. The marine scene on Mars was all oddly familiar, and strangely different.

The Martian sky was blue a few billion years ago, and there were a few clouds, just as Mars has now. It was mostly cold, and extremely cold at the poles, except for the equator, where it was warm. Martian volcanoes erupted with regularity, and in the Red Planet’s low gravity they assumed formations that couldn’t exist on Earth; they were larger and higher. In these ancient Martian conditions of two or three billions years ago, life could have formed and evolved, just as life appeared on Earth within a billion years of this planet’s existence. The volcanoes, especially the ones close to reservoirs of water, or polar ice, created hot spots where life would most likely have formed on Mars. No one knows how far it developed, or if it ever got underway. It might have remained dormant most of the time, for tens of millions of years at a stretch. Or it might have progressed beyond simple bacteria; there might have been Martian insects crawling around, adapted to the Red Planet’s lower gravity, lower density atmosphere, and cooler temperatures. These variations suggested life forms that were spindly, similar to insects. The skeletons might have been external, with many legs to take advantage of the lower gravity. As for the cooler temperatures, life on Earth has shown remarkable adaptive creativity. “Some insects winter-proof themselves with glycerol, a common antifreeze used in automobile radiators,” Carl Sagan theorized. “There is no conclusive reason why Martian organisms should not extend this principle, adding so much antifreeze to their tissues that they can live and reproduce in the extremely cold temperatures occurring on Mars.” The ancient Martian atmosphere would have required similar creativity in the creatures’ breathing apparatus. If they had evolved to the point of multi-cellular differentiation, they might have developed enormous gills or lungs, relative to their size. Even if life never reached this advanced stage of evolution on Mars, it is still possible that tiny organisms formed in the water-drenched Martian rock, and then, for some reason, died off, leaving fossilized remains hidden beneath the surface. It was as though Nature initiated an experiment but abandoned it in the early stages.

Ancient Mars was more turbulent than Mars is now. In the young and volatile solar system, it was constantly bombarded by chunks of asteroids. It is possible that at some point in Martian history, an asteroid of such dimension struck Mars and created cataclysmic changes in the planet’s climate and geography that whatever life forms had managed to take hold were snuffed out, leaving only their skeletons, which became fossilized. Or perhaps the death of Martian organisms came about slowly, as the planet lost its atmosphere a little at a time to space, and its water eventually disappeared below the surface, or vanished with the atmosphere, leaving behind a desiccated, celestial sandbox.

If we had been able to observe the first few billion years in the life Earth and Mars from a vantage point in distant outer space, we might have noticed several common trends. We would have seen watery places on both planets. We would have seen volcanoes on both planets, their plumes of smoke, their pollution of the atmosphere. We would have seen clouds on both planets, and we would have detected seasonal waxing and waning of the polar caps. As the eons passed, subtle differences between the two planets would have become apparent. If we had been looking closely, we might have noticed the atmospheric changes. We might have seen the dramatic increase in oxygen in Earth’s atmosphere, and a corresponding spread of vegetation on its surface; if we were very perceptive, we might have noticed the spread of plant life in its oceans, in the form of algae.

At roughly the same time, we would have seen that Mars was losing its nitrogen-rich atmosphere. It was thinning out, disappearing into the frigid vacuum of space. More obviously, we would have seen the great Martian standing bodies of water recede, exposing a complex erosional system of gullies and playas and rearranged boulders, many of them acting as signposts to the water’s former whereabouts and actions. During the last few hundred million years, if we were sufficiently attentive, we might have noticed the spread and intensification of vegetation on Earth, as the biomass increased and diversified, and various life forms competed for natural resources, or evolved ways to cooperate, or both. At about the same time, we might have watched Mars continue to regress to its early state, with some important differences. It contained geological traces of water, and perhaps traces of biology – clues, ultimately, to its origins, and to ours.

Where did the elusive Martian water and its life-giving properties go? Come to think of it, where did the water come from? Where did water on Earth come from, for that matter? At the Lunar and Planetary Institute in Houston, Steve Clifford has spent years studying water on Mars, and he told me there are several schools of thought concerning the origins of water on this planet and on Mars. “One is that after the Earth was formed, comets bombarded the planet, adding volatiles over perhaps the first billion or half billion years.” A comet is basically a celestial snowball, bearing ice from somewhere – God knows where – to here. “The other school of thought is that much of the water we have on the Earth was contained in the early material that formed the planet. As the Earth started to accrete asteroidal material and dust in the early Solar nebula, it gradually reached a size where the quantity of radioactive material was sufficient to heat up the planet and cause it to differentiate. The heavier stuff sank toward the middle, which is how we got an iron core, while the lighter stuff, which may have contained water, was released during the formation of the crust and atmosphere.” A similar process may have occurred on ancient Mars at about the same time it happened on Earth.

Steve surprised me by suggesting that water on Mars may still linger beneath the surface, more than a little. He was talking about “sizable reservoirs of ground ice and ground water.” The evidence he has for large volumes of water on Mars is mostly indirect. He calculates the amount of “pore space” to be found in Martian rocks and soil; water could be stored there. If it is, some of the water could be in liquid form, especially well below the surface. “Like the Earth, Mars is thought to be radiating internal heat due to the decay of radioactive elements, which means the deeper you go below the surface, the warmer the temperature gets,” he says. “And if you go down several kilometers, you could easily get temperatures that are consistently above freezing,” which means liquid water might exist on Mars today. In fact, he thinks there might be two types of water reservoirs on Mars, a region of permafrost near the surface, as well as larger and warmer reservoirs at greater depths. There you might find liquid water in great quantities, and water, of course, leads to life. This subsurface system would act as a powerful preservationist of life, no matter how harsh conditions on the surface. “If life ever evolved on Mars, and adapted to a subterranean existence, then its survival would be assured for the indefinite future.”

Subterranean life on Mars could survive the loss of the atmosphere, it could survive intense cold on the surface, it could even survive the largest life extinguisher we know about, the impact of a large asteroid. Imagine what would happen if an asteroid the size of Manhattan collided with Earth, Steve says. It would certainly be calamitous and likely sterilize the surface of the planet down to a depth of several meters or so, but not below that. It would kill life on the surface, but it wouldn’t eliminate all life on Earth, because the impact’s thermal and chemical effects would be limited to the uppermost part of the surface, with the exception of the area where the impact occurred. After the impact, life far below the surface of the Earth would go on. The same holds true on Mars, Steve says: “any microorganisms that might have evolved four billion years ago, when the planet might have been warmer and wetter at the surface, could readily survive to the present day at depths of several kilometers.” If he’s correct, or even partly correct, life could very well exist within the Red Planet’s ancient reservoirs, awaiting discovery.

The Best Guess Scenario assumes that some kind of simple life did exist on Mars a few billion years ago, as Steve described. And it assumes that asteroids have bombarded Mars ever since, pockmarking its surface with craters. Sixteen million years ago, according to the scenario, a refugee from a disorganized asteroid belt struck the surface of Mars with tremendous force. Since Mars has only 38 per cent of Earth’s gravity, the impact was sufficient to drive pieces of rock buried beneath the surface high into the Martian sky and beyond. The pieces shot into space five times faster than a bullet – fast enough to escape the Red Planet’s gravity. Until a few years ago, it was thought the shock of impact would vaporize or severely deform the ejected material – the ejecta – along with everything in it, including any signs of life, but recent computer modeling has shown that the physics involved would allow the ejecta to remain intact. In the model, the asteroid comes in at an angle, strikes, and creates a vapor cloud that sweeps across the surface at an extremely high speed and carries material off Mars into solar orbit. The whole process might take five or ten seconds, long enough for some fragments of Mars to remain intact. “That’s a fairly gentle way to get stuff off the surface,” says Mark Cintala, who studies craters at NASA’s Johnson Space Center – gentle enough to launch a fossil-bearing meteor on a trajectory to Earth.

There’s a variation in the Best Guess Scenario that incorporates another method of ejecting material safely from the surface of Mars: spallation. Much of the work on the spallation model was done by Jay Melosh at the University of Arizona, and it’s extremely simple, in theory. You put a quarter on a tabletop, rap the underside of the table, and bump the quarter into the air; that’s spallation. “You’re sending a stress wave through the table, and that stress wave is transmitted to the quarter. Imagine that happening on Mars,” Mark Cintala says. In that case, the asteroid’s impact would create a compressional wave, as if it were a depth charge below the surface. The resulting shock wave would bounce a rock fast enough to escape the relatively weak Martian gravity and send it on its way. “At least, the calculations say it can.”

In the Best Guess Scenario, one of these dislodged pieces of Martian rock sped off in the direction of Earth, a cosmic message in a bottle floating through an ocean of outer space. The journey lasted millions of years, and the ancient chunk of Mars crashed to the surface of Earth a mere 13,000 years ago. The size and shape of a potato, it buried itself in the Allan Hills of Antarctica. The meteor had become a meteorite.