by Marc Kaufman
Mumma pointed on his screen to a large, ancient Martian volcano named Syrtis Major, traces of which spread 745 miles. His group had detected a methane plume around Syrtis Major, but it wasn’t coming from the area around the volcano mouth. Instead, it came from an area to the other side that planetary geologists had determined to be quite unusual and perhaps the site of a deep underground collapse of what once had been a huge chamber of molten rock, or magma. Mumma was intrigued. “This collapse could create underground conduits, tunnels for the methane to escape. Or it could provide conduits that are colonized by the bugs that consume hydrogen gas and then produce the methane. At this point we don’t know, but either would be consistent with the geology.” Mumma’s colleague Käufl couldn’t help but suggest that the conduits could also be the fertile and protected home to large herds of farting cows.
For decades now, the conventional wisdom about Mars has been that no interaction exists between the subsurface and the planet’s surface and atmosphere; that Mars once had volcanoes but magma is no longer coming from its depths; and that there are no hydrothermal vents or earthquakes on the planet, either. These destructive events are hugely important in terms of the origins and maintenance of life on Earth because they allow for essential elements and compounds to be cycled for use and reuse. Without Earthlike tectonic plates moving on the planet’s surface to shake and heat things up, it’s also hard to imagine how anything from below the parched surface could make it up and out without freezing when the temperatures average –81 degrees Fahrenheit. But a sense of how a release of gas or even water vapor could occur on Mars came to Mumma one day while he was driving up to visit relatives in Connecticut. It was a cold day, and it had recently snowed. Driving north, he passed through many cuts made through hills and mountains, and gradually the obvious pattern emerged: The north-facing sides of the road cuts were covered in ice, while the south-facing sides, which received more sunlight, were often dripping wet. In what passed for a near-eureka moment, Mumma blurted out to his wife, “That’s Mars.” The planet does warm up during summers and temperatures do travel above the freezing point in some areas, although not necessarily for long. But extreme forms of life don’t necessarily need a long time to live and reproduce—like wildflowers sprouting in a desert after a rain.
More specifically, what he had in mind was information not contained in his initial published findings related to additional methane gas discovered in an area near Arsia Mons. That’s a large (270 miles across) and ancient volcano in a region many miles from where they made their initial discoveries, but close to Olympus Mons, the thirteen-mile-high volcano and mountain that is the largest in the solar system, nearly three times taller than Mount Everest. Arsia Mons, he said, is home to the biggest mountain glacier on Mars (now buried, but as much as three miles deep when snow was falling in ancient times, climate modelers have concluded), and the area is filled with hundreds of miles of deep fractures in the ground, or “fossae,” as such Martian features are called. It’s also part of a line of volcanoes reminiscent of geology on Earth produced where continental plates meet and collide. Since volcanoes and plate tectonics play such an important role in enabling life on Earth, the possibility that similar dynamics were once at play on Mars was intriguing and suggestive. Methane, Mumma concluded, just might be seeping out of those kinds of cracks.
Even more intriguing was the area farther to the east, where there’s a stress fracture in the surface, a deep gash that runs 500 miles long, 70 miles wide, and at points several miles deep. “Look here, what’s the geology telling us?” he said, likening the big fractures to the rift valleys of eastern Africa, where the Earth was pulled apart by tension in the crust. “The net effect is to expose the cliff face, expose the layered strata of permafrost. Sunlight could certainly hit the edges, the faces of these scarps.” That’s where that model of the road cuts comes in, where the north-facing side has icicles and the south-facing side has water. Why wouldn’t the same dynamic occur on Mars? “Crater walls, rock faces, they often show gullies, coming out from a layer below the surface—we don’t know what, but stuff is coming. We think this is a possible mechanism for gases from below the surface to emerge when ice-clogged pores open in late spring and early summer.”
At this point in our observing session the team had gotten Mars directly into its sights, which on the computer screen showed a bright ball between the slits created to focus the spectrometer. The image was blurry—not the kind of clear view you get from a powerful visible-light telescope—but you could make out some of the contours of the planet. Although the Mars on view was hardly spectacular, it was providing greater spectroscopic resolution of the planet than any image collected before because of the power of the telescope, the power of the spectrometer, and the increasingly refined use of a process called adaptive optics, which eliminates distortions created by the Earth’s atmosphere. This is usually done by focusing on a guide star, but the team was delighted to find that for the first time they could achieve adaptive optics by locking on Mars itself.
Mumma takes a systematic approach to addressing the questions of the day: Is there definitely methane on Mars, where is it coming from, and what are its basic characteristics? Translated into scientific research, the overall goal of the campaign then becomes most pressingly to map Mars for methane and water, and to see where they coincide. “I want the planet, the whole planet, and in all seasons.” Mumma asserts that good research practice makes it ultimately unimportant whether the Martian methane is produced geologically or biologically; the goal is simply to find which is the correct answer. Nonetheless, his working hypothesis appears to be that the methane is, or was, produced by organisms—that is to say, extraterrestrial life.
The goal of mapping for methane involves the age of the accompanying water vapor. It seems improbable, but the Paranal telescope and the CRIRES spectrometer can actually tell Mumma’s team whether the Martian water vapor being detected is “new” (from the surface of the planet) or “old” (from its geological depths). If “old” water was convincingly detected in a methane plume, that would require a major reassessment of the long-held view that there is no direct interaction between the planet’s lower depths and its surface and atmosphere. It would also significantly increase the chances that something alive is, or was, down there.
Pulling up slides on his computer with innumerable charts and graphs, Mumma explained that the water would be old if it had a lower percentage of deuterium, or “heavy water,” in its H2O vapor and new if it had a higher level in its H2O vapor. Deuterium is an isotopic variation of hydrogen (with a proton and neutron in its nucleus, rather than just a proton) and that extra weight keeps it from sailing off into space as quickly as regular “light” Martian hydrogen does. The result of this process is that hydrogen in current-day H2O (the kind found as ice at the Martian poles and circulating around the planet as vapor during some times of the year) has more deuterium and so is “heavier” than Martian water used to be. This dynamic is apparent in the famous Allan Hills 84001 Mars meteorite found in Antarctica. NASA scientists set off a huge controversy when they said the meteorite showed signs of ancient Martian life, but there was no real dispute about the determination that the meteorite was 4.5 billion years old and that its remnant H2O was very light, with a ratio of deuterium to hydrogen at a very low 2. The Martian atmosphere today has an average deuterium to hydrogen ratio of about 5, meaning that much of the pure hydrogen has been lost. This is not just theory; scientists know and can measure these things. Although the difference is only one tiny particle in the atom’s nucleus, the signature of heavy “deuterated” water on a spectrometer is easily distinguished from that of common “light” water.
And here’s the clincher: Life generally prefers and produces lighter forms of its component chemicals; it’s a pattern across all elements. So measuring which forms of hydrogen (or carbon) are present in Martian methane and water is a potentially big deal. If methane is found alongside “heavy” water, that
means the gas is probably from near the surface; “light” water would mean it comes from deep below. Such are the clues, the inevitably indirect measurements, that will someday result in an announcement that Mars methane is or is not produced by living things—puzzle pieces understood only through rigorous science and no small amount of imagination and inspiration.
But the interplanetary forensics get ever more complicated. The spectrometer, which takes in light and other photons from the mirror of a telescope directed toward Mars, also takes in spectral information from the Earth’s atmosphere, as well as light originating from the sun. One reason the formal unveiling of Mumma’s methane-on-Mars paper took so long is that the team was creating models for measuring how much of the methane being detected was from Earth’s atmosphere, how much from the sun, and how much actually from Mars. That’s where Geronimo Villanueva comes in. An expert in applied physics, he worked out over five years the algorithms that allow the team to make these calculations. He also worked to make sure readings were not misconstrued because of surface weather and condensation on Mars, or because of a slew of other factors that could prejudice the results. Asked for a ballpark estimate of how many steps were involved in making his measurements—the building and calibrating of the instruments, the complex science of actual observing, and then the massaging and analyzing the data—he replied with a matter-of-fact geniality similar to Mumma’s: “about as many as it takes to build a car.”
Villanueva scrolled to a color-coded map that showed where on Mars they had found the methane. “We have this idea that Mars was very wet four billion years ago. If all the organics from that period and the water were stored in the subsurface and preserved there, then this is the place you can have a release,” he said, pointing with an almost conspiratorial pleasure to an area in bright red. Villanueva, a native of Argentina, described their search as if the methane-water release was a plane ride away, rather than 155 million miles. “The moment you make that discovery of an active connection between the subsurface and the surface, then you open a Pandora’s box of possibilities and processes happening. You can be talking about reservoirs of water, can be talking about biology and geology, a lot of things that are hard to think of in the hostile environment of the surface. The moment you see this release—boom—you have the discovery that Mars is wet in the subsurface.” He’s not talking about water ice; scientists already know that is there. He’s talking about actual liquid water, kept warm by forces at work deeper into the planet. So Mumma and his team are not only exploring for methane, they’re also trying to be the first to find signs of concentrations of liquid Martian water.
Mumma turned reflective about the challenge ahead. “In this kind of science, we can’t really prove anything to be correct; we only can prove to be wrong. That’s why we’re always trying to confirm more. I learned pretty early on: Do not fall in love with your own interpretations and ideas. Be ready to accept a different view.” When you’ve followed a path like Mumma’s, when you’ve pushed back all your life against the world as it is presented, it is impossible to be content with what you think you know.
• • •
Now that the search for Martian life is focused on both methane and the microscopic creatures that we know can live in extreme environments, researchers have fanned out across the globe to identify, analyze, and better understand similar habitats. Pan Conrad, an astrobiologist for NASA and a co-investigator for the agency’s landmark Mars Science Laboratory mission, has taken a lead in this far-flung fieldwork. Since 2006, she has mapped in intensive detail small sections of extreme places like the Mojave Desert and Mono Lake in California, as well as the McMurdo Dry Valleys of Antarctica and the Svalbard archipelago in northern, arctic Norway. She takes the temperatures of rocks and minerals, she scans for signs of static electricity and magnetic fields, she details the chemical makeup of whatever spare, frigid, or blasted terrain she is focused on, and she takes samples that will allow her to know what lives there and what organic compounds can be found. Death Valley does not leap to mind as an obvious place to study the conditions that allow for life, but actually few are better. In this spot, the lowest not covered by water in the Western Hemisphere, we might as well have been on Mars—which is exactly the point.
I joined Conrad at Badwater in California’s Death Valley before dawn because she wanted to do some before-and-after measurements on the salt-mineral scramble: before dawn, when the ground retains its nighttime conditions, and again when the baking sun was high. She had defined a small area of jumble off a salt-slicked path and was into her third round of measurements when her voice rose in excitement: The static electricity meter was delivering a surprise. Laid on the crusty salt, the pocket-size meter was hardly moving. But when placed on the dun-colored toppings—mostly sulfur-based minerals—it shot up. She repeated the measurements several dozen times and found the same pattern repeated every time. “That,” she said, “is just so cool. I have no idea what it means, but it’s telling a story and I want to know it.” We would return to the spot twice more that day, once in the afternoon heat and once in the dark of night.
Conrad is an expert, a pioneer really, in studying these extreme minihabitats. She’s a mineralogist by training, though she’s also performed as a professional opera singer and was moviemaker James Cameron’s companion for a trip to the Pacific floor in a Russian submersible. She began measuring and probing these miniature worlds after being selected in 2004 as one of several dozen investigators for a collection of instruments on NASA’s next big mission to Mars, the Mars Science Laboratory. Three times larger than any previous Mars rover, the MSL is designed to travel as far as twelve miles from its landing site on its official quest to determine whether that small piece of Mars turf, selected with painstaking care, is or was ever habitable. That’s a step short of the 1976 Viking goal of actually searching for Martian life, but because of the controversy and confusion over the Viking results NASA has never again flown a “life detection” mission to Mars. The agency still doesn’t consider the time to be right, but the Mars Laboratory—scheduled to launch in late 2011 and arrive on Mars the next year—is a significant step in that direction.
The collection of instruments that Conrad and her colleagues are in charge of is called SAM, Sample Analysis at Mars. SAM’s job is in many ways the most ambitious on the rover: to search for organic material, the kind of carbon-based compounds needed for life as we know it. Conrad’s approach is based on this logic: MSL will be sending back the most detailed information ever about the chemical makeup of the rocks, minerals, and atmosphere of one promising destination on Mars, and if all goes well it will do that for several years. Because the location is certain to be extreme, like all of Mars as it’s currently known, her team needs to know as much as possible about extreme environments on Earth so members can better understand the information that MSL will be sending back. She doesn’t know what will or won’t be helpful, but she wants to have an encyclopedia of extreme conditions data at her fingertips in case it becomes suddenly relevant. NASA’s Mars mantra has long been “follow the water” as the surest path to habitable places and possibly life; Conrad’s goal is to add other guideposts based on the presence, structure, and behavior of particular molecules, compounds, and minerals.
As she explained it, the actual job of looking for current or past extraterrestrial life is not what people imagine. Typically, extraterrestrials are envisioned as strange but visible, touchable creatures or vaguely human-looking aliens. But what Conrad, the MSL team, and future missions will be looking for is the presence, or former presence, of a life too small to see without a microscope—the kinds of microbes found in those South African mines or under Antarctic glaciers. As a result, they have to look at how that microbe may have changed the site’s organics, minerals, and rocks, at the possible gases created by the current or past presence of a living bacteria-like creature, or at the chemical and electromagnetic landscape to see if it could conceivably support life. Physics, a
stronomy, meteorology, organic chemistry, spectrometry, the relatively new field of geomicrobiology—they all provide important tools in the forensics of extraterrestrial life. A lot of work for a seemingly limited return, but do remember what’s at stake. There is a general scientific consensus that if life of any sort is found on another body in our solar system, and if that life has a detectably different origin than life on Earth, then all the calculations about life in the cosmos change dramatically. One genesis in a solar system and it could be a fluke. Two geneses and suddenly life becomes more of a feature than an anomaly; a cosmic commonplace. And if life is common elsewhere, then there’s every reason to believe it has undergone evolution as on Earth, and could have become complex or even intelligent. One small microbe for Mars, one giant leap for life in the cosmos.
Intrigued by the different charges found in the brown crusts and the white carbonate “fluffies” all around them, Conrad decided to return later in evening with one of her big guns, a portable Raman spectrometer. A sophisticated (and, at twenty-three thousand dollars, expensive) piece of equipment, it can tell researchers in the field what molecules make up a particular rock or sediment or mineral they encounter. Used in mining and chemistry of all kinds, the Raman laser spectrometer (named after the man who theorized how it might work, C. V. Raman) has been adopted by astrobiology as an indispensable tool for analyzing other planets and celestial bodies, as well as their Earthly analogues. The portable spectrometer, called a “Rockhound,” looks rather like a clunky but powerful ray gun, with a point-and-shoot laser beam that can harm the eyes or burn the skin. But the instrument loses its Star Wars menace when it’s tethered to the Toughbook laptop computer it needs to perform.
