First Contact (14 page)

The first days of the campaign had been devoted to assessing whether concentrations of methane tended to be released alongside concentrations of water. The data on that had previously been inconclusive, but now the team would be able to simultaneously detect and map, via CRIRES, the methane and water at a particular location better than before, and for the first time to detect methane and its biologically important relative ethane. Simultaneously, they would examine the isotopic characteristics of the water (seeing if some of the hydrogen had an extra neutron) and would search for other
hydrocarbons related to methane. But most important, the campaign would involve replicating and expanding on data about the presence and dynamics of those gas plumes. Most of that work would be done in the months ahead at Paranal and at the W. M. Keck Observatory, atop Mauna Kea in Hawaii, together probably the two most cutting-edge centers for ground-based astronomy on Earth.

Mumma sat me down to lay out what was about to happen, as well as what they had found in the several nights before, when the “seeing”—the cloud, wind, and other atmospheric and deeper space conditions that affect astronomical data collection—was better than this night.

Mumma pulled up a map that showed where methane had been found and where the Mars Global Surveyor, a spacecraft that orbited Mars from 1997 to 2006, found the weak remnants of what had once been a strong magnetic field. The two distributions overlapped a lot. Mumma explained that a remnant magnetic field had been found in what is known to be the most unchanged, oldest Martian terrain. That meant, Mumma said, those areas had not been covered by the flooding lava of volcanoes or the transforming impacts of meteor strikes. (Mars is pockmarked with numerous craters, including the Hellas basin, the deepest one in the solar system.) Wherever the original Martian crust was modified significantly, the magnetic signature was gone. So usually was the methane, which generally was not found around volcanoes or lava flows, and definitely not in craters. The gas releases, then, were associated with an ancient Mars that was once well protected by a magnetic field, and by current estimations was most likely both wet and warm. In other words, a Mars that was at its most hospitable to life.

Water is the key to Mumma's methane work. Determining the origins of the methane alone would be impossible from Earth because there would be no telltale differences to measure. But methane on Mars along with water just might provide the necessary clues. So part of the search involves looking for water (as ice or vapor) and methane together. NASA has been trying to “follow the water” on Mars for decades, and now is quite
convinced that it once flowed as a liquid on the surface and can be found in huge amounts as ice just below the surface. In 2008, the lander Phoenix found water ice inches below the surface on a polar plain, and in 2009 the Mars Reconnaissance Orbiter found ice much closer to the equator when it detected white, shiny material at the bottom of small craters recently created by meteorites. Many scientists believe the mystery of what happened to the abundant water of early Mars has largely been solved—some escaped into space but the rest is lying below the surface in huge reservoirs of ice.

All the recent discoveries about extremophiles, and especially those living in ice, raise the possibility that living creatures could remain in an arctic-like permafrost just below the Martian surface, one that changes from frozen to semiliquid with the seasons. NASA astrobiologist Richard Hoover recently found microbes deep in an Alaska tunnel at a level determined to be thirty-two thousand years old. They were inactive in the ground, but when warmed they came alive and even moved and, if they were methanogens, began to produce methane. Something similar could happen on Mars. Methane could also be stored in huge reservoirs produced long ago and now deep below the surface. It could escape when the warmer weather opens small pathways to the surface. And then there's ethane, a decomposition product of methane clearly associated with living things. Mumma is searching for that, too.

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 H
₂
O vapor and new if it had a higher level in its H
₂
O 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 H
₂
O (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 H
₂
O 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.