First Contact

by Marc Kaufman

  On Earth, much of the methane now produced comes from cows, forest fires, and landfills. But the earliest biological source was no doubt methanogens—primitive microorganisms that both produce and consume methane, and have been here making their “marsh gas” since earliest times. They appeared before oxygen was abundant in Earth’s atmosphere, and so the dearth of oxygen on Mars would be no problem for these tiny round or rod-shaped organisms; they can survive for some time in the presence of oxygen, but generally live without it. In theory, then, similar methanogens could be doing the same on Mars near the surface or even far below, and they could be doing it on other planets or moons as well. The Mars methane release would, in this scenario, occur when the right climatic conditions arrive for an explosion of the methanogen population, or it could come from a melting of surface ice that then allows subterranean, bacteria-produced methane to escape. In other words, during the relatively warmer Martian summer.

  But there are also two geological contenders as the source of the methane. The first involves a process called serpentinization, where water and carbon dioxide interact with particular minerals in a way that makes methane as a by-product. The mineral most subject to this serpentinization process is called olivine—also known in its gemstone form as peridot—and it is common on Mars. The second possible geological source is erupting volcanoes. Methane is known to accompany lava as a volcano erupts, but on Earth the gas sulfur dioxide is always present as well. So far, sulfur dioxide has never been detected in the Martian atmosphere. A final possibility is that huge reservoirs of the methane remain deep underground and leak slowly up. They may have been produced biologically, geologically, or as part of the process that brought Mars into existence some 4.5 billion years ago.

  But what is known for sure is that the methane releases occur regularly, because the gas doesn’t stay in the Martian atmosphere for long. On Earth, methane produced by bogs or cows can remain for a decade; on Mars, for reasons that are not fully understood but imply a photochemical destruction process unlike anything now known, the gas is destroyed in under a year. Identifying that short lifetime was one of the major accomplishments of Mumma’s team because it allowed them to break with the conventional wisdom—that there was little or no methane on Mars—and show that at certain places and at certain times, there are major releases. The amount of gas being released is substantial: about 20,000 metric tons of methane in the big plumes during summer in the northern hemisphere. That rate is comparable to the natural hydrocarbon seep at Coal Oil Point off Santa Barbara, California, which is the largest of its kind in the Western Hemisphere and the second largest in the world. The natural gas seepages may well be the result of different dynamics on Mars and Earth, but Mumma considers the comparable sizes to be significant.

  Determining how these plumes of Martian methane were being produced would seem impossible from Earth, yet there are promising theories about how to do this. They involve observations and calculations that are stunningly complex, and their absolute accuracy probably won’t be known until astronauts land on Mars and perform tests that can only be done on the surface itself. But Mumma has put together what he describes as a campaign to accelerate his breakthrough work. NASA and many of the major observatories in the world are now eager to support his team with an almost unprecedented twenty-three observing runs on the world’s most powerful telescopes in the next few years.

  Potentially even more important, the methane discovery abruptly changed both American and European plans for the next generation of missions to Mars. The previously planned European ExoMars expeditions of 2016 and 2018 became a joint NASA-ESA mission within months of Mumma’s methane announcement, and searching for methane became a major—probably the major—focus. The missions will feature an orbiter equipped to locate the most interesting gas releases, and then the deployment of landers two years later to explore the best of those sites. The explicit goal will be to search for biology on Mars, something that hasn’t really happened since Viking in 1976. Mumma’s methane discovery probably saved the NASA Mars program from a significant downsizing, and the European Mars mission as well.

  Mumma’s recent campaign began in late summer of 2009 in the Atacama Desert of northern Chile. The Very Large Telescope observatory at Paranal, built and operated by the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), sits atop a desert mountain, with four big telescopes at the peak and eight smaller ones nearby. The area is the copper belt of Chile, where much of the nation’s wealth is pulled from the ground. But not around Paranal—for at least thirty miles in all directions there are no people at all, no animals, no trees, hardly any plants or even insects. Once out of the environs of the sprawling, gritty port town of Antofagasta, what you see are bare hills and coarse, sandy plains. To encounter a boulder—or better yet, a field of boulders deposited by fast-running water last seen hundreds of thousands of years ago—is about as visually exciting as it gets. By many measures, this is the driest place on Earth, or at least among the top three. The harshness of the area was what drew ESO to Paranal in the mid-1990s, because environments that support plants and animals generally bring people, and people produce nighttime light. Operating a complex, high-precision set of very expensive telescopes is hard enough on its own; doing it surrounded by towns, villages, and their light makes the job much harder. Terrestrial light is definitely the enemy at Paranal, and fortunately there are eighty miles between the telescopes and the bright lights of Antofagasta.

  The road to the observatory breaks off from a newly paved highway after some ninety minutes of desert driving. The observatory road loops over small hills and down to a gentle but equally parched valley with dozens of all-white buildings large and small. At first encounter they seemed evacuated. Only later did I learn that outside activity is discouraged during the day because the level of harmful ultraviolet light in the area is dangerously high. Everyone, as a result, was inside. My ESO guide, former astronomer Laura Ventura, parked beside a white prefab building; off to the left was a large, low-slung half-dome in the gravel. We stepped out into the piercing sunlight, Ventura told me to grab my suitcase, and we headed toward what appeared to be a futuristic maintenance building or storehouse. We came to a long, declining ramp that led us below ground level to a pair of heavy metal doors. We tugged them open and passed through to a small, pitch-dark room leading to another set of doors. I pulled open the second door and it was as if we’d been swept suddenly and miraculously away to the Amazon or Costa Rica or any evergreen equatorial rain forest. Outside was the driest desert on Earth, but inside was the tropics, and it was bathing us in sultry, humid air.

  Before us was a small, sloping jungle of full-grown palms, ferns, and banana trees, all under that half-dome, and all underground. A swimming pool shimmered at the bottom of the faux hillside. We had arrived at La Residencia, the hidden home of all who explore the heavens at Paranal. My arrival was accompanied by an admonition to keep my room windows covered by the blackout shades once the sun goes down, and not to worry if the ground began to shake—earthquakes in the area are common. I was introduced to the all-important wake-up call system that rouses researchers at all hours of the night and told to be up at two-thirty in the morning.

  What brought Mumma, his Goddard collaborator Geronimo Villanueva, and former Mumma postdoc and now ESO “Infrared Instrument Scientist” Hans-Ulrich Käufl to Paranal was an unusually precise piece of equipment designed and modified with their methane-on-Mars work in mind. It was recently attached to UT1, one of the four eight-meter mirrors of the Very Large Telescope array atop the mountain nearby. At the time, the instrument—CRIRES, or the cryogenic high-resolution infrared echelle spectrograph—may have been the most powerful land-based astronomical instrument in the world for identifying and characterizing gases such as methane on distant planets and stars, allowing for a more precise locating of the methane plumes than ever before. Ironically, the team’s most pressing concern before arriving at Paranal was tha
t their target—Mars—might be too close for the instrument to produce good measurements. A telescope and spectrometer designed to see into distant space could have a hard time with an object as near as Mars.

  The process of collecting photons from around the universe through the telescope, funneling them into a vacuum-sealed, supercooled (to –328 Fahrenheit) spectrometer like CRIRES, and coming up with potentially useful data is a marvel of precision. It requires a multitude of transformations, adaptations, reconfigurations, and judgments. That afternoon I was ferried to the mountaintop and introduced to the telescopes and the spectrometer, which is affixed to the base of the big mirror like an oversize parasite to its host. At its most basic, CRIRES operates under the same logic as a simple visible light prism: It takes in photons and breaks them down into component parts, to their equivalent of a rainbow. CRIRES works in the infrared band of the spectrum, but other spectrometers read radiation sources ranging from low-frequency radio and microwaves to visible “white” light and to higher-frequency ultraviolet and X-ray. What the instruments read is often the movement of electrons inside an atom or molecule that have been excited by starlight and other energy sources. The excitation makes the particles move in a detectable way that provides a recognizable signature in photons for one, and only one, element or molecule.

  It’s all a function of quantum physics, so it is both vaguely mysterious and remarkably precise. The result is that when Mumma and his colleagues search for methane on Mars, they are not using the kind of detection instruments you’d find in the oil and gas industry, or to identify a gas leak, or to monitor releases from landfills. And he’s not looking through the lens of a telescope. Instead, he’s reading spectra on a computer screen.

  Scientists have known about the dynamics of the electromagnetic spectrum for two centuries, but the usefulness of spectroscopy for astronomy only became apparent in the early twentieth century. It began in 1859 with construction of the first spectrometer by German chemist Robert Bunsen (of Bunsen burner fame). In 1864, two amateur British astronomers—Sir William Huggins and his wife, Margaret Lindsay Murray Huggins—used a rudimentary spectrometer to discover that the sun is made up largely of hydrogen. Spectroscopy led directly to the 1868 discovery of helium by an amateur British astronomer, Norman Lockyer, who came across unusual spectral lines coming from the outer atmosphere of the sun during an eclipse. But it was only in the early twentieth century, after quantum physics and quantum mechanics revolutionized our understanding of how particles move and spin on the atomic level, that its full potential was revealed.

  More recently, a spectrometer of the orbiting Hubble Space Telescope in 2001 detected the first element isolated from an exoplanet when it found sodium in the atmosphere of a planet fifty light-years away. Spectroscopy has since been used to measure the evaporation of hydrogen from the atmosphere of a planet 160 light-years away, and more recently the presence of carbon dioxide and methane surrounding a large gaseous planet 63 light-years away. Without spectroscopes, astronomy would lose half its ability to see into the cosmos.

  Mumma has had a lot of experience with spectroscopy: His early work at Goddard focused on comets, then on the possibility of finding the organic gas ammonia on Mars. After that petered out, his search for methane began. The year was 1989, two decades before he finally went fully public with his findings. In the worlds of planetary science and astrobiology, discoveries generally don’t come fast.

  It is a tradition at Paranal to introduce newcomers like myself to the telescopes at sunset. Not only are the four enormous domes grand and sparkling in the low golden sunshine, but the mountaintop is said to be an auspicious place to see the “green flash.” The flash is a very brief glimmer of green light that, for the lucky few, can be seen seconds after the sun has gone down over the horizon. It’s a real optical phenomenon, as opposed to an optical illusion, that involves the refraction of light and the differing frequencies of blue-green light versus red-orange. It’s best seen over the ocean, and we had a glorious view of the Pacific. Or so I thought. I had sensed that something was slightly off, that the water seemed closer than it should be, but nonetheless I was seeing waves head toward shore and I even saw “islands” in the water. It took a while, but it gradually became apparent that those waves were in the clouds and those islands were hilltops and mountain peaks. The huge, shoreline bank of clouds that typically rolls along the Atacama coastline fooled me, as it has many others. Perhaps it was because we were watching the sun set over Pacific clouds rather than the Pacific Ocean that the green flash didn’t appear, but the sky did turn a bright orange and then an otherworldly bloodred. As the sunset played out to the west, the big domes behind us began to open, the telescopes were set into motion to a series of groaning, ghostly sounds, and the night’s observations began.

  But Mars wouldn’t rise in the sky until early morning, so we returned to La Residencia for a brief sleep and that middle-of-the-night wake-up call to return to the observatory. But first some stargazing. From our high Atacama perch, the visible universe held an infinite collection of starshine. The Milky Way was not a distant smudge but a clear and vast disk of stars; the wispy Magellanic Clouds (two very near and star-packed galaxies) looked like so much celestial cotton candy; the supergiant star Betelgeuse (which gives off one hundred thousand times more light than our sun) glowed red. Reluctantly, we piled into several cars for the ten-minute ride up to the telescopes, built on a platform atop a flattened 8,650-foot peak. The drivers, of course, did not turn on their lights, so the sharp mountain turns demanded practiced care. We arrived alongside the four big scopes—named in the local Mapuche language Antu (the sun), Kueyen (the moon), Melipal (the Southern Cross), and Yepun (Venus)—and headed for a small side entrance of the first, then up two flights of stairs, around a bend, and into the control room. It was alive with computers and screens of all kinds, but not with many people. The telescope itself was also nowhere to be seen; its huge mirrors, located behind a thick wall in a cavernous chamber, take in photons and send them to various instruments to cut and slice as the researchers need. The Mumma team prepared its instruments and computers for the coming Mars-rise.

  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.