How might atmospheric chemistry offer evidence of life? Consider the atmosphere of the Earth and the other planets nearby. On Mars and Venus what atmospheric chemistry goes on is purely driven by sunlight; nothing on the surface is putting gases into the atmosphere that will react with each other. On the Earth life is endlessly churning out new gases, and the atmosphere is full of things that react with each other, such as methane and ammonia, carbon monoxide and oxygen and so on. In the 1960s James Lovelock, a British scientist and inventor, argued that this was a fundamental part of what it was to be a living planet. Life anything like the Earth’s would have to use its planet’s atmosphere both as a source of raw material and as a place to dump waste. The stuff it took out would not be the same as the stuff it put back, because it would only take out what it needed to use, and when it returned it that use would have changed it. Life will thus keep a planet’s atmosphere from settling into the sort of equilibrium seen on lifeless worlds. The methane and ammonia and oxygen in the Earth’s atmosphere are evidence of the flow of matter through a biosphere which uses the Sun’s energy to transform that matter—of the biogeochemical cycles that knit the animate and inanimate into a living world. The insight that life kept atmospheres off-kilter in this way was an early step on the road to Lovelock’s later Gaia hypothesis: the idea that life, through the creation of such disequilibrium, plays a fundamental role in keeping planets habitable, rather as riding keeps bicycles balanceable.
Not all of James Lovelock’s ideas about Gaia have been widely accepted. The idea that life creates chemical disequilibrium in planetary atmospheres, though, has. By the early 21st century, theorists saw it as their best chance of diagnosing life over astronomical distances. But no one knew whether such observations might work in a practical setting. There is, after all, only one planet known to be life-bearing available for study—the Earth—and there are no observatories beyond the Earth that are set up to analyse earthlight spectroscopically.
Hence the observations made by astronomers in Provence and Arizona on a near-solstice night in 2001. The closest thing the sky has to offer to the experience of looking at another living world is to look at this one, reflected back from the distant mirror of the night-dark Moon.
THE BELIEF THAT THE MIRROR MOON REFLECTS NOT JUST SUNLIGHT but an image of the lands of Earth and the great ocean held to surround them dates back to ancient Greece, where it was embraced by some of the followers of Pythagoras. The arguments that this is clearly not the case go back almost as far. In “On the Appearance of the Face in the Orb of the Moon”, the first treatise on the Moon—and one that would be read for its insights for more than a thousand years—Plutarch, a first-century-CE Platonist, argued strongly that the features seen on the Moon were those of the Moon itself, not reflections of Earthly geography. Features taken to be seas on the Moon did not share the shape of the great continent-girdling ocean of the Earth. What’s more the Moon, unlike the image in a mirror, looked the same from every angle.
Nevertheless, the idea of the Moon as a reflection of the Earth persisted. In the early 17th century Kepler’s patron, Rudolf II, apparently held it to be true, not least because he believed that he could see on the Moon the shapes of Italy, Sicily and Sardinia. Almost two centuries later Alexander von Humboldt recorded that the view was still held by educated Persians: “It is a map of the Earth… what we see on the Moon is ourselves.”
There is no map; but what people see when they look at the Moon is indeed, for the most part, a reflection of themselves—of their preoccupations and theories, their dreams and fears. It has been used for such reflection, or projection, in science and fiction alike. The history of the Moon is a history of ideas about the Moon; and it is from those ideas that its future will grow. The Moon, always marginal, is hard put to support meanings of its own. It is there to be filled with the concerns of the big bright world that shines down from its jet-black sky.
In the second half of the 20th century, as the world was gripped by the prospect of wars that technology would make more dreadful than any before, the Moon reflected back conflict and contest; it was reimagined both as a battlefield and as the prize a winner might claim after a race. But those decades of conflict and contest also made it a more literal object of reflection.
Just before noon on January 10th 1946, a three-kilowatt radar transmitter which had been used for long-range detection of enemy aircraft sent a pulse of radio waves from Fort Monmouth, in New Jersey, to the rising Moon. Two and a half seconds later—the time it takes light, or radio waves in this case, to travel the 380,000km there and back—the signal returned. The engineers had become, at least in their own eyes, the first humans to touch the Moon.
At a time when the brilliant light of the atomic bomb threw a new shadow across the future, this seemed, to the cognoscenti, a wonderful event. As the trade magazine Radio News put it in an ecstatic editorial:
Radar has now taken us out of this world, plunged us into the infinite, challenged the universe with spears of radio impulses that have prodded the moon and returned to open new floodgates of human mental activity. No longer can the defeatists tell us that mankind must settle down to the uninspiring prospect of making the most of our little world… [e]ven as radio has been a vital factor in shrinking our own world, so does radio now break our fetters and carry us to worlds beyond.
True to its marginal nature, though, the Moon itself was somewhat incidental to what the Army called “Project Diana”. Radio operators depended on the ionosphere, a layer of charged particles in the Earth’s upper atmosphere which bends and reflects radio waves, to get signals to travel over long distances. A better understanding of the ionosphere thus had great practical value, and getting radio waves to go all the way through it and then bounce back promised to improve that understanding. What was more, if space travel were to become possible—as the advent of long-distance rockets and nuclear power were leading some to suspect that it would—it would be important to know that the travellers could stay in touch with the planet they had left behind.
Indeed, it was possible that radio communication might not just be necessary for the support of space travel: it might be its purpose. Shortly before Project Diana, Arthur C. Clarke, a young British electrical engineer who had worked on radar during the war, wrote a paper on the role that “extraterrestrial relays”—communication satellites, in particular those in “geosynchronous” orbits that take 24 hours to circle the Earth, and thus seem fixed at a specific location in the sky—could play in providing worldwide radio and television coverage. “We have as yet no direct evidence of radio waves passing between the surface of the earth and outer space,” he noted, “[but] given sufficient transmitting power, we might obtain the necessary evidence by exploring for echoes from the moon.” I do not know that the men of Project Diana knew of Clarke’s seminal paper, but their counterparts in the US Navy did, and so did some in the press. On February 3rd 1946 the Los Angeles Times ran a front-page story on the idea, noting of Clarke’s proposed Moonbounce test that “the US Army Signal Corps has just done this.”
Project Diana thus showed both the feasibility of communication satellites and that the Moon could function in such a role. The first was the more important. Some subsequent military projects used signals bounced off the Moon instead of off the ionosphere when keeping in touch with far-flung components of the Cold War apparatus. But once Clarke’s communication satellites were realised, they usurped the Earth’s natural satellite.
Not all the radio reflections from the Moon were deliberate. In 1960 there was consternation when the displays at an American early-warning radar in Greenland suddenly lit up with unexpected returns: the Moon was rising slap in the middle of the radar’s beam and bouncing its signals back to them. Contrary to some accounts, this did not look enough like a missile strike to cause a genuine false alarm. But it did lead the Air Force to reprogram its computers to ignore any radar return with a delay of more than two seconds, thus ensuring that the Moon could
not confuse any further operations.
Scientists, for their part, made use of such reflections to further their understanding of the Moon’s surface. But not all the subsequent radar work was scientific. In the 1960s the Soviet Union deliberately aimed beams from its newest and most powerful missile- and satellite-tracking radars at the Moon, presumably to calibrate them, sometimes for half an hour at a time. This offered the United States a nice opportunity for some celestial espionage. William Perry, an electrical engineer who would later become US secretary of defence, led a secret programme that studied the Soviet radar by using a radio-astronomy dish at Stanford to pick up its signals scattered back from the Moon. Filtering out signals from a local taxi company’s dispatchers, who were using the same wavelength, was a headache, but what they managed to discover about the radar’s capabilities showed that it was not sophisticated enough to target anti-ballistic-missile defences.
As far as I know, spooks no longer use the Moon this way. Just as artificial satellites provide better communication channels than our natural one does, so they are probably better suited to the needs of such snooping. Radar beams are still occasionally bounced off the Moon for scientific purposes. Other radiation is sent there and back, too: the Apollo missions left little mirrors behind, and various observatories regularly bounce laser beams off them to measure precisely how far away it is and how fast it is receding.
And if satellites have robbed the Moon of a professional position in the radio-reflecting business, it still competes on an amateur basis. Radio hams have no way of getting a signal farther than by bouncing it off the Moon and back to the Earth, and since some of them measure their prowess by the distances over which they communicate, excellence in EME (Earth-Moon-Earth) communications, which require big antennae, good equipment and a lot of patience, is a badge of pride in parts of the community.*
Artists use it too. In the 1980s Pauline Oliveros, an avant-garde composer and musician, staged an event called “Echoes from the Moon” at various sites. She would send sounds made on stage down a telephone line to a ham radio enthusiast, who would send them to the Moon, pick up their reflections and play them back. The sound of a gas-pipe whistle and Tibetan cymbals came out particularly well, she believed, after the first experiments; at later shows she played her accordion via the Moon. On some occasions audiences got to send their own voices there and back, too (at one such show this was achieved using the same Stanford dish that Bill Perry had used to snoop on the Russians). The audiences loved it.
In 2007 another artist, Katie Paterson, translated the notes of the first movement of Beethoven’s “Sonata 14 in C Minor”—the Moonlight—into Morse code. She had the resultant dots and dashes bounced off the Moon and translated the signal that was reflected back into a score that could be read by an automated piano. The resultant installation, “E.M.E.”, is magnificent. Various science fiction writers had previously imagined the Moonlight Sonata being played on the Moon. But none had imagined it being played via the Moon—and being reinterpreted through the imperfections of that lunar reflection. Some notes are lost, some are changed. The stately progression and even tempo of the music highlight the holes left by notes lost in transmission; the brokenness personalises the otherwise perfect technology of the playerless piano. The surface of the Moon, as touched by technology, is made present as a set of random absences. In all reflections there is loss.
THE ASTRONAUTS OF APOLLO 8 TOOK NO MUSIC WITH THEM, NOR did they bring any back. Cassette players weren’t allowed on spacecraft until the following year.* And they didn’t actually touch the Moon. But over Christmas 1968 the crew of Apollo 8, Frank Borman, Jim Lovell and Bill Anders, became the first men to follow in the path of earthlight and Project Diana and travel to the Moon and back, encased in the honeycombed aluminium and steel of their command module, fed packaged food and bottled air, recorded on magnetic tape, pushed down by thrust, floating free, sometimes spacesick, sometimes sleepless, endlessly following instructions, doing their jobs, isolated, crowded, keeping it together, experiencing it. Seeing. Changing.
The Apollo programme’s later command modules had names of their own: Gumdrop, Charlie Brown, Columbia, Yankee Clipper, Odyssey, Kitty Hawk, Endeavour, Casper and, finally, America. The Apollo 8 spacecraft had no name other than that of the mission itself. It took off from Cape Kennedy at 07:49, local time, on December 21st. The engines of its Saturn V booster lifted it to orbit in less than 12 minutes. The crew started to check out the systems on their spacecraft
—OK, this is a tape recorder test: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10; 9, 8, 7, 6, 5, 4, 3, 2, 1.
as the Earth passed beneath them at just under eight kilometres a second, blue and green and white and big.
—I mean, let’s get comfortable. This is going to be a long trip.
Three hours later
—You got the redundant components checked, Bill?
the third stage of the Saturn V, to which the command module was still attached, fired up again
—Three, two, light ON. IGNITION
and flung the spacecraft away from Earth. Three days later it crossed the Moon’s orbit just ahead of the Moon itself, a mouse scurrying over railway tracks in front of an express. As the Moon barrelled past a few hundred kilometres behind them, its bulk cut the astronauts off from Mission Control. They prepared the spacecraft’s engine for the four-minute burn
—Jesus, four minutes?
needed to put them into orbit around the Moon. Helium forced fuel and oxidizer out of the propellant tanks and into the engine. There was no order sent up from Earth to tell them when ignition should be. There was, as far as they were concerned, no Earth. Just empty space, and a single engine stopping them from falling even farther out into it.
—Longest four minutes I ever spent.
Until this point they had not seen the Moon. The spacecraft had been pointed the other way. Once in orbit, though, they turned their vessel around and saw a wall of darkness rimmed by a curve of stars. They circled the blackness for ten minutes before
—I’m just going to move my eye away, because the sun’s going to peek over here any second now.
the horizon in front of them overtook the night-edge, and light returned to the world.
For three orbits they stared down as the Moon passed under their windows at two kilometres a second
—It looks like a big—it looks like a big beach down there.
disturbingly real but oddly indistinct. In the 40-minute periods they spent over the daylit surface they tried—and, frequently, failed—to pick out the features
—Hey, you know something; it’s gray, huh?
of the strangely lit sideways-seen land below—features which, a few months later, would guide their comrades on the Eagle, Apollo 11’s lunar module, down to the first landing. In the 40-minute nights they attended to their own needs, and those of their vessel.
It was only on the fourth orbit, when the spacecraft’s orientation had changed, that they had the vision for which their mission will always be remembered. Shortly after they had swept from night to day, a bright, colourful complexity came past the limb of the Moon and into view
—Oh my God! Look at that picture over there! Here’s the Earth coming up. Wow, that is pretty.
and life returned to the world.
The men scrambled to get a photograph, tourist-happy and something more. Borman claimed to have caught it first, in black and white, its terminator just above the limb of the Moon. Anders
—Hand me that roll of color quick, would you?
caught it higher, a bit more than its own width clear of the limb, its white and blue and green and ochre a comment on the grey waste below it, a contradiction.
It has been called
—Oh that’s a beautiful shot.
the most important picture of the 20th century. If you have eyes and live in a world of books or screens, I know that you have seen that picture almost as surely as I know that you have seen the Moon in the sky.
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br /> TO REFLECT, LITERALLY, IS TO BEND BACK. THE IMAGE ON THAT roll of colour turned something which had been thought important because of where it was going into something which was important because of where it had come from. An unparalleled achievement became a passing platform from which to appreciate the true prize: the place left behind.
When originally presented to the press, the picture showed the lunar surface as a wall on the right, the Earth in darkness to the left. It is an orientation that makes them both properly Copernican bodies in space—the same orientation that George Lucas used when the Death Star came into view around the planet Yavin in “Star Wars” nine years later. It was evocative in part because it seemed so strange.
By the time the picture was on the cover of Time and prompting reflections by writers of all sorts, it had been rotated 90°. The Moon was a landscape with a horizon, the blackness of space was the sky and the Earth was rising into it. This is the orientation Stanley Kubrick had used for similar shots in “2001: A Space Odyssey” the year before, one that feels both more cosmic and more personal than the side-to-side arrangement. By evoking the familiar rising Sun, or Moon, it locates the viewer; making sense of the picture this way puts you into it.* Indeed, in a rather pre-Copernican way, it makes you its centre.
“Earthrise”, thus displayed, has three elements. There is the background black, achromatic and featureless; you do not need to see it as an echo of Kazimir Malevich’s iconic “Black Square” (1915), which the artist proclaimed to be the first picture unrelated to any real-world subject, to see it as an unsurpassable negation.
The Moon Page 3