In the opening chapter of the 1963 Reader's Digest Great World Atlas, a panorama of Earth's closest planetary neighbors is depicted. Beneath each fuzzy photograph are a few helpful factoids. When readers peek below the picture of a rust-colored Mars riddled with dark spots, they see this caption: "The patches of color in this picture are believed to be zones of vegetation."
Those alleged jungles eventually turned out to be nothing more than huge dust storms darkening vast areas of the planet. The mistake of the early 1960s is understandable in context of what was known at the time. No probes had been sent to the Red Planet, meaning scientists could only peer through telescopic lenses and attempt deductions from 40 million miles away.
The inspiring notion of life on other planets dates back to Metrodorus, who first speculated on the subject 2,400 years ago: "To assume that the Earth is the only inhabited world in infinite space," he said, "is as absurd as to assert that on a vast plain only one stalk of grain will grow." This concept later proved fodder for Roman writers Lucian of Samosata and Antonius Diogenes, both of whom pioneered the notion of interplanetary exploration in literature . . . complete with indigenous lifeforms.
Mars historically emerges as the natural starting point for an actual investigation. While visible in the sky as the bloody sword-point of the Roman god of war, Mars actually lies nine months away if we took our fastest rockets. It also falls within the proverbial "Goldilocks zone," which appears conducive to life since it is neither too close nor too far from its sun.
In the next couple of years, a bevy of international probes are scheduled to arrive at the Red Planet. They will be turning high-powered eyes onto the planet's southern pole, which has just recently intrigued some scientists. They think something special might be there: a zone of vegetation with methane.
The Martian Wolf
Science doesn't like to cry wolf unless they have one on a dissection table. The size of the universe seems to affirm Metrodorus' prescient words, and the Drake Equation peppers such a philosophy with statistical favoritism. We know life formed at least once in the span of the universe. If such an occurrence is confined to Earth then, as Matthew McConaughey says in the film Contact, the rest of the cosmos "would be an awful waste of space."
Short of SETI picking up an extraterrestrial sitcom, we have no hard data to support an idea. Even so, there have been seven times in the history of modern science when a cry of "Martian wolf" has been sounded. Some of these claims have been retracted, others float in limbo until more data is obtained. Currently planned visits stand to tip the debate in either direction. Will NASA cry wolf? Or will it find one?
When Italian astronomer Giovanni Schiaparelli took advantage of Mars's close approach in 1877, he unintentionally set the stage for the "Mars has life" movement. Schiaparelli was able to distinguish dark and light areas on the planet, which he roughly grouped into "seas" and "continents." He also noted the presence of "channels," as in liquid water cutting through rocky terrain. The Italian word is canali which an imaginative public interpreted as "canals" and associated them with engineering achievements of an alien Venice.
Twenty years later, Percival Lowell heaped lavish detail onto Schiaparelli's ideas. Lowell was an energetic polymath with the heart of an explorer. He built an observatory at a high-altitude point in Flagstaff, Arizona and studied Mars for several years. He concluded that there were indeed vast Martian irrigation canals, and his enthusiasm led him to write three books on the subject which sparked the imagination of the world. That same decade, H. G. Wells would recount a fictional Martian invasion in The War of the Worlds, and the pulp magazines of the early twentieth century cheerfully depicted our neighboring world as a lush green setting inhabited by lusty green princesses. Canals optional. Canals would eventually be discredited; Martian jungles would persist for nearly a century. Such "zones of vegetation" (as the aforementioned atlas called them) represent the second cry of Martian wolf. Trading in the idea of an alien civilization for the more modest notion of alien foliage, this hypothesis lingered until the 1965 Mariner 4 probe arrived at Mars and proved the planet was a cold, barren, lifeless world. It also put a wellspring of science fiction under attack. Suddenly there were no Martian princesses for pulp hero John Carter to seduce, no Martian scholars to teach Heinlein's Valentine Michael Smith how to "grok," and none of Bradbury's gold-eyed Martians cruising the horizon in sand ships. Mars was an empty, red Sahara.
But eleven years later, a new cry of wolf would be sounded. This time, that wolf would have a face.
Cydonia and the Martian Invasion
Few people today haven't seen the infamous Face on Mars. First photographed in 1976 by the Viking probes, the results sparked a global uproar. Several unusual geological features on the Martian plateau of Cydonia appeared to show pyramids, octagons, and a human-like face. Suddenly Lowell seemed vindicated.
It was a firestorm in believer circles and much subsequent ufology literature devoted endless chapters to these images. Clearly, an alien race had constructed vast earthworks (marsworks) in a kind of ghostly parallel with our own Egypt. The comparison was specifically cited by many authors like Zecharia Sitchen and Erich von Daaniken. Why a Martian civilization would build a human face was rarely asked, though there was an answer for that too: the Martians had actually visited Earth and engineered us out of early hominids! The so-called "missing link" was from Mars!
Subsequent analysis proved human beings just love to see faces. The oddities of Cydonia don't look so odd from other angles. Since we are masters of pattern-recognition and trained from birth to identify the human face, it is a small wonder that we so often see visages in mountains, clouds, tree bark, rock formations, and even a piece of toast. Unsurprisingly, this mundane explanation led to the charge that NASA was keeping proof of otherworldly civilizations under wraps.
It was clear we needed to land on the Red Planet to conduct any serious investigation, and the Viking probes did just that. Touchdown! The search for Martian life was really on, at long last. Several experiments were conducted with negative results.
Then came the Labeled Release experiment. The Viking probe injected Martian soil with various nutrients and then closely monitored it for signs that the nutrients were being metabolized by microorganisms. The test results came in: positive.
The Martian wolf had been discovered! Yet before the press releases could go out, the results needed to be confirmed and they never were. Although additional tests were performed, the Labeled Release results have been debated by biochemists and biologists for years. Actual organic molecules were not uncovered by the experiment; rather, the chemical reaction of the soil suggested metabolic processes of bacteria. The final tally is that there is no final tally. The fourth cry of Martian wolf, while not conclusively dismissed, is far from conclusively confirmed.
The fifth episode in this strange saga occurred not on Mars, but right here on Earth. In 1984 in Antarctica (the same year and setting for John Carpenter's The Thing) several meteorites were discovered and determined to have come from Mars. The meteorites demonstrated isotopic concentrations of gas similar to the Martian atmosphere. Apparently, some nasty collision long ago jettisoned part of Mars into space, and Earth's gravity well captured a few rocks. This conclusion is the general consensus even today, and new examinations have reaffirmed a Martian origin.
This idea is not so radical. What was inside the meteorites, however, has been called revolutionary.
Wormlike structures resembling fossilized tubular bacteria were uncovered, and in 1996 President Bill Clinton gave a public address on the subject: "If this discovery is confirmed," Clinton said, "it will surely be one of the most stunning insights into our universe that science has ever uncovered."
If the discovery is confirmed, sure. Part of the problem is that the Martian meteorites are in a depressing state of limbo. In short, it depends on who you ask. Some scientists look at the rock's interior and see fossilized bacteria. Others see a curious geological formation. It calls to mind the varying impressions of Cydonia: Now you see the face, now you don't!
There's little denying the meteorite structures are unusual. The problem is that even NASA is in a civil war over this. In 2007, two separate NASA teams went several rounds with each other. Douglas Ming of NASA and Dadigamuwage Golden of Hernandez Engineering announced at the Houston Lunar and Planetary Science Conference that they had managed to replicate the results of the Mars rock by superheating material and then dropping it into water.
Not so fast. David McKay, leader of the NASA team which made the meteorite discovery, refuted the Ming-and-Golden conclusion by saying that the conditions of their experiment differed from the conditions undergone by the meteorite itself. Kathie Thomas-Keprta, also of the original NASA team, further pointed out that the lab-produced results don't even look like the "fossilized bacteria" of the Martian meteorite.
In other words, the scientific community is flirting with an all-out fist fight while the debate drifts in space.
Springtime on Mars
In the late 1990s, amid this debate over rocks, astronomers began noticing a peculiar feature near the Red Planet's southern poles. Small dark spots were appearing each Martian spring and vanishing by the beginning of winter. Observations confirmed that approximately 70 percent of the spots reappeared in the same location, each and every spring. known as the Dark Dune Spots. Was it Martian vegetation blooming?
That was the suggestion made by Hungarian astronomers in 2001 and published in the Lunar and Planetary Society publication. The title of their paper effectively states their position: "PROBABLE EVIDENCES OF RECENT BIOLOGICAL ACTIVITY ON MARS: APPEARANCE AND GROWING OF DARK DUNE SPOTS IN THE SOUTH POLAR REGION."
Critics have been at pains to offer an alternative explanation, though NASA's position is that the dune spots are just dark sand blasted out from beneath melting ice each spring by high-speed jets of carbon-dioxide. Until someone can focus a camera on that area of the planet we won't know the truth. Geyser or weed? Stay tuned!
Yet surely if Mars has life, there would be some kind of chemical trace in the atmosphere . . . even granting that the atmosphere is notoriously thin. Life alters a planet. If native creatures live there, there should be atmospheric footprints for a robotic Sherlock Holmes to track down. And this brings us round to the seventh cry of Martian wolf: methane found on Mars.
The very recent confirmation that methane exists on the Red Planet has stirred the cauldron once more. A NASA press release states, "The first definitive detection of methane in the atmosphere of Mars indicates the planet is still alive, in either a biologic or geologic sense."
Once again, there are two interpretations of scant data; two schools of thought orbiting the metaphorical punch bowl. One is volcanic, the other organic.
This may be the last howl before exobiologists give up on Mars and follow more promising bread-crumbs elsewhere. The mysterious warm ocean of Enceladus, the rumored sea of Europa, the thick atmosphere of Jupiter, the murky bogs of Titan, and even possible water-ice within Ceres have been steadily crowding out Mars as best sites for alien life. A bevy of missions are being planned to probe these locales, and the sentiment at NASA is turning outwards, to the Jovian and Saturnian regions.
Yet clearly Mars is not gone from the stage. Methane represents the best clue yet, and coupled with the mystery of the Dark Dune Spots, we have all the justifications needed to conduct a serious investigation. NASA is presently narrowing a list of landing sites for its upcoming Mars Science Laboratory project. That list includes ancient riverbeds, dead seas, craters containing flood deposits, and clay-rich mountains. Should an upcoming mission prove life is there, then the Martian meteorites would likely move out of limbo. And in a strange irony, this would also confirm the notion that Martians brought life to Earth . . . in a way. Not so much Chariots of the Gods as a rain of scattered microbe-bearing debris.
The matter needs to be resolved. Mars clearly represents the best possible site for a viable otherworldly colony. It provides long-term advantages that space stations and even the Moon cannot match. If there is indigenous life, we'll need to know about it. Before we set about terraforming a world to suit us, what of the bioethical concern over how it will impact native organisms; xenocide isn't to be taken lightly. Furthermore, an entire archaeological industry—and possibly the key to our own life story—might just be lurking beneath the permafrost.
Scientists are generally in agreement that Mars was once a wet planet. If organisms existed during this happy state of affairs, and if some water persists below the Martian surface, then the conditions for life are still present, and something may have survived whatever calamity destroyed the atmosphere and surface. A tract of plants spreading wide their petals to greet the sun? A colony of photosynthetic bacteria growing across the dunes? Or another blow to our quest for life on other planets?
Meanwhile, the Martian wolf prances through the fields of our imaginations and hopes.
 "The Man in the Moon." Carl Sagan. Parade Magazine. June 2, 1985. Pg. 12.
 "The Viking Biological Investigation: Preliminary Results." Harold P. Klein and Gilbert V. Levin. Science. October 1, 1976. Pgs. 99—105.
 "Bill Clinton's Speech at White House on Search for Life on Mars Conference." August 7, 1996.
 "Annual Reappearance of Biogenic Dark Dune Spots on Southern Polar Region of Mars." A. Horváth. 6th Vernadsky/Brown Microsymposium on Comparative Planetology. Oct. 14-16, 2002. Moscow.
 "Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region." A. Horváth. Lunar and Planetary Science XXXII. 2001.
 "Martian Methane Reveals the Red Planet is not a Dead Planet." Bill Steigerwald. Official NASA website. January 15, 2009.