AROUND A MINOR G-TYPE STAR fairly far out toward one edge of a medium-sized galaxy the planets of that star swung as usual, just as they had for billions of years, under the influence of a slightly modified inverse square law that shaped the space around them. Three of them were big enough, as planets go, to be noticeable; the rest were mere pebbles, concealed in the fiery skirts of the primary or lost in the black outer reaches of space. All of them, as is always the case, were infected with that oddity of distorted entropy called life; in the cases of the third and fourth planets their surface temperatures cycled around the freezing point of hydrogen monoxide - in consequence they had developed life forms similar enough to permit a degree of social contact.

On the fourth pebble out the ancient Martians were not in any important sense disturbed by the contact with Earth...
(Stranger in a Strange Land by Robert A. Heinlein)

IN THE REAL WORLD, on the third pebble, called Earth by its inhabitants, there developed a civilization with a level of technology sufficient to send robot spacecraft to probe the surface of the fourth planet. The inhabitants of the third planet were quite excited by the data and photographs transmitted back to them by these probes, as well as the data and photographs transmitted back by orbiting probes. Some of them even found in the photographs surface formations that appeared to have been made by intelligent beings, although that interpretation of these formations was in great dispute on the third planet. The probes that landed on the surface of the fourth planet did not, by the criteria of the scientists of Earth, detect evidence of life in the areas in which they landed. The inhabitants of Earth, who called themselves humans, had begun developing a technological civilization a few thousands of revolutions of the third planet about the sun earlier, and had been speculating about the possible existence of life forms on the fourth planet for quite some time.

A couple of thousand years before, people called Romans, ancestors of the current humans, had named the fourth planet Mars, after their god of war, because the fourth planet was observed to be the color of human blood. Through the ensuing centuries, the name Mars was kept, rightly or wrongly, for the fourth planet, as were the Roman names for the other planets.

The fourth planet attracted special attention from the humans even before they had instruments that would allow them to observe it closely. One particular group of humans, known as astrologers, showed particular interest in Mars because, at certain times, it appeared to move backwards in its orbit. Astrologers were a semi-religious group who believed that they could predict the future from the motions of the planets and stars. Most early astronomers were also astrologers, and this apparent backward motion of Mars was quite disconcerting to them.

In the year 1609, a human astrologer/astronomer named Johannes Kepler used the visual observations of another astrologer/astronomer named Tycho Brahe to determine that the seemingly strange orbit of Mars about the sun was a result of that orbit's being an ellipse, rather than a circle as had been thought previously.

Also in 1609, another human astronomer took a device called a spyglass and improved it into what became known as the telescope. His name was Galileo Galilei, and the next year he became the first human to see Mars as a disc through one of his telescopes. He and Kepler were friends, and Kepler wrote to him that he expected Mars to have two moons, although none had been discovered. Kepler, as we said, was an astrologer as well as an astronomer, and he wrote many papers in which he claimed to find mathematical relationships in the orbital distances of the planets from the sun, and in the number of moons each would have, as well. He was later found to be right about Mars, but he also calculated that Mercury and Venus should have one each. He was quite wrong.

The next major observations of Mars were in 1659, and were made by a Dutchman named Christiaan Huygens, who improved on Galileo's telescope by grinding better lenses and by inventing the compound eyepiece. He used his improved telescope to observe Mars and to actually make the observation that it rotated on its axis, just as the Earth did. He also was one of the the first humans to draw maps of Mars showing the features that he was able to observe through his more powerful telescopes. One of these was a broad dark area known as Syrtis Major, also known as "the Hourglass Sea".

A few years later, in 1666, an Italian astronomer named Gian D. Cassini was able to calculate the Martian day at 24 hours 40 minutes, which was quite a remarkable feat for the time. He is also said to have been the first to observe the Martian polar ice caps,although this is said to be debatable.

Mars was beginning to look quite similar to earth - 24 hour day, polar ice caps, and changing surface features that looked a bit like changing seasons on Earth might look from such a distance. Not much more was learned about Mars over the next century. Too much was happening on Earth, with the settling of the "new world" and all. Telescopes mostly collected dust. The next major observations of Mars were by astronomer William Herschel in 1783, who calculated its diameter and determined that it had a thin atmosphere.

In 1858, observations of Mars began to become much more lively, as Pietro Secchi, director of the Observatory of Rome, described what he thought was a river on Mars, calling it a "canale". Secchi believed that Mars had seas and rivers that swelled with the seasonal melting of the polar ice caps.

Throughout all of these observations, no one had found any moons orbiting Mars. Kepler had predicted in the 17th century that Mars would have two moons, and in 1726, as unlikely a source as the writer Jonathan Swift's Gulliver's Travels, speaking of the fictional Laputans, beings who flew around the skies in flying cities,said:

They have likewise discovered two lesser stars or satellites, which revolve about Mars; whereof the innermost is distant from the centre of the primary planet exactly three of the diameters, and the outermost five; the former revolves in the space of ten hours, and the latter in twenty-one and a half; so that the squares of their periodical times are very near the same proportion with the cubes of their distance from the centre of Mars; which evidently shows them to be governed by the same law of gravitation, that influences the other heavenly bodies.

He was amazingly accurate, as Asaph Hall found when he finally discovered the two moons of Mars in 1877. What was astonishing was that the moons hadn't been discovered sooner. Soon everyone was seeing them, even with less powerful telescopes than Hall's.

That same year marked the Mars observations of the Italian astronomer Giovanni Schiaparelli. His excellent vision, combined with an 8.6-inch Merz refractor telescope, enabled him to see details that had been previously hidden. The maps that he made at the time showed unusual linear features that he, like Secchi, called "canali". His intended meaning was "channels", by which he meant something like rivers, but the similarity of the word "canali" to the word "canals", with its meaning of artificially constructed waterways, seized the popular imagination. Many astronomers, though, never saw the canals."

Seeing the canals was contagious, though. Soon some of the other astronomers were seeing them, and more. Camille Flammarion believed he saw canals and yellowish-red vegetation, and in 1891 William Henry Pickering claimed not only to see canals, but to be able to count lakes on Mars from his observatory in the Peruvian Andes Mountains. However, many astronomers could still see no canals at all, even with the best telescopes.

In 1894, Percival Lowell, not an astronomer, but a man from a family that had gained its wealth in the textile industry, was convinced by William Pickering to finance the construction of an observatory in Arizona for the purpose of viewing Mars at its coming opposition in October of that year. Lowell, however, was determined to be more than merely a patron. He had been interested in astronomy since childhood, and he soon had taken control of the project. Flagstaff was chosen as a site for the observatory, and the observations of Mars began in the late summer. The first disappointment came when Pickering determined that the light reflected from the dark areas was not polarized, which meant that these areas were not water. Lowell embraced the idea that they must then be vegetation and that the Martians had constructed the vast canal systems to funnel water from the poles for irrigation. Lowell also believed that Mars had a temperate climate.

In the popular press and in the minds of the public, the question of life on Mars was a seed that grew into an obsession. 1897 saw the publication of writer H.G. Well's fictional War of the Worlds, in which the Martians, after watching Earth for years, decide to come and take Earth for themselves. A bubble of hype about life on Mars began to grow.

For the opposition of Mars, in 1907, Lowell sent his assistant E. C. Slipher and Amherst College professor David Peck Todd to Alianza, Chile, to photograph the planet with Amherst's 18-inch refractor, which had been shipped to South America specifically for that purpose. Some of Slipher's 13,000 images were alleged to have captured canals, but later examination of the photos failed to bear this out.

The year 1918 was a landmark one in fiction about Mars. That was the year that A Princess of Mars by Edgar Rice Burroughs was published. This was the first of a series that he would publish over the next several decades. Burroughs' Martians were not space travelers, however. His fantasy tales were about an Earthman who mystically travels to Mars from an Arizona desert to find love and adventure among the canals and the spiral cities populated by the many-hued races of Martians.

In August, 1924, the idea of communicating with Mars became popular because on August 23rd Mars and Earth would come to within 55.7 million kilometers of each other, their closest approach since 1804. It was hoped by many that the Martians had powerful transmitters and would be trying to contact Earth. The task on Earth would be to try to intercept those transmissions.

Lowell's associate David Peck Todd, Professor of Astronomy at Amherst College, asked the U.S. Government to turn off its high-powered transmitters for five minutes before each hour to give him "silent periods" in which to listen for signals during the close transit with Mars from August 21 to August 23rd. The military responded by ordering all military stations to monitor and report any unusual signals, but didn't cut back normal transmissions. Professor Todd also requested that all radio stations maintain a five minute silence each hour over a two day period, but only WRC in Washington, DC cooperated. During these "silent periods" Todd used a receiver tuned to a wavelength between 5 and 6 kilometers to record any signals coming through, not realizing that signals of such long wavelength would not penetrate Earth's atmosphere, but would have been reflected back into space. Todd received only a jumble of dots and dashes whose source was never determined.

Over the next three decades, interest in Mars was pushed into the background by the Great Depression, and then by World War II.

There were discoveries made, however, such as the fact that there were only minute quantities of water vapor in the Martian atmosphere and that its atmosphere was mostly carbon dioxide, with practically no detectable oxygen. The ice caps were thought to be water ice, but most astronomers felt that liquid water could not exist on Mars because of the extremely low air pressure, which would cause it to boil away even at low temperatures. The changing colored areas were theorized to be gigantic dust storms, not vegetation. The canals vanished from the images seen through the telescopes as mysteriously as they had appeared.

There was, however, a brief resurgence of public interest in Mars in 1938 when a radio broadcast of H.G. Wells' War of the Worlds by Orson Welles was aired. Because of the news-broadcast style of the presentation, many people believed that it was true, that Martians were invading the Earth, and they panicked.

One outcome of the war was the development of the rocket engine. This engine would, over the next decades, allow humans to develop a space technology that would let them learn more about Mars than they had learned in all of the centuries of observation that had gone before.

The First Probes

During World War Two, Germany took existing rocketry, that had been developed earlier in the century, and turned it into a potentially deadly weapon, one that would deliver an explosive through the air to a target over a great distance. The weapon that the Germans developed was called the V-2 rocket, and after the war, the German rocket expert Werner von Braun and some of his associates, along with captured V-2 rockets, were taken to the United States and the Soviet Union, where they continued their work.

In the decades following the war, the United States and the Soviet Union became involved in a competition to develop the new space technology, including the sending of probes to the planets, as well in a deadly competition to develop rockets for the purpose of delivering nuclear bombs.

The first successful attempt by a human nation to launch a device into space using a rocket was by the Soviets in 1957 and was a device called the Sputnik, an artificial satellite that orbited the Earth and transmitted data to the ground. The Soviets were also the first to successfully launch a probe toward Mars, in November, 1962. The launch was timed to take advantage of a close approach of Mars that would occur in January, 1963. The probe was called Mars 1. "Successful" is perhaps an overstatement, because communications with the probe were lost when it was 106 million kilometers away from Earth in March, 1963. It flew uselessly past Mars at a distance of 195,000 kilometers in June, 1963.

The Americans, later in entering the competition than the Soviets, had successfully launched a probe to Venus, in 1962, which had shown that planet to be quite inhospitable in spite of its name. Their first Mars probe failed to reach the proper orbit, but the second probe, Mariner 4, reached orbit around the Earth on November 28, 1964 and functioned properly. The Soviets also launched another Mars probe, called Zond 2, on November 30, 1964.

The Soviets experienced a repeat of their failed Mars 1 mission and lost contact with Zond 2 in May, 1965. America's Mariner 4 was more successful, and flew relatively near Mars on July 14, 1965. Its camera obtained twenty-two images which, although they were of rather poor quality, showed that Mars looked strikingly like the Moon. Surprising everyone, Mars' surface appeared to be old and covered with craters, with no canals in sight. The probe also was able to measure the atmospheric pressure on the surface, which was shown to be very low and due to a thin atmosphere almost completely consisting of carbon dioxide. Scientists who analyzed the results said that liquid water could not have existed on Mars for billions of years and that the polar ice caps were likely frozen carbon dioxide rather than water ice. Suddenly life on Mars seemed highly questionable. The next two American Mars probes, Mariners 6 and 7, in 1969, confirmed the bad news that Mariner 4 had delivered. The air pressure was very low, the dark areas were heavily cratered, and the temperature at the Martian South Pole was -123° C, the temperature to be expected if the pole consisted of frozen carbon dioxide.

As it turned out, however, humans had only glimpsed the worst of Mars. Generalizations based on these early probes were as incorrect as Lowell's canals and vegetation had been.

The next American probe, Mariner 9, was launched on May 30, 1971, and successfully placed in its transfer orbit for Mars. There had been two probes launched, but Mariner 8 had failed to reach orbit. The programming of Mariner 9 was adjusted to compensate so that it would take over some of the functions of the failed probe, but this was at the expense of some of its own planned duties. The Russians also launched Mars probes. One of these failed, but Mars 2 was launched on May 19, and Mars 3 was launched on May 28.

Mars was not willing to cooperate with the Earth probes. Just as they neared the planet, the worst dust storms in years obscured the surface, making photographic survey next to useless. The Americans' Mariner 9 arrived in orbit in November and was immediately shut down to conserve its batteries and to wait out the storms. The Soviet craft were not to be so lucky. They could not be shut down in this manner because they had been preprogrammed to fulfill their functions as soon as they entered Mars orbit. They launched two smaller probes that were intended to soft land on the surface. The first one crashed into the surface; the second landed, turned on its camera, and then went silent. Both were likely casualties of the storms. Meanwhile, the orbital components of the Soviet craft busily snapped photos of a blank, featureless dust storm until their power was gone.

America's Mariner 9 slept, biding its time, and after a month the dust subsided enough for it to begin its task of mapping the surface. Its first pictures were as surprising as those of the earlier probes had been, but in a different way. They showed giant volcanoes such as Olympus Mons, the tallest mountain in the entire solar system, and a canyon that extended a quarter of the way around the planet. The photos also showed what appeared to be dry riverbeds. Mars once had liquid water! Continued surveying showed that Mars seemed to divided into two distinct sections. Southern Mars consisted of ancient, heavily cratered highlands; northern Mars of younger, smoother plains and volcanic features.

Viking and the "Face"

For the humans, the possibility of life on Mars was beginning to look rosy again. Water had been present, at least in the past, and might still be beneath the surface in the form of permafrost. On August 20 and September 8, 1975, two spacecraft called Viking 1 and Viking 2 were launched toward Mars by America. For these two craft, the search for evidence of life was their dominant, although not their only, purpose. The two craft consisted of two parts, an orbiter and a lander. The landers touched down softly and successfully transmitted photos of the areas known as Chryse and Utopia. They carried sets of three experiments designed to detect microbial life in the soil of Mars. Two of the experiments gave positive results, while the third did not. This puzzling outcome was finally decided to be the result of the actions of certain types of clay that can mimic, to some extent, microbial action on nutrient solutions. The organic chemistry tests that Viking also did on soil samples yielded even worse results. No organic chemicals were detected.

At first glance, the photos sent back by the orbiting components of the Viking craft, while awesome to scientists, were not heartening to those looking for evidence of Martians. At least, not at first. There were, however, a couple of frames that showed something that looked like a "face". The National Aeronautics and Space Administration dismissed them as a "trick of light." However, in 1979, two computer scientists with no particular expertise in Martian geology, Vincent DiPietro and Gregory Molenaar, who were working for a contractor at NASA, came across frame 35A72 while going through the Viking photo archives. They computer enhanced the image and concluded that the Face was not a trick of light after all. They also found several mountains that looked like "pyramids" near the Face, and published a book calling attention to the structures. Over the next decade, others found what they said were "cities" and other structures in the Viking images. The debate raged.

In the meantime, a Russian probe and an American probe mysteriously stopped transmitting just as they entered Mars orbit. These events added fuel to the controversy about the "face".

Mars Pathfinder and Mars Global Surveyor

In 1997, the Americans'Mars Pathfinder landed on Mars and the little rover on board called Sojourner captured the Earth's imagination as it moved about from rock to rock, although it found no sign of life. The arrival, later in 1997, of its sister probe, the Mars Global Surveyor, was awaited anxiously, because NASA had promised the public that they would make a special effort to photograph the "face". They did so, but to everyone's disappointment, it no longer looked like a face. With the light coming from a different direction, it looked more like a giant muddy footprint than a face. Here is a comparison of the Viking and Global Surveyor images from Malin Space Systems.

In 1996, NASA scientists shocked the scientific world with claims that they had found fossil evidence of life in a Martian meteorite that had been discovered at Antarctica. The meteorite was found in 1984 in Antarctica’s Allan Hills ice field and designated ALH84001. It was only in 1993 that scientists determined, on the basis of chemical analysis of gases trapped inside it, that the 4.5-billion-year-old rock was blasted away from Mars and floated through space until it fell to Earth. Tiny worm-like structures, resembling fossilized bacteria found on Earth, were found inside the meteorite. The jury, however, is still out on whether these tiny structures are proof of Martian life. No solid vedict on these claims has been reached.

Humans have not yet given up hopes of finding some form of life on Mars. There is solid evidence that Mars was once more Earth-like, warmer and with oceans and rivers. There are large quantities of water ice at the poles, and some of the violent storms near the poles contain water ice crystals, as this Hubble image shows. There is sometimes frost or snow on the Martian surface even away from the poles, and there may be water permafrost beneath the surface. Large caves have been discovered on Mars as well.

For more information about current Mars missions, see Missions to Mars

What if no life is found by any of the probes? Humans have the technology, and they might, if the expense can be justified, someday send a manned expedition to Mars, whether evidence of life is found or not.

Terraforming

Many scientists are beginning to think in terms of making Mars habitable in the future, by a process known as terraforming. Terraforming is, literally, the process of making Mars more like the Earth. This would involve:

1. Warming Mars up. Although Pathfinder found the daytime temperature to reach 70° F, the nighttime temperatures plunge to -100° F.
2. Giving Mars more atmosphere. The air pressure on Mars is as low as 1/100th that of Earth.
3. Putting more oxygen in the atmosphere.
4. Making liquid water readily available.
5. Providing protection from the strong ultraviolet rays bombarding the planet.
6. Introducing life on Mars.

Most of the speculation about terraforming Mars involves (1)warming the planet first. Two main ideas are proposed. One is to cover the surface, or at least the poles, with some sort of dark dust, perhaps mined from one of Mars' moons. The darker color would absorb more heat and raise the surface temperature. The second idea is to place giant mirrors in orbit around Mars to focus light & heat from the sun on the poles. Either way, the idea is to melt the frozen carbon dioxide that is at the poles. The additional carbon dioxide thus released into the atmosphere would increase the atmospheric pressure and would also increase the greenhouse effect and warm Mars even more. Both of these would contribute to making liquid water available(4), and as Mars gradually warmed even more, then water vapor would be produced, which would also contribute to giving Mars an atmosphere(2). As Mars warmed, the water ice in the permafrost beneath the surface would melt, and surface water would form lakes and rivers and maybe even seas. A thicker atmosphere would have better heat-retaining capability, which would help to reduce the large drop in temperature at night. Another option that is sometimes mentioned is to introduce CFCs(chlorofluorocarbons) into the atmosphere. However, these chemicals would work against the later formation of an ozone layer, which is what would be needed for (5).

The next step, and one that is fascinating, is to introduce life, especially one particular form of life known as blue-green algae(6). This particular form of algae can exist at a wide range of temperatures, and it converts carbon dioxide into oxygen rather well(3). More oxygen means more atmospheric pressure, plus, the UV rays would react with the oxygen in the upper atmosphere to produce ozone, and that would produce the beginnings of an ozone layer to provide some protection from those UV rays themselves(5). In a few thousand years,Mars would be warm enough, wet enough, and have enough oxygen to support an ecosystem, particularly at the bottoms of deep craters, where the atmospheric pressure would be highest. Humans might then put colonies in the deeper craters or underground and they might even dig a series of canals to bring water in for agriculture. The settlers would likely still have to wear some sort of protective clothing and breathing apparatus, at least until they had adapted to life on Mars, if that ever became possible. There is a series of slides depicting how terraforming might gradually change Mars at: Future of Mars.

Of course, we might find that some type of life already exists on Mars. What then? Terraforming would probably destroy it. Would humans have any right to do so, even if the only life they found were some form of bacteria in the soil?

Print References: • Cosmos by Carl Sagan • The Demon-Haunted World by Carl Sagan • A Treveler's Guide to Mars by William K. Hartmann