Mars: the most beguiling of the planets;

a lecture by William Sheehan
given to the Astronomical Society of South Africa
at the old Union Observatory
Johannesburg, South Africa
October 10, 2001

It's a great pleasure for me to be in South Africa. I remember growing up and being tantalized by the great Mars images obtained in 1939 & 1954 by Earl C Slipher at Bloemfontein, above all the color images - by far the best of their era - obtained in 1954 & 1956 by W. S. Finsen with the 26½-inch refractor just down the hill from where I am speaking tonight. For a long time, the two leading observatories monitoring Mars were the Lowell Observatory at Flagstaff, Arizona and the Union Observatory at Johannesburg, South Africa; both had the power to pique the imagination of one who, as early as at age ten, was rapt with Mars.

A hundred years ago, H. G. Wells, in his science-fiction classic The War of the Worlds, envisaged large-brained, octopus-tentacled Martians arriving on the Earth to begin the conquest of the brave new world they had chosen for their home ( they were thwarted not by men but by the least of our microbial brethren, bacteria - germs to which the Martians had not acquired immunity ). Now an invasion is indeed fully underway - not of the Earth by Mars, rather of Mars by the Earth.

From prehistoric times, Mars appeared as a "wandering star" which perennially flared into angry brilliance; then, seemingly appeased, it retreated again into safe and distant obscurity. Like a mountain seen from afar, it long formed a remote backdrop to human activity. Perhaps its presence was noted by our wandering ancestors of the savannah, whose footprints crossed the Laetoli plains of East Africa. Certainly it must have been remarked by the European cave-dwellers of the Ice Age, who saw in our seven dipper stars the form of a she-bear (Ursa Major) 30,000 years ago and followed the tracks of the Moon and the brighter planets. These wanderers - a little like Leonardo da Vinci's sinistral handwriting - generally trend in a backward direction ( but see below ); i.e., they move right to left - west to east - relative to the general drift of stars. Recently, the cave paintings of Lascaux, which date back 18,000 years, to before the last Ice Age, have been found to contain depictions of star-groups, including the Pleiades, Taurus the Bull, and Corona Borealis.

From a vivid red dot among the rest of the stars, Mars has come to loom steadily larger in our field of view. In our own time, it has become a mountain all but filling it. But if there is something to the mountain analogy, then the mountain Mars begs to be climbed. "Every high mountain," writes historian Daniel Boorstin, "was idolized by people who lived in its shadow; the Hindus had their High Places, the Himalayas; the Japanese had their Fujiyama; and the Greeks their Olympus, with a purer air, a whiter clarity, where the gods could taste of happiness forever." We have - Mars.

Are we alone in the universe, or a mere detail dictated by the "cosmic imperative"? Clearly we can answer these questions only by familiarizing ourselves with worlds beyond our own. Mars is the most convenient and hopeful world where this perennial question - one of the most fundamental humanity can ask - can be tested.***

Mars has just passed ( on June 12 ) an exquisitely eventful opposition, its first of the new century, approaching within 67 million kilometers of the Earth. Oppositions are the perennial occasions on which Mars lines up on the side of its orbit opposite from the Sun to the Earth, minimising the separation between the two. At the present opposition, Mars was 26 degrees south of the celestial equator, which put it practically overhead from Johannesburg. If a Martian would have dropped a plumbline from the zenith, it would have hit us on our heads (!).

It has now retreated far from the Earth, but will be coming to an even better opposition on August 28, 2003, and once again very favorably placed in the South African sky. Reaching a distance of less than 56 million kilometers, the red planet will actually be marginally closer than at any time in all human history.

These first two oppositions of the 21st century are remarkably favorable; a suitable beginning to a century that may well deserve to be remembered as the "Martian" century - a century in which a flotilla of automated spacecraft will set out to explore Mars, to be followed, in time, assuming all goes well, by manned missions. It is even likely that the first man (or woman) to set foot on Mars has already been born.

But why should we go to Mars?

Human fascination with Mars stretches across millenia. I will briefly describe the history of that fascination, also some of the themes that seem to be of current importance. No other planet beyond the Earth has so richly beguiled humanity as Mars.

To begin with, this may have had something to do with its vivid color. The reason for the red color is indeed the same as that for the reddish color of a drop of blood - when ferrous iron in Mars's soil combines with oxygen, it turns to ferric iron, more popularly known as rust - the same chemical reaction that is harnassed in the hemoglobin molecule. Mars, indeed, has always reminded men of a drop of blood. We now know that, in a real sense, it is quite literally blood-red.

To early star-watchers - less jaded perhaps than we are - the red color of Mars evoked a strong emotional response. For that matter, there can be no doubt that red is a special color - it is especially reactive on our nervous systems.

As primitive vocabularies grow to describe colors, the first color they include after black and white is red. It is the last part of color vision to disappear in cases of brain damage, also the first to come back during recovery. It is an ambiguous stimulus; red signals danger, as in the eyes and bodies of some poisonous tree frogs, but it is also a sexual attractant. From the red star Aldebaran (the eye of the Bull) we get the familiar phrase "seeing red." Flowers use it to attract insects, while cosmetic makers (and restaurateurs) know its ability to command attention and heighten sensual arousal.

Though Mars early collected around itself a raft of mythological associations - usually inspiring thoughts of warfare and bloodshed - it wasn't until much later that it began to be the subject of scientific inquiry. At first its motions were of interest. Discuss *Retrograde motions, when Mars walks "crablike" - backward - across the sky. Ptolemy's theory. Copernicus's theory. Tycho Brahe, the wizard-figure who lost his nose in a duel and who, in reverence, always sauntered out under the heavens in his robes. 1609 - publication of Kepler's laws, based on Kepler's methodical reduction of Tycho's observations of Mars, of the elliptic motions of the planets. The shape of Mars's ellipse explains, by the way, why its oppositions aren't all created equal.

Kepler was a dreamer as well as a man of exact calculation. He dreamed of a more illustrious era than his own troubled lifetime, fraught with fighting between Catholics and Protestants, when Germany and later Bohemia were ravaged by the Thirty Years War and when even the dead scholar's bones could not achieve piece - the cemetery in which he had been laid to rest was dug up for a battlefield. He dreamed of when men would learn to fly, and reach the Moon or even the other planets: "Ships and sails proper for the heavenly air should be fashioned. Then there will also be people, who do not shrink from the dreary vastness of space." Such sails and ships remained centuries off, but Kepler's wide-ranging imagination conceived of them.

When they finally came, those sails and ships would follow elliptical paths around the Sun, and on approaching the Moon or a planet would be swung into elliptical paths around them. The laws of spaceflight are also Kepler's laws. The open road to Mars was paved by the mind of Johannes Kepler from a dingy little room in Prague.

So even before it began to emerge as a planet - a rotund world, a place - like our own, Mars, in the work of Tyco and Kepler, had already helped us to define our place in the universe.

The same year Kepler published his first two laws, the telescope was invented. Kepler applauded the instrument: "O you much knowing tube, more precious than any sceptre. He who holds you in his right hand, is he not appointed king or master over the work of God!"

The first telescopes were too small and optically inefficient to show much of anything on Mars, a small planet, never less than 140 times the Moon's distance from the Earth. It could be dismissed by the late seventeenth century astronomical writer Bernard de Fontenelle as "not being worth the trouble" of stopping at. The result of observational astronomers was not quite a negative summation. In 1659, the Dutch astronomer Christiaan Huygens, son of a diplomat, poet, and confidante of the artist Rembrandt, first recognized dark patches - in particular, the one long known as the Hourglass Sea and late called Syrtis Major, the Great Bog , which allowed him to work out the period of rotation, 24-plus hours. (I pause here to note how significant - for the citizens of a small country with generally lackluster skies - the contributions of the Dutch astronomers have been, beginning with Huygens. Let me say to any members of the audience who may be of Dutch descent, "Goienaand, Hoe gaan dit? Goed dankie."). Huygens and Giovanni Cassini, the leading astronomer at the Paris Observatory at the time, independently made out the bright south polar cap. Cassini's nephew, Maraldi, who also worked at the Paris Observatory, and added the discovery that the cap was not centered directly over the rotational south pole. Thus the coldest point on Mars does not coincide with the pole itself. (We now know that Maraldi was absolutely right: the point where the cap's elevation is greatest is offset from the pole by 225 kilometers).

Maraldi deserves to be considered the first explorer of the Martian Antarctic. Maraldi, curiously, hedged as to the nature of the caps; the first person to suggest that the caps were snow was William Herschel, who wrote, "the bright polar caps are owing to the vivid reflection of light from frozen regions."

The reason for the interest in the Martian Antarctic is that the south polar cap promises to be one of the richest areas in which to hunt for water on Mars. As has long been known, the cap becomes very large during the southern hemisphere winter; but it is almost entirely composed of dry-ice (frozen carbon dioxide), and is rapidly eaten away during the Martian summer to a small residual cap. (The residual north polar cap, on the other hand, consists of a mixture of water and carbon-dioxide ices.) However, as spacecraft observations have shown, the small residual cap of frozen carbon dioxide stands upon a large southern plateau, extending nearly 100 kilometers beyond its outer edge, and it is quite possible that this plateau consists mostly of buried ice.

At the present epoch, the Martian ice caps are found (in spacecraft images) to be surrounded by abrupt scarps rimming their perimeters, strong evidence that the cap margins are eroding in the current Martian climate. Also, both polar regions are surrounded by vast tracts of layered terrain. This means that there were once much larger polar expanses in the remote past. Yet if Mars once sported much larger caps of ice, where is all the water now?--That, for Mars, is the question.

Detailed studies of the polar caps were first carried out in the nineteenth century by an Italian astronomer - one of the greatest observers of Mars of all time - Giovanni Schiaparelli. He was the uncle of the fashion designer, Else Schiaparelli, and would become known as the man who created a new fashion of looking at Mars. Schiaparelli (the astronomer) was born in Savigliano, Italy, in 1835, educated at Turin, and after studying at Berlin and Pulkova, rose to the directorship of the Brera Observatory in Milan. His great work forging a link between comets and meteors was carried out there. (Among other things, he showed that the August meteors, the Perseids, were debris thrown off from Comet Swift-Tuttle of 1862. He later showed that the Leonids - which may put on a spectacular display in November of this year - were debris thrown off from Comet Tempel-Tuttle. Since this comet circles the Sun once every 33 years, when the Earth crosses the part of the comet's orbit soon after the comet itself has been there, spectacular showers of meteors have been seen, such as the great storms of 1833, 1866, and 1966. There's a good chance we may be in for another "meteor storm" this year.)

Schiaparelli's career as a planetary observer did not begin until he was over forty, and awaited the hitherto optically-challenged Brera Observatory's acquisition of a decent telescope - an 8.6-inch (22-cm) aperture Merz refractor. I had the opportunity to visit Brera in March of this year, when I was asked to give a talk on Mars at the Hoepli Planetarium. Unfortunately, I left my slides at home, so I'll have to do my best to describe it to you. The observatory had been founded in 1760 by Roger Boscovich, as part of the Jesuit college established in the old Spanish Palazzo of Brera. It is down the street from the famed opera house La Scala, and boasts its own art gallery founded by Napoleon. Today it is mainly used as a studio for training artists and designers. One enters from the Via Brera; passes into a colonnaded square, arrayed with copies of classical sculptures - nymphs and heroes, gods and goddesses - and by means of a stairway (just down a hall set off with a niche occupied by a marble Patroclus in the arms of Menelaus) progresses, in Dante-esque fashion, "to the stars." The dome was on the rooftop, in Schiaparelli's day, looking out upon the still pellucid skies of Lombardy. In the summer the air boiled violently above the red-brick tile rooftops heated by the afternoon sun, but at other seasons the seeing was often magnificent. Clouds of industrial smoke did not yet hang heavily in an oppressive cope over Milan's rooftops, cathedral, and observatory.

In 1877, Mars came to one of its very favorable oppositions - almost as good as that of 2003 will be. In Washington, D.C., Asaph Hall discovered the two miniature moons of Mars, Phobos and Deimos. Despite the grandness of the opportunity, Schiaparelli was a methodical man, and does not, at first, seem to have been particularly interested. He was busy doing routine work - measuring double stars. Then one night in August, while watching an eclipse of the Moon, he decided to turn his telescope on Mars. One can still imagine the magic of that night; it was a scene that might have been scored by Verdi (Schiaparelli's neighbor; La Scala, the famous opera house, is just down the street from Brera). Eclipsed blood-red moon, and Mars, nearby, glowing like an ember in the sky. A dark, olive-skinned, bearded man, with sharp penetrating black eyes, turns the telescope toward Mars. What floats into his telescope is wonderfully enchanting: a beautiful faberge-egg of a planet, a salmon disk streaked here and there with patches of cinnabar, vermillion, and cinnamon-brown. His first vision is confused; "I must admit," Schiaparelli wrote, "on comparing the aspect of the planet with the recently published maps this first attempt did not seem very encouraging." But his interest had been stirred. He made a first sketch, then returned to the planet again a few nights later. The markings began, with practice, to gather into recognizable shapes. From the first look of a curiosity-seeker, Schiaparelli became a dedicated connoisseur of the Red Planet. He resolved to draw up a new, more accurate, map, on which he would introduce a nomenclature based on the geography and mythology of the classical world. He was a passionate classicist, immersed in the old literature. Such names as Syrtis Major, Chryse, Utopia, Elysium, and Tharsis, still in use today, were first introduced on this map. He also made out linear markings - *canali*, he called them, from the Italian word meaning grooves or channels (and, I hasten to add, not necessarily artificial). They extended between the dark patches which he regarded as water-filled seas (of which more anon!)

From the comfort of his warm Italian observational redoubt, Schiaparelli also provided full descriptions of the chill Martian polar regions, comparing them with those of the Earth. Schiaparelli returned to his tower to observe Mars again at the oppositions of 1879, 1881, 1884, 1886, 1888, and 1890 - launching expedition after expedition, unfurling his telescopic sails upon the seas of interplanetary space. Like the Portuguese Henry the Navigator, who from his rugged promontory at Sagres had sent caravel after caravel to reach farther and farther around the unknown coast of Africa, a series of expeditions that would culminate (after Prince Henry's death) in the triumphs of Bartholemieu Dias and Vasco da Gama, so Schiaparelli, from his observatory in Milan, commenced the "first organized continuous enterprise" into the unknown world of Mars. He was in his day in the forefront of Martian research - and he knew it. He wrote to his friend, the Belgian astronomer Francois Terby, in 1886 that he had begun the exploration of "a New World, this world of Mars ... which we must conquer little by little. It will be a less difficult and bloody conquest than the exploits of Cortes and Pizarro. But there are, alas, no more than ten observers seriously occupied with it even during the most favorable periods of the oppositions."

All that was about to change. A man who always regarded Schiaparelli as his "maitre Martien" (Martian master), but who was to surpass even his master in the ability to raise public interest in the planet, appeared suddenly on the scene. This was the American, Percival Lowell, who was (as his cousin James Russell Lowell said of Edgar Allen Poe) "two-fifths of him genius, and three-fifths sheer fudge." He was an amateur; perhaps the greatest amateur of his time. Through his influence, enthusiasm about Mars attained to a greater pitch than at any time before or since. He was born in 1855, scion of one of the oldest, wealthiest, and most distinguished families in America (according to the well-known toast, "in the town of the bean and the cod,/ Lowells talk only to Cabots,/ and Cabots talk only to God.") Harvard-educated, Lowell in his twenties took on management of some of the family's business interests, including cotton mills, trusts, and electric companies. However, he became profoundly dissatisfied with this conventional upper-class role. After six years of business and a romantic crisis in which he broke off an engagement to an unidentified socialite, he bailed out and booked passage to Japan. He spent a decade living mostly in the Far East, served as the American diplomat to Korea, and wrote four books about a part of the world then little known in the West. (In Japan, he is still regarded as one of the hundred most important men of the twentieth century - for his role as a diplomat and his books about Korea and Japan, not for his thinking about Mars.)

Despite an initial attraction to Japanese art and gardens, Lowell's romantic impulse for the Far East was soon tempered by his irritation at what he came to regard as the inefficiency and irrationality of premodern people. As his infatuation with the Far East waned, his mind increasingly returned to a dormant boyhood interest in astronomy. At Christmas 1893, he was stirred by reading a book by the French astronomer Camille Flammarion: "The present inhabitation of Mars by a race superior to ours is very probable." Flammarion quoted Schiaparelli, who in the 1880s had recorded changes in some of the dark markings on the surface of the planet and had exclaimed: "The planet is not a desert of arid rocks. It lives!" Here was a destination even more exotic and romantic than the Far East. Lowell was thirty-nine years old when he decided to give up everything else in pursuit of his Martian obsession. It might seem an advanced age for a new career - not, however, when you're a Lowell and neither money nor security are factors. He was neither as old as Columbus when he set his westward course for the Indies nor as old as Schiaparelli when he first took up the study of Mars.

Funding his interest with his personal fortune, he borrowed a telescope, an 18-inch refractor by Pennsylvania optician John A. Brashear, and went west, to Arizona Territory, to observe Mars for its forthcoming opposition in 1894. He was assisted by Harvard astronomer William H. Pickering, just back from Peru where he had observed Mars with one of the finest refractors ever made, a 13-inch Alvan Clark -- it is now at Bloemfontein! - and on indeterminate leave, also Pickering's assistant A. E. Douglass. Lowell's observing logbook records his first impressions with the 18-inch. On June 1, 1894, Mars was still four months from opposition; inconveniently placed before the dawn, it had to be sought by early-risers at 3 o'clock in the morning, to whom it appeared as a small gibbous in the field of the eyepiece. Even so far away, its disk tantalized and rewarded scrutiny: "Terminator shaded," Lowell mused, "limb sharp and mist-covered forked-bay vanishes like river in desert." Lowell's use of the term desert is remarkable, given that contemporary views of Mars - including Schiaparelli's - stressed an interpretation of the planet in which the dark areas were oceans, the lighter areas lands. But Lowell's imagination had already been captured by the starkly beautiful Arizona deserts located south of the fir-covered mesa on which he had built his observatory, and it continued to be stirred by such vistas, especially those of the Painted Desert as seen in remote perspective from the San Francisco Peaks. So-called because the marls and soft rocks of which the hills are composed are of many colors - chocolate, red, vermillion, pink, buff, and gray - the Painted Desert conjured up for Lowell the same delicate palette of colors he found in the Martian globe: The resemblance of its lambent saffron to the telescopic tints of the Martian globe is strikingly impressive. Far forest and still farther desert are transmuted by distance into mere washes of color, the one robin's-egg blue, the other roseate ochre, and so bathed, both, in the flood of sunshine from out of a cloudless burnished sky that their tints rival those of a fire-opal. None otherwise do the Martian colors stand out upon the disk at the far end of the journey down the telescope's tube. Even in its mottlings the one expanse recalls the other.

From the first, Lowell was keen to see the canali -- or canals, as they had already become universally known in the English-speaking world. But they were all but absent from the disk. Indeed, in June, he had confided to his notebook: "With the best will in the world, I can see no canals." Was it possible his expedition to the Arizona Territory had been for naught? He returned, briefly, to Boston in July, having made out only a few of the canals; but on his return to Flagstaff in August, they were a blooming presence on the disk (though seen only a few at a time in moments of exquisite seeing). They were there along with the dark spots (seen by Pickering from Peru in 1892 and called by him "lakes" his brother, Edward Pickering, the director of Harvard, had wired back skepticism, "how do you know they are lakes?") which partook in the sweeping changes affecting the rest of the disk; changes not so much of size as of color. The lakes deepened and became richer in hue, which to Lowell's mind gave a clue to what they were. They seemed like Flagstaff itself, a verdant spot on the verge of a desert. "When we put all these facts together," he wrote, "... one solution instantly suggests itself of their character, to wit: that they are oases in the midst of that desert." And he continued: "Here then we have an end and reason for the existence of the canals and the most natural conceivable one - namely that the canals are constructed for the express purpose of fertilizing the oases.... And just such inference of design is in keeping with the curiously systematic arrangement of the canals themselves.... The whole system is trigonometric to a degree."

The straightness of the canals (their traveling along geodesic lines, the shortest distance between two points on the planet's surface) could mean only one thing: they were artificial. This was not such a howlingly unreasonable surmise. One of the first things stressed in art schools has always been that nature never draws a straight line, a principle abundantly borne out by the astronauts' views of the Earth from orbit. As Story Musgrave, veteran of six Earth-orbital flights in the Space Shuttle, once told me: "Nature never makes a straight line; every time you see a straight line that's humanity at work. Nature likes curves, humans like straight lines"). Given the existence of a network of linear markings like the canals of Mars - assuming they were true features of the planet, and had the forms depicted in Lowell's drawings - his deduction became not only logical but inescapably so: they must be the handiwork of denizens of the planet.

This, in a nutshell, was Lowell's theory: Mars, being a smaller world, had evolved more rapidly than the Earth; it had already lost much of its water-supply, and was well on its way to utter desiccation. In order to survive, its inhabitants had had to build a vast system of irrigation channels to transport precious water from the melting polar caps to the equatorial regions. These, Lowell deduced, were the system of canals that Schiaparelli had first recorded in 1877. (One must consider this in the light of the day - it was an era of railroad building and canal building. The Suez Canal had been completed in 1869, or virtually on the eve of Schiaparelli's discovery of his lines on Mars.)

All this Lowell deduced from the small and blurry images he obtained through his 18" Brashear telescope, images of a planet never closer than 56 million kilometers from the Earth. He clung to this belief - despite a withering tide of opposition from professional astronomers - right up until his death in 1916.

We now know that the Martian canals were illusions - their reality was finally disproved when Mariner 4 bypassed the planet in 1965, showing a heavily createred surface like the Moon's but no canals. They are artifacts of the eye-brain system's tendency to link up disconnected patches and chaotic details into order and system. In larger telescopes - and in spacecraft cameras - the canals disappear like the face of the "Man in the Moon" into a mass of irregular details. But Lowell's influence was more lasting than the canals. For a long time a broadly Lowellian view of the planet - with a wave of darkening sweeping down from the melting polar cap observed seasonally, and suggesting to most astronomers the active processes of vegetable growth and decay - continued to be in vogue, while his vision of embattled Martians struggling to stave off the impending doom of planetary desertification lived on in the science fiction of H. G. Wells and Edgar Rice Burroughs, but also of Ray Bradbury, who still featured canals prominently in the landscape of *The Martian Chronicles* as late as 1948.

The first spacecraft vistas of Mars - woefully selective, and obtained over a series of postage-stamp regions of the planet representing only one percent of the surface - were obtained by Mariner 4 in 1965. The images came as a shock to generations who had been suckled on Lowellian romances. Mars appeared to be another moon; stark, cratered, forlorn. Two more fly-by Mariners, in 1969, shortly after the Apollo 11 landings, did nothing to change the dour impression.

Finally, Mariner 9, which went into orbit in 1971, showed the real Mars, or much more of it than the flyby Mariners had shown. Mars was no mere lunar wasteland of cosmic bombardments from the embryon ages of the Solar System. After emerging from a violent youth which it shared with other planets, it has continued to evolve, and bears on its surface the legible hieroglyphs of change inscribed boldly in polar caps asserting the importance of seasons and in aeolian features attesting the action of forces of erosion and deposition. There are patent signs of great geological upheavals: shield volcanoes such as Ascraeus Mons and Olympus Mons, towering 25 kilometers above the Martian sea-level and far more imposing than the Hawaiian shield volcanoes of the Earth. Equally impressive is a vast equatorial-trending canyon rifting the crust a sixth of the way around the planet's circumference - a failed tectonic rift. This is the Grand Canyon of Mars, Valles Marineris, next to which the Grand Canyon of the Colorado or even the Great Rift Valley of East Africa pale into insignificance.

Above all there are ancient floodplains and dry river valleys, which prove that water was once abundant and flowed freely on the surface of Mars. There were deluges covering the surface to depths of hundreds of meters over hundreds of square kilometers, there may even have been in the Northern Hemisphere - though the evidence is much debated - seas. And where there was water, could life have been far behind?

Twenty-three years ago, the two Viking landers first looked out, from ground-level, upon the surface of Mars. Because they were first - and to increase their chances of safe arrival - the Viking landers were directed to flat-lands, bland and featureless rolling plains of Chryse (the Land of Gold) and Utopia. More daring was Pathfinder, which arrived at the Ares Vallis flood plain near the equator, on American Independence Day, 1997 - cushioning its plunge onto the Martian surface by coming down on a pillow of airbags. Its first pictures made those of the Viking landers look bland by comparison. Now bone-dry, the Ares Vallis landing site - located at the mouth of the ancient flood plain - bears evidence even to non-geologists of past catastrophic floods. Boulders in the so-called Rock Garden have flat tops, and are slanted and stacked in the same direction; frozen in positions where they were abandoned by torrents washing down the valley. Some are igneous; others display the layered structure suggestive of sedimentary (sediment-deposited) rocks.

The skies of Mars present an intense, ever-changing panorama. Despite the thinness of the Martian atmosphere (about the same thickness as that of the earth's stratosphere), it has been known, ever since Viking 1, that the Martian skies are remarkably bright ("like the skies over Los Angeles on a smoggy day"). Early in the Viking mission, their color had at first been rendered in evocatively earthlike blue. In the end, it was decided it was no true-blue; rather the product of our having so long drunk, to intoxication, the idea of an earthlike Mars. Later images were recalibrated with greater sophistication to Martian salmon-pink. The Martian sunrises are majestic Homeric stirrings: glorious bursts of color and light in a white sky tinged with the faintest hint of blue, lilac- rather than rosy-fingered affairs. As the Sun climbs higher above the horizon vanish vanished without a trace, and the skies revert to dusty brownish-orange - the strange skies of a rust-red world.

So far, Pathfinder is as close as we have gotten to Mars, though incredible results have also been obtained from the Mars Global Surveyor, which has been monitoring the planet from orbit, and more are expected when the next spacecraft, NASA's 2001 Mars Odyssey, enters orbit two weeks from now.

What is it we will find out?

I can tell you what we *want* to find out. Above all we want an answer to the question: where has all the water gone? Probably deep beneath the surface, where the water is trapped as permafrost and, at great depths, even as underground rivers. Apparently, however - and there is tantalizing data from Mars Global Surveyor to support this - under certain circumstances it can flow, and has flowed, even in the relatively recent geological past, onto the surface; breaking the mold as the chick does the shell, bringing relief to the otherwise eternal and unrelenting aridity of the Martian deserts. It is obvious that these outbreaks of water-seepage onto the surface must be triggered by local climate changed. In the past, however, the global climate on Mars was obviously much more benign than at present; the planet had a thicker atmosphere, and liquid water flowed on the surface to produce the dry riverbeds discovered by Mariner 9. We know there were organic materials likewise - carbon-based, complex molecules - mixed in with the ices that fed the planet from comets (which ultimately came from David Block's all-pervasive cosmic dust) just as on Earth.

The raw materials seem to have been present - liquid water and organic molecules - for life to have formed on Mars. Hence, in part, the excitement over the possible fossil life-forms - nano-bacteria sized - in a Martian meteorite announced with much fanfare in 1996. The case, by the way, remains highly controversial. Since meteorite's do arrive from Mars, obviously - about a baker's dozen have been identified, including a bit alleged to have struck dead a dog at Nahkla, Egypt, in 1911 - it is even possible the seeds of life on Earth were sewn from Mars. In that case we ourselves are - Martians.

If life did develop independently on Mars, we want to know how far that life resembles life on Earth - both in general plan and in detail (e.g., are the same amino acids used; the same nucleic acids; are the DNA and RNA used like that in ourselves, etc.?).

If life did not develop on Mars, it will be equally important to know that. Is life a "cosmic imperative," to use the phrase coined by Nobelist Christian de Duve in his best-selling book *Vital Dust*, is it written into the heart of the evolution of the planets from their dodgy beginnings in meteoritic fire-storms - or even earlier, during their incubation in the gloomy, cold, but protective and harboring womblike caves of interstellar dust-clouds? Is it common, or is it a rare happening? Are the starry skies at night filled with the eagle-aeries of other beings; or are they vast uninhabited deserts, in which case we are alone, terribly and inconsolably alone, in the cosmic voids?

Are the worlds in space rife with life, or are most of them tenantless, hanging empty like rejected weaver's nests?

Mars is our best chance so far to learn the answers to these perennial questions -- questions that have burned in the human imagination ever since Mars was perceived only as  a glowing coal in the dark cave of the night-time sky.

Bill Sheehan