Destination Mars

by Rod Pyle

  Pulling farther back, we can see that almost half the northern hemisphere is covered by the Borealis Basin. Its origins are uncertain, but it was likely the result of a huge, planet-shifting impact. What is apparent is that there are far fewer craters in this area, and the Tharsis Bulge was formed subsequent to the events that spawned Borealis. If it is an impact feature, it would again be a record setter as the largest in the solar system. And the object that impacted Mars would have been about the size of Pluto, and probably arrived during the Late Heavy Bombardment period of about four billion years ago.

  In the southern hemisphere can be found Hellas Planitia, another huge impact basin, about 1,430 miles wide with a depth of about 30,000 feet. It is so deep that the atmospheric pressure at the bottom is about 90 percent more than at the surface, enough to allow liquid water to exist for brief periods. While much smaller than the planet-girdling Borealis Basin, it is the largest obvious impact feature clearly visible on Mars. Like its northern cousin, it is thought to be about four billion years old.

  Drawing a line from Hellas Planitia through Mars's interior to the other side of the planet, we return to Alba Patera, home of the Tharsis volcanoes. It is hypothesized that the impact at Hellas was sufficient to cause at least part of the formations on the antipodal, or opposite, side of the planet, as the seismic shock rattled through, slamming into the far side.

  Much of the southern hemisphere, ranging a bit into the north, is extensively cratered, another result of the Late Heavy Bombardment, when copious amounts of interplanetary junk smashed into the rocky, or terrestrial, planets.3 Overall, the southern regions sit much higher than the northern hemisphere, and the crust of the planet is over twice as thick in the south.

  The geological record of Mars can be summarized in three eras:

  The Noachian Period, 4.5 to 3.5 billion years ago, was when the oldest parts of the planet that remain were formed. These regions are covered with extensive, overlapping craters and show more of them than other areas due to their advanced age. The Tharsis Bulge formed during this period in Mars's early, and violent, history.

  The Hesperian Period, 3.5 to about 3 billion years ago, when basaltic magma flowed out from the planet's interior and formed the filled basins we see today.

  And the Amazonian Period, about 3 billion years ago through today. Olympus Mons and its associated lava flows were formed during this period, and less cratering is evident due to their younger age. This topography can be quite varied.

  Maps of Mars list two general sets of features. The first are those differentiated by apparent brightness, called albedo features. Albedo is the amount of sunlight reflected back from another world. On maps, these have Latin names. One such example is the enormous Sinus Meridiani, or Meridian Bay, one of the few major features visible through a telescope from Earth. It is noteworthy that the darker of these features were originally thought to be seas or other bodies of water, and were named accordingly. Hence, some of the major features in this group are Mare Erythraeum (Erythraean Sea), Mare Sirenum (Sea of Sirens), and Aurorae Sinus (Bay of the Dawn). The largest dark feature seen from Earth is Syrtis Major Planum, a classical Latin name for a region near present-day Libya. Areas thought at the time to be dry land include Arabia Terra (Land of Arabia) and Amazonis Planatia (Amazonian Plain). The north polar cap is Planum Boreum (Nothern Plain), and the southern cap is Planum Australe (Southern Plain).

  Now it is time to discuss dirt. Earth has dirt, also called earth. But on Mars, and other solid bodies like the moon, one cannot properly refer to the soil as dirt. The proper term is regolith, from the Greek rhegos or blanket, and lith or rock. It denotes a layer of loose material over bedrock, essentially ground-up rocks. Spacecraft have studied or observed the regolith of our own moon, Titan (moon of Saturn), Venus, and Mars. In this book, however, we will generally refer to regolith as soil for the sake of expediency.

  Martian soil is highly alkaline, and apparently filled with perchlorate. It is highly toxic stuff, at least so far as lower forms of life are concerned. But the areas of Mars sampled as yet are small, and orbital data inconclusive, so the true nature of planetwide soil is yet to be decisively determined.

  Most of the planet is also overlain by a thin layer of oxidized dust, which gives Mars its red color. This dust is very finely grained and, when winds whip up, can stay suspended in the atmosphere for weeks or even months.

  The planet has two icy polar caps, some of the first features to be observed through early telescopes. With a tilt of about 25 degrees, these polar areas experience growth in the local winter and shrinkage in the local summer. This led many eighteenth-century astronomers, most notably Percival Lowell, to conclude that poles were water ice and melted in the summers, sending life-giving water cascading to the equatorial regions of the planet and contributing to the “wave of darkening” that seemed to occur every Martian year, thought then to be plant life gone wild as the moisture from the poles nourished it. We now know that the poles are a mix of a thin layer carbon dioxide ice, or dry ice, and water ice. The CO2 freezes groundward in the local summer and then is re-released into Martian skies in the summer. This seasonal exchange can account for over a quarter of the atmosphere freezing out, then being released back into the air. The water ice below also melts in the summer; evidence of flowing meltwater, once thought to be very unlikely, is seen in orbital images of the planet.

  In fact, the observation of subterranean and frozen water is becoming relatively common on Mars. At one time thought to be dry, arid, and dead, Mars is turning out to be quite active in terms of weather and erosional processes. Wind is of course the primary agent of erosion today, but water is slowly, stubbornly revealing itself more and more.4 The southern ice cap alone, the smaller of the two, is thought to have enough water tied up in its frozen reservoir to cover the entire planet to a depth of over thirty feet—but not for long. The atmosphere is so thin, at less than 1 percent of Earth's, that liquid water quickly boils away in the tenuous air. But scratch the surface, literally, and there is plenty of water ice all over the planet.

  That water was far more evident in the past than it is today, slumbering beneath the dust, dirt, and sand of the present Mars. Huge features called outflow channels, about twenty-five of them, litter the surface of Mars, indicating a truly massive and disastrous outpouring of water at some time within the last few million years—and smaller ones are still being formed to this day, via liquid water. There are also areas strongly resembling river deltas, alluvial fans, and channels that speak to a once-watery Mars.

  So what's the big deal about water? Simply this: life as we understand it needs water to exist. Increasingly, extreme forms of life on Earth are discovered that can survive on trace amounts and in hideously difficult environments, but all forms need some water. So when we find water in any form on Mars it is exciting, for it allows us to think, once again, of Martians…microscopic though they might be.

  And why are microbes on Mars so important? It's not like they will be the next explosive market for Big Macs® or directly impacting our daily lives if discovered. But the discovery of some form of life on Mars would be a game changer in other ways. Philosophy, religion, and of course science would all be rocked by such a discovery. The existence of life on Mars would, for some, seem to diminish our special place in the universe as humans. Of course, if this life were something more akin to streptococci than your next door neighbor, it's hard to get too intimidated. But for some, any discovery of life elsewhere would be a threat.

  For others, it would be a delight. The idea that life, that poorly understood miracle of amino acids and organic compounds, could have sprung up independently on another world is a big one. Some scientists have hypothesized that life may not have even begun here on Earth, that is may have started first on Mars and then hitchhiked a ride to Earth via a meteoric fragment. This idea has gained credibility in the last few decades, when meteors found on Earth (in Antarctica) were definitively traced back to Martian origin. And
, since Mars calmed down from its evolutionary throes much sooner than Earth, this idea makes some sense. Life could have slowly evolved there, then come to Earth and survived once our own planet was less volatile. It would certainly give the organisms more time to mature in evolutionary terms.5

  Of course, there are others who consider this to be hogwash, and still others who consider these ideas blasphemous. The former group will likely come around given sufficient evidence. The latter will never be convinced, regardless of the science; the idea is simply too threatening.

  The important thing is this: until we go to Mars, sift through the soils, test its properties, and search cracks, crevices, caverns, glaciers, the polar caps, the equatorial regions, and everything in between for microbial (or other) life, we will probably not know the answer. And it may well take the hand of humanity present on the surface of that cold, ruddy world to make this work—robots are simply too limited and too inflexible.

  It's almost time for us to visit the red planet. But first, let's look back a few millennia, to a time when Mars was not a destination, not yet even a plane, but a harbinger of death and destruction in the night sky.

  Of course, long before NASA's Vikings invaded Mars, the planet had been prominent in the mind of humanity. Viking was simply a logical outgrowth of our curiosity; a byproduct of the heyday of space exploration in the 1960s and early 1970s. This was a time of great political rivalries when the United States and the Soviet Union sought to show the world which political system was superior in both technological and economic achievement. It was, true to the time, a flexing of national muscles and a brute-force approach to space exploration—a war without bullets or bombs. America won the moon first and, despite some close misses by the Soviets, Mars as well.

  But the interest in Mars goes as far back as its visage in the night sky. Every major culture worshipped it until the Age of Reason; most commonly as a baleful godly eye. The late Babylonians addressed Mars as Nergal, representing fire, destruction, and war; in their system, Mars won out over the god of the sun, who was an earlier incarnation of Nergal, god of the underworld.

  The Hindus referred to Mars as the deity Mangala, born of the sweat of Shiva (another cosmic troublemaker), meaning “auspicious,” “a burning coal,” and “the fair one.” In Sanskrit, the name is Angaraka, a celibate (and probably frustrated) god of war. Egypt first called the red planet Horus Am Akhet (Horus on the horizon), then later Her Deshur (Horus the red). The city of Cairo is named after Mars, from Al Qahira, an ancient Arabic name for the planet.

  The ancient Chinese and Koreans saw Mars as a portent of bane, grief, war, and murder. It was named “fire star.” This followed the Chinese mythology of the Five Elements: wood, earth, metal, water, and of course fire. One can guess where Mars fell in the lineup.

  Plato's Greece called Mars Ares, the son of Zeus and Hera (of course he would be a warrior with these two for parents). Two of Ares's three children were Phobos (fear) and Deimos (terror), after whom Mars's two moons are named. Later Greece referred to the planet as Pyroeis, meaning “fiery.” In either identification, it's difficult to get past the idea that Mars portended a bad day.

  When Rome came onto the scene, it adopted the gods of Greece under new names. Ares became Mars, born of the goddess Rhea-Silvia, and producing two sons, Romulus and Remus. This led to the founding of Rome, so perhaps their warlike ways were preordained, as Mars was the most widely worshipped of their gods.

  By the Middle Ages, Europeans characterized Mars's influence over humanity in more detail:

  Mars rules catastrophe and war, it is master of the daylight hours of Tuesday and the hours of darkness on Friday, its element is the fire, its metal is iron, its gems jasper and hematite. Its qualities are warm and dry, it rules the color red, the liver, the blood vessels, the kidneys and the gallbladder as well as the left ear. Being of the choleric temper it especially rules males between the ages of 42 and 57.1

  Interestingly, while they may have missed the boat regarding gallbladders and “daylight hours on Tuesday,” NASA rovers have found hematite and, of course, oxidized iron in abundance on the Martian surface.

  In any ancient culture, Mars was one of a handful of planets visible to the naked eye, and the only one of marked color, so the planet demanded attention. Its distance to Earth varies with two-year cycles, and its brightness waxes and wanes correspondingly to the intersection of these orbits. At the far end of this ever-changing distance it is over 250 million miles from our planet and a dim red star, distinguished only by its very un-starlike motions in the night sky (all visible planets move at rates different from the starry backdrop). At its closest, about 35–62 million miles from our world (depending on the year), it is the third-brightest object in the evening sky after the moon and Venus, Earth's other close planetary neighbor. Add to this that Mars has the most elliptical orbit of any planet (only Pluto's is more elongated, but that small body was recently demoted from the roster of planets in our solar system).

  To further stand out from its astral competition, Mars did the remarkable: it moved backward from time to time. Called retrograde motion, when the Earth (which orbits inside the ellipse traveled by Mars) closes on Mars and passes it, Mars appears to go from a forward motion to a backward one (“retrograde”) when viewed against the backdrop of stars.2 Ptolemy came up with an explanation for this back in the Mars-worshipping days, but it assumed the Earth as the center of the universe and was mechanically flawed. Copernicus, as refined by Kepler, redesigned this mechanical explanation with the sun at its proper place at the center of the solar system, between 1510 and 1514 (the ancient Greek Aristarchus of Samos had posited this in the third century BCE, but it was traded off for the Earth-centric model). Kepler also spent an additional eight years working out the elliptical nature of Mars orbit, with the sun at one focus-point of the ellipse.

  In 1659, Christian Huygens, working in Holland, observed and drew Syrtis Major on a sketch of Mars. It was the first such recorded observation. Seven years later, in 1666, Giovanni Cassini measured the rotational period of Mars (i.e., its day) at 24 hours, 40 minutes (he was off by less than three minutes). Then, between 1777 and 1783, English astronomer William Herschel noted the axial tilt of Mars and deduced that it should have seasons not so different perhaps than Earth's.

  No matter how rational the great thinkers were regarding Mars, a planet (especially the color of blood) which occasionally traveled backward was sure to gain notoriety. Remember that in a time when electric lights were unknown and the entire world fell under a carpet of darkness except for the flickering flames in individual dwellings, a red star above stood out much more markedly than it does in modern times.

  But for our purposes it is the age of modern science, beginning in earnest in the 1800s, that is important. While men like Kepler toiled to develop concrete notions about the true nature of nearby space and the planets (including his laws of planetary motion), the pace accelerated dramatically with the advent of the large optical telescope.

  What was known about Mars at that time can be summarized thus:

  Fourth planet from the sun

  Smaller than Earth—about half of our planet's diameter

  Larger orbit than Earth's

  Thought to have no moons

  Thought to have oceans and continents

  Perhaps a thin, yet Earth-like, atmosphere

  And, in a colossal misinterpretation of telescopic observations, one English astronomer stated in 1860, “There is no portion of the planet Mars that cannot be reached by ship.”3

  Mapping Mars came into vogue in the late 1800s as well, with the advent of improved optics, larger telescopes, and better tracking mechanisms. Astronomers like Camille Flammarion, an influential French scientist and spiritualist; Asaph Hall, an American in government employ; Giovanni Schiaparelli, who assiduously mapped Mars's surface through his telescope; and Percival Lowell, an American amateur astronomer, began to understand Mars as a planet. It was, however, a somewha
t flawed vision.

  Flammarion (1842-1926) was perhaps the more interesting of the lot, as he was not just an astronomer with his own observatory (as Lowell would become) but also an avid spiritualist who believed, among other things, that Martians were trying to communicate with Earth. He was an avid student of the occult sciences, as he called them, and had spent time as a young man studying in a Paris seminary. Flammarion apparently believed in reincarnation and was very spiritual. Yet, when it came to Mars, he at least made the attempt to remain somewhat objective, considering the era.

  In 1873, he wrote:

  In Mars there is neither an Atlantic nor a Pacific, and the journey round it might be made dryshod. Its seas are [M]editerraneans, with gulfs of various shapes, extending hither and thither in great numbers into the terra firma, after the manner of our Red Sea. The second character, which also would make Mars recognizable at a distance, is that the seas lie in the southern hemisphere mostly, occupying but little space in the northern, and that these northern and southern seas are joined together by a thread of water. On the entire surface of Mars there are three such threads of water extending from the south to the north, but, as they are so wide apart, it is but rarely that more than one of them can be seen at a time. The seas and the straits which connect them constitute a very distinctive character of Mars, and they are generally perceived whenever the telescope is directed upon that planet.4

  Then, in the same treatise, Flammarion teased his readers with rationality, only to dash it again:

  We speak of plants on Mars, of the snows at its poles, of its seas, atmosphere, and clouds, as though we had seen them. Are we justified in tracing all these analogies? In fact, we see only blotches of red, green, and white, upon the little disk of the planet; but, is the red, terra firma; the green, water; or the white, snow? Yes, we are now justified in saying that they are. For two centuries astronomers were in error with regard to spots on the moon, which were taken for seas, whereas they are motionless deserts, desolate regions where no breeze ever stirs. But it is otherwise as regards the spots on Mars.