Destination Mars (3 page)

Once again, Viking 1 did not disappoint. The first image, black and white but glorious nonetheless, slowly assembled, again, a strip at a time. The tension broke slightly as the first strip came in,
but like a good mystery novel, Mars was only revealed a small bit at a time. The results were well worth the wait. After years of preparation, a billion dollars, and a journey of many times the 119 million miles then separating Earth from Mars, the first landscape was in. The data was still coming back long after the orbiter was out of touch, given the long transmission travel time across the vast darkness, and the lander went into a base-operation mode while out of communication.

But the picture…oh, that second picture. It lacked color and was obscured on the bottom by various parts of the spacecraft. But there it was, in all its monochromatic glory: the horizon of Mars. Low, arid hills were off in the distance, and between the lander and those hills was an expanse of sharp, jagged rocks. Hundreds of them. And off to the right, dominating the horizon there, was the bright glow of the sun, unseen and above the frame. It was a dry, cloudless spectacle. For someone seeking the serenity of an English tea garden, or the Mars of Percival Lowell, it would not do. But for any human pining for a glimpse of another world, a world we could relate to, another planet to which we might one day travel, it was nirvana.

Viking 1 was, however, oblivious to such human emotion. The outbursts and cheers from Earth remained unheard. It had a primary mission of just sixty days on the surface, with an extended mission target of 120. At that point, Mars would pass behind the sun and communication would be lost for weeks. And while controllers on Earth planned to “safe” the lander during this time, their confidence in reawakening the machine after this period was limited. But true to what would become JPL's legacy of performing near miracles with distant machines, the first lander operated successfully for well over
six years.
And the tale of its ultimate demise is not one of equipment failure, but of human error.

With Viking's successful landing, there was now time—well over two months in the primary mission alone—to perform the tasks it was designed to do. The instructions came up from Earth
in carefully coded batches, to be processed and executed in sequence. With mechanical exactitude, Viking 1 began its primary labors—taking color images of the surrounding surface, digging scoops of soil and dumping them carefully into small funnels that led to an onboard laboratory, and fulfilling its primary objective: the search for life on Mars.

Just under two months later, on September 3, 1976, the Viking 2 lander settled gently onto Utopia Planitia, 4,200 miles away to the northeast. Humanity now had two outposts on Mars, and the exploration of the red planet began in earnest. Overhead, the Viking orbiters continued to chip away at their intense workload, snapping pictures and sending reams of data earthward. What they imaged and reported would change our understanding of Mars overnight: the Martian Renaissance had begun.

Exploring Mars is a bit like doing brain surgery through a mile-long soda straw. At an average distance of fifty million miles from Earth, with a one-way radio message time of twelve to twenty minutes, roving the dry, treacherous surface requires the utmost in planning and careful execution. One false move can end a mission in seconds, and there are rarely many options to correct a mistake. That is why the people who dare seek the truth about Mars are so remarkable. This is the story of human striving, from early times through tomorrow, to discover what makes Mars tick.

O
rbiting in the dark cold of space at an average of about 140 million miles from the sun, or about half again as far as Earth, Mars is the fourth planet in the solar system. It is also the last stop for the rocky, or terrestrial, worlds before the gas giants Jupiter and Saturn and the icy balls of Uranus and Neptune. It is separated from these giant worlds by the asteroid belt, a planet which failed to form from the large disk of material that still orbits the sun beyond Mars.

The air on Mars is thin and cold; the highest temperatures hover at about 60°F, and can plummet to -180°F at the poles. Its day lasts about 24 hours, 37 minutes, and its axial tilt matches
Earth's at 24 degrees. Its year lasts 686 Earth days. Mars is about half the diameter of Earth, less than a quarter its size, and has only 11 percent of Earth's mass and 38 percent of its gravity. Despite this, it has almost the same dry surface area, due to a lack of seas and oceans; in fact, bodies of liquid water do not exist on its surface. It is a bone-dry, ultracold place with only about 1 percent of Earth's atmosphere.

Why then, one might ponder, are we so fascinated with this seemingly inconsequential world? Because Mars is a planet of dreams. Always, it has inspired feelings in humanity as no other planet in our solar system. Early on, it was the reddish hue, resembling the color of aging blood, that attracted the naked eye. Later, in wavering telescopic images transmitted across the tens of millions of miles from its surface, it was the odd markings and, still later, imagined lines crossing its surface that inspired. One could imagine life there. One could imagine…empires.

And why not? The planet is not that far from Earth, and must then be not so unlike our own world, or so the thinking went. If Venus, one step closer to the molten sun, might be covered with tropical oceans and riotous growths of green, steaming jungles under its impenetrable cloud cover, why couldn't Mars, still within the so-called Goldilocks Zone, harbor an older, wiser, more advanced civilization?
¹

But of course, those dreams vanished along the way. Venus turned out to be an unbelievably hot hellhole with over nine hundred pounds per square inch of pressure crushing its deadly surface. But the real Mars, as we know it today, is not so much less interesting than the one of previous generations. The empires of Edgar Rice Burroughs's green men and eight-legged Thoats (dinosaurlike steeds) might be gone, but in its place is an old, highly weathered, and geologically fascinating place with signs of vast and ancient floods of liquid water, and more recent indications of smaller flows.

The planet seems in many ways to be an older version of our
own. But it is an Earth with planetary evolution gone awry. Once rich with oceans and cloud cover, it is too small to any longer harbor liquid water on its surface for more than a few moments. Its thin atmosphere is almost entirely carbon dioxide, with bits of nitrogen, argon, and oxygen existing in wisps. Most of the life-sustaining oxygen that we prize so highly has been long spent, slowly turning the iron in the soil a ruddy, oxidized red. And that thin atmosphere has also allowed for billions of rocks, most of which would burn up or explode in Earth's denser atmosphere, to slam into Mars's surface with impunity. Many millions of these were large enough to leave wounds on the planet, and some created vast new surface features.

Another seeming indicator of a dead world is Mars's lack of a meaningful magnetic field. This is probably due to a largely inert core, or a cooling one. Whatever the case, there is not the same molten, metallic dynamo that creates Earth's robust lines of magnetic force, and what magnetism Mars does possess is lumpy and erratic. The gravitational field is also unlike Earth's, with mascons (mass concentrations), not unlike those within Earth's moon.
²
Whatever the case, Mars has, proportionally, a much thicker crust and a smaller, less active molten core than our planet.

Still, Mars has possessed life, though not the kind we seem to wish upon it. It was
geologically
alive, with vast lava flows and wind and water erosion working their healing magic upon its tortured and pockmarked surface. While much of the southern half of the planet still bears the scars of bombardment, the northern half is largely covered with younger lava flows that filled in the offending craters. And the source of much of this once-molten rock can be clearly seen with even low-resolution cameras from the myriad probes that have flown past the planet, in the form of the Tharsis Bulge and its huge volcanoes. This region is so remarkably swollen that it noticeably deforms the otherwise spherical planet. And it is home to some of the most impressive mountainous real estate in the solar system.

What follows is a brief primer of Martian geography. Entire sets of texts are available on the subject; what is presented here is merely the briefest of samplings. The intention is to present a general idea of the important regions of the planet in both historical and scientific terms.

First among the huge volcanoes identified within the Tharsis region is Olympus Mons, the largest known mountain anywhere, which flanks the bulge. Three times the height of Mount Everest, the now-extinct volcano soars fourteen miles into the thin Martian air. It is a shield volcano, resembling those that comprise the islands of Hawaii, with a base width of almost four hundred miles. The area it rests upon is roughly the size of Arizona. It is also the youngest of the major volcanic structures on Mars.

Directly atop the bulge and spanning its crest diagonally are three older volcanoes, all shield volcanoes, Arsia Mons, Pavonis Mons, and Ascraeus Mons. While subordinate in size to their larger sibling, these lava factories contributed greatly to the basaltic flows that inundated much of the surrounding area. Overall, the Tharsis region is the size of a terrestrial continent.

The formation of this region was not without its side effects, and a gigantic wound in the planet can be found nearby, stretching east from the Tharsis area and continuing along the Martian equator for about a quarter of the planet's circumference. This gigantic gash in Mars's hide is called Valles Marineris. In keeping with the Texas-style “bigger is better” nature of Martian topography, it is the largest valley in the solar system. Our own Grand Canyon would be scarcely noticeable alongside it. Almost 2,500 miles long, it was formed when the Tharsis region rose out of the planet, and the nearby crust could not take the stresses of this enormous violation. So it cracked and slumped, resulting in the huge channel. It averages 125 miles in width and is as much as 4.5 miles deep. It is outclassed only by the underwater Mid-Atlantic Ridge on Earth.

To the north rests Alba Mons, also known as Alba Patera, the
oddest of the volcanoes and unlike anything else on Mars (or Earth, for that matter). It has the gentlest slope of any Martian volcano, with an inclination of just one-half a degree, or about a tenth of that of Olympus Mons. Its volcanic outflow forms an ellipse almost 2,000 miles across and 1,200 miles north to south, making it (here, again, the Texas-style attributes) among the largest known magma generators in the solar system. There are many theories seeking to explain its productivity, including the existence of highly fluid magma that flowed freely and fluidly out of the caldera and across the surface of Mars. On Earth, the total outflow of the volcano would have covered most of twelve states if centered in Colorado. It's a big beast.

Other volcanic regions include an area thousands of miles west of Tharsis called Elysium. Here we find three main volcanoes: Elysium Mons, Hecates Tholus, and Albor Tholis. Finally, down toward the equator is the region of Syrtis Major Planum with its own volcano of the same name. About 750 miles wide, but only one mile in elevation, this vast, low-lying monster produced lavas that seem to be different than that from the Tharsis volcanoes; it is more complex and differentiated in geological terms and is thought to have formed in the vast three-mile-deep magma chamber below when heavier elements settled out, leaving the lighter lavas to spew forth.

In any case, by the time Mariner 9 had begun sending back images of the Tharsis volcanic complex, any thoughts that Mars had been dull or uninteresting in its youth were banished. While the planet may have slowed down in its old age, in earlier eras it was a geologically active toddler, with regular volcanic tantrums to match.

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.
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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.