The Case for Mars, page 17
That’s the story, and it sounds pretty formidable. Indeed, in November 1971 when the U.S. Mariner 9 orbiter and the Soviet Mars 2 and 3 lander probes reached Mars, a global dust storm was in progress. For four months the surface of the planet was entirely blocked out by dust and Mariner 9 couldn’t see a thing. This didn’t hurt iner 9’s mission very much—it just waited in Mars orbit until things cleared up and then proceeded to image the entire planet without difficulty. However, in the case of the Soviet landers, the story was very different. They had been preprogrammed to target for landing sites near 45° south latitude, and that’s where they went—parachuting right into the heart of the maelstrom. Both were destroyed.
However, while parachuting into a Martian dust storm is a bad idea, the story is very different if you are already on the ground when the dust storm hits. The Martian atmosphere is only about 1 percent as thick as the Earth’s, and, therefore, the dynamic pressure created by a 100 km/hour Martian wind is only equal to that of a 10 km/hour (6 knot) breeze on Earth. Viking landers 1 and 2 operated six and four years respectively on the surface (their design life was 90 days), and both were subjected to many dust storms during their stay. Despite this, no damage to the Vikings or any of their instruments was detected. Furthermore, while the dust storm can block visibility of the surface from orbit, local visibility on the surface is not seriously impaired. The dust does reduce light levels, much as an overcast day does on Earth, but to an observer on the surface the surrounding area is not fogged out. If a surface installation were powered by solar panels, some problems could be expected from dust storms reducing light levels. However, since photovoltaic panels can convert light to electricity even after it has been scattered by dust (a clear optical view of the Sun is not necessary), power loss would not be total. Instead, during a typical bad dust storm, one might expect solar power electric output to fall by about 50 percent. Thus, provided that the power system is designed to insure sufficient power for minimal life-support functions for the duration of the dust storms, things should be okay. Of course, if either a nuclear reactor or a radioisotope generator provides base power supply, or if a large power reserve is available in the form of locally produced chemical propellants (which can be burned in a chemical combustion engine to turn a generator), this problem becomes moot.
Some people have voiced concern that dust deposited by storms could obscure solar panels or other optical surfaces, such as windows or instruments. This problem was not observed on Viking. Apparently, the total quantity of dust actually suspended by the storms is rather small. However, in the case of a human Mars mission, dust deposition certainly wouldn’t be much of a problem. If a solar panel becomes covered with dust the solution is simple; send someone outside with a broom!
So, to sum up, the only real hazard represented by dust storms is to objects that are dominated by aerodynamic forces (because they have a lot of “sail area” compared to their weight), such as balloons or parachute suspended landers. If a lander does not use a parachute for landing (high-altitude drogues are okay too), and the Mars Direct landers do not need to, it should be able to punch its way through a dust storm as easily as an airplane can fly through a cloud. Of course, most pilots would prefer to land under conditions of complete visibility, and this is why the Mars Direct plan has the spacecraft brake into orbit prior to landing. If the weather is bad at the landing site when the hab arrives, the crew can just wait on orbit like Mariner 9 until the skies clear. Interestingly, however, for the decade 2001 to 2010, it is possible to choose Earth-to-Mars trajectories during every launch year that have the ships arrive at Mars during the clear weather season.
Dust storms won’t keep us from Mars.
<3 height="1em">BACK CONTAMINATION
The last of the five dragons infesting the maps of would-be Mars explorers is not only illusory, but hallucinatory. This is the “Threat of Back Contamination.”
The story goes like this: No Earth organism has ever been exposed to Martian organisms, and therefore we would have no resistance to diseases caused by Martian pathogens. Until we can be assured that Mars is free of harmful diseases, we cannot risk infecting the crew with such a peril that could easily kill them, or if it didn’t, return to Earth with the crew to destroy not only the human race but the entire terrestrial biosphere.
The kindest thing that can be said about the above argument is that it is just plain nuts. In the first place, if there are or ever were organisms on or near the Martian surface, then the Earth has already been, and continues to be, exposed to them. The reason for this is that over the past billions of years, millions of tons of Martian surface material has been blasted off the surface of the Red Planet by meteor strikes, and a considerable amount of this material has traveled through space to land on Earth. We know this for a fact because scientists have collected nearly a hundred kilograms of a certain kind of meteorite called “SNC meteorites,”16 and compared the isotopic ratios of their elements to those measured on the Martian surface by the Viking landers. The combinations of these ratios (things like the ratio of nitrogen-15 to nitrogen-14), as well as the fact that the gas trapped in the rock matches the Martian atmosphere, represent an irrefutable fingerprint proving that these materials originated on Mars. Despite the fact that in general each SNC meteorite must wander through space for millions of years before arrival at Earth, it is the opinion of experts in the area that neither this extended period traveling through hard vacuum, nor the trauma associated with either the initial ejection from Mars or reentry at Earth would have been sufficient to sterilize these objects, if they had originally contained bacterial spores.17 Furthermore, on the basis of the amount we have found, it has been estimated that these Martian rocks continue to rain down upon the Earth at a rate of about 500 kilograms per year. So, if you’re scared of Martian germs, your best bet is to leave Earth fast, because when it comes to Martian biological warfare projectiles, this planet is smack in the middle of torpedo alley. But don’t panic—they’re not so dangerous. In fact to date the only known casualty of the Martian barrage is a dog who was killed by one of the falling rocks in Nakhla, Eygpt in 1911. Statistically the hazard presented to pedestrians by furniture being thrown out onto the street from upper story windows is a far greater threat.
The fact of the matter, however, is that life almost certainly does not exist on the Martian surface. There is no (and cannot be) liquid water there—the average surface temperature and atmospheric pressure will not allow it. Moreover, the planet is covered with oxidizing dust and bathed in ultraviolet radiation to boot. Both of these last two features—peroxides and ultraviolet light—are commonly used on Earth as methods of sterilization. No, if there is life on Mars now, it almost surely must be ensconced in exceptional environments, such as a heated hydrothermal reservoir underground.
But couldn’t such life, if somehow unearthed by astronauts, be harmful? Absolutely not. Why? Because disease organisms are specially keyed to their hosts. Like any other organism, they are specially adapted to life in a particul environment. In the case of human disease organisms, this environment is the interior of the human body or that of a closely related species, such as another mammal. For almost four billion years the pathogens that afflict humans today waged a continuous biological arms race with the defenses developed by our ancestors. An organism that has not evolved to breach our defenses and survive in the microcosmic free-fire zone that constitutes our interiors will have no chance of successfully attacking us. This is why humans do not catch Dutch elm disease, and trees do not catch colds. Now, any indigenous Martian host organism would be far more distantly related from humans than elm trees are. In fact, there is no evidence for the existence of, and every reason to believe the impossibility of, macroscopic Martian fauna and flora. In other words, without indigenous hosts, the existence of Martian pathogens is impossible, and if there were hosts, the huge differences between them and terrestrial species would make the idea of common diseases an absurdity. Equally absurd is the idea of independent Martian microbes coming to Earth and competing with terrestrial microorganisms in the open environment. Microorganisms are adapted to specific environments. The notion of Martian organisms outcompeting terrestrial species on their home ground (or terrestrial species overwhelming Martian microbes on Mars) is as silly as the idea that sharks transported to the plains of Africa would replace lions as the local ecosystem’s leading predator.
If I appear to be spending excessive time on beating this idea, it’s partly as a result of a recent NASA planning meeting for the upcoming (robotic) Mars sample return mission during which someone seriously proposed that, to allay alleged public concerns, any sample acquired on Mars be sterilized by intense heat before returning it to Earth. While an extremely unlikely find, the greatest possible treasure a Mars sample return mission could provide would be a sample of Martian life. Yet, certain of those attending the meeting would destroy it preemptively (and a great deal of valuable mineralogical information in the sample as well). The proposal was so grotesque that I countered by asking the assembled scientists, “If you should find a viable dinosaur egg, would you cook it?” The question is not entirely out of line; after all, dinosaurs are our comparatively close relatives and they did have diseases. In fact, every time you turn over a shovelful of dirt you are returning a sample of the Earth’s disease-infested past to menace the current biosphere. Nevertheless, paleontologists do not wear decontamination gear.
Just as the discovery of a viable dinosaur egg would represent a biological treasure trove but no menace, so a sample of live Martian organisms would be a find beyond price, but certainly constitute no threat. In fact, by examining Martian life, we would have a chance to differentiate between those features of life that are idiosyncratic to terrestrial life and those that are generic to life itself. We could thus learn something fundamental about the very nature of life. Such basic knowledge could provide the basis for astonishing advances in genetic engineering, agriculture, and medicine. No one will ever die of a Martian disease, but it might be that thousands of people are dying today of terrestrial ailments whose cure would be apparent if only we had a sample of Martian life in our hands.
THE LUNAR SIREN: WHY WE DON’T NEED LUNAR BASES TO GO TO MARS
We now come to a totally different kind of mythical creature blocking the path to Mars, one appearing not in the guise of a threatening monster or fearsome dragon, but in the alluring dress of a lovely goddess. This is Diana, the Lunar Siren, whose seduceemong has probably done as much to wreck would-be Mars ventures to date as all five dragons combined.
According to Diana’s followers, it is a point of religious belief that we cannot venture human expeditions to Mars until after the goddess has been appeased by the construction of a substantial array of temples—that is, bases—on the lunar surface. This is a commendably original basis for a pagan religion, and it really shows how far we’ve come since the days of the Roman Empire, but the fact of the matter is that it has no basis in reason.
Yes, it is quite true that due to its low gravity and negligible atmosphere, it would be much easier to send a rocket from the surface of the Moon to Mars than to launch it from the surface of the Earth. Furthermore, it is also true that Moon rocks are almost 50 percent oxygen by weight, so that once technologies are developed that can break down the iron and silicon oxides that make up most of the Moon’s materials, a copious supply of liquid oxygen could be made available for spacecraft refueling on the lunar surface. Unfortunately, fuel to burn in this oxygen, such as hydrogen or methane, is essentially unavailable on the Moon. Nevertheless, since the oxygen content of various rocket propellant mixtures varies from 72 percent to 86 percent by weight, the Moon can in principle be made into a base that could support a substantial fraction of required space transportation logistics.
But this analysis neglects some basic facts about solar system transportation. You see, before the spacecraft can refuel at the Moon, it has to get to the Moon. Now the ΔV required to go from low Earth orbit (LEO) to the lunar surface is 6 km/s (3.2 km/s for trans-lunar injection, 0.9 km/s to capture into low Lunar orbit, and 1.9 km/s to land on the airless Moon.). On the other hand, the ΔV required to go from LEO to the Martian surface is only about 4.5 km/s (4 km/s for trans-Mars injection, 0.1 km/s for post-aerocapture orbit adjustment, and 0.4 km/s to land after using the aeroshield—but no parachute—for aerodynamic deceleration). Put briefly, from a propulsion point of view, it is much easier to go from LEO directly to Mars than it is to go from LEO to the surface of the Moon. So, even if infinite quantities of free rocket fuel and oxygen were sitting right now in tanks on the lunar surface (and they aren’t), it would make absolutely no sense to send a rocket there to refuel itself for a voyage to Mars. Basically, refueling at the Moon on your way to Mars is about as smart as having an airplane flying from Houston to San Francisco stop over for refueling in Saskatoon. Putting the lunar refueling node in lunar orbit doesn’t change things very much. You still have to perform almost as much ΔV to move the spacecraft from LEO to lunar orbit as you do to send it to Mars. Add in the supplies required to support the making of oxygen on the Moon along with the hardware and fuel to haul large quantities of it to lunar orbit (you have to ship hydrogen or methane to the lunar surface to use to lift oxygen to orbit) and it quickly becomes apparent that the whole scheme is nothing but a logistics nightmare that would enormously increase the cost, complexity, and risk required to mount a piloted Mars mission.
So, the Moon is not useful as a Mars transportation base. Well then, say Diana’s followers, you still need to use the Moon as a test bed and training site to prepare for a Mars mission.
But lunar conditions are so dissimilar from those on Mars that Antarctica (or Wyoming for that matter) would do just as well for crew training, and at far lower expense. Mars has an atmosphere and a twenty-four-hour day, with daytime temperatures varying between -50°C and +10°C. The Moon has no atmosphere, a 672-hour day, and typical daytime temperatures of about +100°C. While the Earth’s gravity is 2.6 times that of Mars, Mars’ gravity is 2.4 times that of the Moon. Furthermore, the types of resource utilization that one would undertake on Mars (exploitation of the atmosphere in gas-based chemical reactors and extraction of permafrost from soil) are completely different from the high-temperature rock-melting techniques that will be employed on the Moon. In addition, the types of geologic investigations needed on Mars, given its complex hydrologic and volcanic history, will much more closely resemble those that can be done on Earth than those that can be done on Luna. We won’t learn how to live on Mars by practicing on the Moon.
The Moon does have some uses, most notably as a platform for astronomy using a coordinated array of optical telescopes to obtain super-high-resolution views of the universe at large (an “optical interferometer”). It makes sense, therefore, to gain maximum benefit by ensuring that the same set of hardware used to accomplish Mars missions is designed in such a way that it can also be used to support transportation of humans and equipment to the Moon. As discussed in Chapter 3, this is the case with the Mars Direct mission design. Therefore, in much the same way as Apollo lunar hardware could be used as an afterthought to create the Skylab space station, so an ancillary benefit of the Mars Direct mission is that it will give us the capability of setting up lunar observatories whenever we want them.
However, what needs to be clearly understood is that a lunar base is neither necessary nor desirable as an asset to support piloted missions to Mars. With respect to the path to Mars, it is a fatal Siren, a diversion into a dead end. The late NASA administrator Thomas O. Paine knew all about this trap. In one of the last speeches of his life he put it this way: “As Napoleon Bonaparte once said explaining his winning strategy for war with Austria: ‘If you want to take Vienna, take Vienna!’ Well, if you want to go to Mars, go to Mars!”
Well said, Tom. On to Mars.
Simplified topographic map of Mars showing the elevated continents of Tharsis and Syrtis Major and the depressed Vasitas Borealis region which once may have contained a large polar ocean.
6: EXPLORING MARS
We are not sending a cre
w to Mars to set a new altitude record for the Aviation Almanac. We are going to Mars to explore a planet; to determine if it ever harbored life in the past and to survey its potential as a future home for a new branch of human civilization. Sending a few robotic probes, no matter how sophisticated, will never get the job done. Nor will even a few piloted excursions to the Red Planet’s surface, especially if the crews are limited to lingering near their short-term base. No, to learn about Mars, we’ll have to get about Mars, and in a major way.
With a surface area of 144 million square kilometers, the Red Planet has as much terrain to explore as all the continents and islands of Earth put together. Moreover, the Martian terrain is incredibly varied. It includes canyons, chasms, mountains, dried river and lake beds, flood runoff plains, craters, volcanoes, ice fields, dry-ice fields, and “chaotic terrain,” to name just a few surface features. The U.S. Geological Survey currently records no lfe in tan thirty-one types of Martian terrain on its “Simplified Geologic Map,” and all these before real high-resolution imaging of Mars has even begun. Some of the Martian terrain features, such as the 3,000-kilometer-long Valles Marineris, are of continental extent, and the thorough exploration of even a single such feature will require continental scale mobility.
The dry riverbeds discovered on Mars by Mariner 9 are proof that Mars once had a warm, wet climate, suitable for the origin of life. This was possible in Mars’ early years, because in its youth the planet’s carbon dioxide atmosphere was much thicker, endowing it with a very strong “greenhouse effect.” Venus has a thick carbon dioxide atmosphere today, but it has turned that planet into a baking hell. At Mars’ greater distance from the Sun, though, a thick carbon dioxide greenhouse is just what is needed to create the temperate conditions required for the development of life. Most Mars scientists currently believe that such conditions persisted on Mars for a period of time considerably longer than it took life to evolve on Earth. Current theories on the origin of life regard the emergence of life as a natural development of progressive self-organization by matter that should inevitably occur wherever the appropriate physical and chemical conditions exist. If that is indeed the case, life should have appeared on Mars, because during the period of life’s origin on Earth, Earth and Mars were similar environments. Over geologic time, Mars lost its greenhouse and became the frigid, arid world it is today, and this climatic deterioration almost certainly has driven life from its surface and possibly into extinction. Nevertheless, microscopic organisms can leave macroscopic fossils. We have found some on Earth, called bacterial stromatelites, that date back 3.7 billion years, making them contemporary with Mars’ tropical era. Even if Martian life died out entirely, its fossil remains could still be there. Today, all we know about the chances for the evolution of life is that it occurred on one planet, our own. We have no way of knowing whether that development was a one-in-a-trillion freak chance or whether it was a dead sure bet. Freak chances can occur in a single sample experiment, but never twice in row. If we were to find either living organisms or simply fossils on Mars, we would know that the universe belongs to life.
