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Volume 4851

The Doom of Barsoom
By Oberon Zell  2013 (updated 2017)
In our exposition of what we have gleaned about Mars, we have been careful to indulge in no speculation. The laws of physics and the present knowledge of geology and biology, affected by what astronomy has to say of the former subject, have conducted us, starting from the observations, to the recognition of other intelligent life. We have carefully considered the circumstantial evidence in the case, and we have found that it points to intelligence acting on that other globe, and is incompatible with anything else. We have, then, searched for motive and have lighted on one which thoroughly explains the evidence that observation offers. We are justified, therefore, in believing that we have unearthed the cause and our conclusion is this: that we have in these strange features, which the telescope reveals to us, witness that life, and life of no mean order, at present inhabits the planet.

Part and parcel of this information is the order of intelligence involved in the beings thus disclosed. Peculiarly impressive is the thought that life on another world should thus have made its presence known by its exercise of mind. That intelligence should thus communicate its existence to us across the far stretches of space, itself remaining hid, appeals to all that is highest and most far-reaching in man himself. More satisfactory than strange this; for in no other way could the habitation of the planet have been revealed. It simply shows again the supremacy of mind. Men live after they are dead by what they have written while they were alive, and the inhabitants of a planet tell of themselves across space as do individuals athwart time, by the same imprinting of their mind.

Thus, not only do the observations we have scanned lead us to the conclusion that Mars at this moment is inhabited, but they land us at the further one that these denizens are of an order whose acquaintance was worth the making. Whether we ever shall come to converse with them in any more instant way is a question upon which science at present has no data to decide. More important to us is the fact that they exist, made all the more interesting by their precedence of us in the path of evolution. Their presence certainly ousts us from any unique or self-centred position in the solar system, but so with the world did the Copernican system the Ptolemaic, and the world survived this deposing change. So may man. To all who have a cosmoplanetary breadth of view it cannot but be pregnant to contemplate extra-mundane life and to realize that we have warrant for believing that such life now inhabits the planet Mars. (--Percival Lowell, Mars as the Abode of Life, 1908)1

Since creating my poster map of Barsoom in 2012, by compositing Schiaparelli’s Victorian-era maps of the Martian "canali" with a modern map of Mars by noted planetary cartographer Ralph Aeschilman,2 I have been puzzling over how to reconcile all those detailed maps of Mars made from 1876 through 1971, showing intricate networks of apparent canals, with the bleak and barren Mars we discovered with NASA’s Mariner and Viking missions in the late 1970s, on which no such features can be seen.


Fig. 1: Mars/Barsoom from the 1870s into the 1920s. In this and the following maps I converted Shiaparelli’s and other astronomers’ Mercator maps to a Lambert Equal-Area Azimuthal Projection, and then overlaid them on Ralph Aeschliman’s beautiful image. First, I had to remove all labels (which varied greatly among astronomers); then I had to flip the original maps vertically. It was the convention of astronomers to make their planetary maps with South at the top because that’s the way it looked in their telescopes, which reversed the image. Several of the amateur cartographers [i.e. Larry Ivie, 1962; Leathem Mehaffey, ERBzine #1438] who tried to map Barsoom against Shiaparelli’s and Lowell’s maps missed this, and ended up locating Helium in the Northern hemisphere, with all other locations similarly displaced, and thus unrelated to actual Areography.
The “canals” of Mars were first mapped by Giovanni V. Schiaparelli in his Mappa Aerographica (1876, ‘77, and ’79 editions). Each edition became successively more detailed as Schiaparelli continued to fine-tune his drawings from his telescopic observations during Mars’ oppositions to Earth in the years 1877, ’79, ’81, ‘88 and ’93. Schiaparelli’s drawings of the Martian features remained by far the most accurate for a full century. In fact, on his 1879 map Schiaparelli indicated Nix Olympica (now called Olympus Mons), the immense 14-mile high Martian volcano the size of Nevada that no other observer recorded until NASA’s Mariner 9 expedition in 1971.3

Schiaparelli’s detailed maps influenced all subsequent Martian observers and cartographers, who confirmed and replicated his system of Martian canals: Leo Brenner (1894, ’96, and 1904); Percival Lowell (1893); Scheiner (1916); Eug?ne Michel Antoniadi (1930); Gerard de Vaucouleurs (1941);  Lowell Hess (1956);  E.C. Silpher (1962), and R.A. Wells (1971). Adjusted for projection, the features on Schiaparelli’s final map of 1983 correlate precisely with our most modern NASA mapping—except for the “canals,” for which no evidence can be found today.

Schiaparelli called the lines he saw crisscrossing the surface of Mars canali (“channels”), which was mistranslated in English as “canals.” A number of prominent scientists, particularly noted astronomer Percival Lowell, theorized that these were immense engineering works constructed by an intelligent race in an attempt to convey diminishing water from the polar regions to irrigate their dying planet. Lowell published his speculations in three books: Mars (1895), Mars and Its Canals (1906), and Mars as the Abode of Life (1908), thus validating and popularizing the widespread belief that these markings proved the existence of intelligent life on the Red Planet. And Lowell’s writings inspired Edgar Rice Burroughs to write his legendary series of John Carter novels, which took place on the planet Mars (Barsoom) as it was believed to be by the best scientific minds of the time.

A Princess of Mars was published in 1912, and reports events occurring decades earlier, from 1866 through 1876. Gods of Mars (1913) covers the years 1884-1887. And Warlord of Mars (1914) the final book of the initial trilogy, all takes place in 1888. Thuvia, Maid of Mars (1916) spans 1888-1898, and The Chessmen of Mars (1922) covers 1888-1917. The Master Mind of Mars (1927) spans the years 1918-1925. A Fighting Man of Mars (1930) takes place in 1928; Swords of Mars (1935) spans 1928-1934; Synthetic Men of Mars (1939) covers 1934-1938; Llana of Gathol (1941) covers 1938-1939; Giant of Mars (1940) takes place in 1939; and Burroughs' final unfinished John Carter novelette, Skeleton Men of Jupiter (1942), occurs in 1939-1940.4

Fig. 2: Mars/Barsoom ca. 1930, but drawn in 1956 by Lowell Hess, from Exploring Mars by Roy A. Gallant, Garden City Books, NY, 1956. Hess’ original source: Eugene Michel Antoniadi, “Two hemisphere maps in polar azimuthal equidistant projection,” The Planet Mars. 1st edition: 1930. Hess’ map of Mars is by far the most beautiful ever drawn, and was even made into a globe (Fig.3). As with many of the best maps of Mars, Hess used a Mercator projection, with South at the top. I removed the labels, flipped the image, and converted it to a Lambert Equal-Area Azimuthal Projection in Photoshop. I have added Burroughs' Barsoomian locations, and it is interesting to compare this map with the earlier one by Schiaparelli (Fig. 1). This is how Barsoom looked at the time of the events recounted in Swords of Mars.

Schrödinger's Planet

In 1935, Austrian physicist Erwin Schrödinger posited a “thought experiment” to illustrate the strange nature of quantum entanglement, a characteristic of a quantum state that is a combination of the states of two systems that once interacted but were then separated, and are not each in a definite state. The Copenhagen interpretation of quantum physics implies that the probability state of the two systems collapses into a definite state only when one of the systems is measured. Schrödinger imagined a scenario with a cat in a sealed box, wherein the cat's life or death depended on the random decay of a subatomic particle. According to Schrödinger, the Copenhagen interpretation implies that the cat remains both alive and dead (to the universe outside the box) until the box is opened, whereupon the cat is discovered to be either alive or dead. This paradox is popularly known as “Schrödinger’s Cat.”

The planet Mars may be considered a “Schrödinger's Planet,” simultaneously both alive and dead until it was actually visited by NASA’s Viking Mariner 9 mission in 1971, at which point its quantum state collapsed into the condition we know today. But let’s consider an alternative interpretation in which we reconcile Burroughs' world of Barsoom from the days of John Carter with the dead planet revealed by the cameras of Mariner 9.

Fig. 3: Globe of Mars based on Lowell Hess' map in Exploring Mars by Roy A. Gallant, 1956

I don’t need to recount the history of Barsoom we all know from the Carter Chronicles. It extends over a million years into the past (“The Time of the Orovars”). But the narrative abruptly ends in mid-tale in the year 1940, with John Carter and his incomparable Martian Princess Dejah Thoris kidnapped and transported to the giant planet “Sasoom” by the Skeleton Men of Jupiter.

During the long journey through space from Barsoom to Sasoom, John Carter is told that the Skeleton Men (Morgors) plan to invade and conquer Barsoom, beginning with the twin cities of Helium. One possible way they could accomplish this is by destroying the atmosphere plants upon which all life on the Red Planet depends. The ending of the first novel, A Princess of Mars, had revealed this vulnerability when the southern plant ceased operations upon the death of its mad custodian. John Carter managed to get the doors of the plant to open for a reboot crew barely in the nick of time, with people throughout the world gasping their last breaths. Carter himself lost consciousness, and when he awoke, he was back on Earth.

So the first thing we need to understand is the dessication of Mars/Barsoom, the thinning of its atmosphere, and exactly how the atmosphere plants operated. This can be fully explained in the context of the narrative.

The gravity of Mars is only a third that of Earth, and thus cannot retain lighter gasses. Here is an analysis of the Martian atmosphere from 1956:

 One of the most recent estimates is that the Martian atmosphere is about 96 per cent nitrogen and 4 per cent argon. The presence of carbon dioxide has been shown by the spectroscope; in fact, the percentage of carbon dioxide in the Martian atmosphere is higher than in the terrestrial atmosphere. Traces of water vapor seem to occur occasionally, but most of the time the water in the Martian atmosphere takes the form of floating ice crystals which the spectroscope cannot detect. Whether there is any oxygen present is not established.

 It is almost traditional by now to say that the oxygen that was formerly present in the Martian atmosphere has been tied up chemically in the planet’s crust. Rupert Wildt of Princeton some time ago made an interesting suggestion as to how this may have come about. Higher up in the Earth’s atmosphere the ultraviolet radiation coming from the sun changes a percentage of the oxygen present into the tri-atomic form of oxygen known as ozone. Because of the lower pressure in the Martian atmosphere, such an ozone layer would have been near the ground, and since ozone is far more active chemically than normal oxygen is, it would have been used up in oxidizing the surface about as rapidly as it was formed. The oxygen, therefore, was chemically tied up, with the detour of ozone formation, but in this case the detour is the far more rapid route.5

Mars lost most of its magnetic field about four billion years ago. As a result, solar wind and cosmic radiation interacts directly with the Martian ionosphere. This keeps the atmosphere thinner than it would otherwise be by solar wind action constantly stripping away atoms from the outer atmospheric layer. Most of the atmospheric loss on Mars can be traced back to this solar wind effect.6

The thinning of the Barsoomian atmosphere may have been noticed as early as 800,000 years ago, and the greatest Orovarian scientists of the day set out to do something about it. Realizing that the planet’s oxygen was becoming bound into the soil and rocks due to the oxidation process described above, they sought ways to release it back into the atmosphere. The transportation and processing of sufficient oxidized soil to make any difference proved logistically impossible, so they turned to another process—the electrolysis of water.

It would have become difficult at this point to deny the inevitable. There would have been a dawning realization of this tipping point having occurred, and that ultimately it would mean their descendants’ death. Some would have approached this with apathy, some with religion, most ignored it, others, over time, might have begun to call out for something to be done to preserve life and civilization, and been pushed into an intellectual revolution.

There could have been a brief further flowering of civilization due to accelerated technological progress. All of these lines of investigation and action evolved and converged into “The Great Plan” for survival… Electrolysis of water to produce oxygen was part of the solution, done with the knowledge that on an industrial scale it would accelerate the disappearance of the oceans. The longer term plan was to build an atmosphere plant (which would not only provide breathable air but adjust its composition to ensure a proper balance of greenhouse and non-greenhouse gases) and canals; however these would not be ready in time to prevent significant ecological collapse.7

Fig. 4: The atmosphere plant, by Roberto Castro. From Warlord of Mars: Fall of Barsoom #2, “When Hell Broke Loose,” Dynamite Entertainment, 2011.

Situating a mighty electrolysis plant along a critical waterway—the straits connecting the southernmost extension of the Toonolian Ocean with the Warhoon Expanse—ensured a permanent flow of water as the ocean gradually retreated to become the Toonolian Marshes, and the rest of the waterway eventually dwindled to become the River Iss. Meanwhile another atmosphere plant was built in secret by the Okarians deep within the north polar icecap, where it derived its H2O from ice. The southern atmosphere plant was four miles across and 100 feet in depth, with 20-foot-thick telepathically-operated steel doors.

But on Mars, electrolysis is a one-way process. For it breaks H2O molecules down into their constituent oxygen and hydrogen, but with the red planet’s low gravity, the hydrogen immediately escapes into space and can never be recombined to make water. So over hundreds of thousands of years, the surface waters of Mars were consumed by the atmosphere plant, while the oxygen released by the electrolysis continued to be converted to ozone (O2) by solar radiation, and eventually ended up in the soil, which turned progressively redder with ferric oxide (Fe2O3) over the millennia. The ultimate Doom of Barsoom was thus inevitable.

Additionally, the increasing desertification of the planet destroyed the once-lush forests, and the carbon of the dying vegetation combined with atmospheric oxygen to produce carbon dioxide (CO2). The most recent analysis of the Martian atmosphere reverses the ratios from 96% nitrogen and 4% CO2 in 1956 to 1.89% nitrogen and 96% CO2 in 2013. And today, free oxygen constitutes only 0.146% of the atmosphere.8


So what became of Barsoom?

Let’s pick up the thread of the Barsoom saga from 1940, with John Carter and Dejah Thoris separated and trapped on the planet Jupiter (Sasoom) where they had been transported by the skeletal Morgors. And that’s where Burroughs left them, with no reunion, no resolution, and no return to Barsoom. John Carter’s final words were: “My lonely voyage was over. I had surmounted seemingly unsurmountable obstacles and I had reached my goal. Soon my incomparable Dejah Thoris would be again in my arms.”9  And that’s it. We are left to wonder, what happened next?

Since Burroughs lived to 1950, he could certainly have written more of the story—if there was indeed more to tell. One possibility that makes sense in the context of the saga is that John Carter and Dejah Thoris never returned to Barsoom, and the Morgors destroyed the atmosphere plants in their battle to invade and conquer the Red Planet. But the Morgors found they could not live on the tiny world with virtually no air or water, and their plans for colonization had to be abandoned. Barsoom was left barren and lifeless (as had nearly happened in 1876, at the end of A Princess of Mars).

But perhaps it wasn’t the Morgors who destroyed the atmosphere plants. By 1940, the last remnants of Barsoomian water had dried up with the dwindling River Iss, no longer supplying the great southern atmosphere plant, whose oxygen-producing electrolysis ceased production. At the North Pole, site of the secret Okarian atmosphere plant, water ice had also virtually disappeared, replaced by frozen carbon dioxide (dry ice). Perhaps the great global dust storm of 1939 was related to these events, or even precipitated by them.

Fig. 5: Composite map of Mars by Gerard de Vaucouleurs, compiled from photographs and visual observations made during the oppositions of 1939 and 1941 by Earl C. Slipher at Bloemfontein, South Africa; by Lyot, Carmichel, and Gentili at the Pic du Midi, France, and by de Vaucouleurs at Le Houga Observatory, France. (Courtesy of Macmillan, New York; Faber and Faber, London; Editions Albin Michel, Paris.)

Flipped vertically, with labels removed, and converted from a Mercator projection into a Lambert Equal Azimuthal projection, then overlaid onto a modern image of Mars by Ralph Aeschliman, with Barsoomian locations added—all by Oberon Zell. This is the final map of John Carter’s Barsoom.

But even with the death of Barsoom, surely remnants and ruins of the ancient Barsoomian cities and canals would have survived another three decades to be discovered by Mariner 9 in 1971. Why were these not found?

I think the reason is due to dust storms that, as on Earth’s Sahara Desert, covered and obliterated all signs of civilization.

In A Princess of Mars, about half-way thru (page 71 in the 1979 Ballantine paperback edition), John Carter says: “It was the first march of a large body of men and animals I had ever witnessed which raised no dust and left no spoor; for there is no dust upon Mars except in the cultivated districts during the winter months, and even then the absence of high winds renders it almost unnoticeable.”10

Telescopic observations of Mars confirmed its atmospheric clarity throughout the entire time-frame of the Chronicles:

Later, around 1890 evidence of water waned, perspectives changed and the notion arose that the light areas were desert, and the dark areas the marshy remnants of dried seas. The conception of the Martian atmosphere changed, due to the infrequency of clouds and dust storms, the air was thought to be relatively thin.10
However, in the 1940s, after the destruction of the atmosphere plants, all that changed.

The kidnapping of John Carter from Barsoom by the Skeleton Men of Jupiter can be dated precisely to Dec. 25, 1939, when the distances given all match.11 That year witnessed a great Martian dust storm, which was followed by similar storms every other year for a few years (1941 and 1943).

I propose that these three storms (1939, 1941, 1943) obliterated all evidence of Barsoomian civilization, and subsequent global dust storms in the 1950s and ‘70s continued the process, so that long before we sent our first spacecraft to Mars, there was nothing to be found of Barsoomian life or civilization—it had all been sand-blasted to oblivion or buried beneath the shifting vermillion sands…to await rediscovery by future Terran/Jasoomian archaeologists. Indeed, the first soft landing on Mars was made by the Soviet Mars 3 in 1971. It landed in the midst of a huge global dust storm, and its signals were terminated after only 15 seconds.

Martian global dust storms tend to start in the southern hemisphere with a local dust storm… Local dust storms seem to be swept into huge storms that envelope the entire planet, as was discovered by the Mariner 9 mission in 1971 and Viking missions to Mars in the 1970's. During 1977 the Viking spacecraft, both orbiters and landers, made extensive observations of dust activity. Between the two global dust storms, numerous local dust storms were observed.12

Martian Great Dust Storms12

Year               Observation      Ls(°)     Initial Location
1939              Earth                                Utopia
1941 (Nov)   Earth                                 South of Isidis
1943              Earth                     310      Isidis
1956              Earth                     250      Hellespontus
1958              Earth                     310      Isidis
1971 (July)    Earth                     213      Hellespontus
1971 (Sept)    Earth, Mariner 9   260      Hellespontus
1973               Earth                     300      Solis Planum
1977 (Feb)     Viking                   205      Thaumasia
1977 (June)    Viking                   275
1979               Viking                   225
The atmosphere is quite dusty, giving the Martian sky a light brown or orange color when seen from the surface; data from the Mars Exploration Rovers indicate that suspended dust particles within the atmosphere are roughly 1.5 micrometres across.12
By the 1960s, the best telescopic observations from Earth indicated that the famous Martian canals were fading from view, though they were still just barely visible. Here is the best map of the era, produced in 1962:

Fig. 6: Albedo Map of Mars by E.C. Silpher, Lowell Observatory, United States Air Force, 1962. Flipped vertically, with labels removed, and converted from a Mercator projection into a Lambert Equal Azimuthal projection by Oberon Zell. After 20 years of global dust storms, Barsoom is no more.
When the Mariner 9 probe arrived at Mars in 1971, the world expected to see crisp new pictures of surface detail. Instead they saw a near planet-wide dust storm with only the giant volcano Olympus Mons showing above the haze. The storm lasted for a month, an occurrence scientists have since learned is quite common on Mars.

On June 26, 2001, the Hubble Space Telescope spotted a dust storm brewing in Hellas Basin on Mars. A day later the storm "exploded" and became a global event. Orbital measurements showed that this dust storm reduced the average temperature of the surface and raised the temperature of the atmosphere of Mars by 30°C. The low density of the Martian atmosphere means that winds of 18 to 22 m/s (40 to 49 mph) are needed to lift dust from the surface, but since Mars is so dry, the dust can stay in the atmosphere far longer than on Earth, where it is soon washed out by rain. The season following that dust storm had daytime temperatures 4°C below average. This was attributed to the global covering of light-colored dust that settled out of the dust storm, temporarily increasing Mars' albedo.13

Fig. 7. Global Martian dust storm, 2001. Hubble photos.
In mid-2007 a planet-wide dust storm posed a serious threat to the solar-powered Spirit and Opportunity Mars Exploration Rovers by reducing the amount of energy provided by the solar panels and necessitating the shut-down of most science experiments while waiting for the storms to clear. Following the dust storms, the rovers had significantly reduced power due to settling of dust on the arrays.

Dust storms are most common during perihelion, when the planet receives 40 percent more sunlight than during aphelion. During aphelion water ice clouds form in the atmosphere, interacting with the dust particles and affecting the temperature of the planet.

It has been suggested that dust storms on Mars could play a role in storm formation similar to that of water clouds on Earth. Observation since the 1950s has shown that the chances of a planet-wide dust storm in a particular Martian year are approximately one in three.14

But surely, we must consider, even if the ruins of Barsoomian cities and canals are now buried under the rusty desert sands, and no longer visible to orbiting surveyors, we have landed several roving robots onto the surface which should come across some such remnants of lost civilization. And perhaps someday they will, but to date, none of our landing sites have been anywhere close to the locations of Barsoomian cities or canals. Here is a list of the landing sites of all missions to Mars to date, followed by a map comparing their locations with those of Barsoom:
Missions to Mars: Landings15
1. Mars 3 (USSR) – 1971; 45°S, 158°W (lasted only 15 seconds; buried under huge dust storm)
2. Viking 1 (USA) – 1976; 22°N, 48°W
3. Viking 2 (USA) – 1976; 48.3°N, 226°W
4. Pathfinder/Sojourner Rover (USA) – 1997; 19°N, 33.5°W
5. Spirit Rover (USA) – 2004; 14.6°N, 175.5°E
6. Opportunity (USA) – 2004; 2°S, 354.5°E
7. Phoenix (USA) – 2008; 68°N, 233°E
8. Curiosity (USA) -2012; 4.6°S, 137.4°E
Fig. 8: Landing sites of Mars missions compared to locations of Barsoomian ruins, by Oberon Zell.
A sadder interest attaches to such existence: that it is, cosmically speaking, soon to pass away. To our eventual descendants life on Mars will no longer be something to scan and interpret. It will have lapsed beyond the hope of study or recall. Thus to us it takes on an added glamour from the fact that it has not long to last. For the process that brought it to its present pass must go on to the bitter end, until the last spark of Martian life goes out. The drying up of the planet is certain to proceed until its surface can support  no life at all. Slowly but surely time will snuff it out. When the last ember is thus extinguished, the planet will roll a dead world through space, its evolutional career forever ended. (--Percival Lowell, 1908)16

Footnotes

1. Mars as the Abode of Life, by Percival Lowell, MacMillan Company, NY, 1908. Chapter VI: Proofs of Life on Mars, pp. 214-216.
2. “A New Map of Barsoom” by Oberon Zell, ERBzine Volume 3937.
3. Observations of the planet from Mariner 9 confirmed that Nix Olympica was not just a mountain, but a volcano. Ultimately, astronomers adopted the name Olympus Mons for the albedo feature known as Nix Olympica. http://en.wikipedia.org/wiki/Nix_Olympica
4. “Chronology for the Princess of Mars Trilogy and The Master Mind of Mars,” by Fredrik Ekman; 2nd edition, April 2006. ERBzine Volume 0507; also http://en.wikipedia.org/wiki/Barsoom
5. The Exploration of Mars by Willy Ley and Werner von Braun, Viking Press, NY, 1956.
6. “The Solar Wind at Mars,” NASA Science News, Jan. 31, 2001. http://science1.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/
7. “The Fall of Ancient Barsoom (and Some Thoughts on How This Shaped Barsoomian Race and Culture)” by Steven A. Warner and Oberon Zell, ERBzine Volume 4497
8. “Abundance and Isotopic Composition of Gases in the Martian Atmosphere from the Curiosity Rover.” Sciencemag.org (2013-07-19).
9. E.R. Burroughs, Skeleton Men of Jupiter, © 1942 Ziff-Davis Publishing Co.
10. Burroughs, A Princess of Mars, © 1912 Frank A. Munsey Co.
11. “Matching Mars, the Lost Canals of Percival Lowell,” by Den Valdron, Part of the Exploring Barsoom Series. ERBzine Volume 1414
12. Table 5-1. “Martian Global Dust Storms,” Martian Dust Storms and Their Effects on Propagation, by R.W. Zurek, 1982. http://descanso.jpl.nasa.gov/Propagation/mars/MarsPub_sec5.pdf
13. Lemmon et al., "Atmospheric Imaging Results from the Mars Exploration Rovers: Spirit and Opportunity," Science, Volume 306, Issue 5702, pp. 1753-1756, 2004.
14. “Effect of Dust Storms,” http://en.wikipedia.org/wiki/Martian_dust_storm#Effect_of_dust_storms
15. “List of missions to Mars,” http://en.wikipedia.org/wiki/List_of_missions_to_Mars
16. Lowell, op cit. p. 216.

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