Science should be “sexy”. Once we had decided to write an article on Olympus Mons, we began to consider how to present it in a manner that would appeal to our readers. The regular science article is usually a rather monotonous enumeration of facts, figures and equations and thus heavy to digest for the average reader, but what about science fiction? Not in the generic sense where fiction dominates to the exclusion of science and all sorts of wonderful gadgets are presented in order to titillate the reader. No, we mean a story where fiction is the vehicle used to present science. Also, we chose to summarise current knowledge in the captions to the images selected to illustrate our story with. Thus what you find in the story is our interpretations and opinions as to what is likely and not hard fact! As to the technology, our only invention is the fusion power generators. The rest is what we have today at various stages of development, fast-forwarded about half a century. How well have we succeeded? That is for you to decide!
Currently, research is undertaken by NASA in order to find out how well humans cope with being cooped up together inside a small space for a period of eight months, the time of a journey from Earth to Mars. It is called the Mars Dome Project and is located to the slopes of Hawaii’s Mauna Kea. The long view of the Mars One project is to establish a colony on Mars where astronauts are sent on a one-way trip in groups of four every two years due to the fact that the orbital characteristics of Mars and Earth mean that they are only in a position where a seven-month “short” journey on a so-called Hohman orbit is possible once every two years.
For several reasons, we felt that this project was not sufficient in order to serve as the background to our story. First of all, the Mars One project is too small and too vulnerable to economic and political changes. There is a not inconsiderable likelihood that it could be terminated after the first two or three groups have been sent on their one-way trip. Second, the genetic pool this results in is far too limited to allow for a sustained, long-term presence. Basically, the humans sent there are sent there to die, be it in the first, third or thirteenth generation. Third, the effort is too ethnocentric. Any such mission is and should be a global concern for mankind in its entirety and the aim should be to go there to stay, indefinitely. Furthermore, there is nothing like children to keep us sane even if they sometimes drive us nuts! For these reasons, we decided that as a minimum 300 colonists of as many genetic patterns as possible would be required in order to provide the diverse DNA-pool required for long-term survival, thus truly representing mankind.
How do we get to Mars?
The weight that can be transported from Earth to Mars is severely limited by the inefficient propulsion of our current chemical rockets. The delta-vee provided by oxidising hydrogen is too low but it is what we have accessible, as the far more efficient ion engines such as on the Dawn mission cannot be built on a large enough scale (yet?). The colonization will probably use a type of Aldrin Mars Cycler, named after the second man on the Moon, Edwin “Buzz” Aldrin, who designed the orbit to be used in the early 1980s.
In essence, the Aldrin Mars Cycler is a very large space station on an orbit which regularly passes both Earth and Mars. Earth would launch a rocket with colonists, the equipment for the colony plus supplies for the journey and the fuel needed for the Mars landing. Just before the station passes Mars, the colony rocket disconnects, decelerates and lands whilst the station continues in its orbit headed for Earth. The Aldrin Cycler contains everything needed to survive an extended period in space, including a compartment with heavy radiation shielding against solar flares.
Although it only has to be done once, not only will it take a tremendous amount of fuel to put this station in orbit. The project is such a huge undertaking that it will most likely require the combined resources and cooperation of all the largest and most technologically advanced nations. The major advantages of the Aldrin Mars Cycler is that travel time to Mars can be as short as 5½ months, rather than the 7 months on a Hohman orbit, and that you don’t have to build a new habitation module, launch it from the bottom of Earth’s gravity well and give it enough delta-vee for a journey to Mars with each subsequent expedition. In the long run, the Aldrin cycler is the most practical and economical option available. The disadvantage is that if you miss your launch slot, you have to wait for the station to come round again which at best is two years, but depending on the cycler orbit may be as long as four, six or even more years. For more information, we recommend http://en.wikipedia.org/wiki/Mars_cycler
The colony will need to be self-sufficient in as many areas as possible because re-supply from Earth is weight-limited as well as prohibitively expensive. Food, water, clothing, shelter, furniture etc must be home-grown. Chemical engineering, the ability to synthesise polymers from the “wastes” of the hydroponics garden, will be vital as clothing (and Mars survival suits!) made from cotton, wool or hemp simply is simply just not on. In short, a pair of cotton jeans will be far more rare on Mars than ermine robes and royal crowns are on Earth.
When it comes to mineral resources, the Martian surface seems to have useable amounts of iron and lots of calcium, sulphur and water. But to judge from analysis of meteorites that originally came from Mars, there are only trace amounts of other elements such as the rare earths. The processes that form large concentrations of a range of mineable minerals; the slow cooling of magma reservoirs deep underground, should also have happened on Mars, but such bodies of ore will have formed three times deeper than on Earth. No flowing water and the consequent lack of a rain cycle has led to an absence of deep erosion. This means that such mineral deposits remain inaccessible on Mars, deep underground.
As a consequence, any human settlement of Mars will by default have to be located to areas where a lot of surface has been removed; the North Polar Basin or other very large impact structures. Where magma has occurred much closer to the surface; the Tharsis volcanic province. Or where underground heat has allowed water to bring dissolved minerals up; such the Olympus Mons hotspot. Our colony Olympia is conveniently situated within range of all three.
Another prime requirement for a viable colony is energy, plenty of it. The only two viable options are fusion or fission reactors with the former being far more desirable if not yet operational. Current estimates places this about 25 years in the future. The fusion reactor will require deuterium, which will be obtainable from any source of water ice, and Helium-3. This will be a problem: Helium-3 occurs naturally in the mantle and crust. Measurements of ratios in the lithium-bearing mineral Spodumene yielded ratios of between 2-12 parts He-3 per million of He-4. Helium-3 can be synthesised in fission reactors by the neutron bombardment of Lithium-6 which results in one Helium-4 and one Hydrogen-3 (tritium) which decays into Helium-3 with a half life of 12.3 years. Luckily, fusion only requires tiny amounts and it is one of the few things that could be shipped from Earth (as well as small amounts of rare earth minerals, probably in the form of electronic components, heavily shielded from space radiation). Nevertheless, any Martian colony would want to, and need to, find a local source as it cannot be dependent upon Earth indefinitely.
At the Martian surface, apart from trace amounts in the lithium-bearing minerals Petalite, Scapolite and Tourmaline, the only source of Helium-3 is the solar wind and precious little of that enters the atmosphere. Trapped volcanic gasses may be a source which is yet another reason why Tharsis make a logical location for a Martian colony. It would have to be trapped from long ago since the current rate of outgassing on Mars is very low. Other possible sources would be the surfaces of the Martian moons Phobos and Deimos.
Just like the Mars One project, there would have to be an advance party to set up an initial base which is expanded in order to prepare for further arrivals. The first couple of decades would be spent just getting established in situ and it would not be until decades later that exploration of other areas of Mars could and would be undertaken – and only if there was a pressing need to the survival of the colony, short or long term! Such a need is to find the Rare Earth Elements necessary to maintain the advanced technology vital to the survival of any Space colony.
Transportation, the LLAMA™ (Large Low Altitude Mars Airship)
Getting around on Mars is going to be difficult. The lack of roads and sharp (un-eroded) rocks are hard on regular wheels, and of course wheeled vehicles have problems with steep slopes as well as crossing fissures and chasms. Winged aircraft don’t work well because of the lack of air. Some form of jet engine; compressed air providing thrust, would be required as propellers need far more dense air if they are to “bite” and provide enough thrust. We propose to use a Zeppelin-type craft. It would have to be huge, again because of the lack of air on Mars. However, they can be made huge. On Earth, airships can work in the stratosphere where air pressure is similar to that of Mars. To carry a lift of 50 tons, a Martian airship would need to be something like 400 metres long by 200 wide, and 100 meters tall. It would be filled with hydrogen, which in the absence of oxygen in the Martian atmosphere is safe.
Air pressure on Mars varies by 30% between summer and winter because so much of the atmosphere freezes on to the South Polar ice cap. In order to allow for this, we make the air ship semi-inflatable. Winds on Mars can reach at least 100 km/h, but because of the low atmospheric pressure, they don’t exert much force. The tether is used to secure the air ship. Dust devils may be the main problem. Propulsion is a problem, as propellers don’t work and jet engines don’t go well with an air ship. But compressed air engines should work well which is what we envisage being used. The air ship could also be pulled along the tether by electric motors. Power can be provided by covering the huge upper surface in solar panels; even on Mars where the Sun is only half as strong as on Earth, this would give megawatts of energy. An advantage of Mars is that air pressure does not fall off as fast with altitude as it does on Earth. We run the Graf up to 10 km above the base station, and air pressure here is still 60% of that at the base.
Now why doesn’t our expedition use such a large airship to transport itself from Olympia, their home, to Olympus Mons? In spite of the low force exerted by the Martian winds, with such a large airship, they would still potentially exert enough force to cause major problems for the compressed air engines to overcome. Then there are the dust devils to contend with. An airship would in all likelihood need to run a tether for all of the 500 km, or the expedition could very well find itself doing an unscheduled fly-by of Syrtis Major instead. Even if they could manufacture a strong-enough, non-degradable polymer cable with a safe load of 75 kN such as the strongest man-made fibre at present; Carbon fibre Toray T1000G which has an ultimate tensile strength three times that of a steel cable at 2/9ths the weight, 500 km of such a cable minus anchoring devices would still weigh not less than 155 tons (on Earth), three times the capacity of the above blimp. As this would require an even larger airship, we opted for the safer overland approach and to use a smaller version of the LLAMA during the expedition. But sailing five km above the Martian landscape in a gondola slung below a gigantic airship is indeed a grand vision of the future!
Why don’t we drill deep to take core samples of the various layers? Again logistics! Any drilling done would have to be limited to no more than a few tens to a hundred of metres at most as the logistics for a deep drill (2-3 km+) would be prohibitive, especially for this exploratory survey. The drill rig alone would have required at the very least two extra vehicles in order to transport it. Then there’s the power generator, cooling and lubricating liquids plus the multi-kilometre drill pipes, which typically come in 8-10 m lengths, 7-10 cm in diameter, with a weight of 9.9 kg per metre for the smallest diameter, making it an easy rule-of-thumb of 10 tons per kilometre (on Earth). To be of any use, you would probably have to be prepared to drill at least a couple if not five km or more down. That’s two trucks for the rig, one for generators, fuel and lubrication, and three for every two kilometres of pipe. Now you need a few more trucks for living quarters, supplies etc for those drivers and operators. We’re snowballing here…
Mars has no plate tectonics, and therefore no subduction zones and no spreading centres. Instead it has scattered regions where volcanism occurred. In the absence of subduction or spreading, these must be areas above a more vigorous mantle. Martian lavas appear to be basaltic. Magma is less dense than the mantle but denser than the crust. Therefore, at a certain depth it will have the same density as the surrounding rock. This is the depth of neutral buoyancy, and here is where the magma chambers will form which feed individual volcanoes. On Earth, this is typically at a depth of 4 km. On Mars, because gravity is weaker, the depth is 10-12 km. Larger magma reservoirs may also have existed deeper, where crust and mantle meet, and these could feed eruptions over large areas. Olympus Mons is so large that its magma chamber probably has migrated upwards, under the rising weight above.
Eruptions can be explosive under the right conditions: these are the jets of magma blobs thrown high in the air and raining down some distance away. This depends on the pressure outside of the volcano: high pressure stops the explosions from happening. On Earth, deep water eruptions are not explosive but explosions are possible close to the surface and certainly in the air. Venus has a very dense atmosphere and should not have explosions. Mars at the current time has hardly any atmosphere, and so eruptions can easily be explosive (you do need volatiles; volcanic gasses such as water, carbon or sulphur dioxide, in the magma). But on early Mars, under-water eruptions would not have been explosive, and in air, may not have been. We imagine Olympus Mons changing from non-explosive to explosive as it grew in height (lower air pressure at the top) and the Martian atmosphere was lost aftr the loss of the planet’s magnetic field. Olympus Mons may also have had so-called umbrella explosions, where the lava explodes into such a thin atmosphere that the air can’t stop it. It spreads much higher and further than a normal Plinian eruption, covering a larger area as an umbrella. Models predict that this may happen on Mars once volcanoes grow to a height of 20 km or more, so at 22 km above the datum, Olympus Mons eventually put it’s metaphorical nose just above the point where umbrella explosions would have been possible.
Turning to Olympus Mons itself, it was discovered by Mariner 9 in 1971 and the area was extensively mapped by the Viking Orbiter in 1976. The volcano has been the subject of several studies and papers since at least 1974 and is well described even if not fully explored and thus understood. The height of Olympus Mons depends on where it is measured from. There is no sea level on Mars! There is something called “the datum” which is the average altitude of the Martian surface which if applied to Earth would be about 2 km below our mean sea level. The peak of Olympus Mons is 21 km above datum. The height can also be measured from the local surroundings; from the foot of the surrounding escarpment to the peak which gives a figure of 22 km. Alternatively, it can be taken from the North Polar basin, which yields a height of 27 km. The gradient of the slope is quite shallow with an average of five degrees. Although the escarpment is precipitous in places, typically it is between 15 and 30 degrees.
There is evidence that the lower regions Olympus Mons have been covered by glaciers, even geologically quite recently. The climate on Mars is rather variable because the planet’s angle of tilt changes over time. So even though at the current time Mars only has glaciers near the poles (and mainly the south pole which is much higher), 10 million years ago glaciers would have been present much closer to the equator. This is why our explorers discover layers of ice; ancient glaciers buried, as Elena Trofimova says, “by pyroclastic deposits not hot enough to brew chai on”.
The age of Olympus Mons activity is disputed. It is younger than the Tharsis bulge, which makes it less than 4 billion years. The ground around Olympus Mons is depressed by the weight of the volcano. But there are flows in this area which go in directions which are not ‘downhill’, and are assumed to date from a time before the Olympus Mons had grown so large that its flexure changed the ‘down’ direction. One of these flows is dated by crater count at 3.67 billion years ago, and the suggestion is that Olympus Mons formed during or after this time.
On the other hand, the vast aureole deposits surrounding Olympus Mons to distances well over a thousand kilometres have been linked with collapse of the outer perimeter of the edifice that formed the up to eight kilometres tall escarpment. They must have formed when the mountain was largely its current size. The oldest aureoles are dated at 3.53 billion years, also based on crater counts. So the bulk of Olympus Mons would have formed in no more than 140 million years and possibly much less. That gives an average eruption rate of 0.03 cubic kilometers per year. For comparison, Hawaii’s Mauna Loa has an average eruption rate of 0.09 cubic kilometers per year.
Lava flows on volcanoes on Earth are typically 10-30 m thick. This is mainly determined by how fast the lava moves: the slower it moves, the thicker the flow. On Mars, gravity is 2.5 times less than on Earth, and therefore it moves 2.5 times slower down the mountain. So you would expect the flows to be much thicker than on Earth, up to 80 m. Flows up to 200 m thick are indeed seen on Martian volcanoes. But the flows on the slopes of Olympus Mons are reported to be only around 7m thick, rather less than expected. Near the caldera, thicknesses are around 11 m. These are the flows near the surface, the last ones to erupt. It is not known whether older (buried) flows had similar thicknesses.
The lack of impact craters in some areas is taken as evidence that some of the surfaces are very young, perhaps as young as 3 million years, and that therefore lava flows have continued to occur until the present day. We have chosen to go for Olympus Mons being a long extinct volcano. The reasons are that glacial activity can also resurface areas and wipe out craters. Furthermore, hot spots on Earth don’t live forever, so why should they on Mars?
Our own musings on Olympus Mons
Since Mars is covered by a fine layer of dust which effectively prevents detailed geological survey via spectroscopy from orbit and as no rover has yet explored its slopes, what is known about Olympus Mons is mostly based on educated guesswork such as when it began to form, how long it took to grow to attain its present size and shape and how long it was active. Much of this guesswork, especially the dating, is based on crater counts and the absence of medium to smaller craters is taken as evidence for the volcano to have been active possibly as recently as a few million years ago. However, as we point out in Part II, their absence could equally well be explained by the effects of erosion and landslides over the past 3.5 GY.
We began our own journey of exploration with two graphs, one showing a cross section of the present-day edifice, the other the temporal setting for two hypothetical types of hotspot energy output from circa 3.8 GY BP to about 20 MY BP, the alpha and omega of Olympus Mons according to the current view. Since these were open-ended, we did not exclude the possibility that Olympus Mons began to form below the surface of a primordial and hypothetical Martian Ocean, i.e. it started erupting sub-aquatically, then the eruptions became sub-aerial until loss of atmosphere changed the nature of even basaltic eruptions from effusive to explosive, the post-aerial period. It immediately became apparent that almost the entire edifice is the result of the latter type of eruption, hence even if Olympus Mons may initially have been a shield volcano, it must be regarded as a pyroclastic stratovolcano as the effusive eruptions that form shield volcanoes became impossible once Mars lost most of its atmosphere about 3.8 GY BP.
The current viev is that Mars formed at the same time as Earth and the other planets about 4.5 GY BP. The Tharsis Volcanic Province probably came into existence about or just before 4 GY BP and the giant volcanoes began to form somewhere around or just prior to 3.8 GY BP. This date is very important in the evolution of Mars as the planet lost its magnetic field at that date and any atmosphere would have been, geologically speaking, quickly stripped away by the Solar wind after which Mars was left with a very thin and tenuous envelope of air. Thus it is highly likely that the vast majority of the Olympus Mons edifice was built after this loss of atmosphere.
The Martian atmosphere is very thin, about 1/100th of Earth’s, and the current atmospheric pressure at “sea level” is 600 pascal (0.087 psi), about 0.6% of Earth’s of 101.3 kilopascals. The typical atmospheric pressure at the top of Olympus Mons is 72 pascal, about 12% of the average Martian surface pressure. At this kind of pressure, even the most modest content of volcanic gasses in the (basaltic) magma would result in at least Péléan if not Plinian eruptions. When the two facts of the age and type of eruptions are added together, the conclusion can be none other than that Olympus Mons is a volcanic edifice built by successive layers of pyroclastically deposited strata and thus is a stratovolcano and not a shield volcano, especially if thin layers of water ice lie between such strata as has been proposed as the explanation for the unusual escarpment.
For how long was Olympus Mons active? Without direct samples available for laboratory analysis, an approximation can be arrived at only by guesswork. There are two indirect ways to arrive at a reasonable figure for this. The first of this is a comparison with the hotspots of Earth. The longest chain on Earth is the Hawaii-Emperor Seamount chain that stretches from the still submarine Loihi just east of Hawaii to where the chain is being subducted beneath the Kamchatka peninsula. It is at least 85 MY old. The Kerguelen hotspot in the Indian Ocean is considered to be 130 MY old. The age of the Réunion hotspot has been proven by core samples to be 64 MY. Their age and geochemical data directly link the Galápagos hotspot track on the Pacific Ocean floor to the Caribbean large igneous province, which gives an age of 95 MY. The longest-serving, if the term is permitted, hotspot could be the Icelandic one if its identity as the hotspot responsible for the Siberian Traps Large Igneous Province, LIP, is proven. This would place it at 250 MY, but this proposal is contested. From Earthly evidence, it would seem that hotspots have a maximum age of about 200 million years at the most and there is no reason to think that Martian hotspots would deviate much from this value. From this inferred evidence, the eruptive period of Olympus Mons can be placed to between 3.8 to 3.6 GY BP and we can also postulate that it has been extinct for at least 3½ billion years.
The second method is to consider the lower limit for material erupted that would allow a magma reservoir not to solidify beyond the point of remobilisation. This figure has a lower limit of about 0.015 cubic kilometre per annum. If that is set in relation to the volume of Olympus Mons, we ought to arrive at an outer limit. As mentioned in the article, a cone with a base of 600 km and height of 22.5 km has a volume of 2.2 million km3. But OM is not conical. To begin with, it has a scarp as high as 8 km and much of the edifice extends substantially outside the conical approximation. Then the material lost to the ginormous landslides that cover the surrounding plains up to a distance of 1,000 km and beyond OM have to be taken into account, as well as the crustal deformation caused by the enormous weight of the edifice. If these are factored in, we arrive at back-of-the-envelope calculations of anywhere between 4 and 5 million km3. Were the latter, larger figure to have been erupted at the lowest realistic estimate rate of 0.015 km3 per year, we arrive at an outside figure of 333 million years. Again, the conclusion is that Olympus Mons has been extinct for about 3½ billion years. Thus the recent date derived by crater counts must be in error or the hotspot must have reformed at a later date. Since 3½ billion years of erosion and landslides would account for the dearth of young craters, it is the more likely explanation.
Will we ever explore Olympus Mons and the other Tharsis volcanoes? That depends upon the motives presented in favour of such an exploration. Intellectual curiosity will not be enough, there has to be a “hard need”. We believe that if humans are to successfully colonise Mars, they will require to be self-sufficient and not reliant upon shipments from Earth. In order to maintain the level of technology that their very survival requires, they must in all probability locate and exploit Martian sources of the Rare Earth Elements and Helium-3. This makes Tharsis with its giant volcanoes the best candidate. In all probability, such an initial exploration would take place using robot vehicles, rovers such as the incredibly successful Spirit and Opportunity, long before the final choice of location for our first Martian colony is made. Hence our story is likely to remain just that, a story. But it has been immense fun to write this mini-series and we hope that our viewers will have derived at least half as much enjoyment reading it as we did in writing it.