Introduction II: Brave New Mars

Now narrated by Dagoth Ur!

[Author’s note: Some of the things mentioned here about modern day Mars are very much true, but others are very much not for the sake of making this scenario work. Some things, such as the atmosphere and temperatures, are extrapolated either from pre-Mariner-era papers (such as Salisbury 1962), current work about prehistoric Mars billions of years ago (Ramirez 2017 and especially Palumbo & Head 2018) or are completely made up by me. For immersion’s sake, I did not bother to mark which information is which, you should therefore never use this page as an actual reference for real life current day Mars and instead do your own research.]

Welcome to Mars, ladies and gentlemen. My name is Ogilvy, retired lead-astrobiologist on the Horus-2 Operation. After Horus-1 had already successfully brought the first humans to Mars and made contact with native life, the goal of Horus-2 was to resupply the Horus-1 teams, establish permanent research settlements and to further study the fauna and flora of the planet, which I believe we did a great job at. Horus-2 consisted of five orbital stations powered by nuclear-electric propulsion, each coming with smaller landing crafts attached. The stations were assembled in Earth-orbit and possess each a nuclear reactor at the bottom.

Fig. 1: Horus-22, my old ship, drawn from memory.

Apart from providing heat, the reactor evaporated silicon oils into steam, which then rises through a central shaft to then power a turbine, which generates electricity. The steam that has already passed through the turbine is funnelled into a giant, circular cooler, where the frost of space can condense it again to flow back to the reactor. The main method of propulsion of the stations are ion-thrust chambers, where the generated electricity is used to charge a platinum grid. Through this grid is then blown evaporated caesium. The charge ionizes the caesium-atoms, which are then blasted out into space at a rate of billions per second, thrusting the spaceship forward at incredible speeds. At the top of the ships, opposite the reactor and shielded from it by the cooler, were the living modules that could house teams of up to twenty astronauts and generated artificial gravity through centrifugal rotation. Atop the modules sat the auxiliary landing gears. After circling Earth for four months, enough speed was generated to escape its gravity and slingshot towards Mars for seven months. Once its gravitational field was entered, two more months of deceleration were needed to sink into a lower, stable orbit around the red planet. Once settled, the landing gear was manned and each ship’s crew landed in a different region of Mars. My team, the crew of the ship Horus-22, landed in Arabia Terra to successfully make contact with the previous crew of Horus-14. Despite minor setbacks, the Horus-2 Operation was an outstanding success and laid the most crucial groundwork for all future Horus missions.

The Basics of Mars

Mars is the fourth planet from the sun and the outermost of the rocky planets. Compared to Earth, it has a significantly more elliptical orbit, with Mars being 1.38 astronomical units close to the sun at perihelion to then retract as far as 1.67 AE at aphelion. A year on Mars lasts the equivalent of 687 days (1.88 Earth-years). The day-length on Mars is on the other hand close to that of Earth, lasting 24 hours and 38 minutes (meaning a year actually lasts 668 Mars days). What is more difficult to adjust to for astronauts than the daylength is the low gravity. Mars is only about half the diameter of Earth and thus has only about 38% of our homeworld’s gravity or 0.38 g. Mars has no large moon like Earth, instead only two smaller satellites called Phobos and Deimos, which might either be captured asteroids or the remnants of proto-planetary collisions. The magnetosphere of Mars is weak and partially regionalized by magnetised rocks.

Geography and Geology

Modern Mars lacks any oceans or comparable large bodies of water. Today, the Martian surface consists largely of layers of volcanic rock, lain over by thin sheets of sand and dust. These are what mainly gives Mars its red coloration, as they consist of eroded iron oxides. In general, the Martian crust is much richer in iron than that of Earth, likely because the lower gravity did not pull most of the iron atoms towards the planet’s core during its creation. Under the volcanic layer are often deep pockets of ice and, in warm enough regions, groundwater. Under the ice usually lies primordial regolith. In the more poleward regions, the water lies much closer to the surface in the form of permafrost, creating tundraic environments. Sedimentary rocks are mostly common in the northern hemisphere for reasons soon discussed.

Fig. 2: Topographic map of Mars, showing the distinct difference between the northern and the southern hemisphere, as well as the extreme height of the Tharsis Plateau and the depths of the Hellas Basin.

As Mars lacks oceans by which to cartograph coastlines, the planet’s geography is best explained by use of a topographical map. As can be clearly seen, there is a significant dichotomy between the low-lying and almost smooth-surfaced northern hemisphere and the taller, much more cratered and ancient southern hemisphere. If this difference evolved through massive impact events in the north or through internal tectonic processes is not known. Ironically, the highest point on Mars, the titanic shield volcano Olympus Mons, lies in the northern hemisphere, while the lowest point, the Hellas Basin, lies in the south. There is good reason to believe that most of the lower northern hemisphere was once the basin of an ancient ocean, hence the many sedimentary layers found here and the fossil deltas and estuaries that can be found at the north-south boundary. The remnants of this ocean now lie beneath the surface in the form of massive fields of permafrost ice around the polar circles.

Fig. 3: Mars Odyssey’s map of sub-surface water and ice on the red planet.

Mars has stopped having plate tectonics very early in its history, with features like Valles Marineris being the last remnants of such processes. What mostly shapes the surface of the planet are thus impact and dust storm events, the formation and eruption of massive shield volcanoes, erosion and deposition by seasonal streams of water and especially glaciers, as well as the actions of lithotrophic organisms. Geosyncline forces created by the shrinking of the cooling planet may also be an important, though understudied factor. While the crust is mostly inactive, the core remains molten and many of the volcanoes still show signs of fairly recent activity.

Atmosphere and Biosphere interactions

The average air pressure felt on Mars at mean global altitude is 0.51 bar, which is the pressure you would feel on Earth if you were standing on the highest points of the Alps. One may question how Mars has a relatively complex ecosystem with such low pressures while mountaintops on Earth are deserted, but the latter case is usually more due to the topography than the air pressure. Flat plateaus of similar altitudes in the Andes mountains are stable enough to give vegetation room to grow and animals to roam and such is also the case on the wide plains of Mars.

The air on Mars consists mainly of 75% carbon dioxide, 10% hydrogen, 9-10% oxygen, 3% nitrogen and the remaining 2% consisting of noble and volcanic/biogenic greenhouse gases. This is in stark contrast to Earth’s, where nitrogen and oxygen are the main constituents. While the pressure is survivable enough without a spacesuit, under current conditions, an astronaut with a broken breathing gear will suffocate on Mars, as has infamously and unfortunately happened to a crewmember of the Horus-4 Operation that came after us.

The native life is however perfectly in tune with the planet’s nature. The vast majority of lifeforms on Mars, including the multicellular flora and fauna, are either obligate or facultative hydrogenotrophic methanogens. This means they can react the CO₂ of the atmosphere with H₂ to generate the energy they need for living. The waste products of this metabolism are water and methane, which rise into the air as potent greenhouse gases, before the sun breaks them up into their constituents, which are then breathed in again by the lifeforms. Through this cycle, life on Mars has apparently been able to keep conditions for itself habitable for a long time, though it has not been able to completely stave off the loss of the atmosphere and much of the water vapor to the solar winds.

The large amount of hydrogen in Mars’ atmosphere poses a great mystery. While likely to have been a major part of its primordial atmosphere, like on Hadean Earth, hydrogen is the lightest known element in the universe and the planet’s low gravity would therefore dictate that almost all of it should have quickly escaped into space ever since. That this did not happen suggests either that some atmospheric effect is preventing escape into space or that there is a constant source of free hydrogen resupplying the atmosphere. Neither potential factors have yet to be clearly identified. For the production factor, it has been proposed that some geochemical processes deep inside Mars may be performing natural versions of otherwise industrial hydrogen-generators, such as steam reforming, where heated methane is reacted with steam. Various organisms on Earth are also known to produce hydrogen through anaerobic metabolisms and the same is most likely also true on Mars, though it could be occurring on a much vaster scale deep underground. More radical ideas have also been proposed, such as all of Mars’ current hydrogen coming from a geologically recent event that has been called the “hydrolysis-catastrophe”, where somehow most of the water on the surface was instantly or in multiple phases split up into its constituents. What could have caused this has never been sufficiently explained and it seems highly unlikely that such an event ever occurred given our current evidence. As for the prevention factor, it may be, as mentioned above, that the biosphere recycles the hydrogen before it can escape to space, though this would only work close to the ground. It has been proposed that in the past, when Mars was more habitable, the air was filled by vast swarms of aeroplankton, which would have helped recycle the gas more evenly through the atmospheric column. If true, today’s lack of aeroplankton on most of Mars will have a negative influence on its hydrogen balance in the future, fuelling a self-propelled cycle of worsening habitability. Without hydrogen, many lifeforms will lose a metabolic resource, while the planet will also get drier. While not itself a greenhouse gas, hydrogen’s presence in the atmosphere also lengthens the longevity of methane and ozone, so this trend will also lead to even colder temperatures and worsening UV-radiation.

 Oxygen appeared in the Martian atmosphere only gradually and later in its history and is used only secondarily by its biosphere. Its concentration in the atmosphere is just high enough that macroscopic, multicellular organisms can use it for respiration and also just low enough that anaerobic organisms are not too impeded by its presence. Many of the Martian “animals” possess a complex lung system that can utilize both forms of respiration, though to differing degrees. There are mainly three pathways by which oxygen is produced on Mars and we will discuss these on another page. 

A rather bizarre factor about the atmosphere, and a major challenge to our engines and reactors, is that it is potentially explosive, as hydrogen and oxygen can react violently with each other in the so-called Knallgas-reaction. The autoignition temperature of this reaction is under normal Earth-conditions 500 degrees Celsius, however, and even higher on Mars with its low atmospheric pressure. As most of the planet is very cold and there is not much vegetation to cause wildfires, this reaction does not occur naturally outside of maybe lightning strikes. But lightning is, counterintuitively, not a regular feature of the Martian atmosphere, as it requires a difference in charge between the cloud and the ground separated by a gap of  normally non-conducting medium. Mars lacks this characteristic, as the ever-present dust clouds can fill up the whole atmosphere and act as an electrically conducting medium, leaving no chance for charge-differences between ground and sky to build up (Morden 2021). In the very rare cases where lightning strikes do occur, they are truly devastating. Acts of God is perhaps the only apt description. Thankfully, the fires caused by these explosions are short-lived, as the product of the Knallgas-reaction is water, which douses the flames.

The most major factor that actually impedes life on Mars are the low concentrations of nitrogen (though even on Earth, lifeforms are able to only utilize a very small amount of the nitrogen in the air, with most heterotrophs gaining it through ingestion of other creatures). This has however led to some remarkable innovations by nitrogen-fixing lifeforms.

Weather, Climate, Biomes and Climate Change

Fig. 4: Top: Rough temperature zones on Mars, polar circles excluded. Compare and contrast with the topographical map. White areas encased by a solid black line mark regions of permanent ice. The solid red line marks the 273K-isotherm (0 degrees Celsius). The red dotted line marks the 283K-isotherm (10° C). The black-dotted areas mark regions where the mean annual temperature (MAT) is below freezing point and are therefore dominated by tundra or snow wastes. The blue area between the two isotherms is where the MAT rises above freezing and where meltwater from the highland regions humidifies the ground enough for shrublands to exist, though the actual extent of these biomes is far smaller than the blue area due to the lack of rainfall. In red dotted areas the MAT is above 10°, but the low precipitation only permits steppes, cold deserts and sometimes hot deserts. Only in the Hellas Basin does the MAT reach above 20° and the large amounts of meltwater around the crater create a high groundwater-table. This allows for an environment analogous to a savannah. Bottom: The same map, but with more emphasized color-coding for better convenience.

Mars is generally a very cold place. While the mean annual temperature on Earth is around 14 degrees Celsius, the long distance from the sun and the thinner atmosphere conspire to make the MAT on Mars only about 2° C, only a little bit above the melting point of water. Due to the varied geography, this temperature is however not equally distributed. The southern hemisphere is usually much colder than the northern one, with the geographical delineation between the Northern Lowlands and the Southern Highlands also being the 273 K (0° C) isotherm. Most of the south therefore has an MAT below freezing point and the region is mostly covered in year-long ice all the way up to latitudes 60 degrees south. Temperatures above freezing point occur in most of the highlands only in the warmest parts of summer for only 100 Mars days or less. The exception to this cold southern climate is the quite warm Hellas Basin, thanks to its depth generating higher air pressures and therefore greenhouse effects. Another especially cold region is the very tall Tharsis Plateau, whose volcanic summits stay frozen the whole year. Most of the northern hemisphere meanwhile enjoys mean temperatures that can reach from 10 to 20 degrees. Some of the warmest summer days may even peak above 40. On Earth, such temperatures would be enough to permit trees to grow, however, such vegetation is almost completely absent on Mars due to the aridity. Precipitation in the form of rain occurs only on 0.8% of the planet’s surface and, ironically, only in the Southern Highlands, as the altitude causes adiabatic cooling of the clouds. The majority of precipitation, occurring on about 31% of the surface, instead comes in the form of snow. The north is therefore arid because most of the water that evaporates from it travels south and becomes trapped as snow or ice. Most complex flora is therefore dependent on meltwater coming from the polar ice caps and tundras or groundwater welling up from oases. In terms of the biomes of Mars, as one generally travels from the South to North Pole and ignores special regions, one begins with eternal ice, followed by vast hyperalpine tundra, then thin bands of taiga, shrubland and cold, craggy deserts, flat hot deserts and flat cold deserts or steppes, followed by a thinner strip of flat tundra and then again eternal ice.

Fig. 5: Mars during one of the worser global dust storms. The southern polar cap and the Hellas Basin are barely visible through the veil.

The aridity and lack of deep-rooted vegetation coupled with erosion creates large amounts of dust on Mars, which through summer heat becomes highly activated and can form into gigantic dust storms. These can sometimes envelop the whole planet for a few months. Most organisms have learned to cope with the ever-present dust and some even thrive off it.

The rather bizarre climate dichotomy of Mars’ hemispheres is explained by its seasons. A year on Mars lasts almost twice as long as on Earth and its seasons are caused by its axial tilt. Currently, this tilt is at around 25 degrees, which is not actually that far off from Earth’s value. However, Mars’ orbit around the Sun is far more eccentric than on Earth. These conditions cause the northern hemisphere to be closest to the Sun during its winter and farthest during its summer, creating mild seasons. As a consequence, though, the southern hemisphere is farthest from the Sun during its winter and closest during its summer, making for more extreme seasons, especially combined with the long length of a year. Northern Spring/Southern Autumn lasts 193.3 Mars days/sols, Northern Summer/Southern Winter lasts 178.6 sols, Northern Autumn/Southern Spring lasts 142.7 sols and Northern Winter/Southern Summer 154 sols.

There are plenty of signs that it has not always been like this. Mars, like the Earth, goes through Milankovitch cycles, wherein values like the axial tilt wander between 15 to 35 degrees every 124’000 years, the precession changes every 171’000 years, and the orbit can vary from elliptical like today to nearly circular like Earth every 100’000 years. Sometimes these cycles reinforce each other, sometimes they cancel each other out. There is now strong evidence that between 2 million and 400’000 years ago, a stronger axial tilt and a more circular orbit made Mars go through a warm age, in which the MAT was higher and precipitation by rainfall was more common. Possible fossilized forests in Isidis Planitia may attest to this. Currently Mars seems to be going through a colder phase, with conditions possibly getting even colder in the future, though some models also predict another warm age. As one goes even deeper into the past, changes become more drastic, as evidence amounts that up to two billion years ago an actual ocean had existed on most of the northern hemisphere, the atmosphere was much thicker and global temperatures may have reached 20 degrees on average. Fossils of megafauna and likely ancestors of modern lifeforms are known from this time. We are not currently at the capacity to discuss or interpret these finds in detail, though future volumes such as Sivgin 2345 are currently being worked on and I kindly refer the reader to those. The reason for why Mars has stopped being this Earth-like is likely its lower gravity making space escape of volatile gases in the atmosphere easier. Photolysis by the Sun has broken up much of the former water vapor into its constituents, with the much lighter hydrogen escaping into space and leaving oxygen behind. Though biosphere interactions and the build-up of an ozone layer have partially mitigated this, billions of years of solar bombardment have nonetheless taken their toll.

References:

• Heldmann, Jennifer et al.: FOLLOW THE WATER: APPLYING A MARS EXPLORATION STRATEGY TO THE ARKAROOLA ANALOG REGION, SOUTH AUSTRALIA, in: American Astronomical Society, 6, 2006, p. 71 – 92.
• Morden, Simon: The Red Planet. A Natural History of Mars, London 2021.
  
• Palumbo, Ashley & Head, James: Early Mars Climate History. Characterizing a “Warm and Wet” Martian Climate with a 3-D Global Climate Model and Testing Geological Predications, in: Geophysical Research Letters, 45, 2018, p. 10249 -10258.
• Ramirez, Ramses Mario: A warmer and wetter solution for early Mars and the challenges with transient warming, in: Icarus, 297, 2017, p. 71 – 82.
• Salisbury, Frank: Martian Biology. Accumulating evidence favors the theory of life on Mars, but we can expect surprises, in: Science, 136, 1962, p. 17 – 26.
• Sivgin, T.K.: Life on a Dead Planet. The first 3 billion years of Evolution on Mars, Zürich 2345.

Image Sources:

• Fig. 2: Goddard Space Flight Center
• Fig. 3: Heldmann et al. 2006.
• Fig. 5: JPL photojournal