(2019 Archived) ARGUMENT X: Martian Soil Toxicity and Dust-Issues vs. The Sulphuric Acid Issues on Venus.

Having written this in 2019, and originally published in 2021.. when I was 15 and 17, there would be inaccuracies that I would correct here. Having removed it, I'm publishing  again, for sake of completion so that the efforts wouldn't have gone to vain: Most of this still stands true 

Mars is a brutally cold desert – a desert which is peppered with craters, grooved with valleys, pimpled with mountains, dead volcanoes, rocks and most importantly; covered with soil and dust. Mars is an exotic alien world, thereby making Martian soil and dust, exotic and alien too – unlike anything seen on the Earth. Though it may sound remarkable, this very exoticness and alien-nature of Martian soil and dust can come with the cost of being potential risks for Martian civilization. The impacts of Martian dust on human exploration, colonization and general performance on Mars is a multi-faceted problem^[32]. Martian dust could pose a threat to (1) the Health of the crew, (2) Surface Systems like the habitats, mobility systems, spacesuits etc. (3) EVA and Human-Surface Operations and (4) Near-surface electric fields.

Safe on Mars: Precursor measurements necessary to support human operations on the Martian Surface(2002), published by the National Research Council, was dedicated to addressing those issues. It discussed four principal problems with regards to Martian soil and airborne dust, as follows ^[32]:

1.     Airborne dust and soil on Mars could contain trace amounts of hazardous chemicals, including toxic metals.

2.     Equipment corrosion and Biological degrading.

3.     Hazardous atmospheric gases and Organic compounds.

4.     Inhalation of airborne particulate matter.

It also identified several issues with regard to dust intrusion, dust adhesion, dust accumulation, and dust abrasion.

Certain organic compounds and atmospheric gases, which might have been formed in the Martian atmosphere by photochemical reactions, are found to be toxic and hazardous to a human presence on Mars ^[32]. An ideal example of this is the presence of high concentrations of perchlorate compounds, which was found to be present across the Martian surface by the Mars Odyssey orbiter; which happens to be highly toxic to an exposed human ^[33]. This would be further confirmed by NASA’s Phoenix lander, which found Calcium Perchlorate on the Martian soil, to be at levels of about 0.5% – which is a level considered toxic to humans^[33].

Perchlorates were found not only toxic to humans, but also tend to accumulate in plants which are grown in it: A study in 2013 found that plants grown in concentrations of perchlorates, similar to those found on Mars would have; (1) reduction in the oxidizing power of plant roots, (2) an accumulation of concentrated perchlorates in the leaves, (3) a reduction in the size of the plant both above and below ground, and (4) a significant decline in the chlorophyll content in plant leaves^[34]. Though this would mean devastation to Martian agriculture, there are still counterarguments against it; we’ll see it in a consequent argument. Still, perchlorates could prove to have other dangers – such as when concentrations of it are exposed to the high UV flux at the Martian surface; it breaks the molecular bonds of the perchlorates and create even more dangerous compounds – compounds which are dangerous not only to the Martians or their crops, but even beneficial ecological bacteria ^[35]!

Similarly, there is the risk of toxic heavy metals diffused throughout Martian soil. Mars Pathfinder measurements established the presence of Chromium (a heavy metal) in Martian soil^{[32, 36]}. Though this chromium is primarily speculated to be Trivalent Chromium [Cr (III), which forms a +3 ion], which is rather stable and mildly toxic. But, to our distress, there is a risk of it being Hexavalent Chromium [Cr (VI), which forms a +6 ion], which is a highly toxic and unstable form of Chromium, being present not only in the soil, but also in airborne dust. “If even a modest fraction of the chromium present in the Martian soil and airborne dust is hexavalent chromium (more than 150 parts per million), it would pose a serious health threat to astronauts operating on the surface of Mars” ^[32].

Similar to soil toxicity, there is a risk of airborne particulate matter on Mars being accidently inhaled and ingested. Primary consequences of doing so would range from mild-illness to loss of chew ^{[32, 36]}. But, they might still have the potential to “cause irritation or disease that can compromise an astronaut’s health and their ability to carry out mission objectives” ^[32] – Especially the ‘irritation’ part. The basaltic minerals of Feldspar, Pyroxene and Olivine which are commonly found on Martian terra are quite reactive and oxidative. A similar equivalent of it here on Earth is fresh quartz dust, which inflame and scar the lungs, in a condition known as ‘silicosis’ – mostly felt by miners ^[37]. Except that, the basaltic minerals are much more reactive than regular quartz dust, which would not only inflame and scar the lungs; but also prove to be a carcinogen – a cancer causer ^[37].

More on airborne dust: Martian dust is fine and dry, which means that that they tend to be electro-statically attracted to one another. This could lead to charged dust particles being adhesive and accumulating near surfaces. Accumulation of Martian dust in kinetic and mechanical systems could lead to their abrading and wearing-off. It could also lead to the degrading of EVA suits, clogging of filters, decrease in visibility as in the optical parts of spacesuits, and accumulation of triboelectric charge. Similarly, Martian dust could accumulate in communication antennae and solar-panel arrays, which could disrupt critical interplanetary communication and lower the overall effectiveness of power-generating systems. It is also for this reason that Martian dust might penetrate into Martian habitats after EVA return: Dust might accumulate on EVA suits, which would enter into the Martian habitats along with the Martian ^[36].  But, why is this so bad?

Localized investigations of the Sojourner, Spirit, Opportunity, and Curiosity found compositions of elemental Chlorine in the Martian soil ^[33]. Similar investigations found Sulphur. The concentrations of Chlorine and Sulphur in Martian soil imply that Martian soil and airborne dust could be acidic; which could pose a threat to the Martians, when introduced into Martian habitats ^{[32, 36]}: Acidic soil could degrade human tissues when inhaled. Moreover, once humidified and allowed to penetrate control units; Martian soil could have the potential of corroding sensitive and critical instruments, including the control circuits ^{[32, 36]}.

Similarly, the abrasiveness of Martian dust might cause it to wear-off structures and mechanical machinery over time. Once penetrated Martian dust abrades critical life support systems – like those needed for air generation, air delivery and circulation, Carbon Dioxide removal and fire detection ^[32] – It would leave the Martians might be unable to house a human-supportive biosphere, which is synonymous to their certain doom – simply, due to dust!

The Venusian cloud-tops are devoid of dust on any kind – after all, it’s above the cloud-tops. There are no worries of ‘dust’ penetrating into the cloud-cities or abrading, accumulating, or toxicity. Non-existent dust cannot do any harm. But, the Venusian atmosphere has its own toxic – rather, corrosive – threat: Sulphuric acid. Venus ought to be infamous for its ‘precipitation’ of sulphuric acid, along its other extremities. It is for this reason that, it’s unanimously accepted that the Venusian atmosphere houses many species of sulphur, and sulphur aerosols: “Due to the lack of an ocean, most sulphur species on Venus reside in the atmosphere, attaining concentrations of ~105 times those in the terrestrial atmosphere. Four sulphur species have been firmly identified: SO₂ [Sulphur Dioxide], SO [Sulphur Oxide], OCS [Carbonyl Sulphide], and H₂SO₄ [Sulphuric Acid] (vapours and aerosols)” ^[38].

In order to properly deal with these sulphuric acid issues; everything outside habitats, includingthe outermost skin of habitats and likely-exposed regions, would have to be designed to be acid-resistant. But, how exactly do we make something acid-resistant? We simply have to cover them with acid-resistant coating! But, which materials could be used for the purpose. The HAVOC (High Altitude Venus Operational Concept) team, conducted experiments to find out:

Out of tested materials: Polyvinyl Chloride (PVC) underwent chemical change and lost its transmittance, with transmittance dropping from 80% to 48% in a day, and then to 43% in a month. PVC is not an ideal material for the purpose. But, polypropylene didn’t degrade and had a 90% transmittance. Nevertheless, it might degrade when exposed to temperatures above 50^oC. Teflon, on the other hand, had the highest melting point of tested materials, and performed even better with a transmittance of 90-93% ^[39]. Materials like Lead (Pb) and Tungsten (W) might give similar results as an acid resistant coating ^[8].But, Teflon and polypropylene are currently the most-recommended for solving the Sulphuric acid issues of HAVOC and future cloud-cities.

Since the cloud-cities are independent ecosystem in their own right, the only way Sulphuric acid would be able to intrude would be through a direct opening to the outside; which is almost improbable. Cloud-cities are likely to be connected in clusters – which would minimize the possibilities for direct contact with the Venusian atmosphere. Furthermore, if there were even any reason to be air-shipped from city-cluster to another or even from one archipelago to another; contact with the outside would be quite indirect and would often be a well-planned process. There would be little-to-no room for Sulphuric acid to infiltrate into the cloud-cities. Similarly, we might even be able to use it to our advantage:

While doing so, it would be helpful to get inspiration from how the Sulphuric acid got there in the first place: Owing to the mere magnitude of sulphur species in the Venusian atmosphere being great, Venus hasher own ‘sulphur cycle’. As for the part of the cycle running high-above the surface in the upper atmosphere: “Above the cloud tops, SO₂ is oxidized to SO₃, leading to the formation of H₂SO₄” ^[38]. If we were to simplify it;

At the outset, Sulphur Dioxide reacts with Oxygen to form Sulphur Trioxide, as follows

                           2SO₂ + O₂ → 2SO₃

Afterwards, the Sulphur Trioxide will further react with Water, and produce Sulphuric Acid, as follows:

                      SO₃ + H₂O → H₂SO₄ 

To our advantage, the aforementioned reactions of the Sulphur cycle are reversible! Firstly, it means that Sulphuric acid could thermally decompose into Water and Sulphur Trioxide, via heating [as depicted by (1)]. The Water produced by this reaction, would be safe for consumption; once determined to have a neutral pH, and mineralized. The Sulphur Trioxide, on the other hand, could be further thermally-decomposed into Sulphur Dioxide and Oxygen, as depicted by reaction (2); the oxygen produced is pure and breathable. The Sulphur Dioxide could be used in a Claus process.      

           

             H₂SO₄ + (∆Heat) → SO₃ + H₂O

2SO₃+ (∆Heat) → 2SO₂ + O₂         

Sulphuric acid is a very useful compound – as a reactant, catalyst, reagent and product – but, the above mentioned uses are quite sufficient for the purposes of this argument. I would tell you more of the wonders of Sulphuric acids in a future chapter. But until then, do note that Sulphuric acid is quite useful – after all, we managed to get Water and Oxygen out of it!

If we were to compare the risks of toxic Martian dust with Venusian Sulphuric acid – we would find Venus to be much safer for many reasons: (1) Airborne Martian dust or soil contain toxic compounds like Perchlorates, (2) Airborne Martian dust or soil might contain toxic heavy metals like Hexavalent Chromium. (3) Presence of Hazardous atmospheric gases and Organic compounds on Mars, (4) Inhalation or Ingestion of Martian particulate matter is carcinogenous, and could harm the Martian’s health, (5) Acidity of Martian soil could be harmful when introduced into habitats, (6) Abrasion and Accumulation of Martian dust could disrupt systems. (7) A simple acid-resistant coating is enough to deal with all Sulphuric acid issues. (8) Sulfuric acid is quite industrially and sartorially useful for Venusian civilization – it’s free! This is a wildly generalized list of everything we’ve learned in this argument; and it unanimously leads to the conclution that the Sulphuric acid issues of the Venusian cloud-cities are much easier to deal-with than the constraints of toxic Martian soil and airborne dust, with Sulphuric acid being quite an asset.

[8] Walker, R. (2014, January 12). Will we build colonies that float over Venus like Buckminster Fuller’s “Cloud Nine?”  Retrieved from (https://www.science20.com/robert_inventor/will_we_build_colonies_that_float_over_venus_like_ buckminster_fullers_cloud_nine-127573).

[32] Levine, J.S. (2017). Dust in the atmosphere of Mars and its impact on human exploration: A review of earlier studies. [Paper available online and for download at https://www.hou.ursa.edu/meetings/marsdust2017/pdf/6007.pdf].

[33] David, L. (2013, January 13). Toxic Mars: Astronauts must deal with perchlorate on the Red planet. [Retrieved from https://www.space.com/21554-mars-toxic-perchlorate-chemicals.html].

[34] He, H.&Gao, H.&Chen, G.&Li, H.&Lin, H.&Shu, Z. (2013, May 15). "Effects of perchlorate on growth of four wetland plants and its accumulation in plant tissues". Retrieved from Environmental Science and Pollution Research International, Volume 20, Issue 10, pp 7301–7308. [Retrieved fromhttps://link.springer.com/article/10.1007%2Fs11356-013-1744-4].

[35] The Guardian. (2018, November 27). Mars covered in toxic chemicals that can wipe out living organisms, tests reveal. [Retrieved from https://www.theguardian.com/sciences/2017/jul/06/mars-covered-in-toxic-chemicals-that-can-wipe-out-living-organisms-tests-reveal].

[36] The National Research Council. (2002).Safe on Mars: Precursor measurements necessary to support human operations on the Martian Surface. Chapters 3-4; pages 15-36.

[37] Hecht, J. (2007, March 9). Martian Dust might be hazardous to your health. [New Scientist]. Earth & Planetary Sciences Letters, volume 225, page 41.

[38] Yung, Y.L. & Yang, D. & Lee, C. & Liang, M.C. & Chen, P. (2016, September 2). The Sulfur Cycle on Venus: New insights from Venus Express. [Paper available online and for download at https://www.researchgate.net/publication|252473703704_the_sulfur_cycle_on_venus_new_insights_from_venus_express].

[39] Arney, D. & Jones, C. (2015). HAVOC: High Altitude Venus Operational Concept – An Exploration Strategy for Venus. SPACE 2015: AIIA Space and Astronautics Forum and Exposition. 31 August- 2 September, 2015. Pasadena, California. [Paper available online and for download at https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160006329].

Achinthya Nanayakkara (30.03.2025)

Originally published - 2021 (now removed)

Originally written - 2019