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Water, Martian Dirt and Life

Water, Martian Dirt and Life

In a paper just released, “Mars soil contains a huge amount of water, reports NASA’s Curiosity rover.” (1) If you’re interested in making drinking water, check out this video: So Mars Has Water. Could We Drink It?

Unfortunately, getting potable water out of the soil will be difficult, especially with all the oxychlorine compounds (2). If you’re interested in making rocket fuel to get back to Earth, it’s a lot simpler, especially if you’re willing to deal with liquid oxygen and hydrogen. (3)

But what does this mean for life?

Extremophiles are organisms that can live and even reproduce in extreme conditions: cold temperatures, hot temperatures, high salinity, etc. The rule of thumb is that on Earth, life “finds a way” in conditions that, a decade or two ago would have been considered deserts. It’s convenient that I mention deserts, because the Atacama desert in Chile is one of the driest places on Earth and there are microbes there that are xerophiles. Xerophiles like (or are at least tolerant of) dry conditions. At this point, it’s apparently obligatory for science writers to mention that the mold (mould to my non-American-speaking readers) that grows on bread is a xerophile. (4) Lichens can be xerophiles capable of surviving (although not necessarily growing in) Mars’ atmosphere, radiation, temperature, and so on. (5)

Extremophiles can survive a water activity of less than .8. (6) Observations from orbit produce estimates that Mars may once have had a water activity of .78 to .85 due to salt concentrations, but the water actuvity has dropped severely as Mars dried out. Even during it’s wettest stage, Mars’ water was very briney. Terrestrial Xerohiles evolved from ancestors that evolved in a very wet environment. Can life evolve from nonliving precursors without a decent water activity? If Earthlife first formed in tidal pools or hydrothermal vents, then Mars life would have to have taken a different path and it’s biochemistry will almost certainly be different from life on Earth. But if life evolved from areas that went through cycles of repeated dessication and hydration, then any life on Mars might be surprisingly similar to Earthlife. (7)

It’s worth noting that many xerophiles are also halophiles. The salts in the Martian soil may actually be helpful.

But let’s get back to Mars’ surface now. What’s the water activity in the soil? Is it enough for some sort of xerophile understanding of the chemistry of the Martian regolith (8), it’s a little hard to predict. We can invoke all sorts of chemistry where water is one more nutrient to be scavenged from the environment. But remember that scavenging means pulling something against a gradient, and that takes energy.9) That’s less energy to be spent on reproducing and more on basic survival, which makes life less likely.


Do you remember that I mentioned that organisms that like dry conditions (xerophiles) tend to be halophiles (organisms that like salts)? A lot of salts tend to be hygroscopic. Hygroscopic compounds are ones that pick up water from the environment. Absorption of water is naturally energetically favorable. Every time you pull one of those desiccant packets out of a pill bottle or from the electronics equipment packaging, you see hygroscopic compounds in action.

If there is life on Mars, it’s probably going to have a lot of salts in it. (10) If it’s very salty, it doesn’t have to get rid of much of the salts and those salts might actually allow the organism to extract water from the environment without using energy. Less energy to get water, more energy to reproduce.

Cool how that works out.

But, lest we forget, we don’t know Mars. This is all speculation. I would say we haven’t seen any life on Mars, but then I’d have to get into a discussion about the Viking landers from the 1970s. And there were those meteorite “fossils.” But we’ve not seen any definitive and agreed-upon signs of life on Mars that aren’t easier to explain by non-living processes. We sure don’t know about the biochemistry of any life on Mars if it exists. This article is riffing on possibilities. I like to play with ideas. Heck, I expect Mars will be dead and either never had life or the life went extinct very shortly after forming. But wouldn’t it be pretty if Mars had life today? Giant yellow ducks aren’t the only way I have fun. (11)

Anyone quoting from my article to prove the Face on Mars and the Martian pyramids were created by aliens is totally abusing the science and should be ignored.



  1. The original paper is here, unfortunately behind a paywall: Volatile, Isotope, and Organic Analysis of Martian Fines with the Mars Curiosity Rover. []
  2. Possibly the oxychlorine compounds are perchlorate, which is a serious water pollutant here on Earth and the oxidizing agent in high power rocketry motors. Yeah, my hobbies sometimes come in conflict []
  3. The basic technique for creating oxygen and hydrogen out of the Martian soil is an exercise left to the reader. The actual chemical engineering involved in creating automated stations to create tanks of liquid oxygen and hydrogen on Mars to await human explorers is an exercise left to the people designing the Human Exploration of Mars Project–or second year Chem Es taking a sadistic final. []
  4. Seriously, anything I can find on xerophiles mentions bread. Anything. Really. Tardegrades (water bears) are also mentioned, but they simply go inert with a lack of water. Yes, Mars may have had life a long time ago and it may have survived inert like a tardegrade, but I’m evaluating the concept that there’s something happily reproducing on Mars right now. If there’s a bacteria, Cthulhu fhtagn that lies dead in a Martian crater called R’lyeh waiting for some human to disturb it by adding water, well, that’s nice, but it’s not what I’m interested in right now. And, seriously, if someone finds a dehydrated pathogen on Mars that drives humans mad, I want credit for describing it. []
  5. The resistance of the lichen Circinaria gyrosa (nom. provis.) towards simulated Mars conditions—a model test for the survival capacity of an eukaryotic extremophile, and yeah, it’s behind a paywall, so I could only read the summary. []
  6. Think of water activity as a way of comparing dew points at any temperature, with 1 being water with no impurities, .98 being sea water, .8 being Atacama desert dry and 0 being no water at all. []
  7. If we find life on Mars, the questions will be whether it’s truly Martian life or simply contamination brought from Earth. The best proof that it’s life that evolved on Mars would be that the biochemistry is radically different, using a different set of nucleotides, a different nucleotide code, and/or different basic amino acids. If life evolved in different conditions, the odds the biochemistry is radically different go up. And I feel the need to address the possibility of panspermia from Mars to Earth. Because Mars may have been wet and at least lukewarm before Earth, life that evolved in a brinewater could have been removed from the Martian surface by a meteorite impact and survived the trip to Earth. In this scenario, the Marslife would have had to adapt to excess water, and would have been (relative to Mars life) a hydrophile. Personally, I doubt life evolved on Mars first. Warmer chemical reactions go faster and evolving life from non-life is probably a difficult step. Earth had more “chances” to evolve life because it was warmer. But I could be wrong. I did just write a post about how life does better in cooler ocean water, didn’t I? []
  8. Essentially, regolith is the geologist and planetary word for dirt. []
  9. (Have I mentioned lately how wonderfully useful thermodynamics is and yet how much I hated my three Thermo classes? []
  10. I’m thinking chemistry-type salts here: an anion plus a cation. Salt is, not surprisingly, a salt, but so is magnesium chloride, sodium bicarbonate, etc. []
  11. Pittsburgh where I live has a giant yellow rubber duck floating in one of our rivers right now. I think it’s fun. It’s not logical, it’s fun. If you don’t think 40 ft. high giant yellow rubber ducks are fun, you don’t have to. I do. As strange as this blog has established me to be, apparently my enjoyment of giant yellow rubber ducks is proof I am not totally non-human. A lot of other folks are fascinated by this artwork, too. []

Written by Rob Carr


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