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Friday, November 9, 2018
Vlada Stamenkovi? and his colleagues developed a new model which raises the possibility of oxygen-rich brines on Mars; enough, perhaps, to support simple animals such as sponges. One of our voluntary reporters for Wikinews caught up with him in an email interview to find out more about their research and their plans for the future.
The atmosphere of Mars is far too thin for us to breathe, or indeed, to extract any oxygen at all in our lungs. It has on average only around 0.6% of the pressure of Earth’s atmosphere, and it is mainly carbon dioxide; only 0.146% of that is oxygen. Yet the result of their modeling was clear, these minute traces of oxygen should be able to get into salty seeps of water on or near its surface, at levels high enough to support at least some forms of microbial life that require oxygen, and possibly higher life too.
As interviewed by Wikinews:
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VS: Our work really opens up new possibilities for the Martian habitability, and that’s why it’s so exciting!
As previously interviewed by National Geographic (October 22):
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Vlada Stamenkovi?: We were absolutely flabbergasted. I went back to recalculate everything like five different times to make sure it’s a real thing.
However, the simulations were clear. At the extreme low temperatures found on Mars, microbes, and maybe even simple sponges, may have enough oxygen to survive in these briny seeps.
So, why briny seeps rather than fresh water? Mars is so dry because fresh water is not stable over most of its surface. Even with the higher pressure at the depths of the huge ancient impact crater of the Hellas basin, with a boiling point of 10 °C, it is close to boiling point already at 0 °C, and would evaporate rapidly.
However, salty brines can be liquid at much lower temperatures. Salts and very salty brines can actually take in water from the atmosphere at low temperatures. Curiosity discovered indirect evidence of this process (through humidity measurements). It found that brines form during winter nights in the top 15cm of the soil through deliquescence, taking up water from the atmosphere at around -70 °C. This water then evaporates again as the soil warms up through the day, and the process repeats every day – night cycle.
There is other indirect evidence that salty brines may exist, perhaps more habitable than the Curiosity brines, even though the atmosphere is so thin and the climate so cold. In their paper, the authors mention one of the lines of evidence, the hydrated magnesium and calcium salts associated with the Recurring Slope Lineae. These are seasonal streaks that form in spring on sun facing slopes, extend and broaden through the summer and fade away in autumn. These streaks are not thought to be damp patches themselves but may be associated with thin seeps of brine just below the surface.
If these habitats do exist, scientists have assumed up to now that any life on present day Mars had to be capable of growth without oxygen. Based on Mars simulation experiments, these could include certain blue-green algae such as chroococcidiopsis, some black fungi, and some purple salt loving haloarchaea found in salt ponds and hypersaline lakes on Earth.
The significance of oxygen is that it permits a more energy intensive metabolism and perhaps even true multicellular animal life such as simple sponges. Almost all complex multicellular life uses oxygen.
As previously interviewed by Scientific American (October 22):
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VS: Our work is calling for a complete revision for how we think about the potential for life on Mars, and the work oxygen can do, implying that if life ever existed on Mars it might have been breathing oxygen
The authors cite research from 2014 that showed that some simple sponges can survive with only 0.002 moles per cubic meter (0.064 mg per liter) . Some microbes that need oxygen can survive with as little as a millionth of a mole per cubic meter (0.000032 mg, or 32 nanograms per liter). In their model, they found that there can be enough oxygen for microbes throughout Mars, and enough for simple sponges in oases near the poles.
This isn’t the first suggestion for multicellular life on Mars. Some lichens, such as Pleopsidium chlorophanum are able to survive in close to Mars-like conditions high up on Antarctic mountain ranges, and show promise in Mars simulation chamber experiments. However, they can do this because the algal component is able to make the oxygen needed by its fungal component. Even animal life is not completely ruled out in anoxic brines. These are not candidates for life on Mars, but three species of Loricifera, tiny animals about the size of a large amoeba, are able to survive without oxygen in deep extremely salty mud sediments in the Mediterranean.
However, this new research greatly expands the possibilities for complex life on Mars.
The paper includes a map of potential brine oxygen concentrations for the surface of Mars (their figure 4). These would be higher at the lowest points such as the floor of the Hellas basin, south of the equator, where the atmospheric pressure is highest, reaching around 1% of Earth’s atmosphere and lowest of all in the mountainous southern uplands.
However the highest oxygen concentrations of all, occur when the water is colder, which is most easily attained in polar regions. They studied mixtures of magnesium and calcium perchlorates, common on Mars. In simulation experiments these stay liquid as they are supercooled to temperatures as low as -123 to -133 °C before they transition to a glassy state. They do this even when mixed with the soil of Mars (regolith). It’s at these very low temperatures that the optimal oxygen concentrations can be reached.
They found that oxygen levels throughout Mars would be high enough for the least demanding aerobic (oxygen using) microbes, with around 25 millionths of a mole per cubic meter (0.0008 mg per liter) even in the southern uplands. However it is here at the polar regions poleward of about 67.5° to the north and about ? 72.5° to the south, that oxygen concentrations could be high enough for simple sponges. Indeed the paper suggests that in regions closer to the poles, concentrations could go even higher, right up to the levels typical of sea water on Earth, 0.2 moles per cubic meter (6.4 mg per liter). With their best case estimate and supercooling it could potentially go up all the way through to levels far higher than those in sea water, at two moles per cubic meter (64 mg per liter – a mole of oxygen is a little under 32 grams). . By comparison worms and clams that live in the muddy sea bed require 1 mg per liter, bottom feeders such as crabs and oysters 3 mg per liter and spawning migratory fish 6 mg per liter. Saturated sea water is about 9 mg per liter at 20 °C ranging up to 11 mg per liter at 0 °C.
Wikinews asked him whether their research suggests potential for life as active as this.
((Wikinews)) Does your paper’s value of up to 0.2 moles of oxygen per cubic meter, the same as Earth’s sea water mean that there could potentially be life on Mars as active as our sea worms or even fish?
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VS: Mars is such a different place than the Earth and we still need to do so much more work before we can even start to speculate.
In their model, Oxygen gets into the brines at the poles so readily because they may reach extremely cold temperatures. These are far below the usual cold limit of life. It is not a hard limit because life gets slower and slower at lower temperatures to the point where individual microbes have lifetimes of millennia. Such life is hard to study, to see whether it is active and able to reproduce at those temperatures or dormant. But the usual limit cited is -20 °C. That’s well above the lowest temperatures studied in the paper which go down to -133 °C.
Dirk Schulze-Makuch has proposed that Martian life might evolve an exotic metabolism with the perchlorates of Mars taking the place of the salts inside the cells of Earth life. This would have advantages on Mars, with the brines inside their own cells acting as an anti-freeze to protect them against extreme cold. Also with their salts being so hygroscopic, they may help them scavenge water from the atmosphere and their surroundings.
With this background, Wikinews asked:
((WN)) The temperatures for the highest levels of oxygen are really low -133 °C, so, is the idea that this oxygen would be retained when the brines warm up to more habitable temperatures during the day or seasonally? Or would the oxygen be lost as it warms up? Or – is the idea that it has to be some exotic biochemistry that works only at ultra low temperatures like Dirk Schulze-Makuch’s life based on hydrogen peroxide and perchlorates internal to the cells as antifreeze?
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VS: The options are both: first, cool oxygen-rich environments do not need to be habitats. They could be reservoirs packed with a necessary nutrient that can be accessed from a deeper and warmer region. Second, the major reason for limiting life at low temperature is ice nucleation, which would not occur in the type of brines that we study.
His first suggestion here is that the cool oxygen rich reservoirs could have warmer water come up through them from below. He doesn’t say where the warm water would come from, but one possibility is from geological hot spots. Our orbiting spacecraft have not yet found any, but Olympus Mons has been active as recently as 2.5 million years ago. If sources of warmer water could rise to the surface from below and encounter these cold oxygen-rich brines, life could make use of oxygen where the two mix.
The other possibility is an exotic biochemistry. He remarks that the brines he studies don’t form ice crystals when cooled. Indeed, as they explain in the paper, they smoothly transition to a glassy state after supercooling, which makes the conditions easier for life.
Their research also helps to explain the presence of some minerals on the Mars surface, such as manganese oxides which require conditions of water and oxygen to form. These could be evidence that the early Mars atmosphere was thick and oxygen rich (which doesn’t require life; it could for instance be oxygen rich due to ionizing radiation splitting water). However this new reseach shows that these minerals could form even without an oxygen rich atmosphere.
As previously interviewed by National Geographic (October 22):
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VS: Our explanation doesn’t need any special magic — it works on Mars today,
The idea that Mars had enough oxygen in the past for marine animals, billions of years ago, when the atmosphere was thicker, is not too surprising nowadays since the discovery of those manganese oxides. That it may have enough right now is what is so very surprising about this new research, given that it has such a thin atmosphere, with so little oxygen in it. The atmosphere is unbreathable, its trace amounts of oxygen can’t be used by any form of terrestrial animal life, but the brines may be another story.
The paper is theoretical and is based on a simplified general circulation model of the Mars atmosphere – it ignores distinctions of seasons and the day / night cycle. But it takes account of topography (mountains, craters etc) and the axial tilt. They combined it with a chemical model of how oxygen would dissolve in the brines and used this to establish predicted oxygen levels in the brines at the various locations on Mars.
Wikinews asked if they have plans to look into a more detailed model:
((WN)) and about whether there are any future plans for using a more detailed model with time variation diurnally or seasonally.
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VS: Yes, we are now exploring the kinetics part and want to see what happens on shorter timescales.
Their model took account of the tilt of the Mars axis, which varies much more than for Earth (our axis is stabilized by the presence of the Moon). They found that for the last five million years conditions were particularly favorable for oxygen rich brines, and that it continues like this for ten million years into the future, as far as they ran the model. For the last twenty million years, as far back as they took their modeling, oases with enough oxygen for sponges are still possible.
Remarkably, as they say in the paper, present day Mars would have more oxygen available for life than early Earth had prior to 1.4 billion years ago. On Earth, photosynthesis seems to have come first, generating the oxygen for the first animals. On Mars, with a different source for oxygen, oxygen breathers could arise before photosynthesis, which gives broader opportunities for oxygen-breathing life on other planets.
Wikinews asked Vlada Stamenkovi? if he had any ideas about whether and how sponges could survive through times when the tilt was higher and less oxygen would be available:
((WN)) I notice from your figure 4 that there is enough oxygen for sponges only at tilts of about 45 degrees or less. Do you have any thoughts about how sponges could survive periods of time in the distant past when the Mars axial tilt exceeds 45 degrees, for instance, might there be subsurface oxygen rich oases in caves that recolonize the surface? Also what is the exact figure for the tilt at which oxygen levels sufficient for sponges become possible? (It looks like about 45 degrees from the figure but the paper doesn’t seem to give a figure for this).
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VS: 45 deg is approx. the correct degree. We were also tempted to speculate about this temporal driver but realized that we still know so little about the potential for life on Mars/principles of life that anything related to this question would be pure speculation, unfortunately.
When the Phoenix lander landed on Mars in 2008, what appeared to be droplets formed on its legs. They grew, coalesced, and then disappeared, presumably falling off its legs. It was not able to analyze these droplets, but simulations since then in Mars simulation chambers have shown that such droplets can form within minutes when salt overlays ice on Mars. With this background then Wikinews asked him if he had investigated the timescale, and if so, whether these brines could become oxygenated.
((WN)) How quickly would the oxygen get into the brines – did you investigate the timescale?
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VS: No, we did not yet study the dynamics. We first needed to show that the potential is there. We are now studying the timescales and processes.
It is no wonder that this is a challenge. For instance, Curiosity measures temperature changes of around 70 °C between day and night. Also there are large pressure differences between summer and winter. In Gale crater it varied from under 7.5 mbar to nearly 9.5 mbar. There are also large pressure differences between day and night, varying by 10% compared to a tenth of a percent on Earth. On Earth we see such large pressure differences only during a major hurricane.
((WN)) Could the brines that Nilton Renno and his teams simulated forming on salt / ice interfaces within minutes in Mars simulation conditions get oxygenated in the process of formation? If not, how long would it take for them to get oxygenated to levels sufficient for aerobic microbes? For instance could the Phoenix leg droplets have taken up enough oxygen for aerobic respiration by microbes?
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VS: Just like the answer above. Dynamics is still to be explored. (But this is a really good question ?).
Wikinews also asked how their research is linked to the recent discovery of possible large subglacial lake 1.5 km below the Martian South Pole found through radar mapping.
((WN)) Some news stories coupled your research with the subglacial lakes announcement earlier this year. Could the oxygen get through ice into layers of brines such as the possible subglacial lakes at a depth of 1.5 km?
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VS: There are other ways to create oxygen. Radiolysis of water molecules into hydrogen and oxygen can liberate oxygen in the deep and that O2 could be dissolved in deep groundwater. The radiolytic power for this would come from radionuclides naturally contained in rocks, something we observe in diverse regions on Earth.
There’s research by Möhlmann that suggests that fresh liquid water may form in the Martian polar region a few centimeters below clear ice, a process that happens regularly in Antarctica. If similar clear ice exists on Mars, this process should happen even at very low surface temperatures. Our reporter, referring to this research, asked him:
((WN)) Could it get into a layer of fresh water just 30 cms below clear ice melted by the solid state greenhouse effect, as in Möhlmann’s model (which forms subsurface liquid water at surface temperatures as low as -56 °C).
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VS: See response above.
So, his answer here is that it could be possible by the same process, radiolysis of the ice through radioactivity in the rocks.
If there are indeed biologically friendly oases dotted throughout the surface of Mars then this could make it harder to sterilize spacecraft sufficiently to explore Mars. They have to be sterilized in order to avoid introducing Earth life to the habitats and so confusing the searches. If the surface of Mars has these oxygen rich habitable brines then it makes the sterilization requirements more stringent. As the Scientific American article suggests, it might be necessary to sterilize robots completely of all micro-organisms, which would drive up the cost of missions to Mars. Stamenkovi? as interviewed by Scientific American says
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VS: I think there’s a sweet spot where we can be curious and we can be explorers and not mess things up, We have to go for that.
NASA and ESA both have missions that they plan to launch to Mars in 2020 to search for life but both have the search for past life as their main focus. The last and only missions to search for present day “extant” life on Mars were the Viking 1 and 2 missions in the 1970s. Stamenkovi? would like that to change.
As interviewed by Space.com (October 22) he said.
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VS: There is still so much about the Martian habitability that we do not understand, and it’s long overdue to send another mission that tackles the question of subsurface water and potential extant life on Mars, and looks for these signals
There are many such instruments we could send. One example, the “Chemical laptop” or PISCES under development at JPL is shown to the right. A National Academy of Sciences report released 10th October 2018 emphasizes the need to include in situ life detection instruments on future missions:
“The report highlights the need to include in situ detection of energy-starved or otherwise sparsely distributed life such as chemolithotrophic or rock-eating life. In particular, the report found that NASA should focus on research and exploration of possible life below the surface of a planet in light of recent advances that have demonstrated the breadth and diversity of life below Earth’s surface, the nature of fluids beneath the surface of Mars, and the likelihood of life-sustaining geological processes in planets and moons with subsurface oceans.”
Vlada Stamenkovi? is working on a new instrument TH2OR to send to Mars on some potential future mission. It would search for potentially habitable brines deep below its surface using ultra low frequency radio waves. This is a frequency far lower than that of ground penetrating radar, in the range of a fraction of a Hertz up to kilohertz. Wavelengths are measured in kilometers up to tens of thousands of kilometers or more. Wikinews asked him for more details
((WN)) And I’d also like to know about your experiment you want to send to Mars to help with the search for these oxygenated brines
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VS: We are now developing at “NASA/JPL-California Institute of Technology” a small tool, called TH2OR (Transmissive H2O Reconnaissance) that might one day fly with a yet-to-be-determined mission. It will use low frequency sounding techniques, capable of detecting groundwater at depths down to ideally a few km under the Martian surface, thanks to the high electric conductivity of only slightly salty water and Faraday’s law of induction. Most likely, such a small and affordable instrument could be placed stationary on the planet’s surface or be carried passively or actively on mobile surface assets; TH2OR might be also used in combination with existing orbiting assets to increase its sounding depth. Next to determining the depth of groundwater, we should also be able to estimate its salinity and indirectly its potential chemistry, which is critical information for astrobiology and ISRU (in situ resource utilization).
Wikinews asked if this device would use natural sources of ultra low frequency radio waves, or if it would use TDEM – a method that involves setting up a current in a loop to generate a sine wave and then suddenly switching it off and observing the radio waves generated by transient eddy currents. The eddy currents have been compared to a smoke ring, they propagate downwards and outwards, a circular current that gets wider as it gets deeper, creating secondary radio waves in a broad band including ultra low frequency waves. The Russian Mars 94 mission, canceled during the break up of USSR, would have flown a TDEM device to Mars.
((WN)) Does your TH2OR use TDEM like the Mars 94 mission – and will it use natural ULF sources such as solar wind, diurnal variations in ionosphere heating and lightning?
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VS: The physical principle it uses is the same and this has been used for groundwater detection on the Earth for many decades; it’s Faraday’s law of induction in media that are electrically conducting (as slightly saline water is).However, we will focus on creating our own signal as we do not know whether the EM fields needed for such measurements exist on Mars. However, we will also account for the possibility of already existing fields.
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