User:Robertinventor/Simple animals could live in Martian brines - Extended Interview with planetary scientist Vlada Stamenković: Difference between revisions

Vlada Stamenković of the [[NASA]] [[Jet Propulsion Laboratory]] and colleagues have developed a chemical model of how oxygen dissolves in [[Mars|Martian]] conditions. They found that in the cold conditions on Mars the trace amounts of oxygen in its thin atmosphere gets concentrated into oxygen-rich brines. The coldest brines have enough oxygen, the work suggests, to support simple animals such as sponges. The model was published in ''{{w|Nature (journal)|Nature}}'' on October 22 2018.

This is an expanded verson of the Wikinews article [https://en.wikinews.org/wiki/Simple_animals_could_live_in_Martian_brines:_Wikinews_interviews_planetary_scientist_Vlada_Stamenkovi%C4%87 Simple animals could live in Martian brines: Wikinews interviews Vlada Stamenković] which I collaborated on, with more background information in it and his answers to some additional questions I asked via email (I'm the volunteer reporter who interviewed him).

The {{w|Atmosphere of Mars|atmosphere of Mars}} is far too thin for us to breathe. It would not be possible for lungs like ours to extract oxygen at all because the moisture lining our lungs would boil at well below blood temperature in the thin atmosphere (much like the way that you can't make a good cup of tea at Everest base camp because the water boils at too low a temperature).

The Mars atmosphere has a pressure of only 0.6% of Earth's atmosphere, on average. Also it's mainly carbon dioxide; only 0.146% of that 0.6% is oxygen. Yet the result of their modeling was clear. In the cold conditions on Mars these minute amounts of oxygen can get into the salty seeps of water which may be present there. What's more, the oxygen levels anywhere on Mars could reach the levels needed to support microbial life. Any microbes that depend on oxygen should manage fine in the Martian brines. There's a caveat here, they don't know how long it would take to reach those levels but once it reaches equilibrium with the atmosphere then that's how much oxygen there should be in the brines.

Oxygen permits a more energy intensive metabolism, and many microbes and almost all complex multicellular life on Earth depend on oxygen. They found that cold water would take up much more oxygen than warm water. In the coldest salty water in the polar regions, covering perhaps 6.5% of the Martian surface, oxygen levels on Mars may be get high enough for simple animals such as sponges. It's a similar picture for the Earth, the tropical oceans, which are warmer, have less oxygen than our polar oceans.

As previously interviewed by National Geographic (October 22):

'''''(background information):''''' You might wonder why they focus their research on salty solutions. What about fresh water? Well fresh water would work fine too, but it does freeze of course at zero degrees centigrade and in the thin oxygen atmosphere that means less oxygen.

Also fresh water is likely to be rare on present day Mars. Usually the air pressure is so low that fresh water is not stable even at just above freezing, at 0&nbsp;°C. It does have a higher pressure atmosphere at its lowest points such as at the depths of the huge ancient impact crater of the {{w|Hellas Planitia|Hellas basin}}. This raises the boiling point of fresh water to 10&nbsp;°C, but that means that even there, it is close to boiling point already at 0&nbsp;°C. If any ice melts in the Hellas basin, the water would evaporate away rapidly, indeed the pressure there is so low that ice also isn't stable at 0&nbsp;°C either even in the Hellas basin. <!--see Making a Splash on Mars-->

Curiosity discovered indirect evidence of deliquescence in the equatorial regions (through humidity measurements). These regions are so dry that there is no ice in the surface soil or to considerable depth, yet it found that brines form during winter nights in the top 15cm of the soil when the salts reach temperatures of around -70&nbsp;°C. The water then evaporates again as the soil warms up through the day, and the process repeats every day - night cycle. <!-- "Evidence of liquid water found on Mars" in background information -->

Later research suggests dust flows may also be involved. However the hydrated perchlorate salts observation still has to be explained, as well as the seasonal timing, not correlated with the winds. This is considered to be good evidence that there is at least an element of seasonal hydration associated with the streaks. The literature on this topic has a vigorous dialog between researchers who favour greater or lesser elements of brines in this process.

Before these new results, scientists assumed any present day Martian life would be able to grow without oxygen. Some of the possibilities for Martian life include certain blue-green algae such as {{w|Chroococcidiopsis#Mars colonization|chroococcidiopsis}}, some black fungi, and some purple salt loving {{w|Haloarchaea#As exophiles|haloarchaea}} found in salt ponds and hypersaline lakes on Earth. <!--for the black fungi, Zakharova et al paper in background information-->. Experiments in Mars simulation chambers by DLR in Germany found that lichens such as {{w|Pleopsidium chlorophanum}} also may have potential for surviving in Mars surface conditions without oxygen. They can do this because the algal component is able to make the oxygen needed by its fungal component.

Their lowest values are for the tropical southern uplands, where temperatures are high and the atmosphere is thin, for their brine with the lowest oxygen solubilities, sodium perchlorate. They also calculated this figure using their "worst case scenario" - this means, their least optimistic assumptions. However, they give reasons for believing that their more optimistic best case calculations are close to the true situation.

For calcium perchlorate brines their worst case is a level of 2.5 millionths of a mole per cubic meter (0.0008 mg per liter). This can be reached anywhere on Marsa including the tropical southern uplands.

Levels would be higher at the lowest points such as the floor of the {{w|Hellas Planitia|Hellas basin}}, south of the equator, where the atmospheric pressure is highest, reaching around 1% of Earth's atmosphere.

'''''(background information):''''' Saturated sea water is about 9 mg per liter at 20&nbsp;°C ranging up to 11 mg per liter at 0&nbsp;°C because cold water takes up the oxygen more readily.<!-- see for instance the two "Dissolved Oxygen" cites in the Background sources-->.

The highest oxygen concentrations of all, occur when the water is colder, which is most easily attained in polar regions. That's where they found there would be enough for simple sponges.

Stamenković et al cite a paper from 2014 that showed that some simple sponges can survive with only 0.002 {{w|Mole (unit)|moles}}per cubic meter (0.064 mg per liter) <!-- first page of Nature paper, "Meanwhile, whereas aerobic microbial life and simple animals need O₂ dissolved in liquids in sufficiently large concentrations to survive, recent experiments, observations and calculations have lowered the required limits of concentrations of dissolved O₂ for aerobic respiration to ~10−6 mol m−3 in microorganisms and to ~2 × 10−3 mol m−3 in sponges"-->.

They paid particular attention to two brines, magnesium and calcium perchlorates, common on Mars. If they start off liquid, they can be {{w|Supercooling|supercooled}} to temperatures as low as -123 to -133&nbsp;°C before they transition to a glassy state in simulation experiments. They can be supercooled even when mixed with the soil of Mars (regolith). It's at these very low temperatures that the optimal oxygen concentrations can be reached.

The supercooled calcium perchlorate brines can reach oxygen concentrations high enough for simple sponges in regions poleward of about 67.5° to the north and about 72.5° to the south. Closer to the poles, oxygen concentrations could go higher, approaching levels typical of sea water on Earth, 0.2 moles per cubic meter (6.4 mg per liter).

Wikinews asked him whether their research suggests potential for life as active as the Earth animals that can survive at similar oxygen levels.

'''''(background information):''''' Life gets slower and slower at lower temperatures to the point where individual microbes have lifetimes of millennia. Such life is hard to study. It's almost impossible to tell whether it is a) active and able to reproduce at those temperatures or b) active and not able to reproduce, or c) intermittently sometimes active and sometimes dormant. The reproduction can't be studied using cell counts. But the usual limit cited is -20&nbsp;°C<!-- see discussion in A new analysis of Mars "Special Regions" -->. That's well above the lowest temperatures studied in the paper which go down to -133&nbsp;°C.

:: {{WNIQ}} [asked later] When you talked about warm water encountering the brines from below, in our interview - did you have any thoughts about where the water might come from? Geothermal hot spots?

'''''(background information)''''': His first suggestion here is that the cool oxygen rich reservoirs could have warmer water come up through them from below. In my follow up question I asked about geological hot spots. Our orbiting spacecraft have not yet found any, but subsurface hotspots may be hard to spot from orbit, and Olympus Mons has been active as recently as 2.5 million years ago<!-- see for instance Neukum et al in the background sources -->.

The idea then might be that warmer water could rise to the surface from below, heated by the hotspots, and encounter these cold oxygen-rich brines. Then life in the warmer brines could make use of oxygen where the two mix.

The other possibility is that microbes can continue to function at very low temperatures in the Martian conditions. After the interview I discovered that they go into this in section ''"3.2 The lower temperature limit for life and the potential of aerobic habitats"'' in the supplementary information.

When microbes adapted to extremely cold conditions are cooled down, the interior doesn't freeze but transitions to a glassy state (Intracellular vitrification). This transition is driven by freezing of the external media.

From previous research, the brines he studies don't form ice crystals when cooled. Instead, they smoothly transition to a glassy state after supercooling. In this way, life in calcium or magnesium perchlorates, with no external crystalization, could continue to access this from liquid interiors enabling metabolic processes to continue right down to the supercooling limit of the brines. It would depend on whether the cells can keep their intercellular fluids liquid. If they can, this will keep the viscosity low, and permit vigorous metabolic processes to continue. If not, if they enter a glassy state, then even in vitrified cells, metabolic processes continue at a slow pace, but if the fluids stay liquid then fast metabolic processes are possible.