User:Robertinventor/Simple animals could live in Martian brines - Extended Interview with planetary scientist Vlada Stamenković: Difference between revisions
User:Robertinventor/Simple animals could live in Martian brines - Extended Interview with planetary scientist Vlada Stamenković (edit)
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===Oxygen requirements for complex life such as sponges===
'''''(background information):''''' Saturated sea water is about 9 mg per liter at 20 °C ranging up to 11 mg per liter at 0 °C because cold water takes up the oxygen more readily.<!-- see for instance the two "Dissolved Oxygen" cites in the Background sources-->
'''''Note:''''' The paper uses moles per cubic meter. Many other sources use miligrams per liter. To convert moles of oxygen per cubic meter to milligrams per litre multiply by 32.
Stamenković et al found oxygen levels throughout Mars would be high enough for the least demanding {{w|Aerobic organism|aerobic}} (oxygen-using) microbes, for all the brines they considered, and all the methods of calculation. They published a detailed map<sup>[[#Figure 3|[3]]]</sup> of the distributions of solubility for calcium perchlorates for their more optimistic calculations, which they reckoned were closer to the true case, with and without {{w|Supercooling|supercooling}}. The lowest concentrations were shown in the tropical southern uplands. Brine in regions poleward of about 67.5° to the north and about 72.5° to the south could have oxygen concentrations high enough for simple sponges. Closer to the poles, concentrations could go higher, approaching levels typical of sea water on Earth, 0.2 moles per cubic meter (6.4 mg per liter), for calcium perchlorates. On Earth, worms and clams that live in the muddy sea beds require 1 mg per liter, bottom feeders such as crabs and oysters 3 mg per liter, and spawning migratory fish 6 mg per liter, all within 0.2 moles per cubic meter, 6.4 mg per liter.<!-- see "Dissolved Oxygen" cites -->
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 O<sub>2</sub> dissolved in liquids in sufficiently large concentrations to survive, recent experiments, observations and calculations have lowered the required limits of concentrations of dissolved O<sub>2</sub> for aerobic respiration to ~10−6 mol m−3 in microorganisms and to ~2 × 10−3 mol m−3 in sponges"-->. ▼
Stamenković et al found that even in the worst case they could devise, oxygen levels throughout Mars would be enough for the least demanding {{w|Aerobic organism|aerobic}} (oxygen using) microbes
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.▼
[[File:PIA22546-Mars-AnnualCO2ice-N&SPoles-20180806.gif|thumb|Extents of north (left) and south (right) polar CO<sub>2</sub> ice during a Martian year. These are not photos, rather they are based on infrared data from two instruments that can study the poles even at times of complete darkness. The dry ice here reaches temperature of around -125 °C, well below its sublimation temperature of -78.5 °C, which gives an idea of how cold the Martian poles get in winter. In Vlada Stamenković et al's model the highest oxygen concentrations occur at temperatures down to -123 to -133 °C.]]
▲Stamenković et al found that even in the worst case they could devise, oxygen levels throughout Mars would be enough for the least demanding {{w|Aerobic organism|aerobic}} (oxygen using) microbes, at around 2.5 millionths of a mole per cubic meter (0.0008 mg per liter). That's the value for the tropical southern uplands, where temperatures are high and the atmosphere is thin, and for their brine with the lowest oxygen solubilities, sodium perchlorate. They also calculated this figure using their worst case estimate (where they do the calculations on their least optimistic assumptions). However, they give reasons for believing that their more optimistic best case calculations are close to the true situation.
▲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 O<sub>2</sub> dissolved in liquids in sufficiently large concentrations to survive, recent experiments, observations and calculations have lowered the required limits of concentrations of dissolved O<sub>2</sub> for aerobic respiration to ~10−6 mol m−3 in microorganisms and to ~2 × 10−3 mol m−3 in sponges"-->.
▲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 new research greatly expands the possibilities for complex life on Mars.
===Lowest and highest oxygen concentrations in their maps===
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