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)
Revision as of 01:09, 26 October 2019
, 4 years agono edit summary
No edit summary |
|||
Line 257:
::'''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).''<br><br>''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.
==Technical details - guide to paper==▼
Vlada Stamenković et al's paper explains that their work proceeded by modeling the physics of the solubility of oxygen in brines on Mars. Those were the mixes that permitted the lowest temperatures and so the highest oxygen concentrations. As salts are cooled down, any excess will come out of solution leaving a {{w|Eutectic system|"eutectic mixture"}} that has an optimal mixture of water with the salt (e.g. calcium perchlorate) to keep the brines liquid at the lowest possible temperature or eutectic point. ▼
The brines can be cooled down below this theoretical lowest temperature without freezing, in a process known as supercooling. Experiments with Mars soil (regolith) simulants show that even with soil mixed in with the brines, they can still be supercooled to temperatures as low as -123 to -133 °C before transitioning to a glassy state. ▼
They studied oxygen solubility with and without supercooling. They also studied two ways of modeling the physics, a best case, which matches the available data within a few percent, and a worst case simulation which gives a thermodynamic lower limit, however in their Methods section they say that their "best case" is most likely close to the actual situation on Mars.▼
The main points in their research are summarized in their [https://www.nature.com/articles/s41561-018-0243-0/figures/3 figure 3] which shows two versions of the map, with and without supercooling. The upper figure is the one with supercooling (note the colour-coding is different for the two maps). The map is for calcium perchlorates and they explain that results are comparable for magnesium perchlorates. The dotted lines in that diagram show the polar limit for sponges. The paper says that 6.5% of the surface area of Mars could have oxygen concentrations suitable for primitive sponges. The white and purple colored regions close to the poles are regions that could have oxygen solubilities similar to Earth's oceans, and the paper says that the polar regions have ''"the greatest potential to harbor near-surface fluids "'' at 0.2 moles per cubic meter of dissolved oxygen (6.4 mg / liter). The lowest concentration in their model for their best estimate with supercooling is ~2.5 × 10<sup>−5</sup> moles per cubic meter of dissolved oxygen in the tropical southern highlands (0.0008 mg per liter<!--https://www.google.com/search?q=2.5*32*10^-5-->).▼
Techy aside here, Wikinews asked him about what seems to be a dicrepancy beween Figure 2a and Figure 3.▼
:: {{WNIQ|Wikinews}} The paper itself mentions a lower limit of 2.5 * 10-5 moles per cubic meter. But in Figure 2a it looks more like 1.<something> for the lower limit for both the magnesium and calcium suphates. Wondered which is right, or am I misunderstanding something and there is no discrepancy?▼
::'''VS''': Fig 2 is for an average pressure Pav and Temperature T and Pressure P not being correlated (at a point x on the surface P and T are correlated). Correlated (P,T) are used for Fig 3. Note that the lower limit for perchlorates in Fig 3 is larger than in Fig 2, for correlated (P,T) it is also larger for the other brines, and around lower limit of 2.5 * 10-5 moles per cubic meter.▼
For the effects of the different types of brine, see their [https://www.nature.com/articles/s41561-018-0243-0/figures/2 figure 2]2. This is the one that covers the sodium perchlorate and magnesium perchlorate figures. The brines are colour coded as in [https://www.nature.com/articles/s41561-018-0243-0/figures/1 figure 1], so sodium perchlorate is black, and Magnesium perchlorate is pink. The lowest number in the abstract of 2.5 millionths of a mole per cubic meter is for the sodium perchlorate black bar in figure 2e. The highest figure of 2 moles per cubic meter is for the magnesium perchnlorates pink bar in figure 2a.▼
The theory is covered in more detail in the supplementary information. In their figure S1, they start with a theoretical curve for liquid water at these ultra low temperatures - which achieves the maximum solubility if such was possible (of course in reality water would be frozen). The oxygen solubility is reduced by salting out factors which differ for the different salts. These are shown in their figure S2. Magnesium and calcium perchlorate have the two highest salting out factors but to compensate their brines remain liquid at far lower temperatures than potasium or sodium perchlorate. The upshot is that the highest oxygen concentrations can be achieved with magnesium perchlorate, with calcium perchlorate next.▼
The effects of the variations in the tilt of Mars' axis (obliquity) are summarized in their [https://www.nature.com/articles/s41561-018-0243-0/figures/4 figure 4]. Their figure 4a shows how the oxygen solubility varies with the tilt. The global maximum for supercooling and the best estimate is shown as a red line with purple dots and shows potential for sponges at angles up to around 45 degrees. Then figure 4c shows the effect of the variation in tilt for the last 20 million years and the next ten million years. The supercooling best estimate is shown at the top, the gray shaded boxes are times of atmospheric collapse. They observe in the paper that oxygen solubility levels have been particularly high for the last five million years and will continue in the same way for at least ten million years. They have been high enough for simple sponges for at least twenty million years. You can see how this works from this figure. The paper, discussing oases for simple sponges says that at present they are common poleward of about 67.5° north and about − 72.5° south. ▼
<!-- this para summarizes some of the information from the methane articles at the end of background section -->▼
They also make a connection with the recently discovered, and mysterious, seasonal variation in methane. This is about the variation in the background levels of methane, not the methane plumes observed from time to time by Curiosity. The background levels of methane observed by Curiosity over five years vary in a regular seasonal fashion from 0.24 to 0.65 ppbv reaching a maximum towards the end of the Northern hemisphere summer (Curiosity is a few degrees south of the equator at {{w|Gale crater}}). They suggest that at the solubilities they found in the paper, the oxygen could explain some surprising observations such as the highly oxidized phases in Martian rocks and this seasonable variability of methane in Gale crater.▼
The paper is available to read in its entirety through the link provided on the author's website and the Nature Sharedit sharing initiative.▼
==Background information - historical context==
Line 309 ⟶ 283:
So, if Catling et al are correct in their inference here, then on general energetic principles that an extraterrestrial biosphere with large carbon based animals, at least of 10 cms scale or larger, is going to need oxygen. It seems to apply to Earth anyway. In anoxic environments, Earth animals have found it a challenge to get as large as 1 mm in size without oxygen, though it is possible that larger creatures lived on Earth when the seas were all anoxic.
▲==Technical details - guide to paper==
▲Vlada Stamenković et al's paper explains that their work proceeded by modeling the physics of the solubility of oxygen in brines on Mars. Those were the mixes that permitted the lowest temperatures and so the highest oxygen concentrations. As salts are cooled down, any excess will come out of solution leaving a {{w|Eutectic system|"eutectic mixture"}} that has an optimal mixture of water with the salt (e.g. calcium perchlorate) to keep the brines liquid at the lowest possible temperature or eutectic point.
▲The brines can be cooled down below this theoretical lowest temperature without freezing, in a process known as supercooling. Experiments with Mars soil (regolith) simulants show that even with soil mixed in with the brines, they can still be supercooled to temperatures as low as -123 to -133 °C before transitioning to a glassy state.
▲They studied oxygen solubility with and without supercooling. They also studied two ways of modeling the physics, a best case, which matches the available data within a few percent, and a worst case simulation which gives a thermodynamic lower limit, however in their Methods section they say that their "best case" is most likely close to the actual situation on Mars.
▲The main points in their research are summarized in their [https://www.nature.com/articles/s41561-018-0243-0/figures/3 figure 3] which shows two versions of the map, with and without supercooling. The upper figure is the one with supercooling (note the colour-coding is different for the two maps). The map is for calcium perchlorates and they explain that results are comparable for magnesium perchlorates. The dotted lines in that diagram show the polar limit for sponges. The paper says that 6.5% of the surface area of Mars could have oxygen concentrations suitable for primitive sponges. The white and purple colored regions close to the poles are regions that could have oxygen solubilities similar to Earth's oceans, and the paper says that the polar regions have ''"the greatest potential to harbor near-surface fluids "'' at 0.2 moles per cubic meter of dissolved oxygen (6.4 mg / liter). The lowest concentration in their model for their best estimate with supercooling is ~2.5 × 10<sup>−5</sup> moles per cubic meter of dissolved oxygen in the tropical southern highlands (0.0008 mg per liter<!--https://www.google.com/search?q=2.5*32*10^-5-->).
▲Techy aside here, Wikinews asked him about what seems to be a dicrepancy beween Figure 2a and Figure 3.
▲:: {{WNIQ|Wikinews}} The paper itself mentions a lower limit of 2.5 * 10-5 moles per cubic meter. But in Figure 2a it looks more like 1.<something> for the lower limit for both the magnesium and calcium suphates. Wondered which is right, or am I misunderstanding something and there is no discrepancy?
▲::'''VS''': Fig 2 is for an average pressure Pav and Temperature T and Pressure P not being correlated (at a point x on the surface P and T are correlated). Correlated (P,T) are used for Fig 3. Note that the lower limit for perchlorates in Fig 3 is larger than in Fig 2, for correlated (P,T) it is also larger for the other brines, and around lower limit of 2.5 * 10-5 moles per cubic meter.
▲For the effects of the different types of brine, see their [https://www.nature.com/articles/s41561-018-0243-0/figures/2 figure 2]2. This is the one that covers the sodium perchlorate and magnesium perchlorate figures. The brines are colour coded as in [https://www.nature.com/articles/s41561-018-0243-0/figures/1 figure 1], so sodium perchlorate is black, and Magnesium perchlorate is pink. The lowest number in the abstract of 2.5 millionths of a mole per cubic meter is for the sodium perchlorate black bar in figure 2e. The highest figure of 2 moles per cubic meter is for the magnesium perchnlorates pink bar in figure 2a.
▲The theory is covered in more detail in the supplementary information. In their figure S1, they start with a theoretical curve for liquid water at these ultra low temperatures - which achieves the maximum solubility if such was possible (of course in reality water would be frozen). The oxygen solubility is reduced by salting out factors which differ for the different salts. These are shown in their figure S2. Magnesium and calcium perchlorate have the two highest salting out factors but to compensate their brines remain liquid at far lower temperatures than potasium or sodium perchlorate. The upshot is that the highest oxygen concentrations can be achieved with magnesium perchlorate, with calcium perchlorate next.
▲The effects of the variations in the tilt of Mars' axis (obliquity) are summarized in their [https://www.nature.com/articles/s41561-018-0243-0/figures/4 figure 4]. Their figure 4a shows how the oxygen solubility varies with the tilt. The global maximum for supercooling and the best estimate is shown as a red line with purple dots and shows potential for sponges at angles up to around 45 degrees. Then figure 4c shows the effect of the variation in tilt for the last 20 million years and the next ten million years. The supercooling best estimate is shown at the top, the gray shaded boxes are times of atmospheric collapse. They observe in the paper that oxygen solubility levels have been particularly high for the last five million years and will continue in the same way for at least ten million years. They have been high enough for simple sponges for at least twenty million years. You can see how this works from this figure. The paper, discussing oases for simple sponges says that at present they are common poleward of about 67.5° north and about − 72.5° south.
▲<!-- this para summarizes some of the information from the methane articles at the end of background section -->
▲They also make a connection with the recently discovered, and mysterious, seasonal variation in methane. This is about the variation in the background levels of methane, not the methane plumes observed from time to time by Curiosity. The background levels of methane observed by Curiosity over five years vary in a regular seasonal fashion from 0.24 to 0.65 ppbv reaching a maximum towards the end of the Northern hemisphere summer (Curiosity is a few degrees south of the equator at {{w|Gale crater}}). They suggest that at the solubilities they found in the paper, the oxygen could explain some surprising observations such as the highly oxidized phases in Martian rocks and this seasonable variability of methane in Gale crater.
▲The paper is available to read in its entirety through the link provided on the author's website and the Nature Sharedit sharing initiative.
== Sources ==
| |||