Protecting Mars special regions with potential for life to propagate

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A special region on Mars for the purposes of Planetary protection is a region classified by COSPAR where terrestrial organisms are likely to propagate, or interpreted to have a high potential for existence of extant Martian life forms.[1][2][3]. . Based on current understanding, this includes any region with a high enough temperature for Earth organisms to propagate (above -18°C), and with water in a form accessible to them (water activity higher than 0.6) [4], both requirements to be satisfied simultaneously.

Other environmental factors such as the perchlorates and other chemistry [5], ionizing radiation[6] }}., UV radiation[7] }}, and low atmospheric pressure[8] are not used to restrict special regions, because some Earth microbes tolerate them. The presence of multiple environmental factors simultaneously is also not used to restrict special regions because of the existence of polyextremophiles that can withstand multiple simultaneous extreme conditions[9].

In principle native Martian life could have additional capabilities, and so, be able to propagate at lower temperatures or with lower water activity (one suggestion is a mixture of water and hydrogen peroxide as internal solvent in the cells[10] ). However, since these capabilities are unknown, they are not used to determine special regions.

The requirements also apply to spacecraft induced special regions. Missions need to study these in the planning phase, for instance the potential to create them through impact or sources of thermal energy foreign to Mars[1]. If a hard landing risks biological contamination of a special region, it has to be sterilized sufficiently to prevent this (COSPAR category IVc)[1].[11][1].

Missions need to study their potential to create Spacecraft-Induced special regions during the planning phase and take action to make sure they are not inadvertently created. Spacecraft also need to avoid special regions if not sterilized sufficiently to prevent contaminating them[11]. The risk of spacecraft induced special regions needs to be evaluated separately for each mission, taking account of the spacecraft and the landing ellipse[1].

There are currently no confirmed special regions. However there are many uncertain regions such as the recurring slope lineae. These are treated as special regions for the purposes of planetary protection, until more is known[12].

Catherine Conley, NASA's Planetary protection officer[1] at the time, explains why the spacecraft we send to Mars are sterilized, 33 seconds into this video

Third video on overview page of the NASA Office of Planetary Protection.

“So we have to do all of our search for life activities, we have to look for the Mars organisms, without the background, without the noise of having released Earth organisms into the Mars environment”

See also

Limits of water activity 0.6 and temperature -18°C[edit | hide all | hide | edit source]

The term "Special region" is understood to apply to any region on Mars where liquid and not too salty water can occur in a temperature range suitable for terrestrial life. The water activity for terrestrial life has to be above 0.6. As an example, honey in dry air has a water activity level of 0.6, and no terrestrial microbes can grow in honey. [1]

The temperature also has to be above -18°C and both of these have to be satisfied simultaneously[13]. Water that is too salty but warm enough or too cold with enough water activity does not count as a special region.

If a margin is added, as in previous reports, a special region would be defined as one with water activity higher than 0.5 and temperature above -23°C [4]

The report remarks that the water activity limit of 0.6 is well determined with no terrestrial life known that can reproduce below that. They do note that some lichens and some cyanobacteria can use the humidity of the air alone but say they haven't found definite evidence that any terrestrial organism can use ambient humidity alone for cell reproduction [14]. For more recent experiments see Lichens, cyanobacteria and molds growing in humidity of simulated Martian atmosphere.

Microscale habitats are a particular challenge[15]. The microenvironments can include vapour aerosols in the atmosphere or within soil cavities, porous rocks etc, vapor-phase water or liquid coming off ice, deliquescing salts, aqueous films on rock or soil grains, thermal springs, and condensation of dew[16]

The lower temperature limit of Earth life is not so well understood, because of practical difficulties measuring extremely low rates of metabolism and cell division. However they were asked to check only for reproduction of Earth life on Mars 500 years into the future. They give the example of cryptoendolithic microbial communities in the Antarctic Dry Valleys which successfully invade sandstone over time periods of 1,000 to 10,000 years. The -18°C limit they give is sufficient to protect Mars from Earth life over a 500 year future timeframe[17].

The Mars surface is abundant in chaotropic agents that disrupt hydrogen bonding, such as MgCl2,CaCl2, FeCl3, FeCl2, FeCl, LiCl, and perchlorate salts. These can disrupt biological processes at higher temperatures. However, at temperatures below 10°C, they are beneficial for numerous species of microbes, reducing the lowest temperature for them to propagate by up to 10°C to 20°C. They found no research into whether this effect also occurs at -18°C or below. They note the possibility that this could depress the lower temperature limit, but experiments haven't been conducted on long enough timescales, with a potential doubling time of between several months and years [19]

Perchlorates, ionizing radiation, UV, low pressure and multiple stressors not used to limit potential special regions[edit | hide | edit source]

COSPAR considered many other environmental factors on Mars in addition to the temperature range and water activity. None of these were used to limit potential special regions.

  • The chemical environment of the Mars surface, including the perchlorates, are considered favourable for life, in particular, perchlorates can be an oxidant for hydrogen and carbon monoxide oxidizing organisms [5]
  • The low pressures of the Mars atmosphere can be tolerated by some terrestrial bacteria [8]
  • The UV flux is blocked by less than 1 mm of regolith or other organisms [7]
  • From the MSL RAD measurements, ionizing radiation levels from cosmic radiation are so low as to be negligible. The intermittent solar storms increase the dose only for a few days and the Martian surface provides enough shielding so that the total dose from solar storms is less than double that from cosmic radiation/ Over 500 years the Mars surface would receive a cumulative dose of less than 50 Gy, far less than the dose where 90% of even a radiation senstiive bacterium such as e-coli would die (LD90 of ~200 - 400 Gy). These facts are not used to distinguish Special Regions on Mars[6].
  • On Mars multiple stressors are present simultaneously, but polyextromphiles can often cope with multiple simultaneous stresses either using the same mechanism for them all or multiple mechanisms [9]

Extant life with additional capabilities are not used to deliminate uncertain or special regions[edit | hide | edit source]

The report briefly discusses the phrase:

‘‘any region which is interpreted to have a high potential for the existence of extant martian life forms is also defined as a Special Region’’

There has been speculation that Martian life might be able to tolerate conditions that are outside of the range of terrestrial life, for instance, able to reproduce at much lower temperatures, and perhaps also in conditions with less water activity than is possible for terrestrial life.

The report[1] doesn't give examples, but one such is Joop Houtkooper and Dirk Schulze Makuch's proposal in 2007 that life on Mars may be using a mixture of water and biogenically created hydrogen peroxide as its internal solvent. He gave this as a possible form of life to explain some puzzling aspects of the Viking lander biological experiments. On cooling, the eutectic of 61.2% (by weight) mix of water and hydrogen peroxide has a freezing point of −56.5 °C, and also tends to super-cool rather than crystallize. It is also hygroscopic, an advantage in a water-scarce environment.[20][21]. It would prefer regions with lower temperatures, and would avoid liquid water. Conditions at the poles would be optimal, but it could also survive in the equatorial regions visited by Viking[10]

However the capabilities of any Martian life are currently unknown. The review committees on the Martian special regions have decided that since we lack any data on their capabilities, this requirement can't be used to determine any additional special regions. So they use the capabilities of Earth life exclusively [22]

No known special regions[edit | hide | edit source]

So far there are no known special regions. Most of them would require verification of existence of microhabitats that are impossible to see directly from orbit. However, there are many uncertain regions where it is possible that as we advance our knowledge of Mars, some of them turn out to be special regions. Amongst the top candidates are the Warm Seasonal flows on Mars (Recurrent Slope Lineae).[1]

Another top candidate is based on the droplet like features that formed on the landing legs of the Phoenix lander. It landed in what is thought to be an ancient ocean bed near the north pole, the first and so far the only spacecraft to land successfully in polar regions[23]. In December 2013, Nilton Renno[24] and his team using the Michigan Mars Environmental Chamber were able to simulate the conditions at its landing site and the droplets[25]. They formed salty brines within minutes when salt overlaid ice, with the salt, especially perchlorates, acting as an "antifreeze"[26]. The team concluded that suitable conditions for brine droplets may be widespread in the polar regions[27][28]. Nilton Renno talks about their results in this video

For more on these and other candidates, see

Spacecraft induced special regions in nominal landings or impact scenarios[edit | hide | edit source]

The requirements also apply to regions that may be made into a special region by a spacecraft, for instance through impact melting ice, or sources of thermal energy foreign to Mars[1]. If a hard landing risks biological contamination of a special region, it has to be sterilized sufficiently to prevent this (COSPAR category IVc)[1].

Missions need to study their potential to create Spacecraft-Induced special regions during the planning phase and take action to make sure they are not inadvertently created. Spacecraft also need to avoid special regions if not sterilized sufficiently to prevent contaminating them[11]. The risk of spacecraft induced special regions needs to be evaluated separately for each mission, taking account of the spacecraft and the landing ellipse[1].

Special regions could be caused during a nominal landing through the warming effects of rocket exhausts, and temporary special regions could also be created when the hot aeroshell, heatshield, backshell or skycrane compnents land on icy ground in a nominal landing[1]. The spacecraft is normally well insulated, so thermal sources within do not leak much radiation. However, special regions can also be caused in normal use of the lander or rover, by vibration or drilling. Examples include the vibrating sieve on the Viking sampler, the Rock Abrasion Tool (RAT) on the Mars Exploration Rover, the drills on Curiosity or ExoMars, and wheel slip or scuff if the rover gets temporarily "stuck". The lifetime of the special region would depend on the volume melted and whether or not it is heated enough for boiling to be initiated, which can happen at low temperatures with the low Martian atmospheric pressures (over much of the surface, pure water boils at 0°C). Once boiling starts, it may self deplete rapidly and so self-destruct. [1]

The analysis must also look at the outcomes of an off nominal "Breakup and Burnup" scenario. Ice could be heated up by direct transfer from a potentially hot structure from atmosphereic heating as well as the kinetic energy of the impact converted to heat. Any radioisotope heating unit and the RTG's would generate heat energy for several decades. If it lands within a dry capping layer of regolith then it's likely to be separated from the wet layer it causes, but if fully buried in ice or icy soil it could cause pooling and persistence of water near to the RTG[29] The report looked at distributions of ice and concluded that ice in the tropics is buried too deep to be a consideration[30]

However the 2014/5 review corrected this due to evidence of ice present at depths of less than one r in pole-facing slopes[31]

The report also considered the droplets that formed on the Phoenix legs as well as a reported stickiness of its excavated soil samples that was reduced on exposure to the atmosphere, both of which suggested deliquescence, and concluded that these also need to be taken into consideration[32]

The 2014 report[1] provided a map of regions of Mars where there may be ice below the surface as well as potential RSL's. The 2015 review however said that such maps are most useful if accompanied by cautionary remarks on their limitations, as they are subject to change with new discoveries and because of the potential for microhabitats[18]. See #Caution on use of maps below.

Revisions of the definition of a special region[edit | hide | edit source]

The definition of a special region has been revised several times. In the 2006 study it was implicit that a special region must be defined by warm enough temperatures combined with sufficient water activity. If the Mars surface is mapped using those requirements alone and requiring them to overlap, the map would be blank [33]. The only place where habitats could occur for the 2006 report were deep below the surface, or perhaps places like the gully systems where water could be exposed to the surface dynamically from the subsurface.

However the 2014 study finds that though the temperature and water activity conditions are not present simultaneously, often they are present at the same location on the surface within a 24 hour period of each other due to the extreme day - night cycles on Mars. That then makes it possible that terrestrial biology could bridge the gap (e.g. retain the water through to warmer temperatures in the same day). For instance at the Curiosity and Viking sites temperatures in the daytime are regularly high enough for replication and at night relative humidity was above 0.6 and nearly always close to 1.0, and since both conditions occur in the same 24 hour period, there may be a way for organisms to connect the favorable aspects of these different periods through biotic adaptation [34]

The report remarks that they didn't have any evidence yet that terrestrial organisms could bridge that gap, and they had some evidence that suggested it might be unbridgeable. However where the atmospheric pressure is above the triple point of water, precipitation that reaches the ground could melt and provide a temporary habitat. Also some materials such as clays, and the organisms themselves could retain more water than the soil itself. It also remarks on the potential occurrence of small-scale habitats, especially in the subsurface, not detectable with space instruments either existing or planned.

Before the 2014 report was published, both NASA and ESA took steps to have it reviewed independently. This 2015 review concurred with 29 findings of the original report. They did not support one of them and proposed modifications to 15 others[12]. The 2015 review comittee in their report[18] said that they believe that some important aspects were not covered in the previous report[35]. For instance:

  • The possibility of terrestrial contamination blown in the Martian dust.

Although UV radiation would sterilize life quickly, this can be attenuated by the dust. Also the life can occur in larger cell chains, clumps or aggregates, and the cells in the interior of these aggregates can be protected from UV.

The review says that research so far is not sufficient to answer the question and that the possibility of this form of contamination could be confirmed or rejected in terrestrial Mars simulation chambers[36]

  • The ability of multi-species microbial communities to alter dispersed small-scale habitats.

Cells in biofilms are embedded in a matrix of externally produced substances (such as polysaccharides, proteins, lipids and DNA) and adjust environmental parameters to make them more habitable[37]. There are many examples of small-scale and even microscale communities on Earth including biofilms only a few cells thick. Microbes can propagate in these biofilms despite adverse and extreme surrounding conditions.

  • microscale habitats that can't be detected from orbit.

The 2014 report briefly considers these. The 2015 review expands on this topic, and says that to identify such potential habitats requires a better understanding of the temperature and water activity of potential microenvironments on Mars, for instance in the interior of craters, or microenvironments underneath rocks. These may provide favourable conditions for establishing life on Mars even when the landscape-scale temperature and humidity conditions would not permit it. [38]

  • Ice close to the surface needs to be taken account of for spacecraft induced special regions.

The 2014 report looked at distributions of ice and concluded that ice in the tropics is buried too deep to be a consideration[39]

However the 2014/5 review corrected this due to evidence of ice present at depths of less than one meter in pole-facing slopes[40]

  • Utility of maps

The 2014 report[1] provided a map of regions of Mars where there may be ice below the surface as well as potential RSL's. The 2015 review however said that such maps are most useful if accompanied by cautionary remarks on their limitations, as they are subject to change with new discoveries and because of the potential for microhabitats[18].

Caution on use of maps[edit | hide | edit source]

The committees for the 2014/5 revisions caution that maps of regions with higher or lower probability to host special regions should be accompanied by cautionary remarks on their limitations. Any such map can only represent the current state of konwledge, which is incomlete and subject to change as new information is obtained. [41]

Instead each mission needs to be considered on a case by case basis using all the available data. They give the example of Schiaparelli where, for example, all HiRISE images of the landing site were inspected for the possible presence of RSL's. [42]

YouTube Videos[edit | hide | edit source]

See for instance

  1. 1.001.011.021.031.041.051.061.071.081.091.101.111.121.131.141.151.161.171.181.191.201.211.221.231.241.251.261.271.281.291.301.311.321.331.341.35 Rummel, J.D., Beaty, D.W., Jones, M.A., Bakermans, C., Barlow, N.G., Boston, P.J., Chevrier, V.F., Clark, B.C., de Vera, J.P.P., Gough, R.V. and Hallsworth, J.E., 2014. A new analysis of Mars “special regions”: findings of the second MEPAG Special Regions Science Analysis Group (SR-SAG2).
  2. COSPAR. (2011)COSPAR Planetary Protection Policy[20October 2002, as amended to 24 March 2011], COSPAR,Paris.
  3. Planetary protection for ExoMars, ESA

    !The ExoMars mission is classified as Planetary Protection Category IVb based on the mission objectives to search for life on Mars and in agreement with the COSPAR Planetary Protection Policy. The ExoMars mission does not intend to access a Mars special region.

    (A special region is considered to be "... a region within which terrestrial organisms are likely to propagate, or a region which is interpreted to have a high potential for the existence of extant Martian life forms. Given current understanding, this applies to regions where liquid water is present or may occur." (Reference: COSPAR 2002 & 2005, NASA, 2005))"

  4. 4.04.1 (see section 7.1.1. Recommended organism-based parameters defin-ing the limits of life, and the requirements for Mars Special Regions, page 940 of[1])

    Conditions on the surface of Mars are often described as being cold and dry (along with dusty and cratered). As it happens, those conditions are critical to the ability of terrestrial organisms to replicate in any environment. If it is too cold (or too hot) or too dry, terrestrial microbes will not replicate. Thus we define the basic parameters of a Special Region (without margin) as a location where

    (1) the temperature (T) is 255 K (-18°C) or above (Finding 3-1) and
    (2) water activity (aw) is above 0.60 (Finding 3-4).

    ...

    While it can be shown that organisms can be more sensitive to aw than the accuracy of measurement suggested by a value of 0.60, the practicality of measuring water activity at the same accuracy as an organism senses it has not yet been established.

    Under the definition adopted by MEPAG in 2006, ‘‘if a martian environment can simultaneously exceed the threshold conditions of-20°C and aw over 0.5, propagation may be possible’’ (italics added). Both of those parameters in 2006 had margin placed on them, to lower the temperature as well as the water activity required for describing a location as an Uncertain region, which could be expected to host microbial life if it were introduced therein.

    With equivalent margin added, the basic parameters of a Special Region would describe a location where(1) the temperature (T) is 250 K (-23°C) or above and(2) water activity (aw) is above 0.50.

  5. 5.05.1 (see section 2.1, page 891 of[1]).

    Finding 2-1: Modern martian environments may contain molecular fuels and oxidants that are known to support metabolism and cell division of chemolithoautotrophic microbes on Earth

  6. 6.06.1 (see 3.6. Ionizing radiation at the surface page 891 of[1]).

    Finding 3-8: From MSL RAD measurements, ionizing radiation from GCRs at Mars is so low as to be negligible. Intermittent SPEs can increase the atmospheric ionization down to ground level and increase the total dose, but these events are sporadic and last at most a few (2–5)days. These facts are not used to distinguish Special Regions on Mars.

    Over a 500-year time frame, the martian surface could be estimated to receive a cumulative ionizing radiation dose of less than 50 Gy, much lower than the LD90 (lethal dose where 90% of subjects would die) for even a radiation-sensitive bacterium such as E. coli (LD90 of ~200–400 Gy)

  7. 7.07.1 (see 3.5. Ultraviolet radiation on the surface of Mars page 901 of[1]).

    Finding 3-7: The martian UV radiation environment is rapidly lethal to unshielded microbes but can be attenuated by global dust storms and shielded completelyby<1 mm of regolith or by other organisms.

  8. 8.08.1 (see 3.4.3. Pressure of[1]).

    Finding 3-6: Most terrestrial bacteria tested fail to grow below 2500 Pa. However, a small subset of bacteria havenow been identified that can reproduce (on rich hydratedagar media) in a ‘‘martian’’ atmosphere (anoxic, CO2)ataverage martian pressure (700 Pa) and 0°C. This fact isnot used to distinguish Special Regions on Mars.

  9. 9.09.1 (see 3.7. Polyextremophiles: combined effects of environmental stressors of[1]).

    Finding 3-9: The effects on microbial physiology of more than one simultaneous environmental challenge are poorly understood. Communities of organisms may be able totolerate simultaneous multiple challenges more easily than individual challenges presented separately. What little is known about multiple resistance does not affect our current limits of microbial cell division or metabolism in response to extreme single parameters.

  10. 10.010.1 Houtkooper, Joop M.; Dirk Schulze-Makuch (2007-05-22). "A Possible Biogenic Origin for Hydrogen Peroxide on Mars". International Journal of Astrobiology. 6 (2): 147. arXiv:physics/0610093Freely accessible. Bibcode:2007IJAsB...6..147H. doi:10.1017/S1473550407003746. 
  11. 11.011.111.2 Section 8. Summary of [1]

    Thus, during the planning phases, missions will study their own potential to create Spacecraft-Induced SpecialRegions by the presence of a lander itself or by non-nominaloperations during the descent phase and will take action toensure that Special Regions are not inadvertently created.Robotic spacecraft will need to avoid Special Regions if they are not clean enough to avoid contaminating those regions. Although current requirements are the same as those met by the Viking missions of the mid-1970s, no spacecraft sent to Mars since that time has been clean enough to enter a Special Region

    Cite error: Invalid <ref> tag; name "spacecraft_impact" defined multiple times with different content
  12. 12.012.1 Mars Special Regions Redefined NASA Appel Knowledge Services News Digest
  13. see section 7.1.1, page 940 of[1]
  14. (section 3.8.1. Possible microscale environments on Mars of[1])

    Finding 3-12: We have not found definitive evidence hat any terrestrial organism can utilize ambient humidity alone to achieve cell reproduction. In experiments ublished and examined to date, liquid water is needed at some point in an organism’s life cycle to reproduce. onetheless, there does not appear to be a fundamental arrier to microbial reproduction under these conditions.

  15. (see section 3.8. The issue of scale: detecting microbial microenvironments, page 904 of[1]).

    Finding 3-10: Determining the continuity/heterogeneityof microscale conditions over time and space is a majorchallenge to interpreting when and where Special Regionsoccur on Mars

  16. see section 3.8.1. Possible microscale environments on Mar, page 904 of[1] Table7.Summary of Potential Microscale Environments on Mars of Potential Relevanceto Terrestrial Microbes
    • Vapor-phase water available: Vapor or aerosols in planet’s atmosphere; within soil cavities, porous rocks, etc.; within or beneath spacecraftor spacecraft debris
    • Ice related: Liquid or vapor-phase water coming off frost, solid ice,regolith or subsurface ice crystals, glaciers
    • Brine related: Liquid water in deliquescing salts, in channels within ice,on the surface of ice, within salt crystals within haliteor other types of ‘‘rock salt’’
    • Aqueous films on rock or soil grains: Liquid water on regolith particles of their componentssuch as clay minerals, on surface of ice, on and withinrocks, on surfaces of spacecraft
    • Groundwater and thermal springs(macroenvironments): liquid water
    • Places receiving periodic condensation or dew: Liquid water on regolith particles of their componentssuch as clay minerals, on surface of ice, on and withinrocks, on surfaces of spacecraft
    • Water in minerals: Liquid water bound to mineral
  17. section 3.1, page 894 of[1]
  18. 18.0018.0118.0218.0318.0418.0518.0618.0718.0818.0918.1018.11 Board, S.S., European Space Sciences Committee and National Academies of Sciences, Engineering, and Medicine, 2015. Review of the MEPAG report on Mars special regions. National Academies Press.
  19. (see section 3.1.3. Chaotropic substances, page 896 of[1]).

    Finding 3-3: Chaotropic compounds can lower the temperature limit for cell division below that observed in their absence. There exists the possibility that chaotropic substances could decrease the lower temperature limit for cell division of some microbes to below -18°C (255 K),but such a result has not been published.

    Revised version from chapter 2, page 10 of [18]

    Revised Finding 3-1: Cell division by Earth microbes has not been reported below –18°C (255K). The very low rate of metabolic reactions at low temperature result in doubling times ranging from several months to year(s). Current experiments have not been conducted on sufficiently long timescales to study extremely slow-growing microorganisms.

  20. Houtkooper, Joop M.; Dirk Schulze-Makuch (2007). "The H2O2-H2O Hypothesis: Extremophiles Adapted to Conditions on Mars?" (PDF). EPSC Abstracts. European Planetary Science Congress 2007. 2: 558. Bibcode:2007epsc.conf..558H. EPSC2007-A-00439. 
  21. Ellison, Doug (2007-08-24). "Europlanet : Life's a bleach". Planetary.org. 
  22. From 1.1.2 Special regions of [1]

    At present there are no Special Regionsdefined by the existence of extant martian life, and this study concentrates only on the first aspect of the definition.

  23. First liquid water may have been spotted on Mars, New Scientist, February 2009 by David Shiga
  24. Nilton Renno - Faculty page, Mitchigen State University - Honors, Awards and Accomplishments, and Publications, etc
  25. https://www.researchgate.net/publication/283504377_The_Michigan_Mars_Environmental_Chamber_Preliminary_Results_and_Capabilities
  26. Gough, R.V.; Chevrier, V.F.; Tolbert, M.A. (2014). "Formation of aqueous solutions on Mars via deliquescence of chloride–perchlorate binary mixtures" (PDF). Earth and Planetary Science Letters. 393: 73–82. Bibcode:2014E&PSL.393...73G. doi:10.1016/j.epsl.2014.02.002. ISSN 0012-821X. 
  27. Liquid Water from Ice and Salt on Mars, Aaron L. Gronstal -Astrobiology Magazine (NASA), Jul 3, 2014
  28. Fischer, E., Martínez, G.M., Elliott, H.M. and Rennó, N.O., 2014. Experimental evidence for the formation of liquid saline water on Mars. Geophysical research letters, 41(13), pp.4456-4462.
  29. section 5 of[1]).

    Finding 5-1: Thermal perturbation of the local environment by a spacecraft could induce localized SpecialRegions.

  30. [1]

    SR-SAG2 Finding 5-3: Depths to buried ice deposits in the tropics and mid-latitudes are considered to be >5 m.

  31. Chapter: 3 Martian Geological and Mineralogical Features Potentially Related to Special Regions, SNOW, ICE DEPOSITS, AND SUBSURFACE ICE of [18]

    Revised Finding 5-3: In general, depths to buried ice deposits in the tropics are considered to be >5 m. However, there is evidence that water ice is present at depths of <1 m on pole-facing slopes in the tropics and mid latitudes. Thus, a local detailed analysis for a particular area is necessary to determine if it could be a Special Region.

  32. (section 5.8 of[1])

    Finding 5-9: Mineral deliquescence on Mars may betriggered by the presence of a nearby spacecraft or by the actions of a spacecraft

  33. (see page 941 of[1])
  34. Referring to the Viking and Curiosity (MSL) landing sites they say (page 941 of[1])

    ... where in some seasons the temperature required for microbial replication was regularly reached during the driest part of the day, whereas at night, when the temperature was too low for replication, the relative humidity at the site was above 0.6 and nearly always close to 1.0. The non-overlap of the required values for a Special Region is reflected in Finding 4-12, but the fact that both could be reached within the same 24 h period, regularly, suggests that there may be a way for organisms to connect the favorable aspects of those periods across a bridge of biotic adaptation.

  35. Chapter 2: The Assessment of the Potential of Terrestrial Lifeforms to Survive and Proliferate on Mars in the Next 500 Years, from [18]
  36. In chapter 2 of [18]:

    A potential problem with designating Special Regions on Mars is that viable microorganisms that survive the trip to Mars could be transported into a distant Special Region by atmospheric processes, landslides, avalanches (although this risk is considered minimal), meteorite impact ejecta, and lander impact ejecta. In addition to dilution effects, the flux of ultraviolet radiation within the martian atmosphere would be deleterious to most airborne microbes and spores. However, dust could attenuate this radiation and enhance microbial viability. In addition, for microbes growing not as single cells but as tetrades or larger cell chains, clusters, or aggregates, the inner cells are protected against ultraviolet radiation. Examples are methanogenic archaea like Methanosarcina, halophilic archaea like Halococcus, or cyanobacteria like Gloeocapsa. This is certainly something that could be studied and confirmed or rejected in terrestrial Mars simulation chambers where such transport processes for microbes (e.g., by dust storms) are investigated. The SR-SAG2 report does not adequately discuss the transport of material in the martian atmosphere.

  37. In chapter 2 of [18]:

    where the cells are embedded in a self-produced extracellular matrix consisting of polysaccharides and proteins, which includes other macromolecules such as lipids and DNA. These so-called extrapolymeric substances (EPS) provide protection against different environmental stressors (e.g., desiccation, radiation, harmful chemical agents, and predators). Biofilms are highly organized structures that enable microbial communication via signaling molecules, disperse cells and EPS, distribute nutrients and release metabolites, and facilitate horizontal gene transfer.

    The majority of known microbial communities on Earth are able to produce EPS, and the protection provided by this matrix enlarges their physical and chemical limits for metabolic processes and replication. EPS also enhances their tolerance to simultaneously occurring multiple stressors and enables the occupation of otherwise uninhabitable ecological niches in the microscale and macroscale. The presence of EPS within a microbial community has implications for several aspects of the SR-SAG2 report, including the physical and chemical limits for life, the dimension of habitable niches versus the actual resolution capability of today’s instruments in Mars orbit, colonization of brines, and tolerance to multiple stressors. In extreme cold and salty habitats (e.g., brines of sea ice and cryopegs in permafrost), EPS has been found to be an excellent cryoprotectant

  38. In chapter 2 of [18]:

    There are many examples of small-scale and microscale environments on Earth that can host microbial communities, including biofilms, which may only be a few cell layers thick. The biofilm mode of growth, as noted previously, can provide affordable conditions for microbial propagation despite adverse and extreme conditions in the surroundings. On Earth, the heterogeneity of microbial colonization in extreme environments has become more obvious in recent years. To identify Special Regions across the full range of spatial scales relevant to microorganisms, a better understanding of the temperature and water activity of potential microenvironments on Mars is necessary. For instance, the interior of the crater Lyot in the northern mid-latitude has been described as an optimal microenvironment with pressure and temperature conditions that could lead to the formation of liquid water solutions during periods of high obliquity (Dickson and Head 2009). Craters, and even microenvironments underneath and on the underside of rocks, could potentially provide favorable conditions for the establishment of life on Mars, potentially leading to the recognition of Special Regions where landscape-scale temperature and humidity conditions would not enable it.

  39. [1]

    SR-SAG2 Finding 5-3: Depths to buried ice deposits in the tropics and mid-latitudes are considered to be >5 m.

  40. Chapter: 3 Martian Geological and Mineralogical Features Potentially Related to Special Regions, SNOW, ICE DEPOSITS, AND SUBSURFACE ICE of [18]

    Revised Finding 5-3: In general, depths to buried ice deposits in the tropics are considered to be >5 m. However, there is evidence that water ice is present at depths of <1 m on pole-facing slopes in the tropics and mid latitudes. Thus, a local detailed analysis for a particular area is necessary to determine if it could be a Special Region.

  41. chapter 5 of [18]

    In general, the review committee contends that the use of maps to delineate regions with a lower or higher probability to host Special Regions is most useful if the maps are accompanied by cautionary remarks on their limitations. Maps that illustrate the distribution of specific relevant landforms or other surface features can only represent the current (and incomplete) state of knowledge for a specific time—knowledge that will certainly be subject to change or be updated as new information is obtained.

  42. chapter 5 of [18]

    In the case of Schiaparelli, for example, all available data for the proposed site in Meridiani Planum were analyzed to determine if Special Regions existed within the landing ellipse. In particular, all HiRISE images were inspected for the possible presence of RSL.