Protecting Mars special regions with potential for life to propagate: Difference between revisions
Protecting Mars special regions with potential for life to propagate (edit)
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(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))"''}}</ref>. 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) {{refn|name=special_region_def|(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<ref name=MarsSpecialRegions2014/>)
{{quote|Conditions on the surface of Mars areoften described as being cold and dry (along with dusty andcratered). 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<br>
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}}, both requirements to be satisfied simultaneously.
Other environmental factors such as the perchlorates and other chemistry {{refn|name=perchlorates|(see section 2.1, page 891 of<ref name=MarsSpecialRegions2014/>).
{{quote|'''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}}}}, ionizing radiation{{refn|name=ionizing_radiation|(see 3.6. Ionizing radiation at the surface page 891 of<ref name=MarsSpecialRegions2014/>).
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<ref name=peroxide_life/>). However, since these capabilities are unknown, they are not used to determine special regions.▼
{{quote|'''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.}}
{{quote|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)}}
}}., UV radiation{{refn|name=UV|(see 3.5. Ultraviolet radiation on the surface of Mars page 901 of<ref name=MarsSpecialRegions2014/>).
{{quote|'''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.}} }}, and low atmospheric pressure{{refn|name=pressure|(see 3.4.3. Pressure of<ref name=MarsSpecialRegions2014/>).
{{quote|'''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.}}}} 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{{refn|name=multifactor|(see 3.7. Polyextremophiles: combined effects of environmental stressors of<ref name=MarsSpecialRegions2014/>).
{{quote|'''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.}}}}.
▲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<ref name=peroxide_life>{{cite journal | title = A Possible Biogenic Origin for Hydrogen Peroxide on Mars | journal = International Journal of Astrobiology | volume = 6 | issue = 2 | pages = 147 | date = 2007-05-22 | first = Joop M. | last = Houtkooper |author2=Dirk Schulze-Makuch | doi = 10.1017/S1473550407003746 | arxiv = physics/0610093 |bibcode = 2007IJAsB...6..147H }}</ref> ). 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<ref name=MarsSpecialRegions2014/>. If a [[hard landing]] risks biological contamination of a special region, it has to be sterilized sufficiently to prevent this (COSPAR category IVc)<ref name=MarsSpecialRegions2014/>.{{refn|name=spacecraft_impact|Section 8. Summary of <ref name=MarsSpecialRegions2014/>▼
{{quote|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}}}}<ref name=MarsSpecialRegions2014/>.▼
▲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<ref name=MarsSpecialRegions2014/>. If a [[hard landing]] risks biological contamination of a special region, it has to be sterilized sufficiently to prevent this (COSPAR category IVc)<ref name=MarsSpecialRegions2014/>.{{refn|name=spacecraft_impact
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{{refn|name=spacecraft_impact|Section 8. Summary of <ref name=MarsSpecialRegions2014/>
▲{{quote|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}}}}. The risk of spacecraft induced special regions needs to be evaluated separately for each mission, taking account of the spacecraft and the landing ellipse<ref name=MarsSpecialRegions2014/>.
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<ref name=appel/>.
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