# Presentation: 456272

## Findings of the Special Regions Science Analysis Group

**By the MEPAG Special Regions Science Analysis Group (SR-SAG)**
**April 19, 2006**

## AGENDA

- 3:00    5 minutes  INTRODUCTION:  Mike Meyer
- 3:00  10 minutes  SUMMARY AND BOUNDS TO THE PROBLEM:  Karen Buxbaum
- 3:15  20 minutes  MICROBIOLOGY:  Mary Voytek
- 3:35  20 minutes  MARS, WHERE WATER IS IN EQUILIBRIUM:  Bill Boynton
- 3:55  20 minutes  POSSIBLE LONG-TERM DISEQUILIBRIUM ENVIRONMENTS:  Hort Newsom
- 3:15  15 minutes  CONCLUSIONS:  Dave Beaty
- 3:30  30 minutes  PANEL DISCUSSION

## Introductory Remarks
Michael Meyer

**Michael Meyer**

## What is the Problem?

- The existing definition of ‘special region’
- includes several critical terms that are ambiguous, and mean different things to different people
- the short list of practical implementation guidelines is incomplete, and possibly in error
- MEPAG was asked to propose a clarification of the definition that is acceptable to the science community.
- No presumption that what is acceptable to science will be equally acceptable to other stakeholders

## DEFINITION #1

- _Existing definition of “special region” (from COSPAR 2002 & 2005, NASA, 2005):_
- “... 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.  Specific examples include but are not limited to:
- Subsurface access in an area and to a depth where the presence of liquid water is probable
- Penetration into the polar caps
- Areas of hydrothermal activity”

## Team Roster

| Mike Hecht  | JPL |
| --- | --- |
| Vicky Hipkin  | Canadian Space Agency |
| Thomas Kieft | NM Inst. Mining & Tech |
| Rocco Mancinelli  | SETI Institute, ARC |
| Eric McDonald | Desert Research Inst. |
| Chris McKay  | ARC |
| Mike Mellon  | Univ. Colorado |
| Horton Newsom  | Univ. New Mexico |
| Gian Ori  | IRSPS, Italy |
| Dave Paige  | UCLA |
| Andy Schuerger  | Univ. Florida |
| Mitch Sogin  | Marine Biological Laboratory |
| Andrew Steele  | Carnegie Inst. of Wash. |
| Ken Tanaka  | USGS, Flagstaff |
| Mary Voytek  | USGS, Reston |

| Name | Affiliation |
| --- | --- |
| Dave Beaty, co-chair | Mars Program Office, JPL |
| Karen Buxbaum, co-chair  | Mars Program Office, JPL |
| Michael Meyer, co-chair | Mars Program Office, NASA HQ |
| Andy Spry  | JPL |
| Nadine Barlow  | Northern Ariz. Univ. |
| Bill Boynton  | Univ. Arizona |
| Ben Clark  | LMA |
| Jody Deming  | Univ. Washington |
| Peter Doran  | Univ. Illinois |
| Ken Edgett  | Malin Space Sci. Syst. |
| Steve Hancock | Foils Engineering |
| Jim Head  | Brown Univ. |

## Change Speakers to 
Karen Buxbaum

**Karen Buxbaum**

## Special Region

**Clarification of Terms**

_*Special Region*_
*“**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.”*

*Accepted meaning here is  “reproduce,”  NOT grow, survive, or disperse*

*“**likely” is misleading; intent is “could possibly”*

*SECOND CLAUSE:  No data; deferred to future workers*

## Summary of this Presentation

_**Bounds to the Problem**_**:**
- Proposed time scale: 100 years.
- Depth of relevance for most missions:  5m.
_**Key Findings:**_
- Threshold parameters for propagation of terrestrial organisms:  T *and* aw. Other known limits to life are not practically useful for this analysis.
- Where Mars is in thermodynamic equilibrium, T and aw in the near-surface environment are well below the propagation thresholds.
- Some geologic environments on Mars are, or could be, in long-term disequilibrium.  Such environments may exceed the propagation threshold values.
- Proposed guidelines for possible naturally-occurring and spacecraft-induced “special regions.”

## Summary of this Presentation

**Summary of this Presentation**

_**Bounds to the Problem**_**:**
- Proposed time scale: 100 years
- Depth of relevance for most missions:  5m
_**Key Findings:**_
- Threshold parameters for propagation of terrestrial organisms:  T *and* aw. Other known limits to life are not practically useful for this analysis.
- Where Mars is in thermodynamic equilibrium, T and aw in the near-surface environment are well below the propagation thresholds.
- Some geologic environments on Mars are, or could be, in long-term disequilibrium.  Such environments may exceed the propagation threshold values.
- Proposed guidelines for possible naturally-occurring and spacecraft-induced “special regions.”

## How Far into the Future?

**How Far into the Future?**

- Timeframe: **100 Years**
- Suggested by the NASA PPO, acceptable to the SR-SAG after significant discussion.
- This is a _MAJOR_ difference compared to PREVCOM study, which considered protection of Mars forever.
- _Primary implication:_ Don’t need to consider _future_ climate change as a result of the obliquity cycle (order of 104 years).  For practical purposes, it is thought the climate will be the same 100 years from today as it is today.

_**PREMISE.**_**  A 100-year time span may be used to assess the potential for special regions that may be encountered by any given mission.**

## A Practical Depth Consideration

**A Practical Depth Consideration**

- Although all of Mars (in 3-D) is protected, the part that has practical relevance is that which can be reached by spacecraft contamination.

## Spacecraft Contamination

_**FINDING**_**.  Although naturally occurring special regions anywhere in the 3-D volume of Mars need protection, only those in the outermost ~5 m of the martian crust can be inadvertently contaminated by a spacecraft crash—special regions deeper than that are not of practical relevance for missions with a mass up to about 2400 kg.**

- _>5 m_.  The SR-SAG proposes that missions involving deliberate subsurface access deeper than 5 m be required to present a specific analysis of the possibility of special conditions, natural or induced, at their proposed landing site, down to their designed access depth.

## Change Speakers to 
Mary Voytek

**Mary Voytek**

## Summary of this Presentation

**Summary of this Presentation**

_**Bounds to the Problem**_**:**
- Proposed time scale: 100 years
- Depth of relevance for most missions:  5m
_**Key Findings:**_
- Threshold parameters for propagation of terrestrial organisms:  T *and* aw. Other known limits to life are not practically useful for this analysis.
- Where Mars is in thermodynamic equilibrium, T and aw in the near-surface environment are well below the propagation thresholds.
- Some geologic environments on Mars are, or could be, in long-term disequilibrium.  Such environments may exceed the propagation threshold values.
- Proposed guidelines for possible naturally-occurring and spacecraft-induced “special regions.”

## Possible Microbial Propagation Factors

- • **Water availability and activity**
- – Presence and timing of liquid water
- – Past/future liquid (ice) inventories
- – Salinity, pH, and Eh of available water
- • Chemical environment
- – Nutrients
- • C, H, N, O, P, S, essential metals, essential micronutrients
- • Fixed nitrogen (the biggest unknown)
- • Availability/mineralogy
- – Toxin abundances and lethality
- • Heavy metals (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some essential, but toxic at high levels)
- • Oxidants (identification and stability)
- • Energy for metabolism
- – Solar [surface and near-surface only]
- – Geochemical [subsurface]
- • Oxidants
- • Reductants
- • Redox gradients
- • Conducive physical conditions
- – **Temperature (temperature minima** for spacecraft contaminants)
- – Pressure (a low-pressure threshold for terrestrial anaerobes?)
- – Radiation (UV, ionizing)
- – Climate/variability (geography, seasons, diurnal, and eventually, obliquity variations)
- – Substrate (soil processes, rock microenvironments, dust composition, shielding)
- – Transport (aeolian, ground water flow, surface water, glacial)

## Limits to Terrestrial Life

- After considerable discussion, the SR-SAG found that given _today’s_ state of knowledge, only two of the factors are of practical use in setting implementation guidelines for ‘special regions.’
- Temperature
- Activity of water

## Temperature Threshold

**Biological activity studies:**

| Citation | Measurement | Temp. min. | Metabolic Category |
| --- | --- | --- | --- |
| Bakermans et al. (2003) | Cell counts of bacteria isolated from Siberian permafrost | -10°C | Cell replication 
Doubling time (DT) 39 days |
| Breezee et al., (2004) | Cell counts Psychromonas ingrahamii, from sea ice from off Point Barrow, Alaska | -12°C | Cell replication
DT 10 Days |
| Jakosky et al. (2003) | Cell counts of bacteria isolated from Siberian permafrost | -10°C | Cell replication
DT 40 days |
| Christner (2002) | DNA and protein synthesis by uptake [3H]thymidine and [3H]Leu respectively in psychrotrophs from polar ice cores | -15°C | Maintenance |
| Gilichinsky et al. (2003) | Assimilation of [14C]glucose by bacteria in cryopegs (brine lenses) found in Siberian permafrost | -15°C | Maintenance |
| Junge et al. (2004) | Respiration observed in brine channel prokaryotes in Arctic sea ice communities by CTC | -20°C | Survival |
| Junge et al. (2006) | Protein Synthesis, [3H]Leu incorporation | -20°C | Maintenance |

## Temperature Threshold (cont.)

| Kappen et al. (1996) | CO2 exchange both uptake and loss by polar lichens | -12°C to       
-18°C | Survival/Maintenance? |
| --- | --- | --- | --- |
| Rivkina et al. (2000) | Incorporation of 14C-labeled acetate into glycolipids by bacterial community from Siberian permafrost | -20°C | Maintenance/Replication?
DT=160 days at -10°C? |
| Rivkina et al. (2002) | Measured evolution of methane by a community of permafrost methanogenic archaea | -16.5°C | Survival? |
| Wells and Demming (2006) | Viral infectivity and production
in natural winter sea-ice brines in the Arctic | -12°C | Microbial evolution (lateral gene transfer) and community succession |
| Carpenter et al (2000) | DNA and protein synthesis by uptake [3H]thymidine and [3H]Leu respectively in psychrotrophs from polar snow | -12°C to        -17°C | Maintenance |

_**FINDING**_**. Terrestrial microorganisms are not known to be able to reproduce at a temperature below -15°C.  With margin added, a temperature threshold of -20°C is proposed for use when considering special regions.**

## Water Activity Threshold

| Water activity (aw) | Condition or response |
| --- | --- |
| 1.0 | Pure water |
| Solute-induced effects |  |
| 0.98 | Seawater |
| 0.75 | Saturated NaCl solution |
| 0.29 | Saturated CaCl2 solution  |
| 0.98 to 0.91 | Lower solute-induced aw limit for growth of various plant pathogenic fungi |
| 0.69 | Lower solute-induced aw limit for growth of Rhizopus, Chaetomium, Aspergillus, Penicillium (filamentous fungi) |
| 0.62 | Lower solute-induced aw limit for growth of Xeromyces (Ascomycete fungus) and Saccharomyces­ (Ascomycete yeast) (growth in 83% sucrose solution) |
| Matric-induced effects |  |
| 0.999 | Average water film thickness = 4 μm  |
| 0.999 | Average water film thickness = 1.5 μm |
| 0.996 | Average water film thickness = 0.5 μm  |

- matric effects are those induced by the adhesive and cohesive properties of water in contact with a solid surface

## Water Activity Threshold

| 0.99 | Average water film thickness = 3 nm  |
| --- | --- |
| 0.97 | Average water film thickness < 3 nm ­ (< 10 H2O molecules thick) |
| 0.93 | Average water film thickness < 1.5 nm ­(< 5 H2O molecules thick) |
| 0.75 | Average water film thickness < 0.9 nm ­(< 3 H2O molecules thick) |
| 0.999 | Matric-induced aw  at which microbial motility ceases in a porous medium |
| 0.97 to 0.95 | Lower matric-induced aw limit for growth of Bacillus spp. |
| 0.88 | Lower matric-induced aw limit for growth of Arthrobacter  spp. |
| 0.93 to 0.86 | Matric-induced aw at which microbial respiration becomes negligible in soil |

- It is difficult if not impossible to establish a threshold value (i.e., a lower limit) for water activity for microbial *survival*.
- Low matric-induced water activities are generally more inhibitory to microbial growth than an equivalent low solute-induced water activity (true for fungi as well as bacteria).

## Thin Films, Solutes

**Adsorbed (hygroscopic) water** adheres tightly to soil particles.

**Capillary water** coheres to adsorbed water and to itself. Surface tension produces the curved water-air interface.

**Thin Films, Solutes**

- We can assume that thin films and salts are both present on Mars.  However, effects of both are implicit in the water activity, which can be calculated without knowing the details of either.

- The presence of solutes reduces aw
- _a_w_	_      _Note_1.0      Pure water0.98    seawater0.75    sat. NaCl solution0.29    sat. CaCl solution

_***THIN FILMS***_

_***SOLUTES***_

## UV Effects

- Thin layers of dust particles may not afford any long-term protection from UV; but thick contiguous layers of dust can.
- Landing scenarios that deposit large amounts of dust into air-bags or onto upper surfaces of soft-landed vehicles may afford significant protection from UV to viable microbes.
- UV inactivation of embedded microbes is possible, if not covered by UV absorbing materials.
- Production of volatile oxidants by UV may impart a significant biocidal factor on Mars (diffusion into spacecraft surfaces and components).
*Due to the limitations discussed above, Mars UV irradiation probably should not be relied upon as a primary means of sterilizing spacecraft components.  But UV irradiation places an extremely harsh selective pressure on the dispersal, survival, growth, and adaptation of terrestrial microorganisms on Mars.*

**UV Effects**

## Microbiology Findings

_**FINDING**_**. Despite knowledge that UV irradiation at the surface of Mars is significantly higher than on Earth, UV effects have not been adequately modeled for the martian surface or near-subsurface to allow us to set thresholds about their effects on growth and proliferation of microorganisms on Mars.  However, UV may be considered as a factor that limits the spread of viable Earth organisms.**

_**FINDING**_**.  Based on current knowledge, terrestrial organisms are not known to be able to reproduce at a water activity below 0.62; with margin, an activity threshold of 0.5 is proposed for use when considering special regions.**

## Change Speakers to 
Bill Boynton

**Bill Boynton**

## Summary of this Presentation

**Summary of this Presentation**

_**Bounds to the Problem**_**:**
- Proposed time scale: 100 years
- Depth of relevance for most missions:  5m
_**Key Findings:**_
- Threshold parameters for propagation of terrestrial organisms:  T *and* aw. Other known limits to life are not practically useful for this analysis.
- Where Mars is in thermodynamic equilibrium, T and aw in the near-surface environment are well below the propagation thresholds.
- Some geologic environments on Mars are, or could be, in long-term disequilibrium.  Such environments may exceed the propagation threshold values.
- Proposed guidelines for possible naturally-occurring and spacecraft-induced “special regions.”

## Equilibrium Thermodynamics

**Equilibrium Thermodynamics**

- Water activity (aw) is related to relative humidity (rh) as follows:    	aw = rh/100
- The relative humidity is defined as the ratio of the partial pressure of water [p(H2O)] and the vapor pressure of ice [Pv(H2O)].
- 	rh = p(H2O)/Pv(H2O)*100.

***Ice ***

***Regolith    ***

***Atmosphere   ***

***p(H******2******O) varies with time and location on Mars, but averages about 0.8 microbar.***

***at equilibrium, Pv(H******2******O) equals p(H******2******O), referred to as the frost point.***

***Calculated T = 195-200K, *****AGREES WITH TES OBSERVATIONS**

## Theoretical Ice Table Depth Today

***No shallow ice***

***Continuous permafrost***

***Discontinuous, episodic permafrost***

***Continuous permafrost***

***Discontinuous, episodic permafrost***

- Ice will be buried to a depth such that the average temperature at that depth is at the frostpoint, ~196 K today.
- As climate warms or frostpoint falls, ice sublimates
- As climate cools or frostpoint rises, ice condenses from atmosphere

*Source: Mellon and Feldman (2005)*

*6 counts/second isopleth from GRS instrument (summer data only)*

## Example Geothermal Gradient

- Ice stable w.r.t. atmosphere.  Operates like a cold trap.

*T = 196 K*

- Addition of heat (from any source) would cause ice to sublime.  Environments warmer than this will become progressively dessiccated.

## Biology-Geology Relationship

## Semi-permeable Crusts

- Some types of desert crust on Earth have formed by processes that could have operated on Mars, and duricrust has been observed on Mars.
- Could crust create conditions that exceed the threshold values?

***Ice ***

***Regolith    ***

***Atmosphere   ***

## Desert Crusts as Vapor Barriers

- Desert crusts are semi-permeable, not impermeable
- Unfractured hydraulic conductivity typically ranges from 0.5 to 0.75 cm/hr.  Permeability to gas is typically higher than permeability to liquid.
- In natural settings, a wide range of processes result in the formation of voids, pores, and fractures that prevent continuous sealing.
- At T = -20C, the water vapor pressure is relatively high, and the water will slowly be driven out unless the recharge rate exceeds the loss rate.
- Recharge:
- Atmospheric.  Will approach vapor-diffusive equilibrium, not concentrate the water.
- Subsurface.  Would require major shallow thermal anomaly, which has not been discovered. It is very difficult to get the subsurface warmer than -20°C, barring an active heat source.  Even then, the temperature in the upper 5 meters will cool to -20°C in a few decades.

## Water on Mars: The Bottom Line

- Mars today is a *desert*
- Plenty of places warm enough for transient water to exist
- Plenty of water in the form of ice in cold places
- No way to get the ice from the cold places to the warm places!
- Mars in the past was likely slightly wetter (104-107 years – outside our time horizons)
- Orbital forcing drives climate change
- Gullies are primary indication of occasional transient water
- Snow was a likely transport mechanism
- Speculative areas where water has survived in disequilibrium would be obvious special regions today
- Vestigial water sources from past epochs (e.g. snowpacks on crater walls)?
- Recent impacts or volcanism?
- There is *no *evidence for any of these phenomena producing liquid water today (_+_ 100 years).
- The only other plausible way to make water today would be through the influence of the spacecraft itself.

## Selected Literature Related to Modern Mars Water

| Possible liquid water on Mars at earlier geologic times | Wallace, D. and C. Sagan (1979)
Carr, M. H. (1983) 
Clow G. D. (1987) 
McKay C.P. and Davis W.L. (1991)
Grotzinger, J.P. et al. (2005) |
| --- | --- |
| Orbital configuration consistent with liquid water in modern times if a source were present  | Haberle R. M., McKay C.P., Schaeffer J.,  Cabrol N.A., Grin E.A., Zent A.P., Quinn R (2001), 
Zent A.P., Fanale F.P., Salvail J.R., Postawko S.E. (1986),
Richardson & Mischna 2005  |
| Mechanisms for producing modern transient liquid in certain geological environments | Farmer C. B. (1976)
Mellon M. T. and Phillips R. J. (2001)
Hecht M. H. (2002)
Costard F., Forget F., Mangold N. , Peulvast J. P. (2002)
Christensen, Phil (2003)  |

***The SR-SAG conclusions are consistent with all of the above.***

## FINDING.  Where the surface and shallow subsurface of Mars are at or close to thermodynamic equilibrium with the atmosphere (using time-averaged, rather than instantaneous, equilibrium), temperature and water activity in the martian shallow subsurface are considerably below the threshold conditions for propagation of terrestrial life.  The effects of thin films and solute freezing point depression are included within the water activity. 

## Change Speakers to 
Horton Newsom

**Horton Newsom**

## Summary of this Presentation

**Summary of this Presentation**

_**Bounds to the Problem**_**:**
- Proposed time scale: 100 years
- Depth of relevance for most missions:  5m
_**Key Findings:**_
- Threshold parameters for propagation of terrestrial organisms:  T *and* aw. Other known limits to life are not practically useful for this analysis.
- Where Mars is in thermodynamic equilibrium, T and aw in the near-surface environment are well below the propagation thresholds.
- Some geologic environments on Mars are, or could be, in long-term disequilibrium.  Such environments may exceed the propagation threshold values.
- Proposed guidelines for possible naturally-occurring and spacecraft-induced “special regions.”

## Disequilibrium Environments

- Certain geological processes can result in local conditions that are out of equilibrium with respect to their planetary setting on timescales from about 102 to 105 years.  For such environments the potential for modern liquid water could be significant.
*Note:  For this purpose, it is necessary to use a time-averaged (e.g. annual), rather than instantaneous, equilibrium.*

## Gullies

- Some authors have proposed water-related origins.

- Typical mid-latitude gullies on the wall of a crater located at 39.0°S, 166.1°W. The picture covers an area 3 km wide.; topography slopes downhill toward the lower right.

*Source: Edgett and Malin (various)*

## Map of Gully Locations (through Sept. 2005)

_**FINDING.**_**  Some—although, certainly, not all—gullies might be sites at which liquid water comes to the surface within the next 100 years.  **

## Pasted-on Terrain

- A southeast-facing slope with a mantle of ‘pasted-on’ terrain (after Christensen, 2003).  This has been interpreted as snow or ice beneath a residue of dust that is protecting the material from further sublimation.

_**FINDING.**_** Because some of the ‘pasted-on’–type mantle has a spatial, and possibly a genetic, relationship to gullies (which in turn are erosional features possibly related to water), the ‘pasted-on’ terrain may be a special region.**

## Possible Glaciers

- The topic of glaciation—even at equatorial latitudes—has been discussed and debated for more than 3 decades.
- Huge possible glacial deposits on Tharsis volcanoes.
- Eskers, drumlins, and other indications of classic wet-based glaciation are absent.  This suggests that cold-based glaciation (typical of polar latitudes on Earth) is a more appropriate analog.
- Although we cannot rule out that there may be some residual ice at depth in equatorial deposits, because of their age it would certainly be below a thick sublimation till—residual shallow ice is highly unlikely.

*Promethei Terra at the eastern rim of the Hellas Basin, 38o S, 104o, ESA/DLR/FU Berlin*

*Deuteronilus Mensae region (40N, 25E, THEMIS v12057009).*

## Map of Possible Equatorial Glaciers

*Source: Head (various)*

_**FINDING.**_**  Although glacial deposits may be present at different latitudes, there is no evidence for melting.**

*Possible glacial deposits shown in yellow.*

## Craters with Residual Heat

| Crater Size (diameter) | Time for which crater environment has potential to retain enough heat to exceed threshold condition |
| --- | --- |
| 3km | 100 years |
| 10km | 1,000 years |
| 30km | 100,000 years |

- A crater could retain heat to the present if:
- Very young (heat lost with time)
- Big (more energy with bigger impacts)

## Large, Fresh Craters 

| LATITUDE (N) | LONGITUDE (E) | DIAMETER (KM) | CENTRAL STRUCTURE | EJECTA* |
| --- | --- | --- | --- | --- |
| 7.03 | 117.19 | 18.0 | Central Peak | MLERSRd |
| 7.16 | 174.41 | 9.6 | Floor Pit | MLERS |
| 8.93 | 43.82 | 10.9 | Summit Pit | MLERS |
| 12.10 | 169.24 | 5.9 | Summit Pit | SLERS |
| 13.70 | 29.52 | 11.5 | Central Peak | MLERS |
| 16.95 | 141.70 | 13.6 | Floor Pit | MLERSRd |
| 19.51 | 141.18 | 9.2 | Floor Pit | MLERS |
| 20.01 | 246.68 | 7.9 | None | SLERSRd |
| 23.19 | 207.76 | 28.3 | Central Peak | MLERSRd |

_**Identification of the most recent large craters**_**.**
- Sharp rim, depth approximates that expected for a pristine crater.
- No superposed features on either crater or ejecta blanket (dunes, floor deposits, tectonic/fluvial features, or small impact craters).
- Ejecta blanket and interior morphologies are sharp and well preserved.
- Crater and ejecta blanket display thermally distinct signatures in daytime and/or nighttime infrared views.

**THE TOP NINE**

## Fresh Crater Example

**11.5 km diameter, 13.70N 29.52E**

*Source: Nadine Barlow*

- We do not have precise ways of dating craters on Mars; however, based on the degree of degradation of the crater morphology we do not have reason to believe that any crater yet observed is as young as the limits specified.

_**FINDING.**_**  No craters with the combination of size and youthfulness to retain enough heat to exceed the temperature threshold for propagation have been identified on Mars to date.**

## Young Volcanics 

- Distribution of the youngest volcanic rocks on Mars (map unit AEC3 from Tanaka et al. 2005).

## Young Volcanics (cont.) 

- Since volcanic heat is lost with time, only extremely young volcanics have the potential to exceed the temperature threshold for propagation.
- Simple calculations show that the temperature at the surface drops to less than -20°C within about 1000 y**.**
- Age can be estimated from albedo and crater density—none are thought to be as young as 1000 years.
- Estimates of the volcanic recurrence interval in the youngest volcanic provinces suggest that the probability of an eruption within a future 100 year period is <10-5.

_**FINDING.**_**  We do not have evidence for volcanic rocks on Mars of an age young enough to retain enough heat to qualify as a modern special region.**

## The Non-discovery of Geothermal Vents 

- An important objective of the THEMIS infrared investigation has been the search for temperature anomalies produced by
- evaporative cooling associated with near-surface water
- heating due to near-surface liquid water or ice, or hydrothermal or volcanic activity.
- THEMIS has mapped virtually all of Mars at night in the infrared at 100-m per pixel resolution, and has observed portions of the surface a second time up to one Mars’ years later.

_**FINDING.**_**  Despite a deliberate and systematic search spanning several years, no evidence for the existence of near-surface liquid water close enough to the surface to be capable of producing measurable thermal anomalies has been found.**

*Source: Phil Christensen*

## Polar Ice Caps

- South Pole

_**FINDING**_**.  The martian polar caps are too cold to be naturally occurring special regions.**

- Mentioned in current COSPAR definition, HOWEVER:
- Maximum summer temperatures typically reach about 200K at the north pole
- The south polar cap, despite receiving more summer sunlight, is protected by a layer of highly reflective CO2 ice, which holds the surface temperature at a constant 145K.
- Contributing to the perpetual low temperature is not only the latitude (hence low sun angle) but also the high conductivity of solid ice.

## Source: Milliken and Mustard (2003)

*Source: Milliken and Mustard (2003)*

- Localized removal (yellow).
- Knobby/wavy texture (cyan).
- Scalloped texture and total mantle cover (red).

**Map of the Mid-latitude Mantle**

_**FINDING**_**.  The mid-latitude mantle is thought to be desiccated, with low potential for the possibility of modern transient liquid water.**

## Dark Slope Streaks

- Some water-related hypotheses are in the literature,       HOWEVER:
- At these equatorial latitudes very near-surface ice is unstable, and
- There is evidence that wind is a controlling factor in the streak occurrence in some cases.

*Source: Phillips, Aharonson*

## Change Speakers to 
David Beaty

**David Beaty**

## Summary of this Presentation

**Summary of this Presentation**

_**Bounds to the Problem**_**:**
- Proposed time scale: 100 years
- Depth of relevance for most missions:  5m
_**Key Findings:**_
- Threshold parameters for propagation of terrestrial organisms:  T *and* aw. Other known limits to life are not practically useful for this analysis.
- Where Mars is in thermodynamic equilibrium, T and aw in the near-surface environment are well below the propagation thresholds.
- Some geologic environments on Mars are, or could be, in long-term disequilibrium.  Such environments may exceed the propagation threshold values.
- Proposed guidelines for possible naturally-occurring and spacecraft-induced “special regions.”

## DEFINITION #2

**DEFINITION #2**

_**Existing definition of “special region” with proposed implementation guidelines:**_
- A special region is defined as a region within which terrestrial organisms are likely to propagate, _or_ a region that is interpreted to have a high potential for the existence of extant martian life forms.
_**Proposed implementation guidelines:**_
_*Definitions*_.  For the purpose of this definition, *propagate* means to reproduce.  Other kinds of activity, including cell maintenance, thickening of cell walls (as aspect of growth), and mechanical dispersal by aeolian processes are not sufficient.
_*Period of applicability*_.  The time period over which these guidelines are to be applied is defined as from the present until 100 years after spacecraft arrival on Mars.
_*‘*__*Non-special’ regions*_.  A martian region may be categorized non-special if the temperature will remain below -20°C ***or*** the water activity will remain below 0.5 for a period of 100 years after spacecraft arrival.  All other regions on Mars are designated as either special or uncertain.

## DEFINITION #2 (cont.)

**DEFINITION #2 (cont.)**

_*Uncertain regions*_.  If a martian environment can simultaneously exceed the threshold conditions of -20°C ***and*** water activity over 0.5, propagation may be possible.  It may not be possible to show that such environments are capable of supporting microbial growth, but such areas will be treated in the same manner as “special regions” until they are shown to be otherwise.
_*Induced special regions*_.  Even in an otherwise “non-special” region, a spacecraft may create an environment that meets the definition of a “special” or “uncertain” region, as described above.  Because of the many dependencies related to spacecraft design, planned or accidental operations, or landing site, the possibility of a mission causing a spacecraft-induced special region should be analyzed on a case-by-case basis.
_*Impact scenarios*_.  As a practical consideration, for evaluating accidental impact scenarios involving both naturally occurring and induced special regions, it is considered sufficient to consider maximum crater depth to be <5 meters for impacting hardware of <2400kg.

## Naturally-Occurring Special Regions

| Classification of martian environments by their potential to exceed the threshold conditions in temperature and water activity for microbial propagation (within the boundary conditions of the analysis). |  |  |
| --- | --- | --- |
| A.  Observed features for which there is a significant (but still unknown) probability of association with modern liquid water | B.  Observed features for which there is a low, but non-zero, probability of a relationship to modern liquid water | C.  Not known to exist, but if examples could be found, would have a high probability of association with modern liquid water. |
| Recent gullies and gully-forming regions
Mid-latitude “pasted-on” terrain  | Low-latitude slope streaks
Low-latitude features hypothesized to be glaciers | Volcanic environments young enough to retain heat. 
Impact environments young enough and large enough to retain heat
Modern outflow channels |

## Map Boundaries of Relevance to Interpreting Special Regions on Mars

**MER-B**

**MPF**

**V-1**

**MER-A**

**V-2**

_***MAP BOUNDARY A***_*. 6 counts/second isopleth from GRS instrument (summer data only)*

- 0

- 30

- 60

- 90

- 30

- 90

- 60

- 0

- 330

- 300

- 270

- 240

- 210

- 180

- 30

- 90

- 150

- 60

- 120

- 180

***MAP BOUNDARY A***

_***MAP BOUNDARY B***_*. Modeled equatorward limit of stability of ice at depth of 5 m.*

_***MAP BOUNDARY C***_*. Observed equatorward extent of either gullies or mantled terrain.*

***MAP BOUNDARY B***

***MAP BOUNDARY C***

## It is possible for spacecraft to induce environments on a time scale of seconds to years that may satisfy the threshold conditions for propagation.
Short-term spacecraft considerations
Rocket plumes
On surface activities (e.g., sampling – scoop, drill,  melt probes)
Burn-up, break up, and surface impact
Long-term spacecraft considerations
Perennial heat sources, i.e., RTGs
Best evaluated on a case-by-case basis. 

- Short-term spacecraft considerations
- Rocket plumes
- On surface activities (e.g., sampling – scoop, drill,  melt probes)
- Burn-up, break up, and surface impact
- Long-term spacecraft considerations
- Perennial heat sources, i.e., RTGs
- Best evaluated on a case-by-case basis.

**Spacecraft-Induced Special Regions**

## Duration of Spacecraft Heating

- It is known that the replication rate for terrestrial organisms is T-dependent and there is latency period before replication can occur.
- It is possible to allow for short duration excursions above the threshold T.
- Limits chosen as before based on data from most extreme case of any documented from terrestrial biology.

| Maximum temperature of spacecraft-induced environment | Minimum time before replication of terrestrial organism could occur |
| --- | --- |
| -5°C | 22 hours |
| 0°C | 3 hours |
| 5°C | 1 hour |

## Using the SR-SAG's boundary parameters and key findings, 
Most of the martian surface/shallow subsurface can be shown to be either too cold (<–20oC) or too dry (aw<0.5) for terrestrial microbial reproduction (i.e., non-special).
Using the SR-SAG’s criteria, some martian geologic environments are uncertain for planetary protection purposes.  Such environments must be treated as special regions.
Spacecraft may induce conditions that would qualify as a special region, even when one was not present before the spacecraft arrived.  These are best evaluated on a case-by-case basis. 

- Most of the martian surface/shallow subsurface can be shown to be either too cold (<**–**20oC) or too dry (aw<0.5) for terrestrial microbial reproduction (i.e., non-special).
- Using the SR-SAG’s criteria, some martian geologic environments are uncertain for planetary protection purposes.  Such environments must be treated as special regions.
- Spacecraft may induce conditions that would qualify as a special region, even when one was not present before the spacecraft arrived.  These are best evaluated on a case-by-case basis.

**Summary**

## Backup Slides

## Mars Duricrust

**Crust on right; coating on left?****(MER-A, Sol 71)**

## New Dune Gullies

**Gully Regions**

- Because of the possibility that new gullies could form within the specified future time period (100 years), we need to think in terms of gully regions, not just specific, already-formed gullies.