Findings of the Special Regions Science Analysis Group

1. Findings of the Special Regions Science Analysis Group By the MEPAG Special Regions Science Analysis Group (SR-SAG) April 19, 2006

2. 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

3. Introductory Remarks Michael Meyer

4. 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

5. 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”

6. Team Roster

7. Change Speakers to Karen Buxbaum

8. Clarification of Terms “likely” is misleading; intent is “could possibly” Accepted meaning here is “reproduce,” NOT grow, survive, or disperse 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.” SECOND CLAUSE: No data; deferred to future workers

9. 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.”

10. 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.”

11. 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.

12. 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.

13. Spacecraft Contamination • >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. 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.

14. Change Speakers to Mary Voytek

15. 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.”

16. 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)

17. 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

18. Temperature Threshold Biological activity studies:

19. Temperature Threshold (cont.) 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.

20. Water Activity Threshold matric effects are those induced by the adhesive and cohesive properties of water in contact with a solid surface

21. Water Activity Threshold • 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).

22. 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. SOLUTES THIN FILMS • The presence of solutes reduces aw • awNote1.0     Pure water0.98    seawater0.75    sat. NaCl solution0.29    sat. CaCl solution 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.

23. UV Effects • UV inactivation kinetics of fully exposed microbes on sun-exposed surfaces are very fast with greater than 6 orders of magnitude reduction possible within several hours on equatorial Mars, at an optical depth of 0.5, and at the mean orbital distance from the sun. • 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.

24. Microbiology Findings 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. 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.

25. Change Speakers to Bill Boynton

26. 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.”

27. 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. p(H2O) varies with time and location on Mars, but averages about 0.8 microbar. Atmosphere Regolith at equilibrium, Pv(H2O) equals p(H2O), referred to as the frost point. Ice Calculated T = 195-200K, AGREES WITH TES OBSERVATIONS

28. Theoretical Ice Table Depth Today Continuous permafrost Discontinuous, episodic permafrost No shallow ice 6 counts/second isopleth from GRS instrument (summer data only) Discontinuous, episodic permafrost Continuous 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)

29. Example Geothermal Gradient Ice stable w.r.t. atmosphere. Operates like a cold trap. Addition of heat (from any source) would cause ice to sublime. Environments warmer than this will become progressively dessiccated. T = 196 K

30. Propagation Possible 1 Proposed Threshold 0.1 Proposed Threshold Water Activity Current Mars shallow subsurface equilibrium conditions 0.01 0.001 0.0001 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 Temperature (deg. C) Biology-Geology Relationship

31. 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? Atmosphere Regolith Ice

32. 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.

33. 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.

34. Selected Literature Related to Modern Mars Water The SR-SAG conclusions are consistent with all of the above.

35. 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.

36. Change Speakers to Horton Newsom

37. 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.”

38. 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.

39. 180 150 120 90 60 30 0 330 300 270 240 210 180 90 60 V-2 30 V-1 MPF 0 MER-B MER-A 30 60 90 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.

40. 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).

41. 180 150 120 90 60 30 0 330 300 270 240 210 180 90 60 V-2 30 V-1 MPF 0 MER-B MER-A 30 60 90 Map of Possible Equatorial Glaciers FINDING. Although glacial deposits may be present at different latitudes, there is no evidence for melting. Possible glacial deposits shown in yellow. Source: Head (various)

42. Craters with Residual Heat • A crater could retain heat to the present if: • Very young (heat lost with time) • Big (more energy with bigger impacts)

43. Large, Fresh Craters 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

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

45. 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.

46. 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

47. North Pole Polar Ice Caps • 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. FINDING. The martian polar caps are too cold to be naturally occurring special regions. South Pole

48. Map of the Mid-latitude Mantle Source: Milliken and Mustard (2003) • Localized removal (yellow). • Knobby/wavy texture (cyan). • Scalloped texture and total mantle cover (red). FINDING. The mid-latitude mantle is thought to be desiccated, with low potential for the possibility of modern transient liquid water.

49. 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

50. Change Speakers to David Beaty