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

• 300 5 minutes INTRODUCTION Mike Meyer
• 300 10 minutes SUMMARY AND BOUNDS TO THE
  PROBLEM Karen Buxbaum
• 315 20 minutes MICROBIOLOGY Mary Voytek
• 335 20 minutes MARS, WHERE WATER IS IN
  EQUILIBRIUM Bill Boynton
• 355 20 minutes POSSIBLE LONG-TERM
  DISEQUILIBRIUM ENVIRONMENTS Hort Newsom
• 315 15 minutes CONCLUSIONS Dave Beaty
• 330 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
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.
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
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 Dont 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

• gt5 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 crashspecial
  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 todays state of knowledge, only two
  of the factors are of practical use in setting
  implementation guidelines for special regions.
• Temperature
• Activity of water

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Temperature Threshold
Biological activity studies
Citation Measurement Temp. min. Metabolic Category
Bakermans et al. (2003) Cell counts of bacteria isolated from Siberian permafrost -10C Cell replication Doubling time (DT) 39 days
Breezee et al., (2004) Cell counts Psychromonas ingrahamii, from sea ice from off Point Barrow, Alaska -12C Cell replication DT 10 Days
Jakosky et al. (2003) Cell counts of bacteria isolated from Siberian permafrost -10C Cell replication DT 40 days
Christner (2002) DNA and protein synthesis by uptake 3Hthymidine and 3HLeu respectively in psychrotrophs from polar ice cores -15C Maintenance
Gilichinsky et al. (2003) Assimilation of 14Cglucose by bacteria in cryopegs (brine lenses) found in Siberian permafrost -15C Maintenance
Junge et al. (2004) Respiration observed in brine channel prokaryotes in Arctic sea ice communities by CTC -20C Survival
Junge et al. (2006) Protein Synthesis, 3HLeu incorporation -20C Maintenance
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Temperature Threshold (cont.)
Kappen et al. (1996) CO2 exchange both uptake and loss by polar lichens -12C to -18C Survival/Maintenance?
Rivkina et al. (2000) Incorporation of 14C-labeled acetate into glycolipids by bacterial community from Siberian permafrost -20C Maintenance/Replication? DT160 days at -10C?
Rivkina et al. (2002) Measured evolution of methane by a community of permafrost methanogenic archaea -16.5C Survival?
Wells and Demming (2006) Viral infectivity and production in natural winter sea-ice brines in the Arctic -12C Microbial evolution (lateral gene transfer) and community succession
Carpenter et al (2000) DNA and protein synthesis by uptake 3Hthymidine and 3HLeu respectively in psychrotrophs from polar snow -12C to -17C Maintenance
FINDING. Terrestrial microorganisms are not known
to be able to reproduce at a temperature below
-15C. With margin added, a temperature
threshold of -20C is proposed for use when
considering special regions.
20
Water Activity Threshold
Water activity (aw) Condition or response
1.0 Pure water
Solute-induced effects 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 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
21
Water Activity Threshold
0.99 Average water film thickness 3 nm
0.97 Average water film thickness lt 3 nm (lt 10 H2O molecules thick)
0.93 Average water film thickness lt 1.5 nm (lt 5 H2O molecules thick)
0.75 Average water film thickness lt 0.9 nm (lt 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).

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
• aw Note1.0     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
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
  -20C, barring an active heat source. Even then,
  the temperature in the upper 5 meters will cool
  to -20C 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
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.
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
Gullies
Some authors have proposed water-related origins.
Typical mid-latitude gullies on the wall of a
crater located at 39.0S, 166.1W. The picture
covers an area 3 km wide. topography slopes
downhill toward the lower right.
Source Edgett and Malin (various)
40
Map of Gully Locations (through Sept. 2005)

• FINDING. Somealthough, certainly, not
  allgullies might be sites at which liquid water
  comes to the surface within the next 100 years.

41
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-ontype
  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.

42
Possible Glaciers

• The topic of glaciationeven at equatorial
  latitudeshas 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 tillresidual
  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).
43
Map of Possible Equatorial Glaciers
Possible glacial deposits shown in yellow.

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

Source Head (various)
44
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)

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
45
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.

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
THE TOP NINE
46
Fresh Crater Example
11.5 km diameter, 13.70N 29.52E
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.
Source Nadine Barlow
47
Young Volcanics
Distribution of the youngest volcanic rocks on
Mars (map unit AEC3 from Tanaka et al. 2005). 
48
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 -20C within about
  1000 y.
• Age can be estimated from albedo and crater
  densitynone 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 lt10-5.

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.
49
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
50
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.

South Pole

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

51
Source Milliken and Mustard (2003)
Map of the Mid-latitude Mantle

• 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.
52
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
53

• Change Speakers to
• David Beaty

54
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.

55
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 -20C 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.

56
DEFINITION 2 (cont.)

• Uncertain regions. If a martian environment can
  simultaneously exceed the threshold conditions of
  -20C 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 lt5 meters for
  impacting hardware of lt2400kg.

57
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). 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). 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
58
Map Boundaries of Relevance to Interpreting
Special Regions on Mars
0
330
300
270
240
210
180
30
90
150
60
120
180
90
60
V-2
30
V-1
MPF
MAP BOUNDARY A
MAP BOUNDARY C
0
MER-B
MAP BOUNDARY B
MER-A
30
60
90
MAP BOUNDARY A. 6 counts/second isopleth from GRS
instrument (summer data only)
MAP BOUNDARY C. Observed equatorward extent of
either gullies or mantled terrain.
MAP BOUNDARY B. Modeled equatorward limit of
stability of ice at depth of 5 m.
59
Spacecraft-Induced Special Regions

• 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.

60
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
-5C 22 hours
0C 3 hours
5C 1 hour
61
Summary

• 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 (lt20oC) or
  too dry (awlt0.5) for terrestrial microbial
  reproduction (i.e., non-special).
• Using the SR-SAGs 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.

62

• Backup Slides

63
Mars Duricrust
Crust on right coating on left?(MER-A, Sol 71)
64
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.