HabitabilityHabitability
Bonnie MeinkeJanuary 27, 2009
Bonnie MeinkeJanuary 27, 2009
IntroductionIntroduction
Define Habitability The Habitable Zone Environment of early Earth
Define Habitability The Habitable Zone Environment of early Earth
Defining HabitabilityDefining Habitability
What do we mean when we say habitable? Earth-like animal life: specific
requirements
Microbial life: broader set of conditions
What do we mean when we say habitable? Earth-like animal life: specific
requirements
Microbial life: broader set of conditions
Defining Habitability
Defining HabitabilityDefining Habitability
What do we mean when we say habitable? Earth-like animal life: specific
requirements (oxygen, water, dry land, temperature range)
Microbial life: broader set of conditions (more extreme conditions ok)
What do we mean when we say habitable? Earth-like animal life: specific
requirements (oxygen, water, dry land, temperature range)
Microbial life: broader set of conditions (more extreme conditions ok)
Defining Habitability
Common basic requirements for life
Common basic requirements for life
Water Stable climate
Water Stable climate
Defining Habitability
What stabilizes the climate?
What stabilizes the climate?
Size - long-term heat source Stellar evolution - incoming solar
energy Impact rate - could result in climate
change Presence of large, natural satellite -
prevents large swings in obliquity Oceans - regulate global
temperatures
Size - long-term heat source Stellar evolution - incoming solar
energy Impact rate - could result in climate
change Presence of large, natural satellite -
prevents large swings in obliquity Oceans - regulate global
temperatures
Defining Habitability
Habitable ZonesHabitable Zones
Why is Earth the only (as far as we know) habitable planet in our solar system?
2 main properties:Abundant liquid water Environmental conditions that
maintain liquid water
Why is Earth the only (as far as we know) habitable planet in our solar system?
2 main properties:Abundant liquid water Environmental conditions that
maintain liquid water
The Habitable Zone
Liquid WaterLiquid Water
Required temperature: 273-373 K Use this as simple requirement for
identifying possibly habitable planets
Where do planets in this temperature range orbit?
Required temperature: 273-373 K Use this as simple requirement for
identifying possibly habitable planets
Where do planets in this temperature range orbit?
The Habitable Zone
Liquid WaterLiquid Water
Where do planets in this temperature range orbit?
Called the Habitable Zone
Let’s work it out…
Where do planets in this temperature range orbit?
Called the Habitable Zone
Let’s work it out…
The Habitable Zone
How does star type affect HZ?
How does star type affect HZ?
Different sized stars have different luminosities
T L1/4
Brighter stars have HZs farther out
Different sized stars have different luminosities
T L1/4
Brighter stars have HZs farther out
The Habitable Zone
How does star type affect HZ?
How does star type affect HZ?
Main sequence (MS) stars have different luminosities throughout their lifetimes
Continuously Habitable Zone: maintains conditions suitable for life throughout MS lifetime of star
Main sequence (MS) stars have different luminosities throughout their lifetimes
Continuously Habitable Zone: maintains conditions suitable for life throughout MS lifetime of star
The Habitable Zone
Is it that simple?Is it that simple?
Albedo, a
Atmosphere - what part of spectrum can pass through
Albedo, a
Atmosphere - what part of spectrum can pass through
The Habitable Zone
Moves HZ inwards
Moves HZ outwards
Moves HZ inwards
Moves HZ outwards
Role of the Carbon CycleRole of the Carbon Cycle
Kasting proposed the Carbon Dioxide Thermostat Extends to HZ for
Earth-like planets Keeps off
temperature extremes
Kasting proposed the Carbon Dioxide Thermostat Extends to HZ for
Earth-like planets Keeps off
temperature extremes
Carbon sources: Volcanic
outgassing Decarbonation Organic carbon
Carbon sinks: Calcium
carbonate formation
Photosynthesis
Carbon sources: Volcanic
outgassing Decarbonation Organic carbon
Carbon sinks: Calcium
carbonate formation
Photosynthesis
The Habitable Zone
Role of the Carbon CycleRole of the Carbon Cycle
The Habitable Zone
Continuously Habitable Zone
Continuously Habitable Zone
Inner edge: 0.95 AU
Outer edge: 1.15 AU
Inner edge: 0.95 AU
Outer edge: 1.15 AU
Were other planets habitable in the past?
Will other planets be habitable in the future?
Were other planets habitable in the past?
Will other planets be habitable in the future?
The Habitable Zone
Mars: Once Habitable?
Still Habitable?
Mars: Once Habitable?
Still Habitable? Early Mars
Evidence of large amounts of flowing liquid water
Warmer temperatures: Heat from interior
would have been higher
Warm climate from greenhouse gases or CO2 clouds
Early Mars Evidence of large
amounts of flowing liquid water
Warmer temperatures: Heat from interior
would have been higher
Warm climate from greenhouse gases or CO2 clouds
Current Mars Gullies may be
due to underground water
Carbon cycle not as active as on Earth
Current Mars Gullies may be
due to underground water
Carbon cycle not as active as on Earth
The Habitable Zone
Characteristics that make a habitable planet
Characteristics that make a habitable planet
The Habitable Zone
•Other Heat sources to sustain liquid water
•Geothermal•Iceland
•Tidal•Europa
•Other Heat sources to sustain liquid water
•Geothermal•Iceland
•Tidal•Europa
•Size of planet•Internal heat comes from
•Accretional heat•Differentiation•Radiogenic decay
•Allows for plate tectonics
•Mars cooled quickly, so no plate tectonics at present
•Size of planet•Internal heat comes from
•Accretional heat•Differentiation•Radiogenic decay
•Allows for plate tectonics
•Mars cooled quickly, so no plate tectonics at present
Characteristics that make a habitable system
Characteristics that make a habitable system
Star Type: stable luminous stars necessary Sufficiently long
lifetime for life to evolve
Large enough so planets don’t tidally lock
Star Type: stable luminous stars necessary Sufficiently long
lifetime for life to evolve
Large enough so planets don’t tidally lock
The Habitable Zone
•Star system•Single star: allows for stable orbit•Binary system:
•Fewer stable orbits exist•HZ calculated on individual basis
•Star system•Single star: allows for stable orbit•Binary system:
•Fewer stable orbits exist•HZ calculated on individual basis
Characteristics that make a habitable neighborhoodCharacteristics that make a habitable neighborhood Galactic Habitable Zone
Area of high metallicity (elements w/ Z>2) Outer region of galaxy
Lower stellar density Lower radiation levels
Galactic Habitable Zone Area of high metallicity (elements w/ Z>2) Outer region of galaxy
Lower stellar density Lower radiation levels
The Habitable Zone
Early EarthEarly EarthEarly EarthEarly Earth
Astr 3300September 16, 2009
Astr 3300September 16, 2009
Environment of early EarthEnvironment of early Earth
• Evidence of a habitable planet 3.8 Ga– Geological evidence near Isua,
Greenland– Limestone and sandstone– We can infer presence of liquid water– Earth must have had temperatures
similar to today’s
• Evidence of a habitable planet 3.8 Ga– Geological evidence near Isua,
Greenland– Limestone and sandstone– We can infer presence of liquid water– Earth must have had temperatures
similar to today’s
Early Earth
Liquid water 3.8 Ga?Liquid water 3.8 Ga?
• Faint young Sun– Sun was 25-30% less luminous– Simple energy balance shows Earth’s
surface temperature would have been below 273 K
• Other heat sources– Geological activity
• More internal heat from radioactive decay and primordial heat
• Plate tectonics release CO2 - greenhouse traps heat
• Faint young Sun– Sun was 25-30% less luminous– Simple energy balance shows Earth’s
surface temperature would have been below 273 K
• Other heat sources– Geological activity
• More internal heat from radioactive decay and primordial heat
• Plate tectonics release CO2 - greenhouse traps heat
Early Earth
Snowball EarthSnowball Earth
• Global glaciations brought on by disruptions in the carbon cycle– Up to 4 occurred between 750 Ma and 580 Ma ago– Geological record shows layered deposits in tropics
attributable to glacial erosion
• CO2 sinks would cease, but sources would continue. 350 times current CO2 levels would accumulate to create a severe greenhouse, causing the ice to melt w/in a few hundred years.
• All eukaryotes today are from the survivors of snowball earth
• Global glaciations brought on by disruptions in the carbon cycle– Up to 4 occurred between 750 Ma and 580 Ma ago– Geological record shows layered deposits in tropics
attributable to glacial erosion
• CO2 sinks would cease, but sources would continue. 350 times current CO2 levels would accumulate to create a severe greenhouse, causing the ice to melt w/in a few hundred years.
• All eukaryotes today are from the survivors of snowball earth
Early Earth
Early HydrosphereEarly Hydrosphere
How did Earth get all it’s water?How did Earth get all it’s water?
Early Earth
Origin of Earth’s WaterOrigin of Earth’s Water
• Delivered by comet impact– D/H ratios of comets are not the same as on earth– This is unlikely the delivery mechanism
• Solar nebula– Unlikely because relative abundance of other
volatiles are higher in the solar nebula than in planetary atmospheres
• From un-degassed interiors of planetary embryos– Most likely scenario– Hydrated minerals could form around 1 AU
• Delivered by comet impact– D/H ratios of comets are not the same as on earth– This is unlikely the delivery mechanism
• Solar nebula– Unlikely because relative abundance of other
volatiles are higher in the solar nebula than in planetary atmospheres
• From un-degassed interiors of planetary embryos– Most likely scenario– Hydrated minerals could form around 1 AU
Early Earth
Origin of Earth’s Atmosphere
Origin of Earth’s Atmosphere
• Only trace amounts of oxygen for the first 1 billion years– O2 resulted from
breakdown of water vapor by UV radiation
• Current atmosphere is oxygen-rich, so where did it come from?
• PHOTOSYNTHESIS!– First developed in
cyanobacteria 3.8-2.5 Ga ago (Archaean era)
• Only trace amounts of oxygen for the first 1 billion years– O2 resulted from
breakdown of water vapor by UV radiation
• Current atmosphere is oxygen-rich, so where did it come from?
• PHOTOSYNTHESIS!– First developed in
cyanobacteria 3.8-2.5 Ga ago (Archaean era)
Early Earth
Banded Iron FormationsBanded Iron Formations
• Geologic evidence for appearance of free oxygen are Banded Iron Formations (BIFs)
• BIFs provide clues as to the oxidation state of ocean and atmosphere at time of formation
• Usually formed in shallow seas - oxygen available here
• Geologic evidence for appearance of free oxygen are Banded Iron Formations (BIFs)
• BIFs provide clues as to the oxidation state of ocean and atmosphere at time of formation
• Usually formed in shallow seas - oxygen available here
Early Earth
Role of hydrothermal systems
Role of hydrothermal systems
• Seawater flowing through hydrothermal vents dissolved iron
• Injected iron into deep ocean through vents
• Deep ocean too oxygen-poor to oxidize iron, so it cycled through system to be deposited in shallow seas.
• Possible iron was consumed by bacteria near vents and transported in drifts of large colonies
• Seawater flowing through hydrothermal vents dissolved iron
• Injected iron into deep ocean through vents
• Deep ocean too oxygen-poor to oxidize iron, so it cycled through system to be deposited in shallow seas.
• Possible iron was consumed by bacteria near vents and transported in drifts of large colonies
Early Earth
Evidence for early life on Earth
Evidence for early life on Earth
• Stromatolites– Oldest known is
3.46 Ga-old– Formed from
cyanobacteria and blue-green algae
– Organisms for gelatinous mat and precipitate calcium carbonate, so it looks like stack of pancakes w/ alternating layers
• Stromatolites– Oldest known is
3.46 Ga-old– Formed from
cyanobacteria and blue-green algae
– Organisms for gelatinous mat and precipitate calcium carbonate, so it looks like stack of pancakes w/ alternating layers
Early Earth
Carbon IsotopesCarbon Isotopes
• Can be used as indicators of biological processes
• Can be used as indicators of biological processes
Early Earth
• 12C and 13C are stable isotopes
• Ratio is affected by physical processes
• More energy efficient to make or break 12C bonds
• 12C is preferentially incorporated into products of chemical reactions
• 12C and 13C are stable isotopes
• Ratio is affected by physical processes
• More energy efficient to make or break 12C bonds
• 12C is preferentially incorporated into products of chemical reactions
Carbon IsotopesCarbon Isotopes
• A negative value can be used as a biomarker, indicating fractionation is due to photosynthesis
• A negative value can be used as a biomarker, indicating fractionation is due to photosynthesis
Early Earth
• Isotopic fractionation
• let’s work it out
• Isotopic fractionation
• let’s work it out€
δ13C =13C
12Csample
13C12Cs tan dard
−1 ⎡ ⎣ ⎢
⎤ ⎦ ⎥×1000
Evolving ComplexityEvolving Complexity
• Ediacaran fauna show distinctive changes in size ~670 Ma ago)
• Ediacaran fauna show distinctive changes in size ~670 Ma ago)
Early Earth
• Life started small (maximum of a few mm in size)
• In the last 600 Ma, evolution of more larger, more complex organisms has occurred
• Life started small (maximum of a few mm in size)
• In the last 600 Ma, evolution of more larger, more complex organisms has occurred
Evolving ComplexityEvolving Complexity
• Ediacaran fauna show distinctive changes in size ~670 Ma ago)
• Tubular, frond-like, radially symmetric
• cm-m in size
• Ediacaran fauna show distinctive changes in size ~670 Ma ago)
• Tubular, frond-like, radially symmetric
• cm-m in size
Early Earth
Increase in size and diversity
Increase in size and diversity
• Subsequently, after 500 Ma ago, sizes increased 2 orders of magnitude
• Dinosaurs• Larger mammals
• Subsequently, after 500 Ma ago, sizes increased 2 orders of magnitude
• Dinosaurs• Larger mammals
Early Earth
Major extinctionsMajor extinctions
• Marked periods of Earth’s biological history
• Reduce diversity• Most recent
– Possibly due to comet or asteroid impact– Die out of the dinosaurs (65 Ma ago)
• Demonstrates how important “environmental stability” is for a habitable planet
• Marked periods of Earth’s biological history
• Reduce diversity• Most recent
– Possibly due to comet or asteroid impact– Die out of the dinosaurs (65 Ma ago)
• Demonstrates how important “environmental stability” is for a habitable planet
Early Earth
Banded-Iron Formations (BIFs)
• Most formed 3Ga-1.8Ga
• Amount of Oxygen locked in BIFs is ~20 times the volume in the modern atmosphere
Banded-Iron Formations (BIFs)
• Formation:– Oxygen produced by cyanobacteria combined with
iron in the ocean (early ocean was acidic and iron-rich)
– Oxidized iron then deposits in a layer– Process is cyclical due to oscillating availability of
free oxygen– Eventually, photosynthesis caught on, the oceans
because well-oxygenated, and the available iron in the Earth's oceans was precipitated out as iron oxides
Banded-Iron Formations (BIFs)
• Snowball Earth cycles may have been the cause of bands– During snowball periods, free oxygen not available
and iron– Followed by oxidizing periods of melt
• Metal-rich brines may also be responsible– Carry iron from the deep ocean (near
hydrothermal vents)– Deposited in shallow seas where it has access to
free oxygen
Carbon Isotopes
• 12C and 13C are stable isotopes• More energy efficient to make 12C bonds• 12C is preferentially incorporated into
products of chemical reactions (like photosynthesis!)
• Ratio of the two isotopes can be used as an indicator of biological processes
Carbon Isotopes
• If 12C has preferentially been incorporated, 13C/12C will be smaller than the standard
• If sample < standard, δ13C is negative
• A negative value can be used as a biomarker, indicating fractionation is due to photosynthesis
€
δ13C =13C
12Csample
13C12Cs tan dard
−1 ⎡ ⎣ ⎢
⎤ ⎦ ⎥×1000
Extreme EnvironmentsExtreme Environments
ASTR/GEOL 3300September 18, 2009
ASTR/GEOL 3300September 18, 2009
OverviewOverview
• Extreme Conditions• Other Worlds
• Extreme Conditions• Other Worlds
Extreme conditionsExtreme conditions
• Conditions on early earth may have been “extreme” compared to present-day
• Extremophiles - organisms that thrive in exteme environments– Heat/Cold– Acids/alkalines– High pressures– dessication
• Conditions on early earth may have been “extreme” compared to present-day
• Extremophiles - organisms that thrive in exteme environments– Heat/Cold– Acids/alkalines– High pressures– dessication
TemperatureTemperature
• Majority of organisms on Earth thrive in the temperature range 20-45 °C (mesophiles)
• Usual response to extreme temperatures:– Cold:
• Formation of ice crystals in the body
– Hot: • Structural breakdown of biological molecules
(proteins and nucleic acids)• Disruption of cells’ structural integrity due to
increased membrane fluidity
• Majority of organisms on Earth thrive in the temperature range 20-45 °C (mesophiles)
• Usual response to extreme temperatures:– Cold:
• Formation of ice crystals in the body
– Hot: • Structural breakdown of biological molecules
(proteins and nucleic acids)• Disruption of cells’ structural integrity due to
increased membrane fluidity
Extreme Conditions
TemperatureTemperature
Extreme Conditions
ThermophilesThermophiles
Extreme Conditions
•Thermophiles live between 50 and 80 °C –Example: Thermoplasma
•Archaea•Lives in volcanic hot springs
•Hyperthermophiles live between 80 and 115 °C–Example: Sulfolobus
•No multicellular plants or animals can tolerate >50 °C•No microbial eukarya can tolerate >60 °C
ThermophilesThermophiles
• First true thermophile discovered in Yellowstone National Park in 1960s
• > 50 hyperthermophiles have been isolated to date– Many live in or near
deep-sea hydrothermal systems (black smokers)
• First true thermophile discovered in Yellowstone National Park in 1960s
• > 50 hyperthermophiles have been isolated to date– Many live in or near
deep-sea hydrothermal systems (black smokers)
Extreme Conditions
Thermophiles: how they cope
Thermophiles: how they cope
• Since high temperatures change membrane fluidity, adaptation is change of membrane composition
• Evolution of proteins to better cope w/ high temps
• Since high temperatures change membrane fluidity, adaptation is change of membrane composition
• Evolution of proteins to better cope w/ high temps
Extreme Conditions
PsychrophilesPsychrophiles
• Supported in frozen environments of Earth
• Lowest recorded temperature for active microbial communities: -18 °C
• Found in all 3 domains of life
• Supported in frozen environments of Earth
• Lowest recorded temperature for active microbial communities: -18 °C
• Found in all 3 domains of life
Extreme Conditions
Psychrophiles: how they cope
Psychrophiles: how they cope
• Low temps mean decrease in membrane fluidity, so adaptation is adjustment of ratios of lipids in their membranes
• Prevent water from freezing with soluble compounds that lower freezing temp of water (e.g. thermal hysteresis proteins)
• Low temps mean decrease in membrane fluidity, so adaptation is adjustment of ratios of lipids in their membranes
• Prevent water from freezing with soluble compounds that lower freezing temp of water (e.g. thermal hysteresis proteins)
Extreme Conditions
RadiationRadiation
• UV and ionizing radiation can do serious damage to DNA– Deinococcus
radiodurans can withstand high-dose radiation because it can accurately rebuild its DNA
– Also able to cope with extreme dessication, so also a xerophile - thus known as a polyextremophile
• UV and ionizing radiation can do serious damage to DNA– Deinococcus
radiodurans can withstand high-dose radiation because it can accurately rebuild its DNA
– Also able to cope with extreme dessication, so also a xerophile - thus known as a polyextremophile
Extreme Conditions
pHpH
• Most biological processes occur in middle of pH scale (4-8)
• Acidophile - thrive at 0.7-4• Alkaliphile - thrive at 8-12.5
• Most biological processes occur in middle of pH scale (4-8)
• Acidophile - thrive at 0.7-4• Alkaliphile - thrive at 8-12.5
Extreme Conditions
pHpH• Acidophile - thrive at 0.7-4
– Occur in geochemical activities
• Sulfur production at hot springs and deep-sea vents
– Cope by pumping H+ out of cells at a high rate
• Alkaliphile - thrive at 8-12.5– Live in soils containing
carbonate and soda lakes
– Above pH of 8, RNA breaks down, so alkaliphiles maintain neutrality inside cells
• Acidophile - thrive at 0.7-4– Occur in geochemical
activities• Sulfur production at hot
springs and deep-sea vents
– Cope by pumping H+ out of cells at a high rate
• Alkaliphile - thrive at 8-12.5– Live in soils containing
carbonate and soda lakes
– Above pH of 8, RNA breaks down, so alkaliphiles maintain neutrality inside cells
Extreme Conditions
Acidic mudpotAcidic mudpot: located in Yellowstone NP, home of Sulfolobus acidocaldarius. Photo courtesy of National Park Service
SalinitySalinity
• Halophiles require high concentrations of salt to live (2-5 times that in seawater)
• Found in Great Salt Lake, Dead Sea, salterns
• Can be coincident with high alkalinity environments
• Survive by producing large amounts of internal solute so as to not lose water via osmosis
• Halophiles require high concentrations of salt to live (2-5 times that in seawater)
• Found in Great Salt Lake, Dead Sea, salterns
• Can be coincident with high alkalinity environments
• Survive by producing large amounts of internal solute so as to not lose water via osmosis
Extreme Conditions
Great Salt Lake, UT.Great Salt Lake, UT. Carotenoids seen here are biproduct of halophiles.
DessicationDessication
• Some organisms survive low-water environments via anhydrobiosis, a state of suspended animation
• Some organisms survive low-water environments via anhydrobiosis, a state of suspended animation
Extreme Conditions
PressurePressure
• Undersea pressures are much greater than surface pressures– Boiling point increases with pressure, so
liquid water at ocean floor could be 400 ºC– Pressure compresses volume, so peizophiles
have increased membrane fluidity so they don’t get “smushed”
• Upper atmosphere pressures are much lower than surface pressures
• Undersea pressures are much greater than surface pressures– Boiling point increases with pressure, so
liquid water at ocean floor could be 400 ºC– Pressure compresses volume, so peizophiles
have increased membrane fluidity so they don’t get “smushed”
• Upper atmosphere pressures are much lower than surface pressures
Extreme Conditions
OxygenOxygen
• Aerobic metabolism is more efficient than anaerobic, but it kills cells quicker via oxidation
• Many organisms with aerobic metabolisms combat oxidation with natural anti-oxidants
• Aerobic metabolism is more efficient than anaerobic, but it kills cells quicker via oxidation
• Many organisms with aerobic metabolisms combat oxidation with natural anti-oxidants
Extreme Conditions
Extremes on other planetsExtremes on other planets
• If we’ve seen life thrive in extreme circumstances on Earth, why not on other planets?
• Mars holds most promise• What about moons in our solar system:
– Europa– Titan– Enceladus
• If we’ve seen life thrive in extreme circumstances on Earth, why not on other planets?
• Mars holds most promise• What about moons in our solar system:
– Europa– Titan– Enceladus
Other Worlds
Possible Earth analoguesPossible Earth analogues
• Hotsprings• The deep sea• Hypersaline environments• Evaporites• The atmosphere• Ice, permafrost, snow• Subsurface environments
• Hotsprings• The deep sea• Hypersaline environments• Evaporites• The atmosphere• Ice, permafrost, snow• Subsurface environments
Other Worlds
EuropaEuropa
• Life exists w/o photosynthesis in the deep ocean
• Europa has a subsurface ocean
• Life may exist beneath the surface
• Life exists w/o photosynthesis in the deep ocean
• Europa has a subsurface ocean
• Life may exist beneath the surface
Other Worlds
EuropaEuropa
• Life exists w/o photosynthesis in the deep ocean
• Europa has a subsurface ocean
• Life may exist beneath the surface– Shielded from
Jupiter’s radiation– Warmer than surface
temperatures
• Life exists w/o photosynthesis in the deep ocean
• Europa has a subsurface ocean
• Life may exist beneath the surface– Shielded from
Jupiter’s radiation– Warmer than surface
temperatures
Other Worlds
TitanTitan
• Airborne micro-organisms?• Extremes to withstand:
– Dessication– Radiation
• Airborne micro-organisms?• Extremes to withstand:
– Dessication– Radiation
Other Worlds
TitanTitan
• On Earth, spores are only things that really “live” in the atmosphere.
• Debate as to weather this constitutes life
• On Earth, spores are only things that really “live” in the atmosphere.
• Debate as to weather this constitutes life
Other Worlds
Mars
• Host to several extreme environments– Deserts– Ice, permafrost, snow– Subsurface
Other Worlds
Mars: deserts
• Driest places on earth– Hottest: Atacama – Coldest: Antarctica
• Bacteria, algae, fungi live on or under rocks– Endoliths– Cryptoendoliths
• Rocks provide shelter from – Temperature extremes – UV radiation
Other Worlds
Mars: ice, permafrost, snow
• Microbes and algae exist in frozen environments on Earth
• Maybe not thriving, but microbial survivors could exist
Other Worlds
Mars: subsurface environments
• Best chance of withstanding Martian extremes– No liquid water at surface
– Low pressure
– CO2-rich atmosphere
– Only 43% solar radiation at Earth
• Subsurface provides– Protection
– Possible liquid water
– Energy source for chemolithoautotrophs
Other Worlds