AstrobiologyAstrobiology 740740 FollowFollow thethe IceIce JanuaryJanuary 13,13, 20062006

Dr. Karen J. Meech, Astronomer Institute for Astronomy, Univ. Hawaii [email protected]; (808) 956-6828 MoonMoon--MarsMars InitiativeInitiative z Implement sustained human / robotic exploration of the solar system and beyond; z Extend human presence across the solar system, z Human return to the Moon by 2020, z Preparation for human exploration of Mars & beyond z Search for evidence of life z Develop the necessary innovative technologies, knowledge, and infrastructures z Conduct advanced telescopic searches for Earth-like planets and habitable environments around other stars z Promote international and commercial participa- tion in exploration WeWe areare AqueousAqueous BeingsBeings……..

z Water is the medium for life’s chemistry z Our cells are mostly water z Water is a liquid for large ∆T z Water ice floats z Water affects Earth’s energy budget z Water involved in geochemical reactions Æ atm chemical balance z Water in Earth’s mantle affects internal melting behavior HabitableHabitable ZonesZones

DependsDepends onon z Planet properties: albedo, atmospheric density & composition, rotation Distance from the central star where the equilibrium T allows z Age of star – luminosity where the equilibrium T allows for the existence of liquid water increases with time z Planetary orbit z Internal heat sources OurOur SolarSolar SystemSystem

Planet Albedo Radius Distance Eccen TBB Mercury 0.119 2439 0.3871 0.206 445 Venus 0.750 6052 0.7233 0.007 238 Earth 0.306 6378 1.0000 0.017 261 Mars 0.250 3397 1.5237 0.093 215 (Ceres) 0.030 456.5 2.7671 0.077 170 Jupiter 0.343 71398 5.2028 0.048 113 Saturn 0.342 60000 9.5380 0.056 83 Uranus 0.300 26200 19.191 0.046 60 Neptune 0.290 25225 30.061 0.010 48 Pluto 0.500 1151 39.529 0.248 38 CosmicCosmic SolarSolar SystemSystem History:History: DeliveryDelivery ofof WaterWater

>4.6 billion yr ISM dark cloud Planets grow Protoplanetary disk

Cometary Delivery RangeRange ofof TemperaturesTemperatures

CH4 worms, Sea of Cortez Ice z PsychrophilesPsychrophiles:: ColdCold loverslovers (T~0(T~0--2020oC)C) z Survive freeze/thaw, Reproduce 2oC z HabitatsHabitats onon EarthEarth z Soils, Deep ocean water, Sea ice IceIce // WaterWater InventoryInventory onon EarthEarth

z Arctic – 4 km deep ocean, covered by ice z Antarctic – up to 4 km deep ice surrounded by oceans

Snow & Ice Area Vol Sea in N Hem Equiv. 106 km2 106 km2 m Greenland 1.73 3.0 7.5 Other 0.532 0.13 0.32 Sea Ice (N) 8.87 Antarctica 13.0 29.4 73.5 Sea Ice (S) 4.2

Material from T. Thorsteinsson IceIce onon EarthEarth

z Extent of Eurasian ice sheet Vatnajokull Ice cap, during glacial max 20,000 yr Iceland

z Pleistocene z Last 2-3 Myr z 20 interglacial periods z Each last 100-150 x 105 yr

Material from T. Thorsteinsson GlaciersGlaciers onon EarthEarth

Vatnajokull Ice cap, Iceland Vatnajokull Ice cap, Iceland

Baffin Bay Greenland z Physical characteristics AntarcticaAntarctica z 5.4 x 106 sq mi z 7000 ft elevation z 75% all fresh water o o z Tavg = -70 F (low -128.6 F) z Winds up to 300 km/hr z Historical z Coal beds Æ Pangea 2 Myr z Dry Valleys z 1901 Expedition z Penetration 1978

z H2O just above freezing Æ greenhouse effect z Enriched from spring runoff IsolatedIsolated EnvironmentsEnvironments z LakeLake HoareHoare –– TaylorTaylor ValleyValley z Environment much like Mars z Permanent ice cover z Life Forms z Microbial mats z Increased oxygen levels; 1% sunlight z Algae draw Fe, S and calcite from water z LakeLake VostokVostok z Most isolated aquatic environment on Earth z Largest of 70 subglacial lakes z Cut off 35-40 Myr ago z 1500 km from coast, z 3500m elevation o o z Tair = -89 F, Tlake = -3 C LakeLake VostokVostok

z 1998 Russian Core Æ 3.623 km z Living organisms from 1500-2750 m (2-5 x 105 yr old) z Low population diversity z Utilized dissolved organic C and O migrating through ice

z 4 climate changes 20,000 to 100,000 yr periods ([CO2]) WaterWater onon thethe MoonMoon

z LunarLunar Prospector:Prospector: NeutronNeutron spectrometerspectrometer z 1010--300300 millionmillion tonstons waterwater iceice inin shadowedshadowed polarpolar regionsregions z CurrentCurrent conditionsconditions MarsMars ScenariosScenarios z 95% CO2, 3% N2

z P 0.006 bar, Tavg ~ 233K z MarsMars VikingViking ResultsResults z Lack of O3 z No organics to 1 ppb z Presently,Presently, liquidliquid HH OO z MarsMars isis aa coldcold polarpolar 2 desert isnisn’’tt stablestable onon MarsMars surfsurf desert z LifeLife Oases?Oases? z AmountAmount ofof HH2OO z Hydrothermal systems 3 z Atm – 1-2 km (10µm z Subsurface reservoirs layer) z Life in Ice z Polar caps 4x106 km3 (30 m layer) WhereWhere’’ss thethe WaterWater onon Mars?Mars? z MarsMars GlobalGlobal SurveyorSurveyor z Polar ice inventory, gullies z Mola Altimetry (N ocean?)

z Hematite (Fe2O3) z MarsMars OdysseyOdyssey

z γ-ray spectrometer: subsurface H2O! z MarsMars ExplorationExploration RoversRovers z Launch Jun-Jul ’03, z Arrive Jan 04 MarsMars GulliesGullies && EarthEarth AnalogsAnalogs z Seepage landforms not cratered Æ geologically young z Resemble terrestrial gullies (landslide promoted by ground water flow)

Mars Mars Iceland

Iceland HematiteHematite FeFe22OO33 z Product of aqueous mineralization z Hot water moves through Fe-rich rocks Æ dissolve Fe z Water cools, Fe-minerals precipitate z Often associated with hydrothermal vents on Earth z Implies sedimentary rocks z Implies long-term H2O stability z Image (MGS) z Meridani Planum z 1500x1200 km OpportunityOpportunity –– BodiesBodies ofof WaterWater

z Habitability at 2 sites: geological, climate, aqueous alteration records z Drilled rocks Æ sulfates z Long term standing water z “Blueberries” – Hematite rich z Wave flow patterns MarsMars MountainMountain Glaciers?Glaciers?

Western Olympus Mons, Mars Alaskan Glacier, Earth Mars,Mars, GlacialGlacial flowflow

Material from J. Head z PhysicalPhysical CharacteristicsCharacteristics EuropaEuropa z Diameter 3,138 km

z Tsurf = 128K -3 z ρ = 3 gm cm , g = -0.135 gearth z TidalTidal heatingheating z F = GMm/r2 z Differential tide raising force z dF proportional to r-3 dr z SusurfaceSusurface OceanOcean z Magnetic induction Æ liquid z ~100 km deep z Beneath > 20 km thick icy shell EvidenceEvidence forfor OceanOcean Chaos Region Lenticulae

z Melt through thin shell z Diapirism – ice convection partly z Diapirism – ice convection partly melts surface ice melts surface ice z Domes ~10 km in diameter z Icy spreading center analog z Warm buoyant ice from below EuropaEuropa && Life?Life?

Material from R. Pappalardo z Plausible sources of free energy and biogenic elements exist z Sub-surface ocean z Tidal stretching – heating z Organics (spectra) z Geological processes permit suface-ocean communication CassiniCassini--HuygensHuygens TitanTitan MissionMission z N2 – CH4 atmosphere z UV from sun produces other organics (ethane, acetylene…..) z Organics must precipitate Æ need to resupply CH4 Material from R. Pappalardo z CH4-ethane rain and lakes? CassiniCassini-- Huygens:Huygens: TitanTitan z Dark Surface z Mixture of water-ice and hydrocarbon-ice z Possible evidence of fluvial erosion at base of “rocks”

15 cm

January 14, 2005 TitanTitan’’ss CoastlineCoastline IcesIces && LiquidsLiquids onon Titan?Titan?

z Drainage channels from 20 km elevation z Hydrocarbon Lake at S Pole IceIce PhysicsPhysics TemperatureTemperature ScalesScales

z KelvinKelvin –– absoluteabsolute scalescale –– atomicatomic motionmotion z CC == 5/95/9 (F(F –– 32)32) z KK == CC ++ 273273

Scale H2O Freeze H2O Boil ∆T Fahrenheit 32 212 180 Centigrade 0 100 100 Kelvin 273 373 100 WaterWater –– FeaturesFeatures RelevantRelevant toto IceIce z Bent molecule (104.52o) – H Bond z Dipole moment z Tetrahedral Crystal structure z Expands upon freezing (less dense) z Negative slope on melting curve z Le Chatlier Principle z Triple Point [S.M.O.W.] 613 z P = 611.657 Pa (0.006 bar) 612 z T = 273.16 K (0.16o C) z D O: 661 Pa, 276.82K 2 611 Pressure [Pa] Pressure [Pa] 610 1 bar = 105 Pa = 105 Nt/m2 -0.02 0 0.02 1 atm = 101325 Pa Temperature [C] WaterWater IceIce PhysicsPhysics z ExistsExists inin 1313 crystallinecrystalline phasesphases (diff(diff TT && P)P) z Phase I: P < 2700 atm z Ih – hexagonal z Ic – cubic (low T, low P) z metastable z High P forms: II to XI z AmorphousAmorphous IceIce z ClathratesClathrates Ice Ial and Iah formation AmorphousAmorphous IceIce z Forms at low T Æ insufficient E for crystal structure z Physical Properties z Large voids: trapped gases z Gases released between 35-120K z Annealing

z 38-68K – transition from Iah Æ Ial z Beginning at 90K Æ Ic (exothermic) z Two forms

z High Density, Iah

z Low Density, Ial ClathrateClathrate HydratesHydrates z CrystallineCrystalline frameworkframework ofof HH--bondedbonded HH2OO molecmolec.. trappingtrapping guestguest moleculesmolecules z GuestsGuests dondon’’tt affectaffect thethe chemistrychemistry z Released upon sublimation of water z Cages unstable without guests z Some physical properties are altered z Some clathrate formation not possible at low T and P z Stability: low T (< 273K), moderate to high P (100 atm) z ImportanceImportance

z May store most SS inventory: CO, CO2, CH4 z Catastrophic destabilization due to T , P z Collapse & flow features z Outgassing z Greenhouse gas budgets ClathrateClathrate HydratesHydrates z Type I

z 46 H2O molecules z 2 small cages, 6 large z 12- and 14- sided polygons z Clathrates in the Solar System

z Traps in ratio 1/7 z CH4 – marine sediments – by 2x exceeds other fossil fuel sources z Type II z CO2 – sequester CO2 in ocean z 126 H O molecules 2 2 2 seafloor from atm (climate) z 16 small cages, 8 large z Destabilization on Mars & z 14- and 16- sided polygons Europa – chaotic terrain? z Traps in ratio 1/17 z CH4 / N2 on Triton – geysers z Air – polar ice sheets – info on atmosphere up to 106 yr ago IceIce RegimesRegimes –– InteriorInterior PressuresPressures z G = 6.67 x 10-11 Ntm2/kg2 2 2 2 z PPc == 22ππGGρρ (R(R –– rr )/3)/3 z ρ = density, kg/m3 z R = radius, m Regime ρ [g/cm3] Size [km] P [bar] Dust:Ice Ices ISgrains 0.1 10-10 –– High den. amorph Comet 0.5-1? 1-10 0.0003-0.1 2:1? Ih, Ic, amorphous KBO 0.5-1? 102-103 3.5-1400 2:1? Ih, II, clath, amorph Europa 2.97 1569 3x104 Ih, II, VII, VIII, clath Triton 2.07 1350 1x104 Ih, II, clathrates Mars Ice 1-1.6 3 300 <100 ppm Ih, clathrates Glacier 0.92 3 300 ppm Ih, clathrates z Phase changes: volume changes Æ fractures z Amorphous Æ Ic, exothermic Æ volatile release z Clathrate destabilization Æ outgassing CometComet ExpectationsExpectations z AmorphousAmorphous iceice z Formation T: 30-100K z CrystallineCrystalline icesices z Solar heating: amorphousÆcrystalline transition peaking at 137K z Balance with cosmic ray processing z LackLack ofof ClathratesClathrates z Small size, low central pressures z Release of volatiles in excess of clathrate capacity z Not necessary to explain activity! CometComet FormationFormation

10 100K

31K 100 AU

z Ices in comets condensed T< 100K z Amorphous form traps other gases z Amounts depend on r z Release of gases z 120-137K amorphous Æ crystalline phase z Annealing (30-120K) z Ic Æ Ih ~ 150 K z Sublimation starts 160-180K CH4 N2 Ar CO Sublimation starts 160-180K SublimationSublimation ofof Volatiles?Volatiles? ] ] 1 1 - - s s 2 2 - - m m molec molec Log Z [ Log Z [

Delsemme (1971) z DelsemmeDelsemme’’ss originaloriginal work:work: albedoalbedo tootoo highhigh z WaterWater--activityactivity outout beyondbeyond JupiterJupiter ActivityActivity inin CometsComets atat LargeLarge rr z AllAll CometsComets activeactive rr LL z C/1999 J2 r=7.11AUL, r=7.81AUK z C/2001 G1 r=8.32AUL, r=10.26AUK z C/2003 A2 r=11.5AUL, r=11.43AUK z AllAll areare dynamicallydynamically newnew

z C/1999 J2 1/aorig = 20

z C/2001 G1 1/aorig = 35

z C/2003 A2 1/aorig = 45

Material from Meech et al, in prep. MechanismsMechanisms ofof ActivityActivity

Material from Meech et al, in prep. Complications:Complications: HeatHeat TransportTransport inin RealReal NucleiNuclei z SolveSolve thethe heatheat conductionconduction equationequation ρρ(z(z)) c(z,Tc(z,T)) dT/dtdT/dt == d/dzd/dz [[κκ(z,T(z,T)) dT/dzdT/dz]] z Boundary condition: Energy Balance Equation z Heat sources: z Solar radiation – cyclic z Radioactivity – declining z Crystallization – transient, front induced z ApproximationsApproximations z IceIce ThermalThermal propertiesproperties veryvery differentdifferent

z κa << κc (4 orders of mag) (a=amorphous, c=crystalline) z κa α T and κc α 1/T z κ = rate of heat transfer through medium [W m-2 K-1] HeatHeat ConductionConduction inin PorousPorous MediaMedia

Porosity: 7.5% 13% 15% 22% z Pores reduce thermal conductivity z Conduction by radiation z Conduction by vapor sublimation Æ recondensation z Releases heat, warming colder areas z Reduces the thermal gradient z Sintering Æ decreases porosity InteriorInterior PressuresPressures z InteriorInterior structurestructure ÆÆ affectsaffects surfacesurface featuresfeatures z ModelingModeling thethe structurestructure ofof aa bodybody z Hydrostatic equilibrium dP/dr = -GM(r)ρ(r)r-2 z Mass continuity dM/dr = 4πr2ρ(r) z Equation of state of material (relation between P, T and ρ for a material). Approx: -1 B z P = K0 B [(ρ/ρo) -1] 11 -2 z K0 = 2-3 x 10 Nm z B = dK/dP ~ 2.2-4; z K = bulk modulus z Heat conduction equation TerrestrialTerrestrial IceIce MassesMasses

500 z TypesTypes ofof IceIce 1000 z Polar Ice: T < Tfr throughout z Temperate: at or below Tfr except 1500 10 kyr top 15 m 2000 z Polythermal: part polar, part temperate 2500 100 kyr 3000

z Temperate: winter cold wave eliminated by latent heat of re-freezing z Polar:

z T below 15m = Tmean z Ice warms near bedrock from geothermmalal heating Material from T. Thorsteinsson DensificationDensification z Physical Processes z Rounding & settling of crystals, ofof IceIce z increase in crystal size z Formation of bonds between crystals z Decrease of air space No air bubbles due to 3 pressure of overlying ice z Densities [kg/m ] z Snow 50-400 z Firn 400-830 Volume expansion due z Glacier 830-920 to warming at bedrock z Rate of transformation z 0oC 15-35m Æ 10-20 yr z -30oC 70m, 200 yr z -55oC 110m, 2000 yr Density (g/cm3)

Material from T. Thorsteinsson IceIce ChangesChanges z AirAir bubblebubble sizesize decrease,decrease, AntarcticaAntarctica z FreshFresh snowsnow crystalcrystal z SingleSingle iceice crystalscrystals fromfrom glacierglacier iceice ((MendelhallMendelhall glacier,glacier, AK)AK)

20 cm

Material from T. Thorsteinsson 5 mm GrainGrain Growth,Growth, ClathratesClathrates

z PressurePressure differencesdifferences acrossacross crystalcrystal boundariesboundaries resultresult inin largelarge grainsgrains growing,growing, smallsmall onesones shrinkingshrinking z GrowthGrowth raterate veryvery TT dependentdependent propprop toto ee(-Q/RT) z IceIce clathratesclathrates cancan formform atat highhigh PP (depth)(depth)

5 cm 5 cm

500 year old ice at 130 m depth. 100,000 year old ice at Average diam: 2 mm 2850 m depth. Average diam: > 2 cm Material from T. Thorsteinsson IceIce RegimesRegimes –– InteriorInterior PressuresPressures z G = 6.67 x 10-11 Ntm2/kg2 2 2 2 z PPc == 22ππGGρρ (R(R –– rr )/3)/3 z ρ = density, kg/m3 z R = radius, m Regime ρ [g/cm3] Size [km] P [bar] Dust:Ice Ices ISgrains 0.1 10-10 –– High den. amorph Comet 0.5-1? 1-10 0.0003-0.1 2:1? Ih, Ic, amorphous KBO 0.5-1? 102-103 3.5-1400 2:1? Ih, II, clath, amorph Europa 2.97 1569 3x104 Ih, II, VII, VIII, clath Triton 2.07 1350 1x104 Ih, II, clathrates Mars Ice 1-1.6 3 300 <100 ppm Ih, clathrates Glacier 0.92 3 300 ppm Ih, clathrates z Phase changes: volume changes Æ fractures z Amorphous Æ Ic, exothermic Æ volatile release z Clathrate destabilization Æ outgassing