Life in the Solar SystemLife in the Solar System1. Study processes that produce current conditions on planets (ne)2. Life elsewhere in Solar System? (fl)Planet TemperaturesFactors in Planet temperature:Greenhouse gas? N2, O2 CO2, H2O CH4, CFC’s no yes yes (Life)Reflecting Light (Albedo)Clouds, Rock, Ice, SnowTwo extremes:Runaway GreenhouseRunaway GlaciationGreenhouse effectTerrestrial Planet AtmospheresBioticEarth0.0379211.015288Mars952.70.16--0.0061~ –50~ 220AbioticEarth96~ 3trace?60290 (> 50)563Venus96~ 3trace< 0.190477750CO2 (%)N2 (%)O2 (%)H2O (%)Pressure (bar)Tavg (ºC)Tavg (K)T = 279K Rapid Rotation, AlbedoApply to Venus, Mars Venus Marsd 0.72 AU 1.52 AUA 0.80 (!) 0.215Tavg220 213(no greenhouse)Tavg750 220(actual)(1 – A) Ld21/4Recall from Chap. 3Venus: Basic FactsSister Planet: R = 0.95 Rd = 0.72 dBUT HOT!Clouds: Sulfuric Acid dropletsRadar “Active” surfaceAge < Age of PlanetBut no large-scale plates⊕⊕View of Venus from Radar MappingEvolution of the AtmosphereUltraviolet ⇒ no oceansH2OHOEscaped < d ⇒ H2O higher in atm⊕⇒ ⇒CO2 remained in atmThick atm, Greenhouse⇒Hot!Runaway GreenhouseExample of positivefeedbackMars: Basic FactsSmaller R = 0.53 RLess Massive M = 0.11 MLess Dense ρ = 0.71 ρMars year = 687 Earth daysMars day = 24.5 Earth hoursSeasons2 small moons (captured asteroids)⊕⊕⊕MarsAncient VolcanoesOlympus MonsThe largest volcanoin the solar system24 km highScarp is 550 km indiameterPolar Ice CapsImage from the HubbleSpace Telescope duringclose approach of Earth andMars.Runaway Glaciation (also positive feedback)Thin atmosphere led to Weak GreenhouseCold temperature led to freeze-out of greenhousegases: T = 175 - 300 KWarm enough for liquid H2O but low pressureActive in past, but not now: Fossil river bedsLiquid H2O for ~ 1 × 109 y (and perhaps more recently)Life?Survive another 0.7 × 109 y in frozen lakes?Analogy to antarctic lakesAntarctica as a model for early MarsDry valleys: Mean T = –20 ºCAnnual precipitation ~ 2 cmBut T > 0ºC for a few days in summer.⇒ Lakes are not frozen solid (though always ice-covered)Algae & bacteria photosynthesize in lakesAlso lichens in rocksIf life arose on Mars, it might have lasted 1 - 2 × 109 yrRecently, a large (140 mile × 30 mile) lakeFound ~ 2.5 miles deep in ice near Vostok stationMay have been under ice for 500,000 yrPlans to drill into lake - look for bacteria (but contamination)Viking Mission2 spacecraft 19761. Chryse Planitia 22º N. Lat2. Utopia Planitia 48º NCameras, …Organic Matter Analysis3 life detection experimentsSampler armOrganic Matter Analysis• Could detect carbon molecules– Few/billion if more than 2 Carbons– Few/million if 1 or 2– 100 to 1000 times less than desert soils– Could be left over, brought by asteroids, …• No organic molecules foundLife Detection Experiments• All assumed microscopic soil organisms– Fairly near surface (shallow trench)– Either heterotrophs• Feed and look for signs of metabolism– Or autotrophs• Look for signs of photosynthesis– If signs of life, do a control experiment• Sterilize firstGas Exchange Experiment (GEX)• Most earth-biased– Assumed Martians would like chicken soup– Pressurized, warmed to 10 C– First mode: humidify• N2, Argon, CO2, O2 released• O2 required chemical reaction– Second mode: wet, nutrients• Monitor for 6 months, no further activity• No sign of metabolizing, earth-like lifeGas Exchange Experiment• Looks for metabolism• Detects gaseousproducts• Using gaschromatographLabeled Release Experiment• Assumed metabolizing Martians– But less Earth like– Simpler mix of nutrients, labeled with 14C– Metabolizing organisms produce 14CO2– Very sensitive to small amounts• Results: immediate release of 14CO2– No further release when more added• Chemical, not biological, reaction suspectedLabeled Release• Looks for metabolism• Nutrients labeled with14CPyrolytic Release Experiment (PR)• Assumed photosynthesizing autotrophs– Adapted to Mars– Supply light, Martian atmosphere– But label with 14CO2 and 14CO• After incubation, remove gases• Burn up (pyrolize)• Look for 14CO2 from burned-up Martians– Interesting ResultsPyrolytic Release• Looks for autotrophs• Supplies gases• Labeled with 14CO2Pyrolytic Release Results• First experiment gave positive result– Could be about 100 to 1000 bacteria• Could have escaped detection with GCMS– Repeat with sterilized sample (175 C, 3days)• Reaction reduced, but not eliminated– Further controls, lower T sterilization• Little change in results• Conclusion: most likely a chemical reactionSummary of Viking ResultsNo organic molecules foundSome apparent activity in pyrolytic release expt.Could be photosynthesis by 100 - 1000 bacteriaThey could have escaped detection by organicmatter analysisBut, sterilized controls did same thing⇒ chemical, not biological, reactionSurface is strongly oxidizing (UV)⇒ Organic matter would be destroyed⇒ Experiments not designed for this⇒ Oxygen rich compounds on surface can react like lifeTo find current Martians (or fossil Martians)….Dig Deeper!And remember that your experiments determine whatyou can find…More Recent Mars Missions• Pathfinder/Sojourner 1997• Global Surveyor 1998• Mars Odyssey 2002• Mars Express (ESA) 2003– Beagle crashed (life detection)• Mars Rovers 2004– Spirit and OpportunityPathfinder & SojournerSee http://mars.sdsc.edu/index.html http://mars.jpl.nasa.gov/default.htmlClose up photos, analysis of rocksMore evidence of past water flowHas “movies” of rover’s journeyGlobal SurveyorMars Global Surveyorhttp://mars.sdsc.edu/mgs/index.html1998 - in orbit around MarsThe “Face” on Mars gets erasedViking SurveyorAnd with Mars OdysseyGlobal Surveyor ResultsLocated areas of floods within last few millionyears (few impact craters)Apparently from undergroundOut through volcanic fissuresLike a geyser - suspect large aquifer a couple ofmiles below surfaceOr maybe snow (Feb. 2003)Mars Odyssey WebsiteMars Odyssey ResultsMapping from OrbitGamma ray spectrometerCosmic rays excite nuclei on surfaceto emit Gamma raysWavelength of gamma rays characteristic of elementAlso neutron detectorCan detect hydrogen (stand in for H2O) in top meterEvidence indicates substantial H2O near south poleMars Odyssey2001 Mars Odyssey Water MapMars OdysseyMars Express• Walls
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