Venus & Mars - Michigan State University

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Venus & Mars Goldilocks Problem Venus is too hot. Why didgreenhouse fail onVenus? Mars is too cold. Why? Homework 4 is due 6amon Tues, 20 Feb.– What happened to Mars’greenhouse?– What happened to Mars’atmosphere– Mars Odyssey/ Search forwaterGoldilocks #1 Venus is too hot; Mars is too cold. Why is theearth just right, not too cold and not too hot?Venus is too close to the sun, and Mars istoo far. This is part of the answer. Reflected light is 2nd ingredient.Greenhouse effect is 3rd ingredient.History is 4th.PlanetPressureSunlightrelative toEarthReflectedTempw/o GHActualTempGreenhousewarmingVenus90 atm1.9276%-44 C477 C521 CEarth1 atm1.0030%Mars0.006 atm0.4325%-18 C (0F) 15 C(59F)-63 C-55 C33 C8CTable from Rampino & Caldeira, 1994, Ann. Rev. Astron. & Astrophys, 32, p83.1

Greenhouse effect Greenhouse effect Sunlight is absorbed by the planet’s surfaceSurface emits infrared radiationInfrared radiation is absorbed by CO2 & H2Oand reradiated many times before it escapesinto space. CO2 & H2O acts like a blanket.Without the greenhouse effect, earth wouldbe frozen.Mars has a small greenhouse effectWhy did Venus evolve to have such a largegreenhouse effect?PlanetPressureSunlightrelative toEarthReflectedTemp.w/o GHActualTempGreenhousewarmingVenus90 atm1.9276%-44 C477 C521 CEarth1 atm1.0030%Mars0.006 atm0.4325%-18 C (0F) 15 C(59F)-63 C-55 C33 C8CThe faint-sun paradox The sun was 30% fainter 3 Byrs ago. The earthreceived 30% less sunlight, but there was liquidwater back then. Why did the earth stay just right,not too cold and not too hot?When the sun became brighter, the earth becamewarmer. More evaporation more rainMore rain loss of more CO2, sequestered in rockLess CO2 less greenhouse effectLess greenhouse Earth cools, lessening effect ofsun brighteningWhen sun was fainter, the earth was cooler. Less evaporation less rain more CO2 wasreleased from rocks by volcanoes moregreenhouse effect Earth warmed, lessening effectof sun dimming Walker, Hays, & Kasting (1981) discovered thiseffect, which provides negative feedback.2

Why did greenhouse run amok on Venus? When the sun becomes brighter, the earth becameswarmer. More evaporation more rainMore rain loss of more CO2, sequestered in rockLess CO2 less greenhouse effectLess greenhouse Earth cools, lessening effect of sunbrightening1. Which is not a possible reason why greenhouse ranamok on Venus?a.b.c.d.Too hot to rainType of rocks cannot sequester CO2There is no plate tectonicsVenus was born without water.Why did greenhouse run amok on Venus? Key observation #1: Earth’s ocean has100,000 X more than Venus’ atmosphere. Deuterium Normal H has 1 proton in nucleus Deuterium D has 1 proton & 1 neutron Q2 Suppose I had a pound of normalhydrogen. I trade a deuterium for everyhydrogen atom. How much would I have? A: 1lb, B: 2lb, C: ½ lb, D: 4 lb. Q3 At the same temperature, which gasmoves faster and is more likely to escape? A: normal H; B: deuterium; C: H2O D: DHO3

Venus lost its water Venus is hotter because it is closer to sun.Water was in atmosphere.Ultraviolet light broke water into oxygen andhydrogen. Hydrogen escaped.No rain no way to get rid of CO2.Models show Earth will suffer same fate ifsunlight increases by 40%. CO2 cycle willnot be sufficient to keep Earth temperate. MarsVenus EarthMarsDiameter0.9510.53Mass0.8110.11Semi-major axis0.7211.52Density0.9610.71Rotation (days)-24311.026Orbit period (days)224365687 Some of the 16 spacecraft that have gone to Mars: Mariner 9 orbiter (1971-72)Viking 1,2 landers (1976-80)Pathfinder lander rover (1997)Climate Orbitor, Polar lander (crashed, 1999).Mars Global Surveyor: orbiting Mars since March 1999.Odyssey: orbiting Mars since October 2001.Rotating Mars4

Some planets and moonsshown in correct relative stoEuropaTritonPlutoGeology Density suggests mostly silicates, but small metalcore No detectable magnetic field Continental highlands cover 50% of planet. Low-lying lava plains average of 4 km lower than continents. Same age as lunar maria - 3-4 billion yrs old.5

Topographic MapFrom Mars Global Surveyor orbiterRed high areas.Blue low areas.Tharsis bulge uplifted continent 10 km high. has 4 huge volcanoes, 15 km high.Rotating MarsOlympus Mons 500 km diameter would cover MI lower peninsula 25 km above surrounding plains largest mountain in Solar System. 100 x volume of Mauna Loa 100 million yrs old (impact crater counts) so Mars is still geologically active.6

Valles Marineris 5000 km long 1/4 way around Mars would stretch clear across US. Huge tectonic crack in Tharsis bulge 8-10 km deep no outlet for water but some minor role of water erosion in side canyons.Martian AtmosphereVenus EarthSurface482o Ctemperature Little air Very cold (almost) no liquid water.Mars20o C-100o C0.007Surface AirPressureCO292196%0.03%95%N23.5%78%2.7% At Mars’ low atmospheric pressure, water should gostraight from ice to vapor. No Greenhouse effect because there is so littleatmosphere.7

Polar Ice CapsSouthern Cap Always below 150o K (-279oF),so CO2 frozen all year. Unknown mix of CO2 and H2Oice.Frozen CO2 layerin winterOnly underlyingH2O ice left insummer, 3 kmthickNorthern CapRotating MarsClimate changeUsed to be lots of runningwater Runoff channels. From rainstorms billions ofyears ago.10 km[Fig. 7.22]8

What happened to Mars’ greenhouse At one time Mars was warm enough for liquid water.CO2 reacts with silicate rocks to convert tocarbonate rocks. CO2 produced by volcanoes & meteors Q5 Why is sequestering of carbon in rocks not fatal onearth?a. The rocks are protected by vegetation.b. Because of plate tectonics, the carbon is releasedagain.c. On earth, this does not happen as much because ofthe oceansMeteor bombardment ceasedBeing smaller, Mars cools faster & volcanoes decreasemore rapidlyCO2 clouds cool Mars more clouds form coolWhat happened to Mars’ atmosphereVenus EarthMars did have H2O &CO2. Where did H2Ogo? H2O dissociates to O2& H2 by UV light Hydrogen escapes Oxygen reacts withrock Stripping by solar wind Core solidified Îmagnetic field wentaway Î strippingof gas by solarwind particles. Low temperaturefreezes water[Fig. 7.27]Escapevelocity0.93Surface482o CtemperatureSurface AirPressure92Early MarsMars10.4520o C-100o C10.007Mars TodaySolar r windAtmospherestrippedaway bysolar wind9

Gammy Ray Spectrometer & NeutronSpectrometer on Mars Odyssey "We have found that in the regions north and south of 60 degreeslatitude, the surface is well over 50 percent water ice by volume. If justthe top meter of ice deposits around the martian north pole weremelted, there would be enough liquid water to fill Lake Michigan,"Boynton -missionsuccess.html)How could Odyssey see belowthe Martian surface? Cosmic rays hits Mars b/cthere is no protectingmagnetic field &atmosphere. Produceneutrons and gamma rays.Hydrogen (in top meter)absorbs energy of neutronsefficiently.Feldman et al, 2002, Science 297, 75. Energy of neutrons istransferred to hydrogen b/cmasses are same. Mass of Silicon, etc is muchgreater than that of neutron.Energy loss is small whenneutron hits silicon.10

Question for reading1. Which is the principal reason the interior ofJupiter is hot?a.b.c.d.Material is falling slowing and moving fasterUranium decaysThe sun heats itThere is a lot of methane11

Venus? Mars is too cold. Why? – What happened to Mars’ greenhouse? – What happened to Mars’ atmosphere – Mars Odyssey/ Search for water Homework 4 is due 6am on Tues, 20 Feb. Goldilocks #1 Venus is too hot; Mars is too cold. Why is the earth just right, not too cold and not too hot?

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HB9DUJ hb9duj@uska.ch HB3YFM hb3yfm@hb9g.ch Comité 2003-2004. REDACTION HB9AFP HB9G-94 PAGE 3 Calendrier 2004 18 septembre Journée porte-ouverte 10 octobre Chasse au renard, à partir de 11 heures, rendez-vous à Soral, lieu du Field-Day. 21 octobre Elaboration fichier ORNI 18 novembre Stamm spécial oscilloscope 20 novembre Gastro annuel au local: traditionnelle râclette offerte par le .