Terrestrial Planets

Today Terrestrial Planets– Earth, Venus, Mars Atmospheres Climate– Greenhouse effect from planetary perspective Factors affecting atmospheres1 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Reminders About First Exam Will be in this room, 9:30-10:45, Thursday Some multiple choice, some short answerSimilar to homework, but you don’t have toexplain your multiple choice answers No calculators, no books, no notes, no phones Bring your student ID, put on desk Bring more than one #2 pencil! We will seat you Leave times at 10:15, 10:35 onwardsHand in to your TA at top of stairs2 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Astrobiology Seminar Friday, October 7, 2011, 12:30 PM “The Search for Life on Mars.A Search forthe Origin of Life on Earth?” Andrew Steele Webcast See http://astrobiology.stsci.edu for details3 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Why the sky is blue Atmosphere scattersblue light from the Sun,making it appear tocome from differentdirections. Sunsets are red becauseless of the red lightfrom the Sun isscattered.4 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Radiation Protection All X-ray light isabsorbed very high inthe atmosphere. Ultraviolet light isabsorbed by ozone(O3).5 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Earth’s atmosphere absorbs light at most wavelengths.The air looks clear to optical light & radio waves;looks like a brick to X-rays and like a fog to the infrared.6 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

The Greenhouse Effect7 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Greenhouse Gas Any gas that absorbs infrared Greenhouse gas: molecules with two differenttypes of elements (CO2, H2O, CH4) Not a greenhouse gas: molecules with one or twoatoms of the same element (O2, N2)– Though oxygen and nitrogen compose the bulkof the atmosphere, they do not absorb in theinfrared so don’t contribute to the greenhouseeffect8 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Main greenhouse gases(on the Earth) Water (H2O) 60% of infrared opacity Carbon dioxide (CO2) 22% Methane (CH4) 7% Others (ozone, CFCs, nitrous oxide) 11%9 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Greenhouse Effect: Bad?The Earth is much warmer than it would bewithout an atmosphere because of thegreenhouse effect. That’s good!(cf. the moon) the same can be said for Venus,only more so.10 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Why is Venus so hot?11 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Why is Venus so hot?The greenhouse effect on Venus keeps itssurface temperature at 470 C (878 F). Thismakes it the highest average temp of anyplanet; even higher than Mercury’s average,even though Venus is farther from the sun.The difference is the greenhouse effect.Why is the greenhouse effect on Venusso much stronger than on Earth?12 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Atmosphere of Venus Venus has a verythick carbon dioxideatmosphere with asurface pressure 90times that of Earth.13 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Greenhouse Effect on Venus Thick carbondioxide atmosphereproduces anextremely stronggreenhouse effect. Earth escapes thisfate because most ofits carbon and waterare in rocks andoceans.14 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Carbon cycle on Earth15 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Runaway Greenhouse EffectMore evaporation,stronger greenhouse effectGreater heat,more evaporation Oceans evaporate; no longer absorb CO2.– CO2 builds up in atmosphere unchecked– “runaway greenhouse” 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley16

Mars: the opposite extreme Low gravity and a thinning atmosphere led to arunaway icehouse. Mars atmosphere currently 1% as thick as Earth’s17 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Seasons on Mars Mars does have seasons; both axial tilt anddistance from the sun matter. Seasons on Mars are more extreme in the southernhemisphere because of its elliptical orbit.18 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Change of Mars’ SeasonsUnlike Earth, Mars has no large moon to stabilize itsaxis. As a result, its axis wanders over tens of millionsof years. What effect do you think this will have on theseasons on Mars?A.No effect; seasons independent of axisB. Seasons more extreme when axis pointsnearer to plane of Mars’ orbitC. Seasons more extreme when axis pointsnearly perpendicular to orbit planeD. No effect: Martians have climate controlE. I don’t know19

Storms on Mars Seasonal winds on Mars can drive huge dust storms. Drive ongoing wind erosion20 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

2004 Opportunity Rover provided strong evidence for abundantliquid water on Mars in the distant past. How could Mars have been warmer and wetter in the past?21 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Climate Change on Mars Mars has not hadwidespread surfacewater for 3 billionyears. The greenhouseeffect probably keptthe surface warmerbefore that. Over time, Mars lostmost of itsatmosphere.22 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Factors affecting atmospheresLightweightgases (helium)Oxygen!Can break upwater vapor;hydrogen escapes 2007 Pearson Education Inc., publishing as Pearson Addison-WesleyWater canfreeze out23

Mars atmosphere was thicker in the past; itsclimate was warmer - liquid water! The atmosphere was gradually lost to spaceor frozen onto surface24 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Today, most waterlies frozenunderground (blueregions)Some scientistsbelieve accumulatedsnowpack meltscarve gullies eventoday.25 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Unique features of Earththat are important for life:1.2.3.4.Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stability26 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

What unique features of Earth areimportant to human life?1.2.3.4.Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stabilityEarth’s distance from theSun and moderategreenhouse effect makeliquid water possible.27 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

What unique features of Earth areimportant to human life?1.2.3.4.Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stabilityPHOTOSYNTHESIS(plant life) is required tomake high concentrationsof O2, which produces theprotective layer of O3.Oxygen is very reactive - would combine withrocks and disappear from the atmosphere if notcontinuously resupplied by plant life.28 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

What unique features of Earth areimportant to human life?1.2.3.4.Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stabilityPlate tectonics arean important stepin the carbondioxide cycle.29 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Carbon Dioxide Cycle1. Atmospheric CO2dissolves inrainwater.2. Rain erodes mineralsthat flow into theocean.3. Minerals combinewith carbon to makerocks on ocean floor.30 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Carbon Dioxide Cycle4. Subduction carriescarbonate rocksdown into themantle.5. Rock melts inmantle and outgasesCO2 back intoatmosphere throughvolcanoes.31 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Long-Term Climate Change Changes in Earth’s axis tilt might lead to ice ages. Widespread ice tends to lower global temperaturesby increasing Earth’s reflectivity. Snowball Earth! CO2 from outgassing will build up if oceans arefrozen, ultimately raising global temperatures again.32 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

What unique features of Earth areimportant to human life?1.2.3.4.Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stabilityThe COcycle acts like athermostat for Earth’stemperature.233 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Some greenhouse effect is natural.Is it being enhanced by human activity?34 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Arcticpermafrostis melting35 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

CO2 ConcentrationinterglacialTice ageCO2ice agetime 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley Global temperatureshave tracked CO2concentration for thelast 500,000 years.ice age Antarctic airbubbles indicate thecurrent CO2concentration is atits highest level in atleast 500,000 years.36

CO2 ConcentrationCO2T Most of the CO2 increase has happened in last 50years. Amount consistent with the fuel burned.37 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

38 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Modeling of Climate Change The recent temperatureincrease is consistentwith human productionof greenhouse gases. Basic physics simple;detailed predictionshard. We are changing thecomposition of theatmosphere we rely on.39 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

What makes a planet habitable? Located at an optimal distance from the Sunfor liquid water to exist40 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

What makes a planet habitable? Large enough for geological activity torelease and retain water and atmosphere41 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Planetary DestinyEarth ishabitablebecause it islarge enough toremaingeologicallyactive, and it isat the rightdistance from theSun so oceanscould form.42 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

What have we learned? What unique features of Earth areimportant for life?— Surface liquid water— Atmospheric oxygen— Plate tectonics— Climate stability43 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

What have we learned? How is human activity changing our planet?— Human activity is releasing additionalcarbon dioxide into Earth’s atmosphere,presumably increasing the greenhouse effect. What makes a planet habitable?— Earth’s distance from the Sun allows forliquid water on Earth’s surface.— Earth’s size allows it to retain an atmosphereand enough internal heat to drive geologicalactivity.44 2007 Pearson Education Inc., publishing as Pearson Addison-Wesley

Why is Venus so hot? The greenhouse effect on Venus keeps its surface temperature at 470 C (878 F). This makes it the highest average temp of any planet; even higher than Mercury’s average, even though Venus is farther from the sun. The difference is the greenhouse effect. Why is the greenhouse effect on