12 Natural Climate Change When Good Planets go Bad

12 Goals What are Venus and Mars like now? What happened to them?

12 The Terrestrial Planets World Atmos. Compsn. Surface Pressure Ave Surface Temp. Winds, Weather Clouds, Hazes Mercury He, Na, O barDay: 800F Night: -280F none Venus 96% CO2 3.5% N2 90 bars880FSlow winds, acid rain Sulfuric acid clouds Earth 77% N2 21% O2 H2O 1 bar60FWinds, hurricanes, rain, snow H2O clouds, pollution Moon He, Na, Ar barDay:260F Night: -280F none Mars 95% CO2 2.7% N bar-60FWinds, dust storm H2O and CO2 clouds, dust

12 Atmosphere Origins Outgassing Volcanoes. CO 2 and H 2 O main gases. Mt. St. Helens

12 Concept Test For which terrestrial planets is the main atmospheric gas one of the two main gases produced by outgassing? a.Only Moon & Mercury b.All five planets c.Only Venus, Earth and Mars d.Only Earth e.Only Venus and Mars

12 Atmosphere Loss 1.Thermal escape “boiling away” by temperature. 2.“Knocking away” by solar wind particles. 3.UV-rays break molecules into smaller atoms. –Lighter atoms boil away. 4.Absorbed by surface 5.“Blasted away” by impacts

12 Thermal Escape Atoms have mass. Attracted to planet by gravity. Temperature is measure of atoms motion. High temperature = high velocity: escape velocity if too light.

12 Knocking away Sun blows off solar wind: –Protons –Electrons –Neutrons Billiards with atmosphere (if no magnetosphere).

12 Dissociation Atoms held together in molecules by electromagnetic forces. UV-rays source of energy. Break molecular bonds. Light elements (H) can boil away. Importance of protective ozone layer.

12 Absorption Chemical reactions. –Rust for O 2. –Carbonate rocks for CO 2 (when H 2 0 is present)

12 Concept Test Under what circumstances is thermal escape likely to be important? a.Light gases on big planets far from the Sun b.Heavy gases on big planets far from the Sun c.Light gases on small planets near the Sun d.Light gases on small planets far from the Sun e.Equally well on any kind of gas from any kind of planet

12 Mars Today Pressure just below triple point of water: 0.01 bar Temperature below freezing: -50 C No rain, some clouds, dust, ice caps.

12 P vs T for H 2 O

12 Gusev

12 Meridiani Planum

12 What went wrong? Size. Too small – core cools Core cools – magnetic field stops (not magnetosphere). Atmosphere CO 2 stripped by solar winds. UV-rays dissociate H 2 O H boils away O rusts rocks No CO 2 or H 2 O, no greenhouse effect. Cold, dry Mars today. Good scientific theory?

12 Concept Test All the following statements about Mars are true. Which one might have led to a significant loss of atmospheric gas to space? a.The rock on Mars is probably red because of chemical reactions with oxygen that had been released into the atmosphere through the outgassing of water molecules. b.Mars lost any global magnetic field that it may once have had. c.The axis tilt of Mars is thought to change significantly with time. d.Mars probably once had a much higher density of greenhouse gases in its atmosphere than it does today.

12 Venus Today Pressure = 90 bars. Temperature = 880 F. No pole/equator temperature difference. No day/night temperature difference. No seasonal temperature difference. No rain hits surface. No storms. Little wind.

12 Venera Landers Venera 13 and 14 color images from red, green and blue filters. Copyright: Don P. Mitchell – Mentallandscape.com

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12 What went wrong? Same size as Earth. Same outgassing as Earth. –Same CO 2 content. –What happened to atmospheric H 2 O? Higher initial temperature.

12 What went wrong? Higher initial temperature. More water evaporates. Atmosphere can hold more H 2 O before rains. H 2 O is greenhouse gas – increases temp. More water evaporates. Feedback mechanism. All H 2 O evaporates. No oceans, seas or lakes.

12 …it gets worse. No water for CO 2 to react. Increases greenhouse effect further. UV-rays dissociate H 2 O. H lost to space. Result, 100% of CO 2 in atmosphere. Runaway greenhouse effect. Hot, dry, Venus today. Good scientific theory? Venus once like Earth?

12 Concept Test Why do we think that Venus has so much more atmospheric gas than Earth? a.Earth has lost much more atmospheric gas than Venus, primarily to condensation of water vapor into liquid water and to chemical reactions that make carbonate rock. b.Venus has gained much more gas through outgassing than has Earth. c.Because of its lack of magnetic field, Venus has been able to gain gas through the process of bombardment, while Earth has not gained gas in this way. d.Earth has lost much more gas to thermal escape than has Venus. e.None of the above.

12 Concept Test What would happen if Venus were moved to Earth’s orbit today? a.Runaway greenhouse would reverse, pleasant climate b.Some decrease in its temperature, but still too hot c.CO 2 would condense as on Mars, fall below freezing d.No change at all e.Slight increase in its temperature, way too hot

12 Homework #17 Due Wednesday 12-Nov: Read Bennett 10.6 Do 20, 21, 40, 42