Curiosity finds metallic meteorite on MarsCourse AnnouncementsAssignmentsExam 2 ResultsQuiz 5 HintsQuiz 5 HintsQuiz 5 HintsGreenhouse Effect on VenusExtreme Greenhouse Effect on VenusThe Runaway Greenhouse EffectThe Runaway Greenhouse EffectThe Runaway Greenhouse EffectThe Runaway Greenhouse EffectThe Runaway Greenhouse EffectDefining a “Habitable Zone”Habitable Zone (“Goldilocks” Zone)Habitable Zone DependenciesVenus’s Magnetic Field and Internal StructureWhy no plate tectonics?Chapter 10Mars vs. EarthMars Data Sheet IMars Data Sheet IIOrbital PropertiesOrbital PropertiesMars Physical PropertiesGlobal ViewsMartian Surface from orbitMartian TopographyMartian TopographyMartian TopographyLargest Valley in Solar SystemLargest Valley in Solar SystemCuriosity finds metallic meteorite on MarsCredit : NASA/JPL/Curiosity TeamCourse Announcements•Thanksgiving Week planningNo classes Wednesday, 23 Nov.•Exam 2 grading complete–Tests ready for pick up•Extra Credit sessions still underwayUpdate to Planetarium ECs1. Regular Planetarium show (+1)2&3. Any two Planetarium movies (+1 +1)•Quiz 5 this Wednesday, 9 Nov.–Hints Today•Exam 3 is Monday, 21 Nov.AssignmentsReading Assignments•Chapter 9: Sections 10.1 – 10.4[Read by Monday, 7 Nov.]•Parallel LecturesCC Astronomy Episode 15: Mars[Watch before Wednesday, 7 Nov.]Mastering Astronomy•Chapter 9 Homework (short assignment)[Due Thursday 10, Nov. at 11:59 EST]Exam 2 Results•Mean: 80.2 pts•Median: 83.75 pts•St. Dev.: 17.2 pts•Top Score: 104.85A’s: 47B’s: 23C’s: 29A job well done everyone. Keep up the good work for upcoming Exam 3.Many, many AsQuiz 5 HintsWhat are the two continent-sized highland regions on Venus?A. Athena Terra and Herodotus TerraB. Osiris Mons and Atan MonsC. Venusian Africa and AustraliaD. Aphrodite Terra an Ishtar TerraE. Solomon Montes and Hammurabi MontesSample questions and conceptsQuiz 5 HintsThis surface feature is unique to Venus.A. HollowsB. CoronaeC. ScarpsD. Caloris BasinE. Shield Volcanoes•Potential alternatives: How do the size of these unique surface features compare to pancake domes?Sample questions and conceptsQuiz 5 HintsWhat is the most abundant gas in the atmosphere of Venus?A. NitrogenB. Carbon DioxideC. MethaneD. Sulfur DioxideE. OxygenSample questions and conceptsGreenhouse Effect on Venus•Given Venus’s distance from Sun and its albedo, the expected surface temperature is ~260 K, about the same as Earth’s expected surface temperature… so why so hot!?!?•Given the 96.5% CO2 atmosphere, Venus’s atmosphere will absorb and reradiate (in all direction) about 99% of all infrared radiation released from the surface.–It’s like the best blanket you can imagine.–Boosts the surface temperature to 730 K!–Thick atmosphere also regulates the temperature planet-wide, so despite 2 month-long nights, the surface temperature is about the same everywhere on Venus.Same as with Earth, nearly the entire atmosphere is a greenhouse gasExtreme Greenhouse Effect on VenusSame as with Earth, nearly the entire atmosphere is a greenhouse gas99% of IR re-radiated by the surface, absorbed by CO2 and sent back out in all direction.The Runaway Greenhouse Effect•Earth and Venus expected to have very similar secondary (outgassed) starting atmospheres, so why is Venus so different from Earth with nearly a pure CO2 atmosphere?–A better question is, “Why is there so little carbon dioxide in Earth’s atmosphere?”–The answer is what is known as the Runaway Greenhouse Effect [Explained in coming slides]•Why on Venus and not Earth?–Most likely as simple as the different distances from the Sun (0.7 AU versus 1.0 AU)Why are Earth and Venus so different?The Runaway Greenhouse Effect•Recall the composition of the secondary atmosphere:–Carbon dioxide, sulfur dioxide, water, and nitrogen compounds•With slightly lower expected temperatures on Earth we the oceans condense and nearly all the CO2 gets locked into the oceans, surface rocks, and eventually into the mantle–Nitrogen compounds split creating N2–Earth was able to condense significant oceans, into which much of the CO2 dissolved–Earth’s rocks reacted with CO2 and trapped the carbon in Earth’s surface•If we could release all ‘locked carbon’ back into Earth’s atmosphere, Earth’s atmosphere would be:–98% CO2, 2% N2, and would be 70x more massive… very Venus-like–How can we do that? Heat the planet up.The reason why Earth and Venus are so differentThe Runaway Greenhouse Effect•30% closer to Sun => 2 times more energy hitting the planetThe Runaway Greenhouse Effect:•Starting Point: Planet warms, evaporating the oceans, which puts the dissolved CO2 into the atmosphere and significantly increasing the amount of water vapor… both are greenhouse gases–As temperature increases, ability to store CO2 in oceans and rocks diminishes.•Positive Feedback, Reinforcing Cycle: More greenhouse gases => more intense warming => more ocean loss and more CO2 out of the rocks => more greenhouse gases => …–This cycle “runs away” (positively reinforced) restoring all the original greenhouses gases back into the atmosphereConsider Earth at Venus’s positionThe Runaway Greenhouse Effect•With slightly higher expected temperatures on Venus there are no oceans to lock in the CO2–Still have Nitrogen compounds split creating N2–Much harder to ‘lock carbon’ into rocks, and would be undone by Runaway Greenhouse Effect–Early Venus may have been able to condense significant oceans, but higher temperatures would eventually led to Runaway Greenhouse Effect•So other than water content (lost to space) and SO2 (into the surface), Venus’s atmosphere has remained very primordial, i.e., as it was when it was formed via outgassingWhy Earth and Venus are so differentThe Runaway Greenhouse Effect•If Venus did have a roughly equivalent amount of water as Earth, where did it go?•As the Runaway Greenhouse Effect increased temperatures and put all the water vapor and CO2 back into the atmosphere, the temperatures would have sky-rocketed•Water a much more efficient greenhouse gas, so in the past, Venus most likely was much hotter, which put the water vapor higher into the atmosphere–There it was destroyed by UV (photo-disassociated) sunlight, and the hydrogen escaped to space while the oxygen mostly reacted with other atmospheric gases–Recent Venus Express measurement confirm loss of hydrogen and
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