Curiosity finds metallic meteorite on Mars Credit NASA JPL Curiosity Team Course Announcements Thanksgiving Week planning No classes Wednesday 23 Nov Exam 2 grading complete Tests ready for pick up Extra Credit sessions still underway Update to Planetarium ECs 1 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 Assignments Reading Assignments Chapter 9 Sections 10 1 10 4 Read by Monday 7 Nov Parallel Lectures CC 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 Many many As Mean 80 2 pts Median 83 75 pts St Dev 17 2 pts Top Score 104 85 A s 47 B s 23 C s 29 A job well done everyone Keep up the good work for upcoming Exam 3 Quiz 5 Hints Sample questions and concepts What are the two continent sized highland regions on Venus A Athena Terra and Herodotus Terra B Osiris Mons and Atan Mons C Venusian Africa and Australia D Aphrodite Terra an Ishtar Terra E Solomon Montes and Hammurabi Montes Quiz 5 Hints Sample questions and concepts This surface feature is unique to Venus A Hollows B Coronae C Scarps D Caloris Basin E Shield Volcanoes Potential alternatives How do the size of these unique surface features compare to pancake domes Quiz 5 Hints Sample questions and concepts What is the most abundant gas in the atmosphere of Venus A Nitrogen B Carbon Dioxide C Methane D Sulfur Dioxide E Oxygen Greenhouse Effect on Venus Same as with Earth nearly the entire atmosphere is a greenhouse gas 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 Extreme Greenhouse Effect on Venus Same as with Earth nearly the entire atmosphere is a greenhouse gas 99 of IR reradiated by the surface absorbed by CO2 and sent back out in all direction The Runaway Greenhouse Effect Why are Earth and Venus so different 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 The Runaway Greenhouse Effect The reason why Earth and Venus are so different 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 Runaway Greenhouse Effect Consider Earth at Venus s position 30 closer to Sun 2 times more energy hitting the planet The 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 atmosphere The Runaway Greenhouse Effect Why Earth and Venus are so different 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 outgassing The Runaway Greenhouse Effect Where did the water go 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 oxygen from Venus commensurate with expectations from this process Defining a Habitable Zone There must be liquid water Appears that there is a threshold distance in our Solar System between 0 7 and 1 0 AU at which point if Earth were closer to the Sun the oceans would evaporate and we would experience a Runaway Greenhouse Effect no liquid water and hence no life As we will see with Mars there is another threshold point between 1 0 and 1 5 AU where a planet would be too cold to have liquid water hence no life The precise locations in a given planetary system where liquid water can exist are deemed Habitable Zones and appear to be the just right zone between boiling oceans away and freezing them So our Solar System s Habitable zone stretches somewhere from 0 7 AU to about 1 5 AU Habitable Zone Goldilocks Zone Defined as location where planets can have liquid water Image Credit Keck Telescope Habitable Zone Dependencies Distance from star depends on type of star G Dwarf Yellow Dwarf M Dwarf Red Dwarf
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