Skies: Atmospheres of the Terrestrial Planets Dr. Henry Throop / University of Colorado 14-Jun-00 ASTR 1110 Announcements ------------- Observing -- kill it Reschedule? Atmospheres ----------- Formation Processes Loss Evolution Structure Comparison Intro ----- Dramatic difference between planets w & w/o atmospheres. We're biased, but there's a lot of chemistry, a lot of fun, a lot of physics, a lot of biology, that happens at that interface between the two. Not much of any of those either entirely in atmo, or entirely underground. Atmospheres are all thin! If were to take atmosphere and smash it down, it adds about 1 m (?) to height of planet. But, in that 1m, and the interface, amazing things happen. What is an atmo --------------- Layer of gas above planet One more layer over crust. Like crust, it gets thinner & lighter as we go up. Can see it -- makes sky blue (also makes it hard for telescopes) Breathe it -- oxygen is used for getting energy out of food Drink it -- drink water after it falls from the atmosphere onto ground Contrasts --------- Venus: thick, dry, hot. 96% CO2, 70 bar Earth: nice. Mostly inert: 77% N2, 21% O2, 1 bar Mars: thin, cool. 95% CO2, 1 mbar Mercury, Moon: 10^-15 bar Composition ----------- Gasses Each absorbs different amounts of light Why is it cold on mountaintops? ------------------------------ 'But it must be hotter -- we're closer to the Sun!' No: Atmosphere is transparent. That's why we can see the sun! Sunlight hits the ground, heats the ground. Has (nothing) to do with air getting less dense Has a lot to do with getting further away from the heat source Demo: bike light Processes --------- Scattering Greenhouse Greenhouse Effect ----------------- Light gets absorbed by surface Turns into a different kind of light -- infrared (aka heat) VG: electromagnetic spectrum (Q: what is the major greenhouse gas?) ------------------------------------ CO2 Ozone H2O Methane? Greenhouse effect is quite good! raises us up 70 deg F Runaway greenhouse effect! Planet heats up Oceans evaporate More greenhouse Planet heats up etc, etc! -or- Do clouds come in, and _reduce_ feedback? Who knows! Temperature depends on: ----------------------- Distance from sun Brightness of planet & atmosphere (albedo) How fast it rotates How much of a greenhouse it is Formation --------- Delivery -- comets Outgassing -- volcanoes; was there at start Sublimation -- Evolution --------- Mars: loses polar caps lost entire atmosphere. Probably used to be similar to earth's. Where did all of Mars' atmo go? Don't know. Earth: pretty stable over long periods of time Goldilocks problem: Too cold, too hot, just right Venus: It's all dry! Thick, but dry. Probably pumped out by volcanoes Moon/Mercury: Might have had something -- same raw ingredients -- but it's unstable, and `boils' away. Loss ---- Several processes -- show VG. What happened on Mercury/Moon? Mars? Could same thing happen to Venus or Earth? Carbonate Cycle --------------- #2: (p. 382) We put out more CO2 Atmosphere heats up More evaporation from water More clouds More rain Rain washes carbonate rocks into ocean Carbon gets trapped in crust, plates Volcanoes put less CO2 out Planet cools off! Slides ------ Mars atmo Venus atmo Earth atmo hurricanes Video: Carter's, _or_ aurora clip of NMS Minute Essays ------------- Summarize what we've done in last three days. What are the key concepts? Tell me what's worked, what hasn't. What's most interesting If there's issues regarding reading, HW, etc. tell me Collab Q's ---------- Why is Earth's What if Earth got colder? What is strongest greenhouse gas? If we want Mars to return to its original state, what can we do? Put water there, which will create greenhouse effect? Darken it, so it will be warmer Re-orbit it, so it's closer to Earth Mine it. What is a major problem with pollution (driving cars)? Destroys the ozone layer Puts out too much ozone into atmosphere Puts out CO2 which heats up Earth All of these None of these If we have a planet around 51 peg, what would we expect it to be like? Hot, since it's close to planet, and boiled away Dense, since it's around a v. heavy planet None of these Any of these