Lecture #32: Out of the Blue and into the Black

I. Importance of the dependence of opacity on wavelength -- scattering opacity: Rayleigh scattering and the blue sky -- Earth is blue due to oceans and atmosphere combination: to see it, put a white piece of paper in the shade -- Neptune is blue for different reason: some Rayleigh scattering in haze above the clouds, but mostly, methane gas appears blue -- absorbing opacity: the Greenhouse effect -- water vapor and CO2 have higher opacity in the infrared than visible -- the thick CO2 and cloudy atmosphere of Venus has a huge Greenhouse effect, whereas it is only a temperate effect on Earth. We are lucky N2 is not a Greenhouse gas-- if it were, we wouldn't be here! -- but all is not peachy-- the Greenhouse effect is unstable: Venus may have the potential for liquid water, if not for the runaway aspect of the Greenhouse effect! -- it's possible that life itself may stabilize the greenhouse effect: witness the long-standing presence of liquid water on Earth through harsh environmental variation, vs. other planets -- role of microbes and photosynthesis in replacing CO2 with O2 II. Temperature structure and the ozone layer on Earth -- troposphere, stratosphere, mesosphere -- what makes the mesosphere, a region of increasing T? -- lightning can form O3 molecules out of O2 -- O3 blocks harmful ultraviolet rays in sunlight -- perhaps in "primordial soup", ultraviolet rays helped fracture protein chains, increase diversity, but now it needs to be limited -- way up: ionosphere, radio reflection: lucky for Marconi in 1901! III. Planetary atmospheres -- Venus: 90 bar of CO2, sulfuric acid clouds -- Mars: extreme change as CO2 leaked away, froze -- Jupiter: dark belts and bright zones, and the Great Red Spot (unknown composition) -- Io: lots of sulfur and sodium -- Titan: only moon with thick atmosphere, similar N2 content to Earth, some methane