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Venus and MarsChapter 10
You have been to the moon and to Mercury, and now youare going to find Venus and Mars dramatically differentfrom those small, inactive, and airless worlds. Venus andMars have internal heat and atmospheres. The internalheat means they are geologically active, and theatmospheres mean they have weather. As you explore, youwill discover answers to four important questions:•What is the evidence that Venus’s surface conditionswere originally more Earth-like than now?•How did Venus form and evolve?•What is the evidence that Mars’s surface conditions wereoriginally more Earth-like than now?•How did Mars form and evolve?Guidepost
The comparative planetology questions that need toalways be on your mind when you explore anotherworld are these:•How and why is this world similar to Earth?•How and why is this world different from Earth?You will see that small initial differences canhave big effects.You are a planet-walker, and you are becoming anexpert on the kind of planets you can imaginewalking on. But there are other worlds beyond Marsin our solar system so peculiar they have nosurfaces to walk on, even in your imagination. Youwill explore them in the next two chapters.Guidepost (continued)
I. VenusA. The Atmosphere of VenusB. The Venusian GreenhouseC. The Surface of VenusD. Volcanism on VenusE. The Rotation of VenusF. A History of VenusII. MarsA. No Canals on MarsB. The Atmosphere of MarsC. The Geology of MarsD. Finding the Water on MarsE. A History of MarsF. Comparative Planetology, Once AgainIII. The Moons of MarsA. Origin and Evolution of Phobos and DeimosOutline
Venus and MarsTwo most similar planets to Earth:•Similar in size and mass•Atmosphere•Similar interior structure•Same part of the solar systemYet, no life is possible on either one of them.
FIGURE 10.2Venus as Photographed by the Pioneer Venus Orbiter.This ultraviolet image showsan upper-atmosphere cloud structure that would be invisible at visible wavelengths.Note that there is not even a glimpse of the planet’s surface. (credit: modification ofwork by NASA)
Extremely inhospitable:96 % carbon dioxide (CO2)3.5 % nitrogen (N2)Rest: water (H2O), hydrochloricacid (HCl), hydrofluoric acid (HF)Very stable circulation patterns withhigh-speed winds (up to 240 km/h)Extremely high surfacetemperature up to 745 K (880oF)Very efficient “greenhouse”!The Atmosphere of Venus4 thick cloud layers(surface invisibleto us from Earth)
The Surface of VenusEarly radar images already revealed mountains, plains, andcraters.Venera 13Colors modifiedby clouds inVenus’satmosphereMore details from orbiting and landing spacecraft:After correctionfor atmosphericcolor effect: