Chapter 10 Notes On Earthlike Planets: Venus and Mars PDF

Earthlike Planets: Venus and Mars Our goals for learning:  How did Martians invade popular culture?  What are the major geological features of Mars?  What geological evidence tells us that water once flowed on Mars?  Lowell’s Mars Globe. One of the remarkable globes of Mars prepared by Per...

Earthlike Planets: Venus and Mars Our goals for learning:  How did Martians invade popular culture?  What are the major geological features of Mars?  What geological evidence tells us that water once flowed on Mars?  Lowell’s Mars Globe. One of the remarkable globes of Mars prepared by Percival Lowell, showing a network of dozens of canals, oases, and triangular water reservoirs that he claimed were visible on the red planet.  Face on Mars. The so-called “Face on Mars” is seen (a) in low resolution from Viking (the “face” is in the upper part of the picture) and (b) with 20 times better resolution from the Mars Global Surveyor. (credit a: modification of work NASA/JPL; credit b: modification of work by NASA/JPL/MSSS)  Surface View from Mars Pathfinder. The scene from the Pathfinder lander shows a windswept plain, sculpted long ago when water flowed out of the martian highlands and into the depression where the spacecraft landed. The Sojourner rover, the first wheeled vehicle on Mars. (credit: NASA/JPL)   Victoria Crater. (a) This crater in Meridiani Planum is 800 meters wide, making it slightly smaller than Meteor crater on Earth. Note the dune field in the interior. (b) This image shows the view from the Opportunity rover as it scouted the rim of Victoria crater looking for a safe route down into the interior. (credit a: modification of work by NASA/JPL-Caltech/University of Arizona/Cornell/Phio State University; credit b: modification of work by NASA/JPL/Cornell)  Olympus Mons. The largest volcano on Mars, and probably the largest in the solar system, is Olympus Mons, illustrated in this computer-generated rendering based on data from the Mars Global Surveyor’s laser altimeter. Placed on Earth, the base of Olympus Mons would completely cover the state of Missouri; the caldera, the circular opening at the top, is 65 kilometers across, about the size of Los Angeles. (credit: NASA/Corbis)  Heavily Eroded Canyonlands on Mars. This image shows the Valles Marineris canyon complex, which is 3000 kilometers wide and 8 kilometers deep. (credit: NASA/JPL/USGS)  Martian Landslides. This Viking orbiter image shows Ophir Chasma, one of the connected valleys of the Valles Marineris canyon system. Look carefully and you can see enormous landslides whose debris is piled up underneath the cliff wall, which tower up to 10 kilometers above the canyon floor. (credit: modification of work by NASA/JPL/USGS)  Three Martian Landing Sites. The Mars landers Viking 1 in Chryse, Pathfinder in Ares Valley, and Viking 2 in Utopia, all photographed their immediate surroundings. It is apparent from the similarity of these three photos that each spacecraft touched down on a flat, windswept plain littered with rocks ranging from tiny pebbles up to meter-size boulders. It is probable that most of Mars looks like this on the surface. (credit “Viking 1”: modification of work by Van der Hoorn/NASA; credit “Pathfinder”: modification of work by NASA; credit “Viking 2”: modification of work by NASA; credit Mars: modification of work by NASA/Goddard Space Flight Center)  Water Frost in Utopia. This image of surface frost was photographed at the Viking 2 landing site during late winter. (credit: NASA/JPL)   Martian North Polar Cap. (a) This is a composite image of the north pole in summer, obtained in October 2006 by the Mars Reconnaissance Orbiter. It shows the mostly water-ice residual cap sitting atop light, tan-colored, layered sediments. Note that although the border of this photo is circular, it shows only a small part of the planet. (b) Here we see a small section of the layered terrain near the martian north pole. There is a mound about 40 meters high that is sticking out of a trough in the center of the picture. (credit a: modification of work by NASA/JPL/MSSS; credit b: modification of work by NASA/JPL-Caltech/University of Arizona)  Mars has many large shield volcanoes.  Olympus Mons is largest volcano in solar system.  The system of valleys known as Valles Marineris is thought to originate from tectonics.  Close-up photos of Mars show what appear to be dried-up riverbeds.  Details of some craters suggest they were once filled with water.  Mars rovers have found rocks that appear to have formed in water.   Runoff and Outflow Channels. (a) These runoff channels in the old martian highlands are interpreted as the valleys of ancient rivers fed by either rain or underground springs. The width of this image is about 200 kilometers. (b) This intriguing channel, called Nanedi Valles, resembles Earth riverbeds in some (but not all) ways. The tight curves and terraces seen in the channel certainly suggest the sustained flow of a fluid like water. The channel is about 2.5 kilometers across. (credit a: modification of work by Jim Secosky/NASA; credit b: modification of work by Jim Secosky/NASA)  Evidence for Liquid Water on Mars. The dark streaks in Horowitz crater, which move downslope, have been called recurring slope lineae. The streaks in the center of the image go down the wall of the crater for about a distance of 100 meters. Spectra taken of this region indicate that these are locations where salty liquid water flows on or just below the surface of Mars. (The vertical dimension is exaggerated by a factor of 1.5 compared to horizontal dimensions.) (credit: NASA/JPL-Caltech/University of Arizona)   Gale Crater. (a) This scene, photographed by the Curiosity rover, shows an ancient lakebed of cracked mudstones. (b) Geologists working with the Curiosity rover interpret this image of cross-bedded sandstone in Gale crater as evidence of liquid water passing over a loose bed of sediment at the time this rock formed. (credit a: modification of work by NASA/JPL-Caltech/MSSS; credit b: modification of work by NASA/JPL-Caltech/MSSS)  Map of hydrogen content (blue) shows that low- lying areas contain more water ice.  What are the major geological features of Mars?  Differences in cratering across surface  Giant shield volcanoes  Evidence of tectonic activity  What geological evidence tells us that water once flowed on Mars?  Some surface features look like dry riverbeds.  Some craters appear to be eroded.  Rovers have found rocks that appear to have formed in water.  Gullies in crater walls may indicate recent water flows. Our goals for learning:  What are the major geological features of Venus?  Does Venus have plate tectonics?  Radar Map of Venus. This composite image has a resolution of about 3 kilometers. Colors have been added to indicate elevation, with blue meaning low and brown and white high. The large continent Aphrodite stretches around the equator, where the bright (therefore rough) surface has been deformed by tectonic forces in the crust of Venus. (credit: modification of work by NASA/JPL/USGS)   Impact Craters on Venus. (a) These large impact craters are in the Lavinia region of Venus. Because they are rough, the crater rims and ejecta appear brighter in these radar images than do the smoother surrounding lava plains. The largest of these craters has a diameter of 50 kilometers. (b) This small, complex crater is named after writer Gertrude Stein. The triple impact was caused by the breaking apart of the incoming asteroid during its passage through the thick atmosphere of Venus. The projectile had an initial diameter of between 1 and 2 kilometers. (credit a: modification of work by NASA/JPL; credit b: modification of work by NASA/JPL)  Pancake-Shaped Volcanoes on Venus. These remarkable circular domes, each about 25 kilometers across and about 2 kilometers tall, are the result of eruptions of highly viscous (sludgy) lava that spreads out evenly in all directions. (credit: modification of work by NASA/JPL)  Surface of Venus. These views of the surface of Venus are from the Venera 13 spacecraft. Everything is orange because the thick atmosphere of Venus absorbs the bluer colors of light. The horizon is visible in the upper corner of each image. (credit: NASA)  Venus has impact craters, but fewer than the Moon, Mercury, or Mars.  It has many volcanoes, including both shield volcanoes and stratovolcanoes.  The planet’s fractured and contorted surface indicates tectonic stresses.  Photos of rocks taken by landers show little erosion.  Venus does not appear to have plate tectonics, but entire surface seems to have been “repaved” 750 million years ago.  What are the major geological features of Venus?  Venus has cratering, volcanism, and tectonics but not much erosion.  Does Venus have plate tectonics?  The lack of plate tectonics on Venus is a mystery. Our goals for learning:  What is Mars like today?  Why did Mars change?  The ellipticity of Mars’s orbit makes seasons more extreme in the southern hemisphere.  Late winter Mid-spring Early summer  Carbon dioxide ice of polar cap sublimates as summer approaches and condenses at opposite pole.  Residual ice of the polar cap remaining during summer is primarily water ice.  Seasonal winds can drive dust storms on Mars.  Dust in the atmosphere absorbs blue light, sometimes making the sky look brownish-pink.  Calculations suggest Mars’s axis tilt ranges from 0° to 60°.  Such extreme variations can cause climate changes.  Alternating layers of ice and dust in polar regions reflect these climate changes.  Mars has not had widespread surface water for 3 billion years.  Greenhouse effect probably kept the surface warmer before that.  Somehow Mars lost most of its atmosphere.  Magnetic field may have preserved early Martian atmosphere.  Solar wind may have stripped atmosphere after field decreased because of interior cooling.  What is Mars like today?  Mars is cold, dry, and frozen.  Strong seasonal changes cause CO2 to move from pole to pole, leading to dust storms.  Why did Mars change?  Its atmosphere must have once been much thicker for its greenhouse effect to allow liquid water on the surface.  Somehow Mars lost most of its atmosphere, perhaps because of its declining magnetic field. Our goals for learning:  What is Venus like today?  How did Venus get so hot?  Venus has a very thick carbon dioxide atmosphere with a surface pressure 90 times that of Earth.  Slow rotation produces a very weak Coriolis effect and little weather.  Thick carbon dioxide atmosphere produces an extremely strong greenhouse effect.  Earth escapes this fate because most of its carbon and water is in rocks and oceans.  Reflective clouds contain droplets of sulphuric acid.  The upper atmosphere has fast winds that remain unexplained.  A runaway greenhouse effect would account for why Venus has so little water. What is the main reason why Venus is hotter than Earth? a) Venus is closer to the Sun than Earth. b) Venus is more reflective than Earth. c) Venus is less reflective than Earth. d) Greenhouse effect is much stronger on Venus than on Earth. e) Human activity has led to declining temperatures on Earth. What is the main reason why Venus is hotter than Earth? a) Venus is closer to the Sun than Earth. b) Venus is more reflective than Earth. c) Venus is less reflective than Earth. d) Greenhouse effect is much stronger on Venus than on Earth. e) Human activity has led to declining temperatures on Earth.  What is Venus like today?  Venus has an extremely thick CO2 atmosphere.  Slow rotation means little weather.  How did Venus get so hot?  Runaway greenhouse effect made Venus too hot for liquid oceans.  All carbon dioxide remains in atmosphere, leading to an extreme greenhouse effect.  Smaller worlds cool off faster and harden earlier.  The Moon and Mercury are now geologically “dead.”  Smaller worlds cool off faster and harden earlier.  Larger worlds remain warm inside, promoting volcanism and tectonics.  Larger worlds also have more erosion because their gravity retains an atmosphere.  Planets close to the Sun are too hot for rain, snow, ice and so have less erosion.  Hot planets have more difficulty retaining an atmosphere.  Planets far from the Sun are too cold for rain, limiting erosion.  Planets with liquid water have the most erosion.  Planets with slower rotation have less weather, less erosion, and a weak magnetic field.  Planets with faster rotation have more weather, more erosion, and a stronger magnetic field. How does the cooling of planets and potatoes vary with size? a) Larger size makes it harder for heat from inside to escape. b) Larger size means a bigger ratio of volume to surface area. c) Larger size takes longer to cool. d) all of the above How does the cooling of planets and potatoes vary with size? a) Larger size makes it harder for heat from inside to escape. b) Larger size means a bigger ratio of volume to surface area. c) Larger size takes longer to cool. d) all of the above