Venus!

Thought Question What is the main reason why Venus is hotter than Earth? Venus is closer to the Sun than Earth. Venus is more reflective than Earth. Venus is less reflective than Earth. The greenhouse effect is much stronger on Venus than on Earth. Human activity has led to declining temperatures on Earth.

Venus in UV light FIGURE 7-10 Venus Venus’s thick cloud cover efficiently traps heat from the Sun, resulting in a surface temperature even hotter than that on Mercury. Unlike Earth’s clouds, which are made of water droplets, Venus’s clouds are very dry and contain droplets of concentrated sulfuric acid. This ultraviolet image was taken by the Pioneer Venus Orbiter in 1979. (NASA)

Venus mapped with Radar FIGURE 7-16 A “Global” View of Venus A computer using numerous Magellan images creates a simulated globe. Color is used to enhance small-scale structures. Extensive lava flows and lava plains cover about 80% of Venus’s relatively flat surface. The bright band running almost east-west is the continent-like highland region Aphrodite Terra. (NASA)

Lots of volcanic features… The surface of Venus FIGURE 7-15 A Map of Venus This false-color radar map of Venus, analogous to a topographic map of Earth, shows the large-scale surface features of the planet. The equator extends horizontally across the middle of the map. Color indicates elevation—red for highest, followed by orange, yellow, green, and blue for lowest. The planet’s highest mountain is Maxwell Montes on Ishtar Terra. Scorpion-shaped Aphrodite Terra, a continent-like highland, contains several spectacular volcanoes. Do not confuse the blue and green for oceans and land. (Peter Ford/MIT, NASA/JPL) Lots of volcanic features…

Venera Probes from 1970’s survived for minutes… Venus’ surface Venera Probes from 1970’s survived for minutes… FIGURE 7-13 The Venusian Surface (a) This color photograph, taken by a Soviet spacecraft, shows rocks that appear orange because the light was filtered through the thick, sulfur-rich clouds. (b) By comparing the apparent color of the spacecraft to the color it was known to be, computers can correct for the sulfurous light. The actual color of the rocks is gray. In this view, the rocky plates that cover the ground may be fractured segments of a thin layer of lava. The toothed wheel in each image is part of the landing mechanism that keeps the spherical spacecraft from rolling. (a: Courtesy of C. M. Pieters and the USSR Academy of Sciences; b and c: Don Mitchell)

Venus’ surface Venus as we might “see” it… FIGURE 7-13 The Venusian Surface (a) This color photograph, taken by a Soviet spacecraft, shows rocks that appear orange because the light was filtered through the thick, sulfur-rich clouds. (b) By comparing the apparent color of the spacecraft to the color it was known to be, computers can correct for the sulfurous light. The actual color of the rocks is gray. In this view, the rocky plates that cover the ground may be fractured segments of a thin layer of lava. The toothed wheel in each image is part of the landing mechanism that keeps the spherical spacecraft from rolling. (a: Courtesy of C. M. Pieters and the USSR Academy of Sciences; b and c: Don Mitchell) … if we could stand the heat, pressure, & sulfuric acid rain!

FIGURE 7-13 The Venusian Surface (c) By correcting for the curvature of this image and a similar one taken with the camera flipped upside down, the actual surface of Venus near the Venera Lander can be shown. (a: Courtesy of C. M. Pieters and the USSR Academy of Sciences; b and c: Don Mitchell)

FIGURE 7-14 A Venusian Landscape A computer combined radio images to yield this perspective view of Venus as you would see it from an altitude of 4 km (2.5 mi). The color results from light being filtered through Venus’s thick clouds. The brighter color of the extensive lava flows indicates that they reflect radio waves more strongly. The vertical scale has been exaggerated 10 times to show the gentle slopes of Sapas Mons and Maat Mons, volcanoes named for ancient Phoenician and Egyptian goddesses, respectively. (NASA, JPL Multimission Image Processing Laboratory)

FIGURE 7-17 Craters on Venus These three impact craters, with extensive ejecta surrounding each, are located on Venus’s southern hemisphere. From left to right, these are craters Danilova, Howe, and Aglaonice—all imaged using radar by the Magellan spacecraft. The colors are based on the Venera images (see Figure 7-13). (NASA/Magellan Images [JPL])

Does Venus still have active plate tectonics? NASA’s Magellan mapped for ~ 4 years Did not appear to have active volcanoes or plate tectonics Based on cratering evidence, entire surface seems “repaved” 750 million years ago.

Venus’ Atmosphere What is it made of? How does it change in height? How does it circulate? FIGURE 7-13 The Venusian Surface (a) This color photograph, taken by a Soviet spacecraft, shows rocks that appear orange because the light was filtered through the thick, sulfur-rich clouds. (b) By comparing the apparent color of the spacecraft to the color it was known to be, computers can correct for the sulfurous light. The actual color of the rocks is gray. In this view, the rocky plates that cover the ground may be fractured segments of a thin layer of lava. The toothed wheel in each image is part of the landing mechanism that keeps the spherical spacecraft from rolling. (a: Courtesy of C. M. Pieters and the USSR Academy of Sciences; b and c: Don Mitchell)

Atmosphere of Venus High altitude reflective clouds contain droplets of sulfuric acid (H2SO4) Upper atmosphere has fast winds that remain unexplained.

Atmosphere of Venus Thick CO2 (carbon dioxide) atmosphere Surface pressure 90 times that of Earth. > 1300 lbs/sq. in.!

Greenhouse Effect on Venus Thick carbon dioxide atmosphere produces an extremely strong Greenhouse Effect. Earth escapes this fate - most of its carbon and water are in rocks & oceans.

Why is Venus so hot? The greenhouse effect on Venus keeps its surface temperature at 470°C (950°F) But why is the greenhouse effect on Venus so much stronger than on Earth?

FIGURE 7-12 The Greenhouse Effect A portion of the sunlight penetrates through the clouds and atmosphere of Venus, heating its surface. The surface in turn emits infrared radiation, much of which is absorbed by carbon dioxide (and to a much lesser degree, water vapor). The trapped radiation helps increase the average temperatures of the surface and atmosphere. Some infrared radiation does penetrate the atmosphere and leaks into space. In a state of equilibrium, the rate at which the planet loses energy to space in this way is equal to the rate at which it absorbs energy from the Sun.

Explaining Venus’ Atmosphere Lots of Volcanoes CO2, H2S04 are outgassed CO2 traps infrared heat Atmosphere heats up Water can’t condense => No Rain! No “flushing” of CO2 FIGURE 7-13 The Venusian Surface (a) This color photograph, taken by a Soviet spacecraft, shows rocks that appear orange because the light was filtered through the thick, sulfur-rich clouds. (b) By comparing the apparent color of the spacecraft to the color it was known to be, computers can correct for the sulfurous light. The actual color of the rocks is gray. In this view, the rocky plates that cover the ground may be fractured segments of a thin layer of lava. The toothed wheel in each image is part of the landing mechanism that keeps the spherical spacecraft from rolling. (a: Courtesy of C. M. Pieters and the USSR Academy of Sciences; b and c: Don Mitchell)

Runaway Greenhouse Effect More evaporation, stronger greenhouse effect Greater heat, more evaporation The runaway greenhouse effect would account for why Venus has so little water.

FIGURE 7-11 Temperature and Pressure in the Venusian Atmosphere The pressure at the Venusian surface is a crushing 90 atm (1296 lb/in2). Above the surface, atmospheric pressure decreases smoothly with increasing altitude. The temperature of Venus’s atmosphere increases smoothly from a minimum of about 173 K (150°F) at an altitude of 100 km to a maximum of nearly 750 K (900°F) on the ground. (NASA/Magellan Images [JPL])

Sun’s UV light disassociates H20 at this height! FIGURE 7-11 Temperature and Pressure in the Venusian Atmosphere The pressure at the Venusian surface is a crushing 90 atm (1296 lb/in2). Above the surface, atmospheric pressure decreases smoothly with increasing altitude. The temperature of Venus’s atmosphere increases smoothly from a minimum of about 173 K (150°F) at an altitude of 100 km to a maximum of nearly 750 K (900°F) on the ground. (NASA/Magellan Images [JPL]) Water condenses into clouds, allowing for rain around 0 C

Thought Question What is the main reason why Venus is hotter than Earth? Venus is closer to the Sun than Earth. Venus is more reflective than Earth. Venus is less reflective than Earth. The greenhouse effect is much stronger on Venus than on Earth. Human activity has led to declining temperatures on Earth.

Thought Question What is the main reason why Venus is hotter than Earth? Venus is closer to the Sun than Earth. Venus is more reflective than Earth. Venus is less reflective than Earth. The greenhouse effect is much stronger on Venus than on Earth. Human activity has led to declining temperatures on Earth.

Carbon Dioxide Cycle “Recycle” CO2 from atmosphere to crust to atmosphere over time Estimate ~25 million years or more for this to occur on Earth

Carbon Dioxide Cycle Step 1: Evaporation/Rain Liquid water evaporates Condenses into clouds in lower atmosphere Rain falls through atmosphere forming Carbonic Acid (H2CO3)  CO2 gas is absorbed 1

Carbon Dioxide Cycle Step 2: Mineral Erosion by Acid Rain Carbonic Acid (H2CO3) in rivers erodes rocks Carbonate (CO32-) ion picked up in minerals washed to ocean Calcium easily absorbed  CO2 is carried to oceans 2

Carbon Dioxide Cycle Step 3: Tying Carbon into Rocks & Life! Calcium from rocks forms CaCO3 (Calcium Carbonate) CaCO3 = Limestone CaCO3 = Coral, Mollusk shells! 3  CO2 accumulates on seafloor

Carbon Dioxide Cycle Step 4: Tectonics & Subduction! Tectonics gradually pulls seafloor down CaCO3 broken back into CO2 & other minerals 4  CO2 now inside crust

Carbon Dioxide Cycle Step 5: Volcanic Outgassing! Eventual Volcanic Activity pushes CO2 back into atmosphere 5  CO2 now in atmosphere again!

Carbon Dioxide Cycle Venus Feedback Loop Failure Too Hot for clouds to form low enough But… Volcanoes don’t stop! 1 5

Carbon Dioxide Cycle Venus Feedback Loop Failure No Rain NO CO2 gas absorbed More CO2 added! Runaway Greenhouse Effect! 1