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Chapter 7: Earth and the Terrestrial Worlds 7.1 Earth as a Planet 7.2 Mercury and the Moon 7.3 Mars 7.4 Venus 7.5 Earth as a Living Planet All picture credits: 2015 Pearson Education, Inc unless stated otherwise. Fall 2015 PHYS271: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 1 7.4 Venus: A Hothouse World Our goals for learning: Is Venus geologically active? Why is Venus so hot? Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 2 Venus Second planet from the Sun, and the closest to us. Nearly circular orbit having an average radius of 0.7 A.U. orbital period of 225 days. Rotation retrograde : in the opposite sense of the Earth and all other planets except Uranus slow: a day on Venus = 243 Earth days. No moons. Radius of Venus= 6 051.8 km 3 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus Retrograde rotation 4 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus Venus missions The Venera missions Soviet exploration of Venus, from 1961 to 1985 Successes included 3 atmospheric probes, 10 landings, 4 orbiters, 11 flybys or impacts, and 2 balloon probes in the clouds. Venera 3 (1966): First man-made object to enter the atmosphere and strike the surface of another planet but no data were transmitted. Venera 4 (1967) measured the surface temperature and atmospheric composition. Venera 5 and 6 (1969) crushed at an altitude of 20 km before sticking the night side of Venus. Venera 7 to 14 (1970-1982) reached the surface Venera 13 landing site Image: Magellan mission 5 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus Venus missions The Pioneer Venus program Two spacecraft launched to Venus in 1978 by the NASA. The Pioneer Venus Orbiter carried 17 experiments to study the atmosphere and surface of Venus It continued to transmit data until October 1992 Map of Venus from Pioneer data Credit: NASA 6 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus Venus missions The Magellan Mission Named after the 16th century Portuguese explorer who first circumnavigated the Earth. Mapped Venus from 1990 to 1994: Picture: Venera 13 Covered 98% of Venus' surface with a resolution of ~ 1 km. Measured surface topography to ~100 m vertical resolution. Measured global gravity field to high accuracy. Provided data for insights on surface geologic processes and the nature of the planet's interior. Image: Magellan mission 7 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus The Magellan mission PHYS 171: Introduction to Astronomy I Is Venus geologically active? Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 9 Cratering on Venus Impact craters, but fewer than Moon, Mercury, Mars Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 10 Volcanoes on Venus Many volcanoes Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 11 Shield volcanoes on Earth (e.g., Mauna Kea in Hawai) A few 10 km wide up to 10 km high, On Venus , between 100 and 600 km wide relatively flat (between 0.3 to 5.0 km with an average of 1.5 km) Widely scattered => no plate tectonic Sif Mons Volcano Image: Magellan 12 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus Unusual volcanoes Pancake dome ~ 15 km in diameter less than 1 km in height 100 times larger than Earth volcanoes formed by highly viscous, silica-rich lava erupting under Venus's high atmospheric pressure. Pancake volcanoes Scalloped margin dome volcanic dome that has collapsed and experienced mass wasting such as landslides on its perimeter. Also called ticks are they seems to have several “legs” Scalloped margin dome: The Tick 13 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus Tectonics on Venus Fractured and contorted surface indicates tectonic stresses Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 14 Erosion on Venus Photos of rocks taken by lander show little erosion Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 15 Does Venus have plate tectonics? Most of Earth's major geological features can be attributed to plate tectonics, which gradually remakes Earth's surface. Venus does not appear to have plate tectonics, but its entire surface seems to have been "repaved" 750 million years ago. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 16 Plate Tectonics Versus Flake Tectonics 17 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus Active volcanism? Evidence for subsurface magma intrusions. ESA’s Venus Express has measured a highly variable quantity of the volcanic gas sulfur dioxide in the atmosphere of Venus. Venus is likely to be volcanically Picture: ESA active however, present-day eruptions have not been confirmed 18 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus Surface Venera landers returned images and other data: Confirmed surface temperature and pressure. Show there is enough light going through the clouds to take pictures. Surface is flat, platy. Chemical composition of the surface: similar to basalt , a common low-Si volcanic rock found on the Earth, Moon, and Mars. Landscape is desolate and totally Picture: Venera 13 inhospitable to life. 19 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus Why is Venus so hot? Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 20 Why is Venus so hot? The greenhouse effect on Venus keeps its surface temperature at 470°C. But why is the greenhouse effect on Venus so much stronger than on Earth? Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 21 Atmosphere of Venus Venus has a very thick carbon dioxide atmosphere with a surface pressure 90 times that of Earth. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 22 Greenhouse Effect on Venus Thick carbon dioxide atmosphere produces an extremely strong greenhouse effect. Earth escapes this fate because most of its carbon and water are in rocks and oceans. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 23 Atmosphere of Venus Reflective clouds contain droplets of sulfuric acid. The upper atmosphere has fast winds Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 24 Runaway Greenhouse Effect More evaporation, The runaway greenhouse stronger effect would account for greenhouse effect why Venus has so little water. Greater heat, more evaporation Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 25 Runaway Greenhouse Effect 26 PHYS 171: Introduction to Astronomy I Chapter 7 Part 2: Venus Question What is the main reason 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. The greenhouse effect is much stronger on Venus than on Earth. E. Human activity has led to declining temperatures on Earth. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 27 Question What is the main reason 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. The greenhouse effect is much stronger on Venus than on Earth. E. Human activity has led to declining temperatures on Earth. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 28 What have we learned? Is Venus geologically active? Its surface shows evidence of major volcanism and tectonics during the last billion years. There is no evidence for erosion or plate tectonics. Why is Venus so hot? The runaway greenhouse effect made Venus too hot for liquid oceans. All carbon dioxide remains in the atmosphere, leading to a huge greenhouse effect. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 29 7.5 Earth as a Living Planet Our goals for learning: What unique features of Earth are important for human life? How is human activity changing our planet? What makes a planet habitable? Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 30 Features important for life 1. Surface liquid water 2. Atmospheric oxygen 3. Plate tectonics 4. Climate stability Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 31 Features important for life Earth's distance from the Sun 1. Surface liquid water and moderate greenhouse effect make liquid water possible. 2. Atmospheric oxygen 3. Plate tectonics 4. Climate stability The Goldilocks zone Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 32 Features important for life 1. Surface liquid water 2. Atmospheric oxygen 3. Plate tectonics 4. Climate stability PHOTOSYNTHESIS (plant life) is required to make high concentrations of O 2, which produces the protective layer of O3. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 33 Features important for life 1. Surface liquid water 2. Atmospheric oxygen 3. Plate tectonics 4. Climate stability Plate tectonics is an important step in the carbon dioxide cycle. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 34 Continental Motion Motion of continents can be measured with GPS.
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