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.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 35 Continental Motion
Idea of continental drift was inspired by puzzle- like fit of continents.
Mantle material erupts where seafloor spreads.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 36 Seafloor Recycling
Seafloor is recycled through a process known as subduction.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 37 Plate Motions
Measurements of plate motions tell us past and future layout of continents.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 38 Carbon Dioxide Cycle
1. Atmospheric CO2 dissolves in rainwater.
2. Rain erodes minerals that flow into the ocean.
3. Minerals combine with carbon to make rocks on ocean floor.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 39 Carbon Dioxide Cycle
4. Subduction carries carbonate rocks down into the mantle.
5. Rock melts in mantle
and outgases CO2 back into atmosphere through volcanoes.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 40 Long-Term Climate Change
Changes in Earth's axis tilt might lead to ice ages . Widespread ice tends to lower global temperatures by increasing Earth's reflectivity.
CO2 from outgassing will build up if oceans are frozen, ultimately raising global temperatures again.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 41 Features important for life
1. Surface liquid water
2. Atmospheric oxygen
3. Plate tectonics
4. Climate stability
The CO 2 cycle acts like a thermostat for Earth's temperature.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 42 These features are intertwined
Plate tectonics creates climate stability. Climate stability allows liquid water. Liquid water is necessary for life. Life is necessary for atmospheric oxygen.
How many other connections between these can you think of?
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 43 Human activity is changing our planet
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 44 Dangers of Human Activity
Human-made CFCs in the atmosphere destroy ozone, reducing protection from UV radiation.
Human activity is driving many other species to extinction.
Human use of fossil fuels produces greenhouse gases that can cause global warming.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 45 Global Warming
Earth's average temperature has increased by 0.5°C in the past 50 years.
The concentration of CO2 is rising rapidly.
An unchecked rise in greenhouse gases will eventually lead to global warming.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 46 CO2 Concentration
Global temperatures have tracked CO2 concentration for the last 500,000 years.
Antarctic air bubbles indicate the current CO2 concentration is at its highest level in at least 500,000 years.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 47 CO2 Concentration
Most of the CO2 increase has happened in the last 50 years!
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 48 Modeling of Climate Change
Models of global warming that include human production of greenhouse gases are a better match to the global temperature rise.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 49 What makes a planet habitable?
Located at an optimal distance from the Sun for liquid water to exist
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 50 What makes a planet habitable?
Large enough for geological activity to release and retain water and atmosphere
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 51 Planetary Destiny
Earth is habitable because it is large enough to remain geologically active, and it is at the right distance from the Sun so oceans could form.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 52 What have we learned?
What unique features of Earth are important for life? Surface liquid water Atmospheric oxygen Plate tectonics Climate stability
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 53 What have we learned?
How is human activity changing our planet? Human activity is releasing carbon dioxide into Earth's atmosphere, increasing the greenhouse effect and producing global warming.
What makes a planet habitable? Earth's distance from the Sun allows for liquid water on Earth's surface. Earth's size allows it to retain an atmosphere and enough internal heat to drive geological activity.
Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 54