Chapter 7: Earth and the Terrestrial W lds - StFXpeople.stfx.ca/klebris/Courses/PHYS171_slides/Chapter 7_3.pdfPHYS271: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial

PHYS271: Introduction to Astronomy I

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 1Chapter 7: Earth and the Terrestrial Worlds

PHYS 171: Introduction to Astronomy I

7.4 Venus: A Hothouse World

Our goals for learning:

Is Venus geologically active?

Why is Venus so hot?



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

Venus

Chapter 7 Part 2: Venus3


Retrograde rotation



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

Venus missions

Image: Magellan mission


Venera 13

landing site


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

Venus missions


Map of Venus from Pioneer data

Credit: NASA


The Magellan Mission

Named after the 16th century Portuguese explorer who first circumnavigated the Earth.

Mapped Venus from 1990 to 1994:

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.

Venus missions

Picture: Venera 13

Image: Magellan mission


PHYS 171: Introduction to Astronomy IThe Magellan mission





Cratering on Venus

Impact craters, but

fewer than Moon,

Mercury, Mars



Volcanoes on Venus

Many 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

Shield volcanoes

Sif Mons Volcano Image: Magellan



Pancake dome~ 15 km in diameter less than 1 km in height 100 times larger than Earth volcanoesformed by highly viscous, silica-rich lava erupting under Venus's high atmospheric pressure.

Scalloped margin domevolcanic dome that has collapsed and experienced mass wasting such as landslides on its perimeter. Also called ticks are they seems to have several “legs”

Unusual volcanoes

Pancake volcanoes

Scalloped margin dome: The Tick



Tectonics on Venus

Fractured and

contorted surface

indicates tectonic

stresses



Erosion on Venus

Photos of rocks taken

by lander show little

erosion



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.



Plate Tectonics Versus Flake Tectonics



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 active however, present-day eruptions have not been confirmed

Active volcanism?

Picture: ESA



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 inhospitable to life.

Surface

Picture: Venera 13







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?



Atmosphere of Venus

Venus has a very thick

carbon dioxide

atmosphere with a

surface pressure 90

times that of Earth.



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.



Atmosphere of Venus

Reflective clouds

contain droplets of

sulfuric acid.

The upper atmosphere

has fast winds



Runaway Greenhouse Effect

The runaway greenhouse

effect would account for

why Venus has so little

water.

More evaporation, stronger

greenhouse effect

Greater heat, more

evaporation



Runaway Greenhouse Effect



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.



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.



What have we learned?


Its surface shows evidence of major volcanism and tectonics during the last billion years.

There is no evidence for erosion or plate tectonics.


The runaway greenhouse effect made Venus too hot for liquid oceans.

All carbon dioxide remains in the atmosphere, leading to a huge greenhouse effect.



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?



Features important for life

1. Surface liquid water

2. Atmospheric oxygen

3. Plate tectonics

4. Climate stability






3. Plate tectonics


Earth's distance from the Sun

and moderate greenhouse effect

make liquid water possible.


The Goldilocks zone





3. Plate tectonics


PHOTOSYNTHESIS (plant life) is

required to make high

concentrations of O2, which

produces the protective layer of

O3.






3. Plate tectonics

4. Climate stabilityPlate tectonics is an

important step in the

carbon dioxide cycle.



Continental Motion

Motion of continents can be measured with GPS.



Continental Motion

Idea of continental drift

was inspired by puzzle-

like fit of continents.

Mantle material erupts

where seafloor spreads.



Seafloor Recycling

Seafloor is recycled through a process known as subduction.



Plate Motions

Measurements of plate

motions tell us past and

future layout of

continents.



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.



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.



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.





3. Plate tectonics


The CO2 cycle acts like a

thermostat for Earth's

temperature.




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?



Human activity is changing our planet



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.



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.



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.



CO2 Concentration

Most of the CO2 increase has happened in the last 50 years!



Modeling of Climate Change

Models of global

warming that include

human production of

greenhouse gases are a

better match to the

global temperature rise.





Located at an optimal distance from the Sun for liquid water to exist



Large enough for geological activity to release and retain water and atmosphere



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.




What unique features of Earth are important for life?

Surface liquid water

Atmospheric oxygen

Plate tectonics

Climate stability




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.


Documents

Chapter 7: Earth and the Terrestrial W lds - StFXpeople.stfx.ca/klebris/Courses/PHYS171_slides/Chapter 7_3.pdfPHYS271: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial