Lecture 12 Flashcards
What is an atmosphere?
An atmosphere is a layer of gas that surrounds a planet
What is the composition of the Earth’s atmosphere?
Mainly nitrogen and oxygen. No hydrogen- it is too light
(the atmosphere is also about 10km thick)
What are the effects of atmospheres?
-create pressure allowing liquid water to exist
-absorb and scatter light
-create wind, weather and climate
-interact with the solar wind to create a magnetosphere
-make planetary surfaces warmer (greenhouse effect)
How does energy from the sun and radiation affect planetary temperature?
Planetary temperature is determined by the balance between energy absorbed from the sun and outgoing thermal radiation
How are reflectivity and temperature related?
-A planet’s reflectivity is called its albedo.
-Low albedo temperatures absorb more sunlight –> higher temperatures
What is the greenhouse effect?
-Visible light passes through the atmosphere and warms the surface.
-Infrared light from the surface is absorbed by the atmosphere, trapping the heat
How do different wavelengths of light interact with the atmosphere?
-x-rays and UV wavelengths are mostly absorbed by the atmosphere
-Visible light can pass through
-Infrared light is trapped beneath
What is the troposphere
-lowest layer
-warmed by the IR irradiated by the Earth’s surface
How is the stratosphere warmed?
Warmed by the UV from the sun
How is the thermosphere warmed?
Warmed by x-ray and UV from the sun
Where is the exosphere?
Fades into space
Why is the sky blue?
The atmosphere scatters blue light from the sun to make it appear like it is coming from different directions
Why are sunsets red?
Sunsets are red because red light scatters less
How does the magnetic field protect the Earth?
The Earth’s magnetic field protects us from solar wind
What is weather?
Daily variation in the wind, clouds, temperature and pressure
What is climate?
Long term average weather of a planet
What are circulation cells?
The hot and cold of the equator and poles produce circulation cells
What are the 4 factors effecting the atmosphere?
- Solar brightening: increasing the amount of sunlight warms planets (billions of years)
- Changes in axis tilt: larger tilts produce more extreme seasons. Smaller tilts keep the poles colder
- Changes in reflectivity: high reflectivity=cool planet
- Changes in greenhouse gases: more greenhouse gas=more warming
How are atmospheres formed?
-outgassing from volcanoes
-evaporation of surface liquid or the sublimation of surface ice
-impacts of particles and photons
How are atmospheres lost?
-molecules approach escape velocity
-condensation of gasses onto the surface
-chemical reactions with the surface
-large impacts that blast gas into space
-solar wind blows gasses away
Do the Moon and Mercury have atmosphere?
The moon and Mercury have very thin atmospheres that come from gases ejected by impacts
What are the seasons on Mars like?
The ellipticity of Mars’ orbit makes the seasons more extreme in the southern hemisphere
What is contained on the polar ice caps of Mars?
-the residual ice of the south cap in the summer is primarily water ice
-carbon dioxide ice sublimates as summer approaches and condenses at the opposite pole
How has climate changed on Mars?
-Mars has not had widespread surface water for 3 billion years
-The greenhouse effect probably kept the surface warmer before that time
-Somehow Mars has lost most of its atmosphere
