1) An atmosphere is a layer of gas that surrounds a world and can be obtained through comet impacts, outgassing during planetary differentiation and volcanism, and ongoing volcanic outgassing. 2) Atmospheric properties like temperature and composition vary with altitude due to interactions with sunlight. 3) Key atmospheric processes include gaining gases through volcanism and impacts and losing them through escape and surface interactions, while the greenhouse effect traps heat from the sun.

1. Chapter 10.1
Planetary Atmospheres

2. 10.1 Atmospheric Basics
• Our goals for learning
• What is an atmosphere?
• How do you obtain an atmosphere?

3. What is an atmosphere?
An atmosphere is a layer of gas that surrounds a world

4. How do you obtain an atmosphere?
– Gain volatiles by comet impacts
– outgassing during differentiation
– Ongoing outgassing by volcanoes

5. Keeping an Atmosphere
• Atmosphere is kept by the world’s gravity
– Low mass (small) worlds= low gravity
=almost no atm.
– High mass(large) worlds = high gravity
= thick atm.
• Gravity and pressure
– Air pressure depends on how much gas is
there ie. The atmospheric thickness.

6. Gravity and Atmospheric Pressure
• The stronger the gravity, the more gas is held by the
world and the greater the weight of atm. on a point

7. Earth’s Atmosphere
• About 10 km
thick
• Consists mostly
of molecular
nitrogen (N2) and
oxygen (O2)

8. Atmospheric Pressure
Gas pressureGas pressure
depends on bothdepends on both
density anddensity and
temperature.temperature.
Adding airAdding air
moleculesmolecules
increases theincreases the
pressure in apressure in a
balloon.balloon.
Heating the airHeating the air
also increasesalso increases
the pressure.the pressure.

9. What do atmospheric
properties vary with altitude?

10. Light’s Effects on Atmosphere
• Ionization:
Removal of an
electron
• Dissociation:
Destruction of a
molecule
• Scattering:
Change in photon’s
direction
• Absorption:
Photon’s energy is

11. Temperature
s and
composition
change
with
Height
giving
structure
to an
atmosphere

12. Earth’s Atmospheric Structure
• Troposphere:
lowest layer of
Earth’s atmosphere
• Temperature drops
with altitude
• Warmed by infrared
light from surface and
convection

13. Earth’s Atmospheric Structure
• Stratosphere:
Layer above the
troposphere
• Temperature rises
with altitude in lower
part, drops with
altitude in upper part
• Warmed by
absorption of
ultraviolet sunlight

14. Earth’s Atmospheric Structure
• Thermosphere:
Layer at about 100
km altitude
• Temperature rises
with altitude
• X rays and ultraviolet
light from the Sun
heat and ionize
gases

15. Earth’s Atmospheric Structure
• Exosphere: Highest
layer in which
atmosphere gradually
fades into space
• Temperature rises
with altitude; atoms
can escape into space
• Warmed by X rays
and UV light

16. What have we learned?
• What is an atmosphere?
– A layer of gas that surrounds a world
• How do you obtain an atmosphere?
– comet impacts.
– outgassing by differentiation, volcanoes,
• Why do atmospheric properties vary with
altitude?
– They depend on how atmospheric gases interact
with sunlight at different altitudes.

17. Atmospheric Processes 1
• Our goals for learning
• What are the key processes?
• How does a planet gain or lose
atmospheric gases?
• How does the greenhouse effect warm a
planet?

18. Atmospheric Processes
• Gaining and losing atmosphere
– Gains: volcanic outgassing, impacts, evaporation.
– Losses: gas escape,impacts,condensation,surface reactions
• Greenhouse Effect
– Infrared energy is re-reflected back to the ground by CO2
• Atmospheric circulation (convection)
– Convection cells move gas from equator to pole and back.
• Coriolis Effect
– Gas dragged sideways by the rotation rate of the world.

19. Atmospheric Gains

20. Atmospheric Losses

21. Greenhouse Effect

23. Air Movement and Flow

24. What have we learned?
• There are 3 ways of adding to atmosphere
and 4 ways of depleting it.
– Gas molecules can transfer out to space or
down to the ground.
• How does the greenhouse effect warm a
planet?
– Atmospheric molecules allow visible sunlight to
warm a planet’s surface but absorb infrared
photons, trapping the heat.

25. Atmospheric Processes 2
Weather and Climate
• Our goals for learning
• What creates wind and weather?

26. Air Movement
Gas molecules move from high density to lower density

27. Atmospheric Pressure
Gas pressure
depends on both
density and
temperature.
Adding air
molecules
increases the
pressure in a
balloon.
Heating the air
also increases
the pressure.
(molecules more
energetic)

28. Atmospheric Circulation
(convection)
• Heated air rises at
equator
• Cooler air
descends at poles
Maximum
Sun
warming

29. Coriolis Effect

30. Coriolis Effect
Coriolis effect deflects north-south
winds into east-west winds

31. Coriolis Effect breaks up
Global Circulation
• On Earth the large
circulation cell breaks
up into 3 smaller ones,
moving diagonally
• Other worlds have
more or fewer
circulation cells
depending on their
rotation rate

32. Coriolis
Effect
Winds blow N or S Winds blow W or EWinds are diagonal
Venus Earth
Mars
Jupiter, Saturn
Neptune, Uranus(?)

33. Total
Atmosphere
Circulation

34. What have we learned?
• What creates wind and weather?
– Atmospheric heating and Coriolis effect.
– Solar warming creates convection cells.
– The coriolis effect drags winds sideways
and breaks up the cells
– The faster a planet spins, the more E-W
gas movement there is

35. Weather and Climate
• Weather is the ever-varying
combination of wind, clouds,
temperature, and pressure
– Local complexity of weather makes it difficult
to predict
• Climate is the long-term average of
weather
– Long-term stability of climate depends on
global conditions and is more predictable

36. Factors that can Cause
Long-Term Climate Change
• Brightening of Sun
• Changes in axis tilt
• Changes in reflectivity
• Changes in greenhouse gases

37. Changes in Greenhouse
Gases
• Increase in greenhouse gases leads to
warming, while a decrease leads to cooling

38. Global Warming

39. Global Warming