1. Planetary Surfaces 4 major processes affect planetary surfaces:
Impact cratering – from collisions with asteroids and comets
Volcanism – eruption of molten rocks
Tectonics – disruption of a planet's surface by internal stresses
Erosion – wearing down or building up geological feature by wind, water, ice, etc.

2. Impact Cratering: The most common geological process shaping the surfaces of rigid objects in the solar system (Terrestrial planets, moon, asteroids)

3. EROSION: the breakdown and transport of rocks and soil by an atmosphere, liquids and/or ices.
Mars
Venus

4. Volcanism Mars Source of current atmospheres Terrestrial planets
Jovian moons
Erases craters
A source of water
Mars

5. Tectonics: refers to the action of internal forces and stresses on the lithosphere to create surface features, i.e., “geological processes”
Can only occur on planets
or moons with convection
in the mantle
Earth & Venus
Europa
Ganymede?

6. Tectonics… raise mountains create huge valleys (rifts) and cliffs
create new crust
generate volcanoes (maintain atmospheres)
can move large segments of the lithosphere (plate tectonics)

7. Portion of Valles Marineris on Mars – created by tectonic stresses

8. Tectonic plates

10. divergent plate boundary (plates move away from each other).
Atlantic Ocean
Great Rift Valley in Africa
Valles Marineris (Mars)

11. convergent plate boundary with subduction : plates move towards each other & one slides beneath the other.
Nazca plate being subducted under the South American plate to form the Andes Mountain Chain.
Island arc system

12. convergent plate boundary without subduction : plates move towards each other and compress.
Formation of Himalayas.

13. Plates sliding past each other: earthquakes, valleys, mountain building

14. Half of the world’s volcanoes surround the Pacific plate
Tectonic plates

15. ATMOSPHERES

16. Atmospheric Basics Layer of gas surrounding a planet.
Usually very thin for terrestrial planets (exception Venus).
Affects conditions on the planet.
We would like to understand how each of the terrestrial planets ended up having such different atmospheres.
Venus’s thick atmosphere

17. (mostly carbon dioxide - CO2)
All terrestrial planets probably had minimal atmospheres at some point after they formed: “primary” atmosphere of H,He
These original atmospheres were swept away from the terrestrial planets early in their life.
Current atmospheres are “secondary” atmospheres, formed primarily by outgassing
(mostly carbon dioxide - CO2)

18. Holding onto an atmosphere requires gravity
The strength of gravity determines the escape velocity from the planet.
The temperature and composition of an atmosphere determines the velocities of atoms and molecules in the atmosphere; lighter molecules will move faster. At a given temperature, H and He will have higher velocities than more massive elements or molecules (recall that K.E. = 1/2 mv2)

19. Holding onto an atmosphere requires gravity
The strength of gravity determines the escape velocity from the planet.
The temperature and composition of an atmosphere determines the velocities of atoms and molecules in the atmosphere.
If the constituents of an atmosphere are moving faster than escape velocity, then a planet or moon will be unable to hold onto an atmosphere.

20. Larger (stronger gravity), cooler (slower moving molecules) planets
can hold onto atmospheres better than
smaller (weaker gravity),
hotter (faster moving molecules) planets

21. Moon and Mercury are “Airless” worlds
gravity too weak to hold onto an atmosphere
“black sky”
The little atmosphere that exists consists of particles of the solar wind that are temporarily trapped.

22. Mars Mars had standing and running water on its surface in the past.
Very little atmosphere today (mainly CO2)
Mars had standing and running water on its surface in the past.
Therefore, it must have had a more substantial atmosphere in the past
Does it have water today? Yes - frozen in polar ice caps and beneath its soil

23. Venus Mostly CO2 Temperature at surface hot enough to melt lead
Densest atmosphere of all Terrestrials
Mostly CO2
Temperature at surface hot enough to melt lead
Pressure at the surface ~ 90 times that on Earth
Perpetual cloud cover, sulfuric acid rain
Weather forecast “awful” all the time.

24. Earth A moderate atmosphere today
Mostly nitrogen (N2), with some oxygen (O2: arises from photosynthetic life), carbon dioxide (CO2), etc.
Enough to enable liquid water to exist (temperature and pressure adequate)
Together the air & water produce erosion

25. The Jovian planets (high gravity, cool/cold atmospheres) have very substantial atmospheres, primarily H & He.
We see the tops of clouds

26. LAYERING OF ATMOSPHERES
Structure is created within an atmosphere through interactions of atmospheric gasses with light

27. hottest layer, v. rarified Thermosphere
Exosphere
hottest layer, v. rarified
Thermosphere
absorbs X-rays, ionized, ionosphere, reflects some radio, aurora
Mesosphere
weakly absorbs UV
Stratosphere
strongly absorbs UV, ozone (O3), stratified (no convection), Earth only Terrestrial planet with one.
Troposphere
absorbs IR (greenhouse); convective; weather

28. Stratosphere absorbs harmful UV
From the perspective of life, stratosphere & troposphere are the most important
Stratosphere absorbs harmful UV
Troposphere provides greenhouse effect

29. A magnetic field creates “magnetosphere” that deflects away solar wind particles.
In the absence of a “magnetosphere”, the solar wind will slowly strip away an atmosphere.

30. The greenhouse effect
Planets heat up by absorbing the Sun’s visible light
Planets cool off by radiating infrared out to space
Greenhouse gasses trap infrared radiation in troposphere (lowest level of atmosphere), thereby heating the lower atmosphere.
greenhouse gasses (e.g., H2O, CO2, CH4 - methane) transmit visible light but absorb infrared light

32. Greenhouse effect raises temperature of lower atmosphere
Greenhouse effect is critical to the existence of life on Earth – it raises temperatures to “habitable” level, permits liquid water