1. Lecture 5
6/8/07
AST1001

2. Geology Basics Can probe the interior of a planet with seismic waves
Core of the planet is dense, made out of metals
Mantle is moderate density
Crust is very thin, contains low density rock

3. The Core
The Earth’s core consists of two parts: the molten outer core and the solid inner core
The Earth is almost entirely rock
Other planets might be similar, but no seismic data
Differentiation causes the density structure of the planets

4. Other Planets The lithosphere is the outer, thin layer of rocks
Mars, Mercury, the Moon have very thick lithospheres that extend almost to their cores
Earth, Venus have very large mantles

5. How Interiors Get Hot Accretion Differentiation Radioactive Decay
Planetesimals collide, bring energy to planet
Differentiation
Heavy stuff moves inward, reducing potential energy
Radioactive Decay
Lots of radioactive elements in core, and radioactive decays produce energy

6. How Interiors Cool Off Convection Conduction Radiation
Hot things rise, cool things fall
Examples: weather and boiling water
Conduction
Contact allows heat transfer
Radiation
Light is radiated into space

7. Group Work
The text does a example surface area to volume calculation on page Repeat the calculation but now calculate the ratio using Mars (radius = 3402 km). What does this tell you about why Mars is no longer very geologically active?

8. Magnetic Fields Magnetic fields occur due moving charged particles
You need 3 things for a planetary magnetic field
An interior region of electrically conduction fluid
Convection in that fluid
Moderately rapid rotation
Earth is the only terrestrial planet to have these things

9. Shaping Planetary Surfaces
There are 4 ways of shaping planets surfaces
Impact Cratering
Volcanism
Tectonics
Erosion

10. Cratering
Impacting objects typically travel at speeds of 250,000 mi/hr
Collisions convert that kinetic energy into moving rock to make craters
Craters can give us information about the planet’s past surface

11. Craters and Surface Aging
Craters should be equally spaced and equally dense on all planets if there is no weathering
Craters can be erased by erosion, lava, etc
We can tell where activity happened by looking at crater density
Smaller planets are less geologically active

12. Volcanism Refers to molten lava coming to the surface
Magma rises because its less dense and is squeezed to the surface
Lava creates volcanoes and volcanic plains
Also creates rocks like basalt
Outgassing can bring different gasses to the surface

13. Tectonics
Refers to the stretching, compression or any other force on the lithosphere
Usually occurs due to mantle convection
We have massive pieces of the crust here on Earth, which leads to plate tectonics

14. Erosion Processes that break down or transport rock
Can also create things like sand dunes, river deltas, deposits, sedimentary rock

15. Small Bodies Maria have formed on the Moon due to lava outflows
Today the surface of the Moon is pretty much unchanging
Mercury is very similar, but probably more volcanically active
Huge feature called Caloris Basin

16. Mars Surface has many dramatic differences
Southern hemisphere has high elevation with lots of craters, including Hellas Basin
Northern Hemisphere is low, has few craters

17. Volcanism on Mars Lots of volcanoes on northern plains
Towering shield volcanoes
The Tharsis Bulge is a continent sized feature
Valles Marineris
Huge canyon
Might have formed due to tectonic cracking

18. Water on Mars Lots of features that look like dry riverbeds
No liquid water on the surface of Mars today
Water is not stable on the surface
Spirit and Opportunity have found lots of minerals that would only form in water

19. Venus
Magellan mapped the surfaces, down to features 100 meters in size
Lots of volcanoes on Venus
Probably active
Lots of contorted features, probably formed by tectonics
Virtually no erosion

20. Map of Venus

21. Tectonics on Earth Ample evidence to suggest that plates drift around
Results in a wide range of unique effects
Earthquakes
Hot spots
Pangaea

22. Atmosphere Basics
An atmosphere is just the gasses surrounding the solid part of a planet
Atmosphere always makes up a tiny fraction of the planet’s mass
Planets have a wide range of atmospheres
Vary widely in composition, density

23. More Basics Atmospheres very thing
2/3 of air on Earth lies within 10 kilometers of surface
Air pressure occurs due to particles running into things
Air is held to the planet with gravity, so there is more air near surface
Bars are used to measure pressure

24. Atmospheric Effects Creates pressure Scatters and absorbs light
Important for liquid water
Scatters and absorbs light
Creates wind and weather
Creates magnetosphere
Can cause greenhouse effect

25. Greenhouse Effect The greenhouse effect is a natural effect
Earth absorbs some light from the Sun, reemits it as infrared light
Greenhouse gasses absorb the IR light, delay its escape
Too much of the greenhouse effect is a bad thing

26. Atmospheric Properties and Height
The atmosphere has structure
Troposphere is closest to the surface
Stratosphere
Thermosphere
Exosphere

27. Magnetosphere
The Sun emits a low density breeze of charged particles called the solar wind
The Earth’s magnetic sphere influences the particles
Particles can get trapped along magnetic field lines
For Van Allen Belts
If they are in the magnetosphere, then you get aurora

28. Mercury and the Moon Very thin atmospheres
Created by “surface ejection” of particles
There might be water ice in polar craters

29. Mars Today
Present day surface of Mars looks a lot like a desert on Earth
Atmosphere is very thin: 1% of pressure as that on Earth
Most UV radiation gets through the atmosphere

30. Martian Seasons Mars has seasons similar to those on Earth
Twice as long
Eccentricity of orbit is important
South has shorter, hotter summers and longer, colder winters than North
Can have strong winds

31. Mars in the Past
For its first billion years, Mars might have been wet and warm
Atmosphere was probably lost once its magnetic field went away
Particles left Mars and went into space
Rocks could have also taken oxygen

32. Group Work
The escape velocity on Mars is about 5 km/s. The average daytime temperature is 230K. Using this information, compare the peak thermal velocity of the atoms in Mars’s atmosphere to the escape velocity. How does this relate to potential atmosphere loss by Mars?

33. Venus Today Surface is searing hot, very high atmospheric pressure
Almost no wind or weather
Temperature is uniform and no seasons
Sulfuric acid in the atmosphere
Mysterious high speed upper winds

34. Venus and Its Clouds Earth gets rid of its carbon dioxide with water
Where did Venus's water go?
Leading theory involves UV rays breaking down the water
Because Venus is slightly closer to the Sun, water evaporates more, creates runaway greenhouse effect