Astronomy Exam #3

Review Sheet for Exam # 3
Planet size controls cooling time: bigger planet – longer period of activity
Planet size controls the ability to retain an atmosphere
More active planets have been resurfaced more recently: surface is younger – fewer craters
Atmospheres can have a big influence on planet temperatures
1. Earth
a. Seismic studies: rocky mantle and iron core (where magnetic field is produced)
b. Interaction of the magnetic field and solar wind: bow shocks, Van Allen belts and northern lights.
c. How was the Earth put together – formation of core (differentiation), oceans and atmosphere (out-
gassing).
d. Role of impacts – did comets deliver water to Earth?
e. What happened to the CO 2 Earth’s atmosphere?
2. Moon
a. Basic properties – size, density
b. Major geologic features – highlands and maria (resurfaced areas)
c. Formation craters and the variation of the cratering rate with time
d. Apollo missions: sample return, measurement of seismic activity, radioactive dating of lunar surface
e. Moon’s origin: impact theory
f. Moon and Mercury: how they are similar and how they are different and why (sizes, densities,
cratering patterns, origins)
3. Venus
a. Basic properties – size density, reverse (slow!) rotation (caused by impact?)
b. No magnetic field (why?)
c. Recently resurfaced – how do we know – yet, no tectonic activity. Volcanic domes – up-thrusting. Dry
and cracked crust.
d. Thick clouds – impactors tend to disrupt before reaching the surface
e. Magellan mapping – high resolution radar imaging of the entire surface
f. High temperatures and atmospheric pressure, sulfuric acid, runaway greenhouse effect, CO 2
atmosphere.
g. What happened to the water? Why is the atmosphere so dense (compared to Earth)? Was early Venus in
the habitable zone?
4. Mars
a. Basic properties – size and density
b. Early observations – canals and martians
c. Different geology in the northern plains and southern highlands, Tharsis region (where the volcanoes
are found), Valles Marineris (the gash)
d. Why the martian volcanoes are so tall and broad
e. Early volcanic activity, declining after that
f. Remnant magnetic field
g. How did Mars lose (most of) its atmosphere
i. Solar wind erosion
ii. Impacts
h. CO 2 (like Venus) thin (unlike Venus) atmosphere.
i. Seasons caused both by rotation-axis tilt and orbital eccentricity; weather predictable – except for
planet-wide dust storms
j. Presently, no rain, lakes or oceans. Where is the water? Permafrost, Northern polar cap (Southern cap
mostly CO 2 )
k. Runoff and outflow channels – most very old (how do we know?), some quite recent
l. Landers: Viking – no organics, chemically reactive soil; Pathfinder/Sojourner: Volcanic melting/floods;
Spirit/Opportunity rovers: blueberries, layered rocks and wavy patterns – pooling water?
m. No evidence of life on Mars but – was early Mars more Earth-like? Early oceans?

Earth Atmosphere 

• An atmosphere is a thin layer of gas bound to a planet by gravity 

• The velocity of gas particles can exceed the escape velocity of the smaller planets 

The Earth's Atmosphere

• 79.1% Nitrogen (O2)

• 20.9% Oxygen (O2)

• .093% Ar

• .035% CO2 (increasing)

• .1-3% water (variable)

How heavy is the gas?

• Light gases can escape easier

  • Hydrogen 

  • Helium

• Hydrogen from our atmosphere escaped and we have very little helium bc the gravity was too light to keep the hydrogen 

Temperature vs. Gravity

• Heavier gasses tend to stay closer to the surface than lighter gases 

Where did the atmosphere come from?

• Volcanic Activity 

  • Moon

    • No tectonic plates (only earth)

    • No active volcanoes

  • IO 

    • Moon of Jupiter 

    • Active volcanoes

Any place with active volcanoes

• Mars - not active

• Cooled down

Why is the earth hot inside?

• Radioactive

• Heat trapped from the formation of the earth 

Earth's Magnetic field

Interior of the Earth

• There is a solid core of iron, surrounded by a liquid iron core 

• High energy, charged particles from the Sun are diverted around the Earth by its magnetic Field

The CO2 cycle 

• Atmospheric Co2 dissolves in oceans

  • Acid rain falls in the ocean and acidifies the ocean

• Erosion carries silicates (sand) to oceans

• Silicates react with dissolved Co2 to form minerals (like limestone)

• Plate tectonic carries minerals to subduction zones

  • Plats force the minerals underground

• Geological activity eventually releases CO2 back into the atmosphere

  • Volcanoes

Exam question?

1. Why does star formation lead to the formation of planets as well?

Star formation leads to the formation of other planets because the dust and raw material from the formation of stars from past star explosions leads to leftover residue. The formation of a spinning star spits out dust and raw material collected to create a planet. Then the materials contract using the skater effect condensing. The spin flattens into a disk around star, and the disk creates planets 

2. Describe the meaning of planetary detection selection effects. In particular, what kind of planets is the Doppler or wobble method likely to detect? 

The Doppler or wobble method is said to detect stars with planets based on whether the star is wobbly or shifting position ever so slightly. This method will likely detect huge planets and their gravity large enough to move the star.

CO2: Earth's Thermostat 

• Co2 is a greenhouse gas, helping to make Earth habitable today

• The amount of CO2 in the atmosphere may have varies in the past to keep Earth comfortable 

Density and Albedo

• The concepts of density and albedo are useful in planetary studies 

• Density = mass/volume

  • Density of water is 1 gram per cubic cm

  • Density of rock is 3 grams per cubic cm

  • Density of lead is 8 grams per cubic cm

• The density of an object can give an indication of its composition 

Phases of Matter 

• Matter has three “phases”

• Solid 

  • Constant volume and constant shape

• Liquid 

  • Constant volume but variable shape

• Gas 

  • Variable volume and variable shape

Atmospheres 

• In general, a gas will expand to fill its container. In the case of planetary atmosphere, gravity is the container

  • The gas particles will have characteristic velocity depending on the temperature at the surface of the planet and on the nature of gas 

Where is carbon stored on Earth 

• Soil, vegetation, atmosphere, ocean layers, limestone, sediments and rocks 

Faint Young Sun Paradox

• Astrophysical models indicate that sun's brightness should have increased significantly over age of solar system 

• So why wasn't earth frozen earlier

Earth atmosphere 

• The Earth's atmosphere is useful in at least three ways:

  • It keeps the earth warmer than it would be otherwise

  • It keeps the harmful UV and X-ray radiation from reaching the ground

  • It allows us to breath 

Reasons to Explore Mars

• Mars is the closest planet to  earth that astronauts can explore

• About 4 billion years ago, mars seems to had a earth like climate, with rivers, lakes, and maybe oceans,

• Mars was warm and wet, life on earth

What are forces that shape the surface of Mars

• Impacts

• Volcanism

  • Largest volcano/mountain in solar system

  • Big enough to have volcanoes but small enough to not have enough gravity to bring it down 

• Tectonics

  • No motion of plates

• Erosion 

  • Wind, sandstorm

The earth has no place with a bunch of creators bc of the wind, rain, waves, lava, and more

Erosion 

• Ancient erosion shows evidence for flowing water in early history of Mars

• Drainage channels were caused by flowing water

• Liquid water cannot exist on mars now bc the atmospheric pressure is so low

Fundamental message 

• Mars was warmer and wet (like earth) when life arose on our planet - maybe it also originated on Mars

• Life on Mars, if it existed may left traces as fossil evidence in some of the sedimentary rocks

• If life evolved with the Changing Martian climate, it may still be thriving in the ricks and in the soil below the surface

• The existence of life in extreme environments on earth (antarctica, arid deserts) suggest that this is possible 

1. Terrestrial Planets

• Mercury 

• Venus

• Earth 

  • moon

• Mars

  • Phobos and Deimos

2. Giant planets 

• Jupitper

  • Many moons

• Saturn 

• Uranus

• Neptune 

3. Dwarf Planet

• Pluto

4. Comets 

• Kuiper belt

• Orbit cloud

Mars

• Contains an atmosphere of CO2

  • Very thin 

  • No protection from UV light 

• Impacts can remove the atmosphere or Solar winds 

• Mars has no protective magnetic field 

• NO tectonic plates

• Dead Volcanoes 

  • Tallest volcano in the solar system 

• Mars has cooled down 

• Water is permafrost 

  • Frozen water 

Did Mars have liquid water on the surface in the past?

• Blueberries 

  • Small rounded pebbles caused by water flow 

• Look at the surface of the ground

  • Ancient water channels on the surface 

  • Craters 

• Enormous dust storms

• Much Smaller than Earth 

Venus and Earth Twin Planets

• Similarities

  • Size

  • Density

  • Have atmosphere

  • Both have cores

• Differences

  • Venus has no moon

  • Venus has no water

  • Venus is very hot

  • Venus has no magnetic field

  • Venus’s atmosphere is pure CO2

When we studied with telescopes

• We find sulfuric acid rain in the clouds of Venus

• Surface is extremely hot and the atmosphere is really thick 

• The pressure on venus is the same as being in the ocean 3000 feet below sea level

• Could nor sustain the kind of life we have on earth 

Volcanism 

• There are many distinct volcanoes on Venus  

• About 80% of the surface is covered with relatively fresh lava plains

• There are unique volcano type on Venus, such as pancake domes

• Long lava channels indicate a very fluid lava flow 

Tectonism 

• Venus displays a different kind of tectonism from that of earth 

• Earth tectonic motions are largely horizontal 

• Venus tectonic motions are largely vertical, resulting in large circular features called “coronae”

Venus and Earth Diverge

• Life on earth after the planet formed, early microbes becan to sequester CO2 dissolves in the ocean in the form of hard parts

• As the microbes died they settles to the ocean bottom, forming layers off calcareous sediments in which the CO2 is still held

• Limestone and dolomite are examples of rocks made of shells and carbonates made by animals from CO2 in the ocean 

The Runaway greenhouse

• Early venus (4 billion years ago)

  • Moderate temperatures

  • Water ocean

  • CO2 dissolved in ocean, or chemically combines with rocks

• Then 

  • Sun brightened, boiling the oceans

  • More CO2 was somehow deposited in the atmosphere

Consequences

• Oceans began to evaporate, releasing CO2 into the atmosphere

• H2O in the atmosphere contributed to heating

• CO2 gas was released from surface rocks

• The atmosphere and surface heated up because the greenhouse effect became stronger

• Heating liberated still more CO2 and H2O from the ocean and rocks, and temperatures continued to rise

The Origin of the Moon 

• What does a theory of the moon's origin have to explain?

  • Why does the earth have a satellite (moon)?

  • The catering history

  • The low density of the moon compared to earth (3.3 compared to 5.5 g/cm^3)

  • Why does the moon have so little metal?

    • Made of solid rock. No CORE

  • The fact the moon was once much closer to earth than it is now

• THe melted Earth began to differentiate

• Metals sunk to the center, and lighter rocky materials floated to the top 

• This formed a core, a mantle, and a crust

How will you get a moon without a core?

• An object about the size of mars collided with Earth, blasting a large quantity of the mantle and crust into space

• Mantle and crust material depleted in metal because differentiation was in progress

• THe nearly molten Earth quickly “healed” from the impact event that ripped off a large piece of the mantle

• This is the Giant Impact theory of the origin of the Moon 

What is Earth's CO2 cycle and how can it compare to Mars and Venus? 

• Mars and Venus have no CO2 cycle 

Ages of Lunar rocks 

• Rocks from the cratered highlands are oldest, most greater than 4 billion years

• Volcanic lava rocks from the maria are younger at 3.2 to 3.9 billion years old

Terrestrial planets

• Low mass 

• High density 

• Slow rotators

• Few satellites

• Close to sun

• Thin atmosphere

• Weak or no magnetic field

Giant planets

• High mass

• Low density

• Rapid rotators

• Many satellites

• Far from sun

• Thick atmosphere

• Strong magnetic field

What is a moon 

• A moon is something that orbits the planet 

Regular and Irregular moons 

Regular moon:

• Nearly circular orbits

• Orbits in the equatorial plane

• Prograde motion 

Irregular Moons:

• HIgly elliptical orbits 

• Orbits inclined to the planets equatorial plane

• Prograde and retrograde motion 

Three Planetary Moons of special note

• Io, the volcanic moon of Jupiter

• Europa, the icy moon of jupiter

• Titan, Saturns moon with a dense atmosphere

Io

• Slightly Larger than earth moon 

• Density 3.53 g/cm^3

• Thin silicate crust with no water

• Iron-rich core

• Molten silicate interior

• No impact craters= very young

• A volcanic caldera and an active eruption by the Galileo spacecraft

• The yellow color is due to sulfur the black features are lava lakes

Why is Io hot inside

• Io is pulled by the gravity of Europa and Ganymede, plus Jupiter

• Slightly elliptical orbit

• Jupiter keeps trying to make the orbit more circular

• The gravity pull causes Io to bend and flex. This flexing produces heat that keeps the interior molten 

Europa

• Broken and tilted icebergs floating in a frozen sea

• No impact craters. Its icy surface shows intricate network of crossing cracks, similar to cracks in the Artic ice packs on Earth 

• There is very to little vertical relief (no mountains of deep valleys)

• Very young surface

• Heated by gravitational effects of Ganymede and Jupiter (like Io), therefore it has an interior layer (“mantle”) of liquid water

Titan: Largest Moon in the Solayer System 

• Orbit period around saturn is 16 days

• Thic atmosphere mainly made of Nitrogen with small amount of methane 

• Which is hydrocarbon 

• Many other hydrocarbons also present

• Colder, but it has a greenhouse effect that warms the atmosphere

• The atmosphere is nearly opaque with organic smog, produced by sunlight acting on methane and nitrogen 

• We can see the surface indisticly at certain wavelengths where the atmosphere is partly transparent