Chapter 9 Flashcards
The following describes which SS body: Highly cratered surfaces, large ring basins, cracks and scarps, surface is relatively low relief with no major continents for mountain structures
Mercury
The following describes which SS body: little surface relief and very few craters of any size
Venus
The following describes which SS body: Bright and heavily cratered highlands, and dark smooth maria. Maria cover approx 20% of the surface
The Moon
The following describes which SS body: craters, volcanoes, plains, and canyons. Clear signs of evolution caused by a variety of factors including internal heating, tectonics, impacts, wind, and water
Mars
The study of rocks, their structure, composition and origin is called
Petrology
What is the compositional relationship between rocks and minerals?
Rocks are made of one or more minerals
A solid chemical compound that occurs naturally (can be different if they are made of the same components but different structure
Minerals
What type of mineral composes the majority of the Earth’s crust and mantle?
Silicate (silicon and oxygen)
What are the 3 main families of silicate?
Olivine (most dense), Pyroxene (chains), and Feldspar (least dense)
What family of silicates make up approx 60% of Earth’s rock?
Feldspar
What are the two categories of feldspar and how are they differentiated?
Othoclase (potassium rich), and Plagioclase (sodium rich)
Which mineral is most common on the icy planets?
Water and methane
How are rocks classified?
By their mineral content and their formation history
What are primitive rocks?
Rocks formed in the protosolar nebula, with element ratios the same as solar abundances (only examples are chondritic meteorites)
How is igneous rock formed?
Through the crystallization of rock melted in the crust or upper mantle
What are the 2 categories of igneous rock?
Intrusive and extrusive
How does sedimentary rock form?
Through the deposition, burial, and lithification of rock that has been weathered through exposure at the surface of the crust
What type of rock is biological (fossils of animal shells)
Limestone
How is metamorphic rock formed?
Through the recrystalization of minerals under high temperature and pressure in the deep and upper mantle (can also be formed by impact)
Give one example of each of the 3 main types of rock
Igneous - Granites, Metamorphic - marble, Sedimentary - sandstone
Who discovered the first lunar craters?
Galelio
When were the first craters discovered on Earth?
It wasnt until the 20th century
What are impact craters circular?
Because the material is blasted out equally in all directions (although the depth may be asymmetrical due to the impact angle)
How many times larger are the impact craters relative to the impactor?
Approx 10x larger
When are shock waves created by impactors?
When the impact velocity is greater than the speed of sound
A highly compressed zone with a high density of energy and matter is what?
A shock
What happens to the rock as a shock wave carries the energy of the explosion into the ground?
The rock will compress and deform like a fluid
The rebound of the inner material of a crater forms what?
A central peak
What for the rim (and maybe rays) around an impact crater?
The fragments that were ejected from the surface
What are the 3 steps to finding the impact energy?
- Find the mass., 2. Find the kinetic energy., 3. Convert to megatons
What what velocity must an object be moving to become an explosion upon impact?
3km/s or faster
What is the max diameter of a microcrater?
10 microns
What property of lunar material can be explained by microcraters?
The age of the lunar material
The fine powder created by impacts that covers the surface of the Moon is called what?
Regolith
How thick is the lunar regolith on the highlands and the maria?
Approx 2km thick in the uplands and approx 10 m thick over the maria
What method of dating craters do we use on inactive worlds?
We can compare the radioactive dating age to the number density of craters on the surface
Why cant we use the number density of craters on the surface of active worlds to ascertain an age?
Wind and water erosion can destroy craters (lowering the number density)
What can we tell about small craters found on the surface of active worlds?
These craters have to be young (and therefore unaffected by weathering)
How can we ascertain the age of other SS bodies if we know their crater number density but cannot gather material for radioactive dating?
We can compare their number density to that of the Moon and extrapolate their age (only for inactive worlds)
What is the cratering saturation equilibrium?
When the cratering density gets too high new craters begin to obliterate the old ones and the density reaches a constant
What is the minimum age range for SS objects that have reached cratering saturation equilibrium?
3.9-4.5 years old
What factor can affect the cratering rate of object?
Proximity to large bodies (more massive bodies attract more asteroids/planetesimals)
How do we know that the Marian moon Phobos is very old?
Its surface is heavily cratered
How do we know that the Marian moon Deimos is younger than its companion moon, Phobos?
Although it is still very close to saturation, it’s surface is less cratered than Phobos
What is the relationship in Jupiter’s moons between distance from Jupiter and bulk density?
The further the moon is from Jupiter, the lower its bulk density
How old are the surfaces of the Galilean moons relative to each other?
Callisto has the oldest surface, Ganymede has some younger areas and some older areas, Europa has a younger surface (fractured and icy) and Lo has a very young face (no impact craters)
What type of heating drives all geological heating on Jupiter’s moons?
Tidal Heating
What feature distinguishes Iapetus (Saturn’s moon)?
One side is jet black (possibly dust from another moon, Phoboe) and the other side is bright (water ice)
What feature distinguishes Encleadus (Saturn’s moon)?
It has plumes (possibly of water) as the result of continuous heating and due to long lived isotopes and tidal forces
What is thought to be the origin of Triton (Moon of Neptune) and Pluto?
Thought to both have originally been members of the Kuiper Belt
What is the approximate surface area of Mercury?
> 3Ga
Why cant small meteorites reach the surface of Venus?
These small meteorites cannot penetrate the atmosphere
Why is the surface of Venus so young?
There is little erosion but there is much erasure from volcanoes
Why is the Earth’s crater density lower than that of the Moon?
Because small craters are eroded
Which Marian hemisphere is “old and which is “young”?
The south is the “old” half and the north is the “young” half
What evidence for the past presence of water do we have on Mars?
We can see splash craters, signs of water erosion, and craters that seemed to have formed in mud
