Assignment #8
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Case Western Reserve University *
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Dec 6, 2023
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Assignment #8
(1) CRATERING
When a meteorite hits one of the terrestrial planets it makes a crater with a
diameter of about 15 times the diameter of the impactor. Use this number to
estimate the size of the impactor that made the following four craters:
(1 pt.) (a)
During the Apollo program the astronauts found lots of craters
about 500 meters in diameter.
According to the x10 to x20 conversion factor from the book, the size of the
impactor would between 500/20 and 500/10, which is between 25m and
50m.
(1 pt.) (b)
Crater C.Bach on Mercury is a double ringed crater about 100 km
across.
100km/20=5km,
100km/10=10km,
Therefore the impactor is between 5km and 10km.
(1 pt.) (c)
Mercury's largest craters, other than the Caloris Basin, are about
625 km across.
625km/20=31.25km
625km/10=62.5km,
So the impactor is between 31.25km and 62.5km.
(1 pt.) (d)
The Barranger Meteor Crater in Arizona is 1.2 kilometers in
diameter.
1.2km/20=0.06km
1.2km/10=0.12km,
So the impactor is between 0.06km and 0.12km.
(1 pt.) (e)
The largest craters on the moon, called maria, look like "seas".
What material flooded these craters?
The material flooded these craters is molten lava from the cores of the
moon.
(2 pts.) (f)
Your textbook discusses the differences between the northern
hemisphere and the southern hemisphere of Mars. Explain: (1) Which
surface is older? (2) What evidence, what observations, allows us to
determine which surface is older?
The southern hemisphere of Mars is older.
Because the southern hemisphere has more impact craters than the northern
hemisphere. Besides, the northern hemisphere is much smoother.
(2 pts.) (g)
How do we know that the rate of cratering on the Moon changed
dramatically about 3.8-3.9 billion years ago? In other words, what is the
evidence which leads us to this conclusion? (Give a brief but clear
explanation in about 3-5 sentences).
Because of the tectonics. The moon has not had tectonics for billions of
years, which means most of the rocks on the moon can stay very long. So
the cratering on the moon has time to form and, especially, stay put for
billions years.
(2) TECTONICS
(6 pts.)
In another solar system, we discover two terrestrial planets with
very different levels of tectonic activity. One planet has lots of tectonic
activity, while the other has almost no tectonics at all. What could cause this
difference? Propose two hypotheses and explain exactly how each
hypothesis could account for this difference.
Hypotheses 1: the planet with more tectonic activity may have more water
on the surface than the other. The constant heating and cooling processes of
the water will have impact on the crust of the earth, which causes them to
move.
Hypotheses 2: the planet with less tectonic activity may have sort of molten
core, the planet can be cooled off and solidified, which result in the thicker
planet crust.
(3) EROSION
(4 pts.)
Today we see runoff channels on the surface of Mars that are very
similar to those created by rivers here on Earth. What do these tell us about
the atmosphere of Mars, either now or in the past.
Since the runoff channels on the surface of Mars are found, the Mars has
atmosphere in the past. However, there is no atmosphere exist in the Mars
because of the lack of water.
(4) INTERIORS
Say we discover two new planets -- Sram and Noom. They are both believed
to have a core of rock surrounded by a mantle of ice. They are the same size
but Sram has a mean density of 1500 kg/m^3 and Noom has a density of
2600 kg/m^3.
(3 pts.) (a)
Which has the thinner mantle of ice? Explain why.
Noom has the thinner mantle of ice. Because the ice has lower density than
rock, the planet with higher density must have higher ratio of rock. The
Noom has higher density which means it has higher ratio of rock, in other
word, thinner mantle of ice.
(2 pts.) (b)
Which is expected to have greater radioactivity heating the
interior? Explain why.
Noom has large core, so more heavier atom mass might be produced during
nuclear fission process in planet Noom. Meanwhile, the thinner mantle ice
indicates more heat might be released out that cause greater radioactivity
heating of the interior.
(2 pts.) (c)
Yrucrem has the same mean density as Sram but Yrucrem has a
radius twice that of Sram. Which planet's interior will have cooled faster?
Sram will have cooled faster. Because the smaller planets have larger
specific surface area (surface area to volume ratio)
(3 pts.) (d)
What would be the evidence that you would look for on the
surfaces of Sram and Yrucrem to confirm your hypothesis of which planet
had cooled first?
I assume we can observe and compare the crater density on the planet. The
planet with denser crater may cool first since only the surface is frozen, the
crater can form.
(5) CRATERS
(8 pts.)
In the distant future, a space probe exploring another solar system
takes pictures of the surfaces of two terrestrial planets which are very close
to each other. One terrestrial planet is densely covered with craters, while
the other has only a few craters over its entire surface. Propose four
different hypotheses to account for this difference, and in each case explain
why your hypothesis would lead to a difference in the quantity of craters.
Hypothesis 1: the planet with less craters may have more active tectonic
plate than the other. The more active the tectonic plate is, the easier the
craters would be smashed.
Hypothesis 2: the planet with less craters may have atmosphere while the
other doesn’t have. The atmosphere act as a barrier of the planet toward the
objects coming from outside, which cause the friction and reduce the size
and speed of the objects entering the planet.
Hypothesis 3: the planet with less craters may have water while the other
doesn’t have. Since the water cause erosion which make it difficult to stay
put in a long time.
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(6) Stars
(3 pts.)
How many star are in our solar system?
There is only one star, which is the sun, in our solar system.