The Solar System Assignment#4 Name _______________________
I.D.#
_______________________
·
Circle the
correct multiple choice answer.
·
Use back
of page for numerical calculations if necessary … but
·
Write
final numerical answer on underline provided with question.
· Use space provided to answer non-numerical questions.
Chapter 10 Moon
1. Why are the oldest Moon rocks older than
Earth’s oldest rocks, even though both worlds formed at nearly the same time?
(a)
The Moon
is colder than Earth so the radioactive decay process used for measuring
elapsed time runs slower on the Moon.
(b)
The
basic premise is incorrect … the Earth was created only 6000 years ago and the
Moon has been around much longer than that.
(c)
The Moon has no atmosphere, which would protect
it surface from large meteor strikes that cover its surface with old rock.
(d)
The Moon has not undergone much geological
activity since it formed. It is small
and it cooled rapidly. Hence, many of its surface rocks have not been subject
to geologic modification as has happened with Earth rocks.
(e)
The Earth’s oldest rocks haven’t been found yet.
2. How do we know that the lunar maria were
formed after the lunar highlands?
(a)
Seas
always form after land.
(b)
We don’t
know this for a fact.
(c)
The maria are all located on the side
of the Moon closest to Earth where they were protected from meteor bombardment.
(d)
The maria
have few craters; hence, they must have formed after the early period of meteor
bombardment had pretty well died out.
(e)
Obviously you cannot have lowlands until
highlands have formed to define them.
3. What is the dominant cause of the tides on
Earth?
(a) The Moon’s differential gravitational force tends to stretch the Earth along … and compress it perpendicular to … a line directed toward the Moon. Since 70% of the Earth’s surface is covered with water, these differential forces create two bulges in the water along a line, more or less directed to the Moon.
(b) The Sun has the greatest effect on the tides on Earth because it is the largest body by far in the solar system.
(c) When large asteroids strike the Earth, they cause its oceans to slosh around.
(d) The rapid rotation of the Earth flings the water out sideways, perpendicular to its axis of rotation.
(e) The tides are lower at night due to cooling and higher at day due to heating of the oceans.
4. Why do most scientists favor the “collisional ejection theory” for the formation of the Moon?
(a)
The Moon is heavily cratered, which are remnants
of all the rocks that fell onto its surface after the collision that ejected it
from Earth’s surface.
(b)
The Moon
is made of green cheese and the impact site that created it has been found in
(c)
The Moon is has
a lot of water, which must have come from Earth after some of Earth’s
oceans were thrown into orbit by the impact of the large body. The water was
part of the material out of which the Moon then coalesced.
(d)
If it
formed by collision of a large planetesimal with Earth, it would be much
smaller than Earth … which it is.
(e)
The Moon is made of material that is similar to
the composition of the Earth’s crust; also measurements made on the South Pole-Aitken basin of the Moon where a large impact exposed rock
down to a depth of 12 km show that the Moon is deficient in material that
comprises the Earth’s core and mantle.
Chapter
11 Mercury
5. Why doesn’t Mercury have a substantial
atmosphere?
(a)
It is not close enough to the Sun to capture any
of its atmospheric gasses.
(b)
The
element Mercury (after which the planet was named) that covers Mercury’s
surface is so toxic that it corrodes any molecules in an atmosphere.
(c)
It is a small planet with a weak surface gravity
and it is close to the Sun so it is very hot.
These two factors cause any gas molecules to move so rapidly that they
would soon escape the planet.
(d)
It does
… but it is invisible from Earth.
(e)
Mercury’s
surprising magnetic field actually funnels solar wind particles strongly into
its polar regions. These charged
particles soon spread around the planet’s surface and provide an electrical
coating that repels any atmosphere into outer space.
6. What is the evidence that supports the
hypothesis that Mercury has an iron core that is large compared to its overall
size?
(a)
Mercury has a very large density for such a
small planet, almost equal to the Earth’s density. Thus, it must be made of
heavier elements on the average.
(b)
Mercury’s
orbit is fairly elliptical and when it approaches perihelion, its light
elements get stripped away by intense solar wind.
(c)
Mercury rotates so slowly that the material that makes it up doesn’t get flung away from
its axis so even though its small, it’s almost as dense as Earth.
(d)
Mercury’s gravity is weaker than Earth’s so only
material that could stay gravitationally bound to it are heavy elements like Fe
and Ni.
(e)
Mercury is so close to the Sun that intense heat
scours its surface of light elements, leaving only heavy ones.
Venus
7. The greenhouse effect on Earth helps warm its surface to an extent sufficient to keep most of the Earth’s surface water liquid, but the process did not “runaway” … ultimately vaporizing the water … as it did on Venus. There are a variety of reasons why Earth is so fortunate: _______
(a) Earth has plate tectonics, which recycles CO2 stored in carbonate rock back into the atmosphere, acting as a temperature regulator.
(b) Earth is a little more massive and a little cooler than Venus. Therefore, H2O molecules that evaporate from any surface liquid do not rise as high in its atmosphere as they do on Venus.
(c) Earth developed a troposphere due to buildup of an O3 layer about 20-40 km high. Ozone absorbs ultraviolet and the resulting heating of the atmosphere at this altitude causes a temperature inversion that keeps planetary gasses such as H2O vapor trapped down low to the surface.
(d) Earth is further from the Sun and the intensity of ultraviolet light incident on its atmosphere is less than on Venus.
(e) All of the above.
8. Evidence indicates that once there were
oceans on Venus. They are not there
now. In fact, its surface is incredibly
dry. What happened to its oceans?
(a)
The molten lava outflow of intense volcanic
activity on early Venus boiled the oceans away.
(b)
About
800 million years ago, pressure build up due to heat generated in the Venusian
core, fractured its crust on a global scale.
The sudden release of pent-up heat evaporated its oceans.
(c)
The oceans evaporated because of the increasing
energy output of the aging Sun and the onset of a runaway greenhouse effect.
Evaporating H2O molecules rose high into unsheltered regions of its
atmosphere where they were broken apart into hydrogen and oxygen by intense
ultraviolet light (photo-dissociation).
The hydrogen escaped into space leaving almost none to re-combine with
oxygen to make water.
(d)
A large
Mars-sized planetesimal passed very close to Venus exerting large tidal forces
on it which stripped it of its water.
(e)
The
enormous magnetic field of Venus traps its water molecules in a “Van
Allen-like” belt around the planet.
9. Why is there so much carbon dioxide in Venus’
atmosphere?
(a)
Plant
life never developed on Venus which could remove the CO2 from
its atmosphere.
(b)
An
extinct Venusian civilization burnt all its fossil fuels which released
enormous amounts of CO2 into its atmosphere.
(c)
Water holds a lot of CO2 in dissolved
form. As Venus lost its oceans, dissolved CO2 was released into its
atmosphere which caused increased surface heating and increased rate of
evaporation and so on … in other words a runaway greenhouse effect.
(d)
Venus doesn’t have any rock like on Earth, which
“locks up” CO2.
(e)
Constant intense volcanic activity on Venus,
much more intense than on Earth, continually ejects large quantities of CO2
into its atmosphere.
10. What is the evidence for … or against …
active plate tectonics on Venus in its recent past?
(a)
Venus has long strings of volcanoes, indicative
of subduction zones formed by the collision of tectonic plates.
(b)
The
surface of Venus is covered with earthquake-generated cracks and deep rifts,
indicative of plate tectonics.
(c)
Venus has a large number of continents, among
them Ishtar and Aphrodite, which is evidence that its surface is fractured by
plate tectonics.
(d)
There is no evidence of continental drift. There is no evidence of subduction zones;
volcanoes do not appear in long chains; they occur only as hot spot volcanoes …
not due to collisions between crustal plates. There are no long faults,
indicative of crustal plate spreading.
(e)
When recent Magellan images of Venus are
compared with telescopic images obtained in the late 1800’s, it can be seen
that the spacing between the continents, Ishtar and Aphrodite has increased,
evidence of recent plate tectonics.
11. Given that Venus’ sidereal rotation period is
243.01 days and its orbital period is 224.70 days, develop a formula and use it
to show that a solar day on Venus lasts 116.8 days. (Hint: the formula relating Venus’ solar day to its sidereal rotation
period and orbital period is similar to the first formula in Box 4-1. Draw a picture! It’s easiest to work things out from the
perspective of a hypothetical Venusian observer. The accompanying picture shows the Sun moving
counter-clockwise (CCW) around Venus (from the Venusian observer’s point of
view) while Venus rotates clockwise (CW).
Start things out with the Sun at position 1 due overhead at noon (Venus
time). Our hypothetical observer rotates
CW at a rate
where TV (= 243.01 days)
is the rotational period of Venus. The
Sun revolves (apparently) around Venus at a rate
where P (= 224.70 days) is the
sidereal period of Venus around the Sun.
Now, after one Venusian solar day (which we’ll call S) elapses, Venus
will have rotated through the angle 
and the Sun will be in position 2 (see figure) relative to
the background stars, having rotated through the angle
. The observer will
again see the Sun directly overhead. Now, do the math to calculate the length
of the solar day …
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12. Section 11-2 in your text describes the
relationship between the length of Venus’ synodic period and the length of an
apparent solar day on Venus. Using this, explain why at each successive inferior conjunction the same side of Venus is
turned toward the Earth as it was before.
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13. Consider a hypothetical planet the same size
and in the same orbit as Venus. Further
suppose that this planet’s atmosphere was opaque
to visible light but transparent to
infrared. Would this planet be hotter,
or colder, than Venus … and why?
(a)
It would
be much hotter because its opaque atmosphere would trap all the heat that it
tried to radiate away.
(b)
It would
be much colder because no light could get to its surface through its opaque
atmosphere.
(c)
It would
be much hotter because the planet’s atmosphere would let all the infrared light
in from the Sun and it would really heat up.
(d)
It would
be much colder because any surface water would pick up no sunlight and
therefore would freeze.
(e)
It would be much colder because visible light
from the Sun would not make it through the planet’s atmosphere, but light at
other wavelengths would. Since visible light contains most of the energy
incident on the planet, it would not be warmed nearly as much as Venus. Furthermore, since infrared radiation could
easily get through the planet’s atmosphere, it would not trap any of its
radiated heat, i.e., it would have no greenhouse effect to help warm it.
Mars
14. Why does Mars have the longest synodic period of all the superior planets, even though its sidereal period is the shortest, only 687 days?
(a) Mars moves slower in it orbit than any other superior planet.
(b) Mars has a thin atmosphere unlike Earth which has a thick one that acts as a tremendous drag on its motion, thus making it difficult to catch up to it.
(c) Frequent volcanic eruptions on Earth act like retro-rockets which slow it down relative to Mars.
(d) Any superior planet will have a synodic period greater than 1 year. Mars is the closest superior planet and its sidereal period is closest to Earth’s. Mars moves faster in its orbit than any other superior planet. Thus, it takes Earth longer to “catch up” to Mars than any other superior planet.
(e) Earth is always in the middle of a retrograde loop when it catches up to Mars, thus delaying the time when opposition occurs.
15. Mars lacks certain geologic features that
would be expected to be present on any planet where plate tectonics would have
helped shape its surface. Such missing
features would be ________.
(a)
Mars does not have a global network of rifts and
subduction zones that you see along tectonic plate boundaries on Earth.
(b)
The Martian surface is perfectly smooth
exhibiting no evidence of any geologic activity.
(c)
Mars has no oceans.
(d)
Mars has no atmosphere.
(e)
Mars has
no large moon.
16. Why is it reasonable to assume that the
primordial atmospheres of Venus, Earth and Mars were roughly the same?
(a)
They all
rotate rather slowly compared to the Jovian planets and therefore would be
expected to have accumulated similar atmospheric constituents.
(b)
All
things in the universe are made of the same fundamental building blocks.
(c)
These terrestrial planets all formed the same
way in very similar environments --- by condensation and accretion out of
almost identical proportions of elements and compounds. Furthermore, they all suffered similar
asteroid and cometary bombardment and at least early
in the history exhibited active volcanism.
Thus, one would guess that their primordial atmospheres were almost
identical --- probably rich in CO2 and H2O.
(d)
...like Carl Sagan said, “We are all
star-stuff!” That includes planetary
atmospheres as well.
(e)
All three either have water on their surface or
show evidence of once having water. The
same should apply to their atmospheres.
17. Mars almost certainly had an abundant
supply of H2O early in its history, just like Earth. Mars was warmer then and volcanic activity
was more prevalent as Mars was venting its heat of formation, heat generated by
widespread comet and asteroid bombardment and core radioactivity-generated
heat. We would expect, then, that it was very much like Earth during its early
existence and, in particular, that its
primordial atmosphere probably started out with approximately the same chemical
composition as Earth. Moreover, Mars is only 50% further from the Sun than
Earth. Nonetheless, the future evolution
of the Martian atmosphere took a different path than Earth’s. Below is a
possible reason why. Which one is most
likely?
(a) Mars has a strong magnetic field. Therefore, much of its CO2 dominated atmosphere was protected from being stripped away by solar wind particles.
(b) Early on, CO2 was injected into the Martian atmosphere by volcanic activity, much like on Earth, and this generated a greenhouse effect sufficient to keep surface water in the liquid state --- for awhile. However, the early Martian oceans dissolved some CO2 and rainfall washed CO2 from the atmosphere, reducing the greenhouse effect that helped maintain its water in the liquid state. So, Mars froze over, and some CO2 remained in its atmosphere since there was no more liquid water to absorb it.
(c) Early “cyanobacteria-type” microbial life on Mars absorbed much of the CO2 in its atmosphere, reducing the greenhouse effect enough that it “froze over.” Everything died, and most of its CO2 is now locked up in the planet’s rock.
(d) The early photosynthetic plant life that emerged on Mars absorbed most of the CO2 that it needed for a strong greenhouse to keep water liquid. Mars, then froze over and the plants died.
(e) Mars has no spinning magnetic field, which tends to throw off atmospheric atoms into space. Thus, it lost the greenhouse gasses needed to keep water liquid.
18. Why is Mars red?
(a)
Its
surface is covered with sandstone, much like the red rock in
(b)
Its
atmosphere absorbs light mostly in the blue – green – yellow region of the
visible spectrum so the sunlight that is reflected from it is reddish in color.
(c)
Mars is
never seen more than 46 degrees above the horizon and therefore light from it
travels though a lot of Earth’s atmosphere. The blue light is scattered; red
light preferentially gets through and thus Mars looks reddish, an effect much
like we see when the Sun sets.
(d)
The CO2
in the Martian atmosphere absorbs infrared and scatters red light, so Mars just
appears to be red.
(e)
Its surface rock is covered with rust ---
basically iron oxide dust. Much of the O
that was generated by the breakup of H2O vapor in the early history
of Mars, reacted with surface rock, rich in Fe to form the iron oxides.
19. Mars Global Surveyor (MGS) was placed in a
polar orbit about Mars in 1997. Its orbital period was 117 minutes. The mass of Mars is MMars
= 6.42 x 10 23 kg and its diameter is DMars
= 6,794 km.
(a)
Calculate
the radius of MGS’ orbit and determine how far MGS is above the Martian
surface. _____________________
(b)
Why was
MGS placed in polar orbit rather than, say, a geosynchronous orbit, much like
the communication satellites that orbit Earth
(Hint: see the formula in Chapter 4
p. 81 of your text)
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20. The two Martian moons, Phobos and Deimos, are not spheres like our Moon. Why?
(a)
Back
during the Hadean era (the period of heavy bombardment that lasted from about
(b)
They are
made predominately of rock, which always takes on an irregular shape.
(c)
Phobos and Deimos are
most likely small, captured asteroids.
They are small enough that gravitation is not the dominant force that
shapes them. The electromagnetic forces,
or atomic forces, are responsible for binding matter together and in the case
of rock, the resulting shape that these atomic forces generate is irregular. When rocky objects are large enough, gravitation
overwhelms the atomic forces and the shape becomes spherical as is the case
with our Moon.
(d)
Initially,
Mars had a single larger, spherically shaped moon in orbit about it, much like
Earth’s. But during the period of heavy
bombardment, it was struck by a passing asteroid and fractured into two
smaller, irregularly shaped moons.
(e)
none of
the above are good explanations.