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Astronomy Midterm #2
Terms in this set (144)
Rank the five terrestrial worlds in order of size from smallest to largest.
Moon, Mercury, Mars, Venus, Earth
Under what circumstances can differentiation occur in a planet?
The planet must have a molten interior.
The core, mantle, and crust of a planet primarily have differences in their
The lithosphere of a planet is the layer that consists of
the rigid rocky material of the crust and uppermost portion of the mantle.
What is the most important factor that determines the thickness of a planet's lithosphere?
The terrestrial planet cores contain mostly metal because
metals sank to the center during a time when the interiors were molten throughout.
What process initially caused the terrestrial planets to be hot enough to be entirely molten?
Which of the following best describes convection?
It is the process in which warm material expands and rises while cool material contracts and
What are the circumstances under which convection can occur in a substance?
when the substance is strongly heated from underneath
The two principal sources for the internal heating of terrestrial planets are
accretion and radioactivity.
Why does the interior of a large planet take longer to cool than the interior of a smaller
Small planets have a larger surface area-to-volume ratio than larger planets.
Which of the terrestrial worlds has the strongest magnetic field?
Why does Earth have the strongest magnetic field among the terrestrial worlds?
It is the only one that has both a molten metallic outer core and reasonably rapid rotation.
Which of the following most likely explains why Venus does not have a strong magnetic
Its rotation is too slow.
What are the conditions necessary for a terrestrial planet to have a strong magnetic field?
both a molten metallic core and reasonably fast rotation
Which of the following has virtually no effect on the internal structure of a planet?
its magnetic field
Which of the following does not have a major effect in shaping planetary surfaces?
Approximately how large is an impact crater compared to the size of the impactor?
10 times larger
Approximately how deep is an impact crater compared to its width?
The relatively few craters that we see within the lunar maria
were formed by impacts that occurred after those that formed most of the craters in the lunar
When we see a region of a planet that is not as heavily cratered as other regions, we conclude
the surface in the region is younger than the surface in more heavily cratered regions.
Volcanism is more likely on a planet that
has high internal temperatures.
What type of stresses broke Earth's lithosphere into plates?
the circulation of convection cells in the mantle, which dragged against the lithosphere
Which of the following best describes tectonics?
the disruption of a planet's lithosphere by internal stresses
Which of the following best describes erosion?
the wearing down or building up of geological features by wind, water, ice, and other
phenomena of planetary weather
Which of the following best describes volcanism?
the eruption of molten rock from a planet's interior to its surface
Which of the following best describes impact cratering?
the excavation of bowl-shaped depressions by asteroids or comets striking a planet's surface
A planet is most likely to have tectonic activity if it has
high internal temperature.
What kind of surface features may result from tectonics?
all of the above
How did the lunar maria form?
Large impacts fractured the Moon's lithosphere, allowing lava to fill the impact basins.
The Caloris Basin on Mercury covers a large region of the planet, but few craters have
formed on top of it. From this we conclude that
the Caloris Basin formed toward the end of the solar system's period of heavy bombardment.
Why do we think Mercury has so many tremendous cliffs?
They were probably formed by tectonic stresses when the entire planet shrank as its interior
The Tharsis Bulge on Mars is most likely the result of
rising material in the mantle of Mars.
How have we been able to construct detailed maps of surface features on Venus?
by using radar from spacecraft that were sent to orbit Venus
What is the most likely reason Venus does not experience plate tectonics like Earth?
Venus's lithosphere is stronger and thicker than Earth's.
Which of the following show evidence of ancient river beds?
Why is mars red?
Its surface rocks were rusted by oxygen.
Where is most of the water on Mars?
in its polar caps and subsurface ground ice
Spacecraft have landed on all the terrestrial worlds except
Which of the following worlds has the thickest atmosphere?
Which of the following planets has the thinnest atmosphere?
Suppose Earth's atmosphere had no greenhouse gases. This would cause Earth's average
surface temperature to be
well below the freezing point of water.
What are greenhouse gases?
gases that absorb infrared light
Which of the following gases best absorbs ultraviolet light?
Sunsets and sunrises often appear red because
sunlight must pass through more atmosphere, which scatters the shorter wavelengths more
than the longer wavelengths, allowing more red light to reach your eye.
There are no auroras on Venus because it
lacks a strong magnetic field.
How is the atmosphere of a planet affected by its rotation rate?
Faster rotation rates produce stronger winds.
Why does Mars have more extreme seasons than Earth?
because it has a more eccentric orbit
In what ways is Earth different from the other terrestrial planets?
All of the above are true.
Why do most scientists accept the claim that climate change is being caused by human
all of the above
What process has shaped Earth's surface more than any other?
Why is continental crust lower in density than seafloor crust?
Continental crust is made from remelted seafloor crust, and the lower density material melts
How fast do tectonic plates move on Earth?
a few centimeters per year
What drives the motion of the continental plates on Earth?
convection cells in the mantle
Ridges in the middle of the ocean are places where
hot mantle material rises upward and spreads sideways, pushing the plates apart.
Deep trenches in the ocean mark places where
one plate slides under another, returning older crust to the mantle.
Which of the following is not directly a product of outgassing?
Which of the following statements about the greenhouse effect is true?
All of the above are true.
Of the four gases CO2, H2O, N2, and O2, which are greenhouse gases?
CO2 and H2O
What are fossil fuels?
the carbon-rich remains of plants that died millions of years ago
Why does the burning of fossil fuels increase the greenhouse effect on Earth?
Burning releases carbon dioxide into the atmosphere.
Considering just the effects of the carbon dioxide cycle, if the Earth were to warm up a bit,
what would happen?
More evaporation and rainfall would reduce the atmospheric CO2 levels, and the greenhouse
effect would weaken.
Which of the following can act like a long-term "thermostat" for the Earth's average
heat stored in the Earth's liquid core
Why would the weather become more severe as the greenhouse effect increased?
Warming would increase the evaporation of the oceans, leading to more water in the
atmosphere and more frequent and severe storms.
Earth's atmosphere contains only small amounts of carbon dioxide because
carbon dioxide dissolves in water, and most of it is now contained in the oceans and
According to current climate models and given the current emission rate of carbon dioxide,
how much will the Earth's average temperature increase by the end of this century?
How is carbon dioxide initially removed from the atmosphere?
dissolving carbon dioxide in water
Given the rate at which human activity is increasing CO2 levels, why can we not depend on
the natural CO2 cycle to prevent global warming?
It operates too slowly.
Mars' atmosphere is mostly carbon dioxide. Why does it not experience a runaway
greenhouse effect like Venus?
Mars' atmosphere is too thin.
In the greenhouse effect, what is the direct cause of extra heating of the Earth's surface?
Additional carbon dioxide makes the atmosphere more opaque to infrared light, trapping more
of the infrared light emitted by Earth.
The greenhouse effect makes Earth warmer than it would be otherwise by about
The footprints left on the moon by the Apollo astronauts will likely last for
millions of years.
Which of these upcoming observations will help test the idea that Mars' atmosphere thinned
due to interactions with the solar wind?
The upcoming MAVEN orbiter will measure present-day gas loss from Mars' atmosphere.
How does the Sun's mass compare with that of the planets?
It is about a thousand times more massive than all the planets combined.
Where does nuclear fusion occur in the Sun?
in its core
Which planet has the highest average surface temperature, and why?
Venus, because of its dense carbon dioxide atmosphere
Which object, other than Earth, has visible water on its surface?
none of the above
Which of the following observations indicates that Mars had a warmer, thicker atmosphere in
There are dried-up riverbeds on Mars.
Which planet has a ring system?
all of the above
Which planet could an astronaut visit without the need for a spacesuit (and survive)?
None; an astronaut would need a spacesuit to survive a visit to any other planet in the solar
Which planet has the most extreme temperature difference between day and night?
Which is the densest planet in the solar system?
The planet with a density most similar to Earth is
Which of the following is not a characteristic of the inner planets?
They have substantial atmospheres.
Which of the following is not a characteristic of the outer planets?
They have relatively high densities.
On average, a cupful of which planet would weigh the least?
Which of the following is the only characteristic Pluto shares with the outer planets?
It has multiple moons.
Where are most of the known asteroids found?
between the orbits of Mars and Jupiter
Which of the following is furthest from the Sun?
a comet in the Oort cloud
In what part of the solar system is Pluto found?
the Kuiper belt
What can we conclude from the fact that Neptune's large moon Triton orbits in a direction
opposite to the direction in which Neptune rotates?
Triton must have been captured by Neptune.
Why did the solar nebula heat up as it collapsed?
As the cloud shrank, its gravitational potential energy was converted to thermal energy.
Why did the solar nebula flatten into a disk?
It flattened as a natural consequence of collisions between particles in the nebula, changing
random motions into more orderly ones.
According to our theory of solar system formation, why do all the planets orbit the Sun in the
same direction and in nearly the same plane?
The laws of conservation of energy and conservation of angular momentum ensure that any
rotating, collapsing cloud will end up as a spinning disk.
Which of the following lists the composition of the solar nebula from highest to lowest
percentage of mass?
light gases (H, He), hydrogen compounds (H2O, CH4, NH3), rocks, metals
What percentage of the solar nebula's mass consisted of hydrogen and helium gases?
If the freezing point of all ices was at a much lower temperature, what change would that
imply for the formation of our solar system?
The gas giants would have to form at a larger distance from the sun.
What kind of material in the solar nebula could condense at temperatures as high as 1,500 K,
such as existed in the inner region of the nebula?
What is the origin of the large moons orbiting in the equatorial planes of the jovian planets?
They were formed by condensation and accretion in a disk of gas around the planet.
Observations of young stars (as well as theory) tell us that when the Sun was young, the solar
was stronger than it is today.
Which of the following are relatively unchanged fragments from the early period of planet
building in the solar system?
all of the above
According to our theory of solar system formation, why do we find some exceptions to the
general rules and patterns of the planets?
Most of the exceptions are the result of giant impacts or close gravitational encounters.
Based on our current theory of Earth's formation, the water we drink likely comes from
water bearing planetesimals that impacted Earth.
The heavy bombardment phase of the solar system lasted
a few hundred million years.
Which of the apparent exceptions to the solar nebular theory cannot be explained by a giant
the orbit of Triton in the opposite direction to Neptune's rotation
Which of the following does the solar nebular theory not predict?
the equal number of terrestrial and jovian planets
The age of the solar system can be established by radiometric dating of
the oldest meteorites.
What do meteorites reveal about the solar system?
They reveal that the age of the solar system is approximately 4.6 billion years.
Suppose you find a rock that contains some potassium-40 (half-life of 1.25 billion years).
You measure the amount and determine that there are 5 grams of potassium-40 in the rock. By
measuring the amount of its decay product (argon-40) present in the rock, you realize that there
must have been 40 grams of potassium-40 when the rock solidified. How old is the rock?
3.75 billion years
Every 4.5 billion years, half of the atoms in a sample of uranium-238 will undergo
radioactive decay and become atoms of lead-206. Suppose you lived in another planetary system
around a faraway star and found a meteorite that was originally made of uranium-238, but is now
one-quarter uranium-238 and three-quarters lead-206. What would be your best estimate of that
planetary system's age?
9 billion years
Why can we assume that a rock sample containing argon-40 had none of this isotope when
the rock initially formed?
Argon-40 is a gas that does not combine with other elements, so it would not be present in a
rock when it formed.
Why do Earth rocks have much younger ages than most meteorites?
Most Earth rocks have been melted and reformed since Earth formed from the solar nebula.
Which of the following is the phase of matter in the interior of the Sun?
What is the approximate temperature of the Sun's core?
15 million K
The core of the Sun is
much hotter and much denser than its surface.
Based on its surface temperature of 6,000 K, most photons that leave the Sun's surface lie in
which region of the electromagnetic spectrum?
Sunspots are cooler than the surrounding gas in the photosphere because
strong magnetic fields slow convection and prevent hot plasma from entering the region.
At the time the hypothesis was suggested, what major problem was identified with the idea
that the Sun was powered by gravitational contraction?
This process would power the Sun for only about 25 million years, but geologists already had
evidence the Earth was much older than that.
What keeps the Sun's outer layers from continuing to fall inward in a gravitational collapse?
outward pressure due to super-heated gas
By what process does the Sun generate energy?
By what process do nuclear power plants on the Earth generate energy?
Hydrogen fusion in the Sun requires a temperature (in Kelvin) of
millions of degrees.
At the center of the Sun, nuclear fusion converts hydrogen into
helium, gamma rays, and neutrinos.
How much mass does the Sun lose through nuclear fusion per second?
4 million tons
Suppose you try to bring two protons close together. Because of the electromagnetic force,
the two protons will
repel one another.
What is the only force that can overcome the repulsion between two positively charged
nuclei and bind them together?
the strong force
What would happen to the core of the sun if its temperature rose slightly?
The rate at which fusion occurs would increase, leading to an expansion of the core, which
would in turn cause the temperature to drop back down.
According to this Doppler map of the sun's surface, about how fast is the sun rotating around
at its equator?
about 2,000 m/s
What is shown by the small-scale changes in the shading in the figure above?
vibrations seen at the solar surface
Which of the following is not a method astronomers use to determine the physical conditions
inside the Sun?
observing X-ray images of the solar interior using satellites
Studies of solar vibrations have revealed that
our mathematical models of the solar interior are fairly accurate.
Imagine that you are trying to stop neutrinos with a lead shield. How thick would you need
to make this shield to ensure that it can stop an average neutrino?
about one light-year
Approximately how many neutrinos pass through your body each second?
about a thousand trillion
What is the solution to the solar neutrino problem?
The electron neutrinos created in the Sun's core change into another type of neutrino that we
did not originally detect.
The light radiated from the Sun's surface reaches Earth in about 8 minutes. However, the
energy of this light was released by fusion in the Sun's core about
several hundred thousand years ago.
What are coronal holes?
areas of the corona where magnetic field lines project out into space, allowing charged
particles to escape and form the solar wind
Why do sunspots appear dark?
They are regions that are significantly cooler than the rest of the photosphere.
Which of the following statements about the sunspot cycle is not true?
The rate of nuclear fusion in the Sun peaks about every 11 years.
Which of the following processes is involved in the sunspot cycle?
the winding up of magnetic field lines inside the Sun due to its differential rotation
What observations characterize solar maximum?
There are many sunspots visible on the surface of the Sun.
It takes ________ for the sun to progress through one sunspot cycle from a maximum area
covered with sunspots, to a minimum, and back to a maximum. Refer to the graph above.
about 11 years
Why does the Sun emit neutrinos?
Fusion in the Sun's core creates neutrinos as a byproduct.
If the sun's surface cooled, how would its appearance change?
It would appear more red.
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