Chapter 8

25 July 2022
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question
The best way to find the exact distance to the Moon is to:
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bounce lasers off the retroreflectors left on the surface by the Apollo landings.
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Mercury is very hard to observe from Earth because:
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it never gets more than 28 degrees from the Sun's glare.
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An atmosphere can escape a planet if the escape velocity is six times the average molecular speed at that temperature.
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true
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Mercury experiences extreme high and low temperatures between night and day because:
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it has no true atmosphere to moderate temperatures over the globe.
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How do the atmospheres of the Moon and Mercury compare?
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Neither body has a permanent true atmosphere.
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Which of the following is NOT a factor in determining whether a body in the solar system retains an atmosphere?
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rotation rate
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One of the effects of Mercury's very slow spin is:
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extreme variations in its surface temperature.
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Mercury has the widest variation in surface temperatures between night and day of any planet in the solar system.
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true
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The lunar mare are found:
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almost entirely on Earth side, where the crust was thinner.
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The youngest features visible with telescopes on the Moon are:
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the craters sitting atop the mare.
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The lunar mare are radioactively dated at:
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3.9-3.2 billion years old, forming after most of the bombardment was over.
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The oldest known features of Mercury's surface formed:
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just under 4 billion years ago.
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The lunar mare radioactively date back to 4.6 billion years, at the origin of the Moon, hence their dark color due to this aging.
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false
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Difference between maria and highlands
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The maria and highlands have distinctive appearances. The maria are dark and smooth, while the highlands are light-colored and rough.
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Maria characteristics
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-low elevations -flat regions -few craters
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Highland characteristics
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-mountainous regions -high elevations -highly cratered
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To measure how Mercury spins, astronomers sent ________ to Mercury and used the Doppler shift to determine how fast it was rotating.
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radar beams
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Which statement about the rotations of the Moon and Mercury is FALSE?
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Like our Moon, Mercury does not rotate at all, keeping the same side facing the Sun.
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What causes Mercury's 3:2 spin-orbit resonance?
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-the planet's very eccentric orbit -the planet's closeness to the Sun -the planet's high density -tidal torques operating on the planet -All of the above are factors.
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What is true of the Moon's orbital and rotational periods?
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they are equal
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The orbit of Mercury is more elliptical than that of any other terrestrial planet.
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true
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Two Mercury years are the same length as three Mercury sidereal days.
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true
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Our Moon is in a 1:1 synch, with a lunar rotation equaling an Earth year.
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false
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The chief erosive agent now on the Moon is:
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the rain of micrometeorites chewing up the regolith.
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The rate of cratering in the lunar highlands shows us that
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they range from 4.6-4.4 billion years old, on average.
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Which type of feature is the best evidence of lunar volcanism?
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rilles associated with lava flows accompanying the mare formation
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The spacecraft which reveal the possibility of lunar ice are:
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Clementine and Lunar Prospector.
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Few of the Moon's craters are actually due to volcanism, as was widely thought prior to Apollo.
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true
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The most recent features on the Moon's surface are the bright rayed craters like Copernicus, sitting atop the older mare flows.
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true
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Ice has been detected near the poles of both the Moon and Mercury.
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true
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Mercury's surface most resembles that of which other body?
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moon
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The hollows on Mercury are:
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clusters of depressions found near the center of impact craters.
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Mercury and the Moon appear similar, but we note that:
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-the lunar mare are darker than Mercury's intercrater plains. -Mercury does not always keep the same face toward the Sun, while the Moon does have the Earthside always facing us. -Mercury has "weird terrain" opposite its huge Caloris Basin. -Mercury has striking lobate scarps due to the shrinking of its core. -All of the above are correct.
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Mercury's surface most resembles which of these?
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the lunar far side
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The Moon's huge Mare Orientale basin has a twin on Mercury named:
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Caloris.
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Mercury has "weird terrain" directly opposite its huge Caloris Impact Basin.
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true
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Caloris is well named, for at every perihelion, it faces the Sun directly.
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true
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Moonquakes on the Moon were detected by:
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the seismographs left these by the Apollo astronauts.
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How does Mercury's magnetic field compare to our own?
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It is 1/100th as strong as ours, but does deflect the solar wind to some degree.
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The presence of a Mercurian magnetic field surprised the planetary scientists on the Mariner 10 team because:
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The dynamo theory predicted that Mercury was spinning too slowly for one.
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Mercury's magnetic field is thought to be due to:
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dynamo action, like the Earth's magnetic field.
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Relative to the size of the planet, Mercury has the largest core of any planet.
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true
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Mercury's magnetic field is surprisingly comparable to the Earth's field in strength.
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false
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Which of these theories seems to best explain the Moon's origin?
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Impact Theory
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Which of these would support the capture theory of the Moon's origin?
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the retrograde orbit and large orbital inclination of Neptune's moon Triton
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Earth is the only terrestrial planet with a large, spherical Moon. Many theories have been proposed to explain this somewhat unusual Earth-Moon system. Which of the following are NOT theories proposed to explain the Moon's formation?
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spin-off
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According to the __________, Earth and the Moon formed at about the same time out of the same pre-planetary matter.
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coformation (or sister) theory
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The _________ states that the Moon formed far from Earth and later became gravitationally bound by Earth after a close encounter.
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capture theory
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A glancing collision between a large, mars-sized object and a youthful, molten Earth led to formation of the moon according to the:
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impact theory
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Coformation theory
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The moon and earth should have very similar compositions
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Capture theory
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-The moon and the earth should have very different compositions -mathematical models would need to predict that the capture of a moon-sized satellite would be likely in Earth's early history
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Impact theory
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-Earth and the Moon should have similar mantles and dissimilar cores. -Computer simulations should predict that a collision between Earth and a Mars-sized object would produce a Moon-sized satellite with a stable orbit.
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Several observations and experiments have helped determine the validity of the theories of Moon formation:
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-Earth has a large iron core, but the Moon does not. -The mantles of Earth and the Moon have similar compositions. -Computer simulations predict that a collision between Earth and a Mars-sized object would produce a Moon-sized satellite with a stable orbit.
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The steps of the impact theory
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According to the impact theory, a glancing collision between a Mars-sized object and Earth led to the formation of the Moon. The iron core of Earth had formed before this collision, leading to the similarity between the composition of the Moon and Earth's mantle. After the collision, any iron core of the Mars-sized object would have been left behind on Earth and eventually merged with Earth's core. The Moon then formed out of the debris thrown into space by the collision.
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The cratering of the lunar highlands shows us:
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they are older than the smoother maria.
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Mercury's evolution was different from the Moon's because:
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dense Mercury had an iron core that shrank, creating the lobate scarps.
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Astronomers believe that the Moon did not differentiate to the same degree as Earth because:
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the less dense and smaller Moon did not have as much radioactivity as the larger Earth in its core.
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the Moon's mass is one-eightieth that of Earth, and the lunar radius is one-fourth Earth's radius. On the basis of these figures, calculate the total weight on the Moon of a 100-kg astronaut with a 50-kg space suit and backpack, relative to his weight on Earth.
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FMoon/FEarth = 0.2
question
Assume that a planet will have lost its initial atmosphere by the present time if the average molecular speed exceeds one-sixth of the escape speed (see More Precisely 8-1 in the textbook). What would Mercury's mass have to be in order for it to still have a nitrogen atmosphere? The molecular weight of nitrogen is 28.
answer
Mmin = 4.2Ɨ1023 kg