Astronomy Midterm 2

According to our basic scenario of solar system formation, why do the jovian planets have numerous large moons?

As the growing jovian planets captured gas from the solar nebula, the gas formed swirling disks around them, and moons formed from condensation accretion within these disks.

Why do asteroids and comets differ in composition?

Asteroids formed inside the frost line, while comets formed outside.

Which of the following is not a real difference between asteroids and comets?

Asteroids orbit the Sun, whereas comets just float randomly around in the Oort cloud.

What is the most important reason why an icy moon is more likely to be geologically active than a rocky moon of the same size?

Ice has a lower melting point than rock

The most volcanically active world in the solar system.

Io

Why are there no impact craters on the surface of Io?

Io did have impact craters but they have all been buried in lava flows.

Why is Io more volcanically active than our moon?

Io has a different internal heat source.

How is Einstein's famous equation, E = mc2, important in understanding the Sun?

It explains the fact that the Sun generates energy to shine by losing some 4 million tons of mass each day.

Why did the solar nebula flatten into a disk?

It flattened as a natural consequence of collisions between particles in the spinning nebula, changing random motions into more orderly ones.

Rank the five terrestrial worlds in order of size from smallest to largest.

Moon, Mercury, Mars, Venus, Earth

What do we conclude if a planet has few impact craters of any size?

Other geological processes have wiped out craters.

What happened during the accretion phase of the early solar system?

Particles grew by colliding and sticking together

What is the primary reason that astronomers suspect that some jovian moons were captured into their current orbits?

Some moons have orbits that are backward (compared to their planet's rotation) or highly inclined to their planet's equator.

Assuming that features you see on Mars are similar to features found on Earth, what would a casual inspection of the interactive photo of Mars lead you to suspect about water on Mars?

Surface water only exists as frozen ice.

According to our present theory of solar system formation, which of the following statements about the growth of terrestrial and jovian planets is not true?

The jovian planets began from planetesimals made only of ice, whereas the terrestrial planets began from planetesimals made only of rock and metal.

According to our theory of solar system formation, which law best explains why the solar nebula spun faster as it shrank in size?

The law of conservation of angular momentum

According to our present theory of solar system formation, how did Earth end up with enough water to make oceans?

The water was brought to the forming Earth by planetesimals that accreted beyond the orbit of Mars.

Which of the following statements about our solar system's terrestrial worlds are true? Their interiors all have a core, mantle, and crust. They all have active volcanoes. They all have surfaces that are heavily cratered today. They are all of nearly the same age. They are all made primarily of rock and metal. They all have lithospheres that extend almost all the way to their cores.

Their interiors all have a core, mantle, and crust. They are all of nearly the same age. They are all made primarily of rock and metal.

A terrestrial world's lithosphere is ________.

a layer of relatively strong, rigid rock, encompassing the crust and part of the mantle

A rocky leftover planetesimal orbiting the Sun is

an asteroid

Leftover planetesimals that formed inside the frost line are known as

asteroids

The bright spherical part of a comet observed when it is close to the Sun is the

coma

The main process by which heat flows upward through the lithosphere is

conduction

Ceres, Pluto, and Eris are all round in shape and classified as

dwarf planets

We could probably learn more about Mars by sending a new spacecraft on a flyby than by any other method of studying the planet.

false

The earthquakes that occur in Southern California generally occur above a

fault

When we say that a liquid has a high viscosity, we mean that it

flows slowly like honey

Robotic spacecraft have different levels of complexity, which contributes to overall cost. Which of the following types of missions are likely to be the cheapest?

flybys

A comet entering the inner solar system from afar will __________.

form a coma and some time later a tail

Hydrogen compounds in the solar system can condense into ices only beyond the

frost line

Which of the following is thought to explain many of the "exceptions to the rules" of our solar system?

giant impacts

Steep-sided stratovolcanoes are made from lava that

has a high viscosity

Shallow-sloped shield volcanoes are made from lava that

has a medium viscosity

Volcanism is more likely on a planet that

has high internal temperatures

The first few hundred million years of the solar system's history were the time of the __________, during which Earth suffered many large impacts.

heavy bombardment

A planet is most likely to have tectonic activity if it has

high internal temp

Ridges in the middle of the ocean are places where

hot mantle material rises upward and spreads sideways, pushing the plates apart.

Old Faithful Geyser at Yellowstone National Park in the United States acquires its energy from a

hot spot

According to our present theory of solar system formation, which of the following lists the major ingredients of the solar nebula in order from the most abundant to the least abundant?

hydrogen and helium gas; hydrogen compounds; rock; metal.

Heat escapes from a planet's surface into space by thermal radiation. Planets radiate almost entirely in the wavelength range of the

infrared

What is the most important factor that determines the thickness, and therefore strength, of the lithosphere?

internal temperature

What fraction of the large moons of the planets orbit in the same direction as their planets rotate?

most

What is the most abundant gas in Titan's atmosphere?

nitrogen

What substances existed as solid flakes within the innermost regions (within about the inner 0.3 AU) of the solar system before planets began to form?

none

The "giant impact hypothesis" refers to the idea that ___________.

our Moon formed when a Mars-size object collided with the young Earth.

Our Moon was most likely formed by a collision between Earth and a Mars-sized

planetesimal

What process has shaped Earth's surface more than any other?

plate tectonics

What substances were found in the innermost regions (within about the inner 0.3 AU) of the solar system before planets began to form?

rocks, metals, hydrogen compounds, hydrogen, and helium, all in gaseous form

The slowly increasing distance between South America and Africa is due to

seafloor spreading

Layered __________ exposed by erosion can be seen when looking at the Grand Canyon in the United States.

sedimentary rock

Which of a planet's fundamental properties has the greatest effect on its level of volcanic and tectonic activity?

size

Mars has two moons that are most similar in character to ____________________.

small asteroids

The era of planet formation ended when the remaining hydrogen and helium gas of the solar nebula was swept into interstellar space by the

solar wind

The extremely deep ocean Marianas Trench is a result of

subduction

The Caloris Basin on Mercury covers a large region of the planet, but few smaller 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.

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 regions was the result of plumes of hot mantle rising in a hot spot within a plate? Japan and the Philippines the islands of Hawaii Alaska's Aleutian Islands the volcano Mount St. Helens all of the above

the islands of Hawaii

Which of the following puzzles in the solar system cannot be explained by a giant impact event?

the orbit of Triton in the opposite direction to Neptune's rotation

What is differentiation in planetary geology?

the process by which gravity separates materials according to density

The lithosphere of a planet is the layer that consists of

the rigid rocky material of the crust and uppermost portion of the mantle.

Very high pressures, like those found deep within planetary interiors, can compress rocks so much that they stay solid even when temperatures are high enough to melt them under ordinary conditions. (T or F)

true

Which two geological processes appear to have been most important in shaping the present surface of Venus?

volcanoes and tectonics

The largest moon in the solar system, this moon has some regions that are heavily cratered other regions that have very few craters.

Ganymede

Which internal heat source still generates heat within the terrestrial worlds today?

Heat from radioactive decay

Which of the following types of material can condense into what we call ice at low temperatures?

Hydrogen compounds

Which of the following show evidence of ancient river beds? Mars the Moon Venus Mercury all of the above

Mars

Falling stars and shooting stars are simply other names for meteors. (T or F)

True

Suppose you start with 1 kilogram of a radioactive substance that has a half-life of 10 years. Which of the following statements will be true after 20 years pass?

You'll have 0.25 kilogram of the radioactive substance remaining.

What are the basic requirements for a terrestrial world to have a global magnetic field?

a core layer of molten, convecting material and sufficiently rapid rotation

How fast do plates move on Earth?

a few cm/ year

In light of what we know about geological activity on the terrestrial worlds, why might it seem surprising to find geological activity on jovian moons?

because they are relatively small in size

The asteroid belt is located _________.

between the orbits of Mars and Jupiter

What are the conditions necessary for a terrestrial planet to have a strong magnetic field?

both a molten metallic core and reasonably fast rotation

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

Meteor showers are associated with debris from

comets

Australia is composed of relatively old and thick

continental crust

What drives the motion of the tectonic plates on Earth?

convection cells in the mantle

Which of the following most likely explains why Venus does not have a global magnetic field like Earth?

its rotation is too slow

The reason that small planets tend to lose interior heat faster than larger planets is essentially the same as the reason that ________.

large baked potato takes longer to cool than a small one

The nebular theory also predicts that the cloud should heat up as it collapses. What physical law explains why it heats up?

law of conservation of energy

The combined mass of all the asteroids in the asteroid belt is

less than any terrestrial planet

What is the name of the outer rigid layer of a planet?

lithosphere

Which of the following does not have a major effect in shaping planetary surfaces?

magnetism

Which two factors are most important to the existence of plate tectonics on Earth?

mantle convection and a thin lithosphere

The cores of the terrestrial worlds are made mostly of metal because ______.

metals sunk to the centers a long time ago when the interiors were molten throughout

The geysers and hot springs of Yellowstone National Park result from

plumes of hot mantle rising in a hot spot within a plate.

What is the longest-lasting internal heat source responsible for geological activity?

radioactive decay

allows us to determine the age of a solid rock.

radiometric dating

Which of the following best describes the lunar maria?

relatively smooth, flat plains on the moon

The jovian planets are thought to have formed as gravity drew hydrogen and helium gas around planetesimals made of __________.

rocks, metals, and ices

Which describes our understanding of flowing water on Mars?

It was important once, but no longer.

According to modern science, what was the approximate chemical composition of the solar nebula?

98% H and He, 2% everything else

Venus has a higher average surface temperature than Mercury. Why?

Because its surface is heated by an extreme greenhouse effect.

According to our present theory of solar system formation, why were solid planetesimals able to grow larger in the outer solar system than in the inner solar system?

Because only metal and rock could condense in the inner solar system, whereas ice also condensed in the outer solar system.

In what way is Venus most similar to Earth?

Both planets are nearly the same size.

The nebular theory also predicts that the cloud will flatten into a disk as it shrinks in size. Which of the following best explains why the collapsing cloud should form a disk?

Colliding cloud particles exchange angular momentum and, on average, end up with the rotation pattern for the cloud as a whole.

What are four key features of our solar system that any theory of solar system formation must be able to explain?

Planets fall into two major categories. There are clear patterns to the rotation and orbits of large bodies in the solar system. There are vast numbers of asteroids and comets. There are a few notable exceptions to the rules.

are intact leftovers of the solar nebula. They contain rocks and metals mixed together, as well as carbon compounds in some cases.

Primitive Meteorites

How do scientists determine the age of the solar system?

Radiometric dating of meteorites

Consider the following statement: "Rocky asteroids are found primarily in the asteroid belt and Kuiper belt, whereas icy comets are found primarily in the Oort cloud." What's wrong with this statement?

The Kuiper belt contains icy comets, not rocky asteroids.

Why aren't small asteroids spherical in shape?

The strength of gravity on small asteroids is less than the strength of the rock.

What is the primary basis on which we divide the ingredients of the solar nebula into four categories (hydrogen/helium; hydrogen compound; rock; and metal)?

The temperatures at which various materials will condense from gaseous form to solid form.

Why are terrestrial planets denser than jovian planets?

The terrestrial planets formed in the inner solar nebula, where only dense materials could condense.

Why do we think Mercury has so many tremendous cliffs?

They were probably formed by tectonic stresses when the entire planet shrank as its core cooled.

All the following statements about Venus are true. Which one offers evidence of a global repaving about a billion years ago?

Venus has relatively few impact craters and these craters are distributed fairly evenly over the entire planet.

What do we mean when we say that the terrestrial worlds underwent differentiation?

When their interiors were molten, denser materials sank toward their centers and lighter materials rose toward their surfaces.

Which is closest to the average distance between asteroids in the asteroid belt?

1 million km

About how large (on average) is an impact crater compared to the size of the impactor?

10x

What percentage of the mass of the solar nebula consisted of elements other than hydrogen and helium?

2%

Suppose you find a rock that contains 10 micrograms of radioactive potassium-40, which has a half-life of 1.25 billion years. By measuring the amount of its decay product (argon-40) present in the rock, you conclude that there must have been 80 micrograms of potassium-40 when the rock solidified. How old is the rock?

3.75 billion years

According to modern scientific dating techniques, approximately how old is the solar system?

4.5 billion years

The verdict at the end of the Extraordinary Claims box says "Likely correct, though may never be possible to prove definitively." In the context of models, which of the following best explains this verdict?

A model that precisely reproduces major characteristics of the Moon would seem likely correct, but we can't go back in time to see that it actually happened that way.

When did the objects that we now see as asteroids and comets form in the solar system?

After solid particles condensed from the gas but before the planets finished forming.

As you've seen, the nebular theory predicts that a cloud that gives birth to planets should have the shape of a spinning disk. Which observable property of our solar system supports this prediction?

All the planets orbit the Sun in the same direction and in nearly the same plane.

As discussed in the Extraordinary Claims box, when the giant impact idea was first proposed, it was generally thought to be so unlikely that it wasn't seriously considered until decades alter, after the Apollo missions to the Moon. What key piece of scientific understanding was missing that made it seem so unlikely when first proposed?

An understanding of the number and size of leftover planetesimals in the early solar system.

Why is Earth's continental crust lower in density than seafloor crust?

Continental crust is made as the lowest-density seafloor crust melts and erupts to the surface near subduction zones.

Why is continental crust lower in density than seafloor crust?

Continental crust is made from remelted seafloor crust and therefore only the lower-density material rises to form it.

Which moon is considered likely to have a deep, subsurface ocean of liquid water?

Europa

Nebular theory predicts that other solar systems that formed in the same way should also have 8 planets.

False

Why does the Moon have a layer of powdery "soil" on its surface?

It's the result of gradual erosion by micrometeorites striking the Moon.

Earth has a relatively strong magnetic field, but Mars does not. Which of the following probably explains why Mars lacks a strong magnetic field today?

Its core is too cool for convention

The __________ extends from about beyond the orbit of Neptune to about twice the distance of Neptune from the Sun.

Kuiper Belt

Suppose we had a device that allowed us to see Earth's interior. If we looked at a typical region of the mantle, what would we see happening?

On human time scales, the mantle looks like solid rock, so not much would be seen.

Based on what the nebular theory tells us about the formation of our own solar system, what does the theory predict for the possibility of other planetary systems?

Planetary systems should be common.

Which of the following is not evidence supporting the giant impact theory for the formation of the Moon?

Scientists have found several meteorites that appear to be the remains of the object that caused the giant impact.

Why are there fewer large impact craters on the Earth's seafloor than on the continents?

Seafloor crust is younger than continental crust, so it has had less time in which to suffer impacts.

The choices describe four hypothetical planets. Which one would you expect to have the most features of erosion? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.) Size: same as Venus. Distance from Sun: same as Mars. Rotation rate: once every 25 hours. Size: same as Mars. Distance from Sun: same as Earth. Rotation rate: once every 18 hours. Size: twice as big as Earth. Distance from Sun: same as Mercury. Rotation rate: once every 6 months. Size: same as the Moon. Distance from Sun: same as Mars. Rotation rate: once every 10 days.

Size: same as Venus. Distance from Sun: same as Mars. Rotation rate: once every 25 hours.

The choices describe four hypothetical planets. Which one's surface would you expect to be most crowded with impact craters? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.) Size: twice as big as Earth. Distance from Sun: same as Mercury. Rotation rate: once every 6 months. Size: same as the Moon. Distance from Sun: same as Mars. Rotation rate: once every 10 days. Size: same as Mars. Distance from Sun: same as Earth. Rotation rate: once every 18 hours. Size: same as Venus. Distance from Sun: same as Mars. Rotation rate: once every 25 hours.

Size: same as the Moon. Distance from Sun: same as Mars. Rotation rate: once every 10 days.

Our solar system was created by the gravitational collapse of the

Solar Nebula

What is the relevance of tidal heating to the possibility of life on jovian moons?

Tidal heating can lead to subsurface zones of liquid water.

The change in fossils at the K-T sediment layer suggests that in addition to the dinosaurs, _________ also went extinct.

about 3/4 of all living species on earth

Which internal energy source produces heat by converting gravitational potential energy into thermal energy?

accretion and differentiation

The three principal sources of internal heat of terrestrial planets are

accretion, differentiation, and radioactivity.

We cannot see tidal forces or tidal heating; rather, we predict that they must occur based on the orbital characteristics of the moons. What observational evidence confirms that tidal heating is important on Io?

active volcanoes on Io

Leftover planetesimals that formed in the region of the solar system now occupied by the jovian planets are called

comets

The objects that are sometimes visible in the night sky with long tails are

comets

Meteorites can come from

comets. the Moon. the cores of asteroids. Mars.

The core, mantle, and crust of a planet are defined by differences in their

composition

Which of the following is not evidence for plate tectonics on Earth? some continental boundaries fit together like pieces of a jigsaw puzzle existence of volcanoes similar rocks and fossils are found in different continents high ocean ridges between the continents earthquakes

existence of volcanoes

Which of the following can contribute to explaining why jovian moons are sometimes much more geologically active than terrestrial worlds of similar (or smaller) size? orbiting far from the Sun ice-rich composition orbiting far from their planet tidal heating having a core of metal and rock

ice-rich composition tidal heating

The terrestrial planet cores contain mostly metal because

metals sank to the center during a time when the interiors were molten throughout.

Particles ejected from a comet can cause a(n) _____________ on Earth.

meteor shower

Pieces of asteroids that have fallen to Earth are called

meteorites

The polar caps on Mars are composed of

mostly solid carbon dioxide and some water ice.

What kind of surface features may result from tectonics?

mountains cliffs valleys volcanoes

Compared to the distance between Earth and Mars, the distance between Jupiter and Saturn is ______.

much larger

A comet's _______ is the frozen portion of a comet.

nucleus

A comet's plasma tail always points directly away from the Sun because __________.

of pressure exerted by the fast-moving charged particles in the solar wind

A typical shooting star in a meteor shower is caused by a ________ entering Earth's atmosphere.

pea-size particle from a comet

A comet's _________ stretches directly away from the Sun.

plasma tail

What are the two geological features that appear to set Earth apart from all the other terrestrial worlds?

plate tectonics and widespread erosion

Which internal energy source is the most important in continuing to heat the terrestrial planets today?

radioactivity

found in the Atlantic Ocean between North America and Europe is composed of dense and relatively young rock.

seafloor crust

Which of the following describes volcanism?

the eruption of molten rock from a planet's interior to its surface

What are the circumstances under which convection can occur in a substance?

when the substance is strongly heated from underneath

Why was it advantageous for the Voyager mission to consist of flybys rather than orbiters?

Each individual spacecraft was able to visit more than one planet.

Which of the following best describes the geological histories of the Moon and Mercury?

Early in their histories, they suffered many impacts and experienced some volcanism and tectonics, but they now have little geological activity at all.

While we may never be able to prove that our Moon really formed in a giant impact, which of the following would give scientists greater confidence that the model is correct? Select all that apply. Finding evidence that other giant impacts occurred in our solar system, with a total number of impacts consistent with what models of solar system formation lead us to expect. Creating more sophisticated models of the giant impact that correctly predict many detailed characteristics of the Earth and Moon. Smashing together two glass marbles in a laboratory and then gluing the remnants together to make marbles that have the same size ratio as the Earth and Moon. Having the giant impact model endorsed by a dozen Nobel prize winners. Observing evidence of recent giant impacts in other solar systems that are currently in the process of formation.

Finding evidence that other giant impacts occurred in our solar system, with a total number of impacts consistent with what models of solar system formation lead us to expect. Creating more sophisticated models of the giant impact that correctly predict many detailed characteristics of the Earth and Moon. Observing evidence of recent giant impacts in other solar systems that are currently in the process of formation.

How did the lunar maria form?

Large impacts fractured the Moon's lithosphere, allowing lava to fill the impact basins.

The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did these elements come from?

They were produced by stars that lived and died before our solar system was born.

Two hypothetical discoveries in Part A deal with moons that, like Earth's moon, are relatively large compared to their planets. Which of the following best explains why finding 1 planet with such a moon is consistent with the nebular theory, while finding 6 planets with such moons is not consistent?

Unusually large moons form in giant impacts, which are relatively rare events.

As a general rule, smaller planets __________ than larger planets.

cool more rapidly

Which two properties are most important in determining the surface temperature of a planet?

distance from sun and atmosphere

Earth is the only terrestrial planet to have experienced tectonic stresses and volcanic activity. (T or F)

false

In the inner solar system, the largest surface features are found on the largest planets. (T or F)

false

When we see a region of a planet that is not as heavily cratered as other regions, we conclude that

the surface in the region is younger than the surface in more heavily cratered regions.

Which of the following describes erosion?

the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather

What mechanism is most responsible for generating the internal heat of Io that drives the volcanic activity?

tidal heating

Consider the three items from Part A that are not relevant to the giant impact hypothesis. As you'll learn in later chapters, the lack of volcanoes is a result of the Moon's relatively small size. But what explains the other two items — the Moon's synchronous rotation and gradually increasing distance from Earth?

Both are results of tidal interactions between the moon and earth

Orbits Saturn and has been observed to be spraying fountains of ice crystals into space.

Enceladus

The nebular theory of the formation of the solar system successfully predicts all but one of the following. Which one does the theory not predict? the equal number of terrestrial and jovian planets the craters on the Moon Planets orbit around the Sun in nearly circular orbits in a flattened disk. the compositional differences between the terrestrial and jovian planets asteroids, Kuiper-belt comets, and the Oort cloud

Equal number of terrestrial and jovian planets

How might its capture be relevant to its geological activity?

Even though Triton is much smaller than our Moon, Triton' surface shows evidence of relatively recent geological activity. This can be because of the tidal heating that occurred when the moon was captured.

According to our modern science, which of the following best explains why the vast majority of the mass of our solar system consists of hydrogen and helium gas?

Hydrogen and helium are the most common elements throughout the universe because they were the only elements present when the universe was young.

The solar system has two types of planets, terrestrial and jovian. According to the nebular theory, why did terrestrial planets form in the inner solar system and jovian planets in the outer solar system?

Ices condensed only in the outer solar system, where some icy planetesimals grew large enough to attract gas from the nebula, while only metal and rock condensed in the inner solar system, making terrestrial planets.

As you saw in Part A, Io's elliptical orbit is necessary to its tidal heating. This elliptical orbit, in turn, is a result of the orbital resonance among Io, Europa, and Ganymede. This orbital resonance causes Io to have a more elliptical orbit than it would otherwise, because __________.

Io, Europa and Ganymede periodically return to the same orbital positions, creating the same gravitational tugs

According to our present theory of solar system formation, which of the following best explains why the solar nebula ended up with a disk shape as it collapsed?

It flattened as a natural consequence of collisions between particles in the nebula.

According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size?

It got hotter, its rate of rotation increased, and it flattened into a disk.

What do we mean by the frost line when we discuss the formation of planets in the solar nebula?

It is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense.

According to present understanding, which of the following statements about the solar wind is not true?

It is even stronger today than it was when the Sun was young.

In what way is Pluto more like a comet than a planet?

It is made mostly of rock and ice

Which statement about Io is true? It is the only moon in the solar system with a thick atmosphere. It is thought to have a deep, subsurface ocean of liquid water. It is the largest moon in the solar system. It is the most volcanically active body in our solar system.

It is the most volcanically active body in our solar system.

Which of the following best describes convection?

It is the process in which warm material expands and rises while cool material contracts and falls.

Which of the following statements about the object called Eris is not true?

It is thought to be the first example of a new class of object.

Why do we think Triton is a captured moon?

It orbits Neptune at a high inclination to Neptune's equator. It orbits Neptune in the direction opposite to Neptune's rotation.

Why do astronomers believe Triton may have been a planet that was captured by Neptune?

It orbits Neptune in the opposite direction of Neptune's rotation.

Why has NASA sent recent orbiters to Mars on trajectories that required them to skim through Mars's atmosphere before settling into their final orbits?

It saves money because the spacecraft uses atmospheric drag to slow down rather than needing to carry enough fuel to slow by firing rocket engines.

Which of the following statements was true beyond the frost line (but not interior to it)?

It was cold enough for hydrogen compounds to condense into ices.

You discover an impact crater that is 10 kilometers across. Which of the following can you conclude?

It was created by the impact of an object about 1 kilometer across.

After the New Horizons flyby, scientists concluded that Pluto has probably been geologically active within the past 100 million years or less. Why?

Large regions of the surface have very few impact craters.

According to our theory of solar system formation, what are asteroids and comets?

Leftover planetesimals that never accreted into planets

We expect a scientific theory to be able to make predictions that can be tested. Which of the following is a prediction of the nebular theory that has been verified by observations?

Many stars should have planets

Most of the Moon's surface is densely covered with craters, but we find relatively few craters within the lunar maria. What can we conclude?

Maria formed after heavy bombardment

Recent evidence suggests that Mars once had a global magnetic field. Assuming this is true, which of the following could explain why Mars today lacks a global magnetic field like that of Earth?

Mars's interior has cooled so much that its molten core layer no longer undergoes convection.

What characteristic distinguishes a meteorite from a terrestrial rock?

Meteorites contain rare elements, such as iridium, that terrestrial rocks do not. A meteorite usually has a high metal content. A meteorite is usually covered with a dark crust from burning in Earth's atmosphere. Meteorites have different isotope ratios of particular elements when compared to terrestrial rocks.

What do asteroids and comets have in common?

Most are unchanged since their formation in the solar nebula.

Which of the following is not a major pattern of motion in the solar system?

Nearly all comets orbit the Sun in same direction and roughly the same plane.

Some of the oldest continental crust on Earth lies in

Northeastern canada

Which of the following statements about asteroids, Kuiper belt objects, and Oort cloud objects is true?

Objects in the asteroid belt and Kuiper belt orbit the Sun in nearly the same plane as the planets, but objects in the Oort cloud do not.

Which of the following Mars surface features provides dramatic evidence that volcanism has played a role in shaping the surface of Mars? the polar caps the southern highlands Valles Marineris Olympus Mons

Olympus Mons

About a trillion comets are thought to be located far, far beyond Pluto in the

Oort Cloud

Why didn't a planet form in the region of the solar system now occupied by the asteroid belt?

Orbital resonances with Jupiter disrupted orbits in this region.

Based on the nebular theory as it explains our own solar system, which of the following should we expect to be true for other star systems? Planetary systems will always have four terrestrial planets and four jovian planets. Planetary systems should generally have all planets orbiting in nearly the same plane. Many extrasolar planets should fall into the terrestrial or jovian categories. Planetary systems should be common. Some planetary systems will have terrestrial planets that orbit their star in a direction opposite to the orbital direction of the jovian planets. Jovian planets always form farther from their star than terrestrial planets.

Planetary systems should generally have all planets orbiting in nearly the same plane. Many extrasolar planets should fall into the terrestrial or jovian categories. Planetary systems should be common. Jovian planets always form farther from their star than terrestrial planets.

have undergone differentiations in larger asteroids. As a result, they are made up of either metals or rocky material rather than a mix of the two.

Processed Meteorites

The choices describe four hypothetical planets. Which one would you expect to have the hottest interior? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.) Size: same as the Moon. Distance from Sun: same as Mars. Rotation rate: once every 10 days. Size: twice as big as Earth. Distance from Sun: same as Mercury. Rotation rate: once every 6 months. Size: same as Mars. Distance from Sun: same as Earth. Rotation rate: once every 18 hours. Size: same as Venus. Distance from Sun: same as Mars. Rotation rate: once every 25 hours.

Size: twice as big as Earth. Distance from Sun: same as Mercury. Rotation rate: once every 6 months.

Which of the following is not an advantage of spacecraft flybys over ground-based telescope observations?

Spacecraft can monitor changes in a planet's atmosphere over long times.

Which of the following best explains why we can rule out the idea that planets are usually formed by near collisions between stars?

Stellar near collisions are far too rare to explain all the planets now known to orbit nearby stars.

Which of the following is not a major difference between the terrestrial and jovian planets in our solar system?

Terrestrial planets contain large quantities of ice and jovian planets do not.

Which of the following statements about the Tharsis Bulge, often simply called "Tharsis," are true? Tharsis is the most heavily cratered region of Mars. Tharsis has higher elevation than surrounding regions. Tharsis has several large volcanoes. Tharsis was probably the site of an ancient ocean. Tharsis is located close to Mars's north pole. One end of Valles Marineris is connected to Tharsis.

Tharsis has higher elevation than surrounding regions. Tharsis has several large volcanoes. One end of Valles Marineris is connected to Tharsis.

What is the giant impact hypothesis for the origin of the Moon?

The Moon formed from material blasted out of the Earth's mantle and crust by the impact of a Mars-size object.

Which of the following is not a line of evidence supporting the hypothesis that our Moon formed as a result of a giant impact?

The Pacific Ocean appears to be a large crater, probably the one made by the giant impact.

The evidence for recent geological activity on Pluto came as a surprise to most scientists, because they did not expect Pluto to retain enough heat to drive such activity. Which of the following best explains why Pluto is so geologically active despite its small size? The activity is driven by heat from the many impacts that occur in the Kuiper belt. The activity is driven by tidal heating caused by Pluto's moons. The activity involves nitrogen ice, so Pluto does not need much heat to cause this ice to undergo change. The activity is driven by the heat of a subsurface ocean. Pluto's tall mountains built of water ice must be unstable, and when they collapse they can cause geological activity

The activity involves nitrogen ice, so Pluto does not need much heat to cause this ice to undergo change.

The following statements are all true. Which one counts as an "exception to the rule" in being unusual for our solar system?

The diameter of Earth's Moon is about 1/4 that of Earth.

What do we mean by the period of heavy bombardment in the context of the history of our solar system?

The first few hundred million years after the planets formed, which is when most impact craters were formed.

What do we mean by accretion in the context of planet formation?

The growth of planetesimals from smaller solid particles that collided and stuck together

Many scientists suspect that Venus has a stronger and thicker lithosphere than Earth. If this is true, which of the following could explain it?

The high surface temperature that has "baked out" all the liquid water from Venus's crust and mantle.

According to our theory of solar system formation, which law best explains why the central regions of the solar nebula got hotter as the nebula shrank in size?

The law of conservation of energy

Which of the following is not generally true of all the terrestrial world lithospheres?

The lithosphere is broken into a set of large plates that float on the softer rock below.

Many meteorites appear to have formed early in the solar system's history. How do these meteorites support our theory about how the terrestrial planets formed?

The meteorites appearance and composition is just what we'd expect if metal and rock condensed and accreted as our theory suggests.

Which of the following best summarizes current understanding of other extinctions in Earth's past history? Mass extinctions like the one that killed the dinosaurs occur about every 10,000 years on average, always as a result of impacts. There have been a few other fairly sudden mass extinctions, but none are as clearly tied to impacts as the dinosaur extinction There have been seven other mass extinctions that also show clear evidence of being caused by impacts. The mass extinction that killed the dinosaurs was a unique event, and all other extinctions have been much more gradual

There have been a few other fairly sudden mass extinctions, but none are as clearly tied to impacts as the dinosaur extinction

The region of our solar system between Mercury and Mars has few asteroids, whereas the region between Mars and Jupiter has many asteroids. Based on what you have learned, what is the most likely explanation for the lack of asteroids between Mercury and Mars?

There were few planetary leftovers in this region because most of the solid material was accreted by the terrestrial planets as the planets formed.

About 2% of our solar nebula consisted of elements besides hydrogen and helium. However, the first generation of star systems in the universe probably consisted only of hydrogen and helium. Which of the following statements is most likely to have been true about these first-generation star systems?

There were no comets or asteroids in these first-generation star systems.

The only moon in the solar system with a thick atmosphere, it also has lakes of liquid methane and ethane.

Titan

Which moon shows evidence of rainfall and erosion by some liquid substance?

Titan

This moon of Neptune orbits "backward" compared to Neptune's rotation.

Triton

Which planet listed has the most extreme seasons?

Uranus

We now know of many Jupiter-size planets around other stars. Suppose that future observations show that one of these planets has two orbiting moons. What additional information, if any, would we need to decide whether these moons experience tidal heating?

We need to know their orbital periods

Based on its surface features, the most important event on Venus in the past billion years or so was _______.

a global "repaving" that erased essentially all the surface features that had existed earlier

The fact that most moons always show the same face to their planet is

a natural consequence of tidal forces acting on the moons.

In the context of plate tectonics, what is a subduction zone?

a place where a seafloor plate is sliding under a continental plate

How many of the planets orbit the Sun in the same direction that Earth does?

all

Consider the hypothetical discovery from Part A reading: "A star's 5 terrestrial planets orbit in the opposite direction of its 3 jovian planets." This discovery would be inconsistent with the nebular theory because the theory holds that __________.

all the planets formed in a rotating, disk-shaped nebula

Where would you expect terrestrial planets to form in the solar nebula?

anywhere between the innermost regions (within about the inner 0.3 AU) and the frost line

Which of the following is not due to tidal forces?

backward orbit of Triton

Smaller worlds generally have thinner lithospheres. (T or F)

false

The magnetic and rotational north poles on Earth are the same. (T or F)

false

There is no erosion of surface features on the Moon. (T or F)

false

Which geologic processes are most clearly evident in the southern highlands of Mars?

impact cratering and erosion

Scientists can estimate the age of a planetary surface by counting __________.

impact craters

According to our theory of solar system formation, where did the comets originally form?

in the outer solar system beyond the frost line

Orbital resonance also gives Europa an elliptical orbit, so it experiences tidal heating, too. However, Europa experiences less tidal heating than Io, because Europa __________ than Io.

is farther from Jupiter

How does the amount of heat released in a planet's interior by radioactive decay change with time?

it drops off with time

Why do astronomers think Miranda has such an unusual surface?

it underwent an episode of tidal heating in the past

Imagine that an alien spaceship crashed onto Earth. Which statement would most likely be true?

it would crash in the ocean

Io experiences tidal heating primarily because __________.

its elliptical orbit causes the tidal force to vary as Io orbits Jupiter.

Which of the following has virtually no effect on the structure of a planet?

its magnetic field

What's the fundamental reason that Mars has so little geological activity compared to Earth?

its small size compared to Earth

The existence of a core-mantle-crust interior structure tells us that a world __________.

once had a molten interior

In essence the nebular theory holds that

our solar system formed from the collapse of an interstellar cloud of gas and dust

In essence, the nebular theory holds that _________.

our solar system formed from the collapse of an interstellar cloud of gas and dust

Based on all we know about the terrestrial worlds, what single factor appears to play the most important role in a terrestrial planet's geological destiny?

size

Which of the following is the underlying reason why Venus has so little wind erosion? its relatively close distance to the Sun its small size its thick atmosphere its slow rotation

slow rotation

During the time that a comet passes through the inner solar system, the comet can appear quite bright because __________.

sunlight reflects off the comet's tail and coma

what types of evidence for recent or ongoing geological activity have been observed on one or more jovian moons?

surfaces with very few impact craters ice crystals being sprayed out into space active volcanoes river valleys feeding into surface lakes of very cold liquids

Which of the following describes tectonics?

the disruption of a planet's surface by internal stresses

Which of the following describes impact cratering?

the excavation of bowl-shaped depressions by asteroids or comets striking a planet's surface

Which of the following is NOT an example of tectonics?

the gradual disappearance of a crater rim as a result of wind and rain

Observations show that interstellar clouds can have almost any shape and, if they are rotating at all, their rotation is not perceptible. However, the nebular theory predicts that a cloud will rotate rapidly once it shrinks to a relatively small size. What physical law explains why a collapsed cloud will rotate rapidly?

the law of conservation of angular momentum

Which of the following does not provide evidence that Mars once had large amounts of flowing water?

the presence of vast canals discovered in the late 1800s by Giovanni Schiaparelli and mapped by Percival Lowell

Consider the hypothetical discovery from Part A reading: "Beyond its jovian planets, a star has two ice-rich objects as large as Mars." This discovery is consistent with the nebular theory, because this theory predicts that _________.

this might have happened in our own solar system if it had taken longer for the solar wind to clear the solar nebula

Earth is the only planet in the solar system known to have plate tectonics. (T or F)

true

Higher temperatures make rocks weaker. (T or F)

true

Mars has virtually no magnetic field. (T or F)

true

Much of the land on the west coast of North America began as volcanic islands in the Pacific. (T or F)

true

Spreading centers are marked by mid-ocean ridges where hot mantle material rises upward and then spreads sideways. (T or F)

true

Synchronous rotation is when a moon's rotation period and orbital period are the same. (T or F)

true

The process in which one plate slides under another is called subduction and is marked by deep ocean trenches. (T or F)

true

The strength of a rock depends on its composition, its temperature, and the surrounding pressure. (T or F)

true

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 highlands.

How does the largest asteroid, Ceres, compare in size to other solar system worlds?

1/4 the size of the moon

Where did the elements heavier than hydrogen and helium come from?

They were produced inside stars

Mars was formed by the ________ of smaller objects.

accretion

From center to surface, which of the following correctly lists the interior layers of a terrestrial world?

core, mantle, crust

How long, approximately, do geologists estimate it takes for the entire seafloor to be replaced due to plate tectonics?

200 million years

What causes synchronous rotation?

A massive planet exerts a tidal force on a moon that causes the moon to align itself such that its tidal bulges always point toward and away from the planet.

The major processes that heat the interiors of the terrestrial worlds are __________.

(1) heat deposited as the planets were built from planetesimals; (2) heat deposited as the planets underwent differentiation; (3) heat released by radioactive decay

Why did the solar nebula heat up as it collapsed?

As the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy.

This moon of Jupiter has an icy surface with very few impact craters, suggesting that craters have been covered by upwelling water

Europa

How does seafloor crust differ from continental crust?

Seafloor crust is thinner, younger, and higher in density.

Which of the following best describes why the smaller terrestrial worlds have cooler interiors than the larger ones?

They have relatively more surface area compared to their volumes.

In general, what kind of planet would you expect to have the thickest lithosphere?

a small planet

Ice can form from a gas through the process of

condensation