Astronomy Chapter 8 Set 2 – Flashcards

In essence, the nebular theory holds that A) our solar system formed from the collapse of an interstellar cloud of gas and dust. B) nebulae are clouds of gas and dust in space. C) the planets each formed from the collapse of its own separate nebula. D) the nebular theory is a discarded idea that imagined planets forming as a result of a near-collision between our Sun and another star.

According to modern science, what was the approximate chemical composition of the solar nebula? A) 50% hydrogen and helium, 50% everything else B) 98% hydrogen and helium, 2% everything else C) 98% hydrogen, 2% helium D) roughly equal proportions of hydrogen, helium, water, and methane

The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did these elements come from? A) They were produced by stars that lived and died before our solar system was born. B) They were produced by gravity in the solar nebula as it collapsed. C) They have been present in the universe since its birth. D) They were made by chemical reactions in interstellar gas.

According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size? A) It got hotter, its rate of rotation increased, and it flattened into a disk. B) Its mass, temperature, and density all increased. C) It gained energy, it gained angular momentum, and it flattened into a disk. D) Its gas clumped up to form the terrestrial planets, nuclear fusion produced heavy elements to make the jovian planets, and central temperatures rose to more than a trillion Kelvin.

Which of the following types of material can condense into what we call ice at low temperatures? A) hydrogen and helium B) rock C) metal D) hydrogen compounds

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? A) hydrogen compounds; hydrogen and helium gas; metal; rock B) hydrogen and helium gas; rock; metal; hydrogen compounds C) hydrogen and helium gas; hydrogen compounds; rock; metal D) hydrogen, water, methane, helium

What do we mean by the frost line when we discuss the formation of planets in the solar nebula? A) It is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense. B) It is another way of stating the temperature at which water freezes into ice. C) It marks the special distance from the Sun at which hydrogen compounds become abundant; closer to the Sun, there are no hydrogen compounds. D) It is the altitude in a planet's atmosphere at which snow can form.

What do we mean by accretion in the context of planet formation? A) the formation of moons around planets B) the growth of planetesimals from smaller solid particles that collided and stuck together C) the solidification of ices, rocks, and metal from the gas of the solar nebular D) the growth of the Sun as the density of gas increased in the center of the solar nebula

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? A) because the Sun's gravity was stronger in the outer solar system, allowing more solid material to collect B) because only metal and rock could condense in the inner solar system, while ice also condensed in the outer solar system C) because gas in the outer solar system contained a larger proportion of rock, metal, and hydrogen compounds than the gas in the inner solar system D) because only the outer planets captured hydrogen and helium gas from the solar nebula

According to our basic scenario of solar system formation, why do the jovian planets have numerous large moons? A) 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. B) Because of their strong gravity, the jovian planets were able to capture numerous asteroids that happened to be passing nearby, and these became the major moons of the jovian planets. C) The large moons of the jovian planets originally formed in the inner solar system and these moons then migrated out to join up with the jovian planets. D) The many moons of the jovian planets remains one of the unexplained mysteries of the formation of our solar system.

According to our theory of solar system formation, what are asteroids and comets? A) the shattered remains of collisions between planets B) chunks of rock or ice that condensed after the planets and moons finished forming C) chunks of rock or ice that were expelled from planets by volcanoes D) leftover planetesimals that never accreted into planets

According to our theory of solar system formation, where did the comets of the Oort cloud form? A) in the inner solar system B) far beyond the orbit of Pluto C) in the region of the jovian planets D) in the asteroid belt

What do we mean by the period of heavy bombardment in the context of the history of our solar system? A) the first few hundred million years after the planets formed, which is when most impact craters were formed B) the time before planetesimals finished accreting into planets, during which many growing planetesimals must have shattered in collisions C) the time during which heavy elements condensed into rock and metal in the solar nebula D) the period about 65 million years ago when an impact is thought to have led to the extinction of the dinosaurs

What is the giant impact hypothesis for the origin of the Moon? A) The Moon formed when two gigantic asteroids collided with one another. B) The Moon originally was about the same size as Earth, but a giant impact blasted most of it away so that it ended up much smaller than Earth. C) The Moon formed from material blasted out of the Earth's mantle and crust by the impact of a Mars-size object. D) The Moon formed just like Earth, from accretion in the solar nebula.

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? A) You'll have 0.25 kilogram of the radioactive substance remaining. B) All the material will have completely decayed. C) You'll have 0.75 kilogram of the radioactive substance remaining. D) You'll have 0.5 kilogram of the radioactive substance remaining.

According to modern scientific dating techniques, approximately how old is the solar system? A) 10,000 years B) 4.6 million years C) 4.5 billion years D) 14 billion years

Which of the following best explains why we can rule out the idea that planets are usually formed by near-collisions between stars? A) Studies of the trajectories of nearby stars relative to the Sun show that the Sun is not in danger of a near-collision with any of them. B) Stellar near-collisions are far too rare to explain all the planets now known to orbit nearby stars. C) A near collision might have created planets, but it could not have created moons, asteroids, or comets. D) A near collision should have left a trail of gas extending out behind the Sun, and we see no evidence of such a trail.

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? A) Hydrogen and helium are the most common elements throughout the universe, because they were the only elements present when the universe was young. B) Hydrogen and helium are produced in stars by nuclear fusion. C) All the other elements escaped from the solar nebula before the Sun and planets formed. D) All the other elements were swept out of the solar system by the solar wind.

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? A) the law of conservation of angular momentum B) Newton's third law C) the two laws of thermal radiation D) the law of conservation of energy

According to our theory of solar system formation, which law best explains why the solar nebula spun faster as it shrank in size? A) the law of conservation of angular momentum B) the law of conservation of energy C) the law of universal gravitation D) Einstein's law E = mc2

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? A) It was fairly flat to begin with, and retained this flat shape as it collapsed. B) The force of gravity pulled the material downward into a flat disk. C) the law of conservation of energy D) It flattened as a natural consequence of collisions between particles in the nebula.

What is the primary basis upon which we divide the ingredients of the solar nebula into four categories (hydrogen/helium; hydrogen compound; rock; metal)? A) the temperatures at which various materials will condense from gaseous form to solid form B) the atomic mass numbers of various materials C) the locations of various materials in the solar nebula D) the amounts of energy required to ionize various materials

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? A) Both types of planet begun with planetesimals growing through the process of accretion, but only the jovian planets were able to capture hydrogen and helium gas from the solar nebula. B) The jovian planets began from planetesimals made only of ice, while the terrestrial planets began from planetesimals made only of rock and metal. C) Swirling disks of gas, like the solar nebula in miniature, formed around the growing jovian planets but not around the growing terrestrial planets. D) The terrestrial planets formed inside the frost line of the solar nebula and the jovian planets formed beyond it.

Many meteorites appear to have formed very early in the solar system's history. How do these meteorites support our theory about how the terrestrial planets formed? A) The meteorites sizes are just what we'd expect if metal and rock condensed and accreted as our theory suggests. B) The meteorites appearance and composition is just what we'd expect if metal and rock condensed and accreted as our theory suggests. C) Their overall composition is just what we believe the composition of the solar nebula to have been: mostly hydrogen and helium. D) Their appearance and composition matches what we observe in comets today, suggesting that meteorites were once pieces of icy planetesimals.

According to present understanding, which of the following statements about the solar wind is not true? A) It is even stronger today than it was when the Sun was young. B) It helped in the transfer of angular momentum from the young Sun to particles that blew into interstellar space, which explains why the Sun rotates so slowly today. C) It swept vast amounts of gas from the solar nebula into interstellar space. D) It consists of charged particles blown off the surface of the Sun.

According to our present theory of solar system formation, how did Earth end up with enough water to make oceans? A) The water was mixed in the other materials in the planetesimals that accreted at our distance from the Sun. B) The water was formed by chemical reactions among the minerals in the Earth's core. C) The water was brought to the forming Earth by planetesimals that accreted beyond the orbit of Mars. D) Earth formed in the relatively narrow region of the solar nebular in which liquid water was plentiful.

What is the primary reason that astronomers suspect that some jovian moons were captured into their current orbits? A) Some moons have a composition that differs from the composition of the planets. B) Astronomers have observed moons being captured. C) Some moons are surprisingly large in size. D) Some moons have orbits that are "backwards" (compared to their planet's rotation) or highly inclined to their planet's equator.

Which of the following is not a line of evidence supporting the hypothesis that our Moon formed as a result of a giant impact? A) The Pacific Ocean appears to be a large crater—probably the one made by the giant impact. B) Computer simulations show that the Moon could really have formed in this way. C) The Moon's average density suggests it is made of rock much more like that of the Earth's outer layers than that of Earth as a whole. D) The Moon has a much smaller proportion of easily vaporized materials than Earth.

Why are terrestrial planets denser than jovian planets? A) Only dense materials could condense in the inner solar nebula. B) The Sun's gravity gathered dense materials into the inner solar system. C) Gravity compresses terrestrial planets to a higher degree, making them denser. D) Actually, the jovian planets are denser than the terrestrial planets.

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? A) 1.25 billion years B) 2.5 billion years C) 3.75 billion years D) 5.0 billion years

How do scientists determine the age of the solar system? A) radiometric dating of Moon rocks B) radiometric dating of the oldest Earth rocks C) radiometric dating of meteorites D) Theoretical calculations tell us how long it has taken the planets to evolve to their present forms.

The region of our solar system between Mercury and Mars has very few asteroids, while 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? A) There were very few planetary leftovers in this region, because most of the solid material was accreted by the terrestrial planets as the planets formed. B) It was too hot for asteroids to form in this part of the solar system. C) Gravity was too weak to allow asteroids to form in this part of the solar system. D) All the asteroids that formed between Mercury and Mars later migrated to the asteroid belt between Mars and Jupiter.

About 2% of our solar nebula consisted of elements besides hydrogen and helium. However, the very 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? A) There were no comets or asteroids in these first-generation star systems. B) Jovian planets in these first-generation star systems had clouds made of water and other hydrogen compounds. C) These first-generation star systems typically had several terrestrial planets in addition to jovian planets. D) Like the jovian planets in our solar system, the jovian planets in these first-generation systems were orbited by rings.