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?
answer
the law of conservation of angular momentum
question
The nebular theory also predicts that the cloud should heat up as it collapses. What physical law explains why it heats up?
answer
the law of conservation of energy
question
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?
answer
Colliding cloud particles exchange angular momentum and, on average, end up with the rotation pattern for the cloud as a whole.
question
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?
answer
All the planets orbit the Sun in the same direction and in nearly the same plane.
question
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?
answer
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.
question
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? Check all that apply.
answer
-Jovian planets always form farther from their star than terrestrial planets.
-Many extrasolar planets should fall into the terrestrial or jovian categories.
-Planetary systems should be common.
-Planetary systems should generally have all planets orbiting in nearly the same plane.
question
Sort the following hypothetical discoveries into the appropriate bins as follows:
Consistent with theory: The statement describes a discovery that we could reasonably expect to find if the nebular theory is correct.
Not consistent with theory: The statement describes a discovery that would force us to modify or discard the nebular theory.
answer
Consistent with theory:
-Beyond its jovian planets, a star has two ice-rich objects as large as Mars.
-A star has 20 planets
-A star is surrounded by a disk of gas but has no planets.
-Of a star's 5 terrestrial planets, 1 has a moon as large as Earth's moon.
Not consistent with theory:
-A star's 4 jovian planets formed in its inner solar system and its 4 terrestrial planets formed farther out.
-All 6 of a star's terrestrial planets have a moon as large as Earth's moon.
-A star's 5 terrestrial planets orbit in the opposite direction of its 3 jovian planets.
-A star has 9 planets, but none orbit in close to the same plane.
question
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?
answer
Unusually large moons form in giant impacts, which are relatively rare events.
question
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 __________.
answer
all the planets formed in a rotating, disk-shaped nebula
question
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 _________.
answer
this might have happened in our own solar system if it had taken longer for the solar wind to clear the solar nebula
question
The materials that made up the solar nebula can be categorized into the four general types as follows. Rank these materials from left to right based on their abundance in the solar nebula, from highest to lowest.
answer
(HIGHEST) hydrogen and helium gas, hydrogen compounds, rock, metals (LOWEST)
question
The materials that made up the solar nebula can be categorized into these four general types. Rank these materials from left to right based on the temperature at which each would condense into a solid, from highest to lowest. Note: For a substance that does not condense at all, rank it as very low temperature.
answer
(HIGHEST) metals, rock, hydrogen compounds, hydrogen and helium gas (LOWEST)
question
The first few hundred million years of the solar system's history were the time of the _________ , during which Earth suffered many large impacts.
answer
heavy bombardment
question
As you've learned from Part B, hydrogen and helium gas never condense under conditions found in the solar nebula. The remaining three categories of material in the solar nebula are shown again here. Rank these materials from left to right based on the distance from the Sun at which they could condense into a solid in the solar nebula, from farthest to closest.
answer
(FARTHEST) hydrogen compounds, rock, metals (CLOSEST)
question
Each of the following statements applies either to the formation of terrestrial planets or of jovian planets (but not both), based on our current theory of solar system formation. Drag the statements into the appropriate bin.
answer
Terrestrial Planets:
-accreted from
planetesimals of
rock and metal
-surfaces dramatically
altered during the
heavy bombardment
Jovian Planets:
-large moons formed
in surrounding
disks of material
-ejected icy planetesimals
that are now Oort
cloud comets
-formed in a region of
the solar system with
lower orbital speeds
-accreted from
icy planetesimals
-formed in regions cold
enough for water to freeze
question
Our solar system was created by the gravitational collapse of the _________
answer
solar nebula
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Our Moon was most likely formed by a collision between Earth and a Mars-sized _________
answer
planetesimal
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Mars was formed by the _________of smaller objects.
answer
accretion
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The era of planet formation ended when the remaining hydrogen and helium gas of the solar nebula was swept into interstellar space by the _______
answer
solar wind
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Ice can form from a gas through the process of _______
answer
condensation
question
Hydrogen compounds in the solar system can condense into ices only beyond the ________
answer
frost line
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________ allows us to determine the age of a solid rock.
answer
Radiometric dating
question
What do we mean when we say that a nucleus undergoes radioactive decay?
answer
The number of protons or neutrons (or both) in the nucleus changes.
question
Suppose you have a rock that, when it solidifies, contains 1 microgram of a radioactive isotope. How much of this isotope remains after five half-lives?
answer
1/32 microgram
question
Approximately what is the half-life of uranium-235?
answer
700 million years
question
Suppose you find a rock and measure that 12.5% of the original uranium-235 still remains it, while the other 87.5% has decayed into lead-207. About how old is the rock?
answer
2.1 billion years
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