ASTR: Our Planetary System

Flashcard maker : Lily Taylor
Rank the objects from left to right based on their average distance from the Sun, from farthest to closest
1. Pluto
2. Saturn
3. Jupiter
4. Mars
5. Earth
6. Mercury
The following images show six objects in our solar system. Rank these objects from left to right based on their mass, from highest to lowest.
1. Sun
2. Jupiter
3. Earth
4. Mars
5. Mercury
6. Pluto

Be sure to notice that the masses of these objects are vastly different. For example, the Sun is more than 1,000 times as massive as all the planets combined, and Jupiter is more massive than all the rest of the planets combined.

The images below show six objects in our solar system. Rank these objects by size (average equatorial radius), from largest to smallest.
1. Sun
2. Jupiter
3. Earth
4. Mars
5. Mercury
6. Pluto

Sizes (radii) do not vary nearly as much as the masses, but the differences are still substantial. For example, the Sun’s radius is more than 100 times that of Earth, while Jupiter’s radius is more than 10 times that of Earth.

The following images show five planets in our solar system. Rank these planets from left to right based on their average surface (or cloud-top) temperature, from highest to lowest.
1. Mercury
2. Earth
3. Mars
4. Jupiter
5. Neptune

Notice that, for these five planets, temperature correlates with distance from the Sun: the closer to the Sun, the hotter the planet. Remember, however, that this is not always the case, because a planet’s temperature also depends on its reflectivity and on the strength of its greenhouse effect (if any). For example, the greenhouse effect gives Venus a higher average temperature than Mercury, even though Venus is nearly twice as far from the Sun.

The following images show five planets in our solar system. Rank these planets from left to right based on the amount of time it takes them to orbit the Sun, from longest to shortest.
1. Neptune
2. Jupiter
3. Mars
4. Earth
5. Mercury

Recall that the time it takes a planet to orbit the Sun is called its orbital period, and that Kepler’s third law tells us that orbital period increases with distance from the Sun. That is why the ranking order for orbital period is the same as the ranking order for distance from the Sun.

The following images show four planets in our solar system. Rank these planets from left to right based on the number of moons that orbit them, from highest to lowest.
1. Jupiter
2. Mars
3. Earth
4. Mercury

Jupiter has many moons as a consequence of its formation, in which moons formed in a disk of material surrounding it and its extended atmosphere at the time allowed it to capture numerous small bodies into orbit. Mars has two very small moons that it presumably captured at a time when it, too, had an extended atmosphere. Earth’s single but surprisingly large moon is thought to have formed as a result of a giant impact. Mercury (and Venus) have no moons.

Which of the following is not one of the four major features of the solar system?

a) Large bodies in the solar system have orderly motions.
b) Several exceptions to the general trends stand out.
c) The solar system contains eight planets plus dwarf planets (including Ceres, Pluto, and Eris).
d) Swarms of asteroids and comets populate the solar system.
e) Planets fall into two major categories (terrestrial and jovian).

c) The solar system contains eight planets plus dwarf planets (including Ceres, Pluto, and Eris)

The precise number of planets is not thought to be of any particular significance, and the division between “planets” and “dwarf planets” is a recent classification scheme that does not affect the basic ideas in the four major features. That is, for the purposes of the four major features, the dwarf planets are considered to be equivalent to large asteroids or comets.

Which of the following correctly describe patterns of motion in the solar system?
-All the planets (not counting Pluto) have nearly circular orbits.
-All the planets (not counting Pluto) orbit the Sun in nearly the same plane.
-Planets closer to the Sun move around their orbits at higher speed than planets farther from the Sun.
Now consider the second major characteristic (two types of planets). Which of the following statements are true?
-Jovian planets have more moons than terrestrial planets.
-Jovian planets are larger in mass than terrestrial planets.
-Jovian planets are larger in size than terrestrial planets.
-Jovian planets orbit farther from the Sun than terrestrial planets.

Knowing these basic differences between terrestrial and jovian planets in our solar system, we can look to see whether the same categories of planets are found in other solar systems.

The solar system contains vast numbers of small bodies, which we call asteroids when they are rocky and comets when they are icy. These small bodies are concentrated in the region(s) of the solar system that we call __________.
-the Kuiper belt
-the Oort cloud
-the asteroid belt

Most asteroids are found in the asteroid belt between Mars and Jupiter. Comets are found in two regions: the Kuiper belt just beyond the orbit of Neptune and the much more distant and spherically shaped region known as the Oort cloud.

All the following statements are true. Which of them are considered to be “exceptions” to the general trends described by the first three major characteristics of the solar system?

a) Jupiter’s largest moon, Ganymede, is even larger than Earth’s moon.
b) Pluto is in the outer solar system but is ice-rich in composition.
c) Venus rotates in a direction opposite to the rotation of the other terrestrial planets.
d) Our Moon has a diameter more than 1/4 the diameter of Earth.
e) Uranus rotates with an axis tilt that lies nearly in the ecliptic plane.

c) Venus rotates in a direction opposite to the rotation of the other terrestrial planets.
d) Our Moon has a diameter more than 1/4 the diameter of Earth.
e) Uranus rotates with an axis tilt that lies nearly in the ecliptic plane.
Consider only the observed patterns of motion in the solar system. Scientifically, which of the following possible conclusions is justified from the patterns of motion alone?

-The planets were born from a giant cloud of gas that rotated in the same direction that the Milky Way Galaxy rotates.
-The planets were not born within the past million years, but instead they must have been born billions of years ago.
-The planets started out quite small and grew to their current sizes as they gradually accreted more material.
-The planets were not each born in a separate, random event.

The planets were not each born in a separate, random event.
Now consider why the observed patterns of motion lead to the conclusion that the planets were not born in separate, random events. The reason for this conclusion is that, if the planets had been born in separate, random events, we would expect that __________.

-planetary orbits would have many different orientations and directions, rather than all being in the same direction and in the same plane
-planets would orbit at much higher speeds than they actually do
-there would be many different types of planets, rather than just two major types
-none of the planets would have ended up with moons

planetary orbits would have many different orientations and directions, rather than all being in the same direction and in the same plane

In science, we form hypotheses to explain something, then use the hypotheses to make predictions that we can test. In this case, we have two alternate hypotheses: random births or birth from a single cloud of gas. The hypothesis of random births predicts random orbits, which does not agree with reality and therefore has been discarded. The hypothesis of birth from a single cloud predicts patterns of motion that match those we observe; this match of prediction and observation provides evidence in favor of the hypothesis.

Today, scientists have a theory (the nebular theory) that explains all the major characteristics of the solar system. In science, we expect a theory like this not only to explain the observed characteristics of our solar system but also to __________.

-predict which planets have life
-predict some major change that will eventually occur in our own solar system
-make testable predictions about other solar systems

make testable predictions about other solar systems

A scientific theory must always make testable predictions, because that is the only way we can evaluate the validity of the theory.

The materials that made up the solar nebula can be categorized into the four general types as follows. (Hydrogen+He, hydrogen compounds, rock, metals)

Rank these materials from left to right based on their abundance in the solar nebula, from highest to lowest.

1. H + He
2. H compounds
3. rock
4. metals

Hydrogen and helium gas constituted about 98 percent of the mass in the solar nebula. Most of the rest was hydrogen compounds, which were nearly three times as abundant as rock and metal combined.

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.

1. metals
2. rock
3. hydrogen compounds
4. hydrogen and gas

In fact, hydrogen and helium gas never condense into solid form under the conditions that exist in interstellar clouds such as the solar nebula. Continue on to Part C to see how the condensation temperatures of the other materials explain why different materials condensed in different regions of the young solar system.

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.
1. hydrogen compounds
2. rock
3. metals

These condensation regions explain the makeup of objects at different distances from the Sun.

In the inner regions of the solar nebula, where temperatures were high, only metal and rock could condense, which is why the inner planets ended up being made of metal and rock. Farther out, hydrogen compounds could condense into ices, which is why comets and outer solar system moons contain large amounts of ice. And because hydrogen compounds are more abundant than metal or rock, some of the solid objects in the outer solar system grew so large that their gravity could pull in hydrogen and helium gas, which explains how the jovian planets formed.

What substances were found within 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

You will see that all the materials of the solar nebula were present in the inner region, but it was too hot for any of them to condense. As a result, they were all in gaseous form.

What substances existed as solid flakes within the inner 0.3 AU of the solar system before planets began to form?
none

Although all the materials were present in gaseous form, the inner 0.3 AU of the newly forming solar system was too warm for even rocks or metals to condense into solid flakes.

Where would you expect terrestrial planets to form in the solar nebula?
anywhere between 0.3 AU and the frost line

Terrestrial planets are made mostly of metal and rock and therefore formed in the region in which it was cool enough for metal and rock to condense but still too warm for hydrogen compounds to condense into ices. This means the region between the rock/metal condensation line at 0.3 AU and the frost line.

The jovian planets are thought to have formed as gravity drew hydrogen and helium gas around planetesimals made of
rocks, metals, and ices

Because ices could condense only beyond the frost line, we expect jovian planets to form only beyond the frost line. Note that many extrasolar planets appear to be jovian but are located close to their stars, leading scientists to suspect that these planets migrated inward after originally forming beyond the frost lines of their star systems.

In what way is Pluto more like a comet than a planet?
It is made mostly of rock and ice.
Terrestrial vs. Jovian
-Jovian planets have rings, and terrestrial planets do not.
-Terrestrial planets orbit much closer to the Sun than jovian planets.
-Terrestrial planets are higher in average density than jovian planets.
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
What is the primary basis upon which we divide the ingredients of the solar nebula into four categories (hydrogen/helium; hydrogen compound; rock; metal)?
the temperatures at which various materials will condense from gaseous form to solid form
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.
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, while ice also condensed in the outer solar system
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.
evidence supporting the idea that our Moon formed as a result of a giant impact?
-Computer simulations show that the Moon could really have formed in this way.
-The Moon has a much smaller proportion of easily vaporized materials than Earth.
-The Moon’s average density suggests it is made of rock much more like that of the Earth’s outer layers than that of the Earth as a whole.
How do scientists determine the age of the solar system?
radiometric dating of meteorites
The terrestrial planets in our solar system are ________.
Mercury, Venus, Earth, and Mars
The jovian planets in our solar system are ________.
Jupiter, Saturn, Uranus, and Neptune
Which moons are sometimes called the Galilean moons?
the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto
The Cassini mission to Saturn consists of ________.
an orbiter that orbits Saturn and a probe that descended to the surface of Titan
When we say that jovian planets contain significant amounts of hydrogen compounds, we mean
ammonia, water, methane
In essence, the nebular theory holds that ________.
our solar system formed from the collapse of an interstellar cloud of gas and dust
According to modern science, what was the approximate chemical composition of the solar nebula?
98% hydrogen and helium, 2% everything else
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.
Which of the following types of material can condense into what we call ice at low temperatures?
hydrogen compounds
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.
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
According to our theory of solar system formation, what are asteroids and comets?
leftover planetesimals that never accreted into planets
period of heavy bombardment
the first few hundred million years after the planets formed, which is when most impact craters were formed
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.
According to modern scientific dating techniques, approximately how old is the solar system?
4.5 billion years
Which planet has the highest average surface temperature, and why?
Venus, because of its dense carbon dioxide atmosphere
Which planets have a ring system?
Neptune
Jupiter
Uranus
Saturn
Which of the following are characteristics of the inner planets?
Their orbits are relatively closely spaced.
They all have solid, rocky surfaces.
They have very few, if any, satellites.
They are relatively smaller than the outer planets.
Which of the following are characteristics of the outer planets?
They all have large quantities of gas.
They are primarily made of hydrogen and helium.
Their orbits are separated by relatively large distances.
They all have rings.
What are the main constituents of the jovian planets?
H + He
Where are most of the known asteroids found?
between the orbits of Mars and Jupiter
Which of the following is furthest from the Sun?

Neptune
a comet in the Oort cloud
an asteroid in the asteroid belt
a comet in the Kuiper belt
Pluto

a comet in the Oort cloud
Astronomers now classify Pluto as really just a large member of
the Kuiper belt.
Why did the solar nebula heat up as it collapsed?
As the cloud shrank, its gravitational potential energy was converted to thermal energy.
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 ingredients of the solar nebula from highest to lowest percentage of mass of the nebula?
light gases (H, He), hydrogen compounds (H2O, CH4, NH3), rocks, metals
Which of the following are relatively unchanged fragments from the early period of planet building in the solar system?

asteroids
Kuiper belt comets
Oort cloud comets
all of the above

all of the above
Based on our current theory of Earth’s formation, the water we drink comes from
comets that impacted Earth.
What do meteorites reveal about the solar system?
They reveal that the age of the solar system is approximately 4.6 billion years.
If the freezing point of ices of all types were 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.
Which of the following statements best explains why the planets orbit in nearly a single plane and in the same direction around the Sun?
The planets formed from a disk of rotating gas.
How do we know the mass of Neptune?
the periods and sizes of the orbits of the moons around Neptune

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