Question 1

Which of the following discoveries would cause us to re-evaluate the nebular theory for forming planets?
A) A star's 5 terrestrial planets orbit in the opposite direction of its 3 jovian planets.
B) Of the star's five terrestrial planets, one has a large moon.
C) Two of the star's planets are rotating in directions backwards compared to their orbital direction.
D) A star has 20 planets.
E) A star has zero planets.

Accepted Answer

The nebular theory predicts that all planets in a given planetary system should orbit the same direction as their parent star. If a star is found to have planets orbiting in opposite directions, it would indicate that either the nebula from which the system formed was disrupted, or the interacting gravitational forces among planets have caused them to re-orient their orbits over time.

Question 2

Hot Jupiters were a surprise to astronomers. What is the current explanation for their existence?
A) Jupiters form as a companion to the host star, but fail to become actual stars themselves because they are not massive enough.
B) Jupiters are supposed to form far away from their host star, then they migrate closer through gravitational interactions with the protoplanetary disk.
C) The temperature of the hot Jupiters is highly uncertain, so they might not be as hot as the astronomers say.
D) Jupiters actually can form close to the host star, since they do not require as much hydrogen compounds and ice as originally thought.

Accepted Answer

Hot Jupiters are believed to have formed farther away from their host stars where gas giants can more easily form, but then migrated closer in to their host stars due to gravitational interactions with the protoplanetary disk.

Question 3

Which of the following statements about our Sun is not true?
A) The Sun's diameter is about 5 times that of Earth.
B) The Sun is a star.
C) The Sun contains more than 99% of all the mass in our solar system.
D) The Sun is made mostly of hydrogen and helium.

Accepted Answer

The Sun's diameter is about 109 times that of Earth, not 5 times.

Question 4

You have observed the wobble in the velocity curves of two otherwise identical stars. Star A has a period of 6 months and Star B has a period of 1 year. What can you say about these stars?
A) Star B must have a planet like Earth.
B) Star A's planet is more massive than Star B's planet.
C) It is impossible to say anything about the planets orbiting these stars.
D) Star A's planet must be closer than Star B's planet.

Accepted Answer

The period of the wobble in the velocity curve is related to the period of the planet's orbit around the star. Since Star A has a shorter period, its planet must be closer to the star than Star B's planet. Therefore, Star A's planet must be closer than Star B's planet. It is impossible to determine the mass or even the existence of the planets orbiting these stars without more information.

Question 5

Which of the following statements about Mars is not true?
A) We could survive on Mars without spacesuits, as long as we brought oxygen in scuba tanks.
B) We have landed spacecraft on its surface.
C) It is considered part of our inner solar system.
D) It is frozen today, but once had flowing water.

Accepted Answer

It is not possible to survive on Mars without proper spacesuits, as its atmosphere does not contain enough oxygen to support human life. Bringing oxygen in scuba tanks would not be sufficient.

Question 6

If a radioactive isotope that was injected into your bloodstream has a half life of 5 hours, how many hours do you have to wait before the amount of this isotope in your body is $ \frac{1}{16} $ its original amount?
A) 20
B) 25
C) 5
D) 10
E) 15

Accepted Answer

The amount of a radioactive isotope decreases by half every half-life. To reach $ \frac{1}{16} $ of the original amount, it must go through 4 half-lives because $ \frac{1}{16} = \left(\frac{1}{2}\right)^4 $. Since each half-life is 5 hours, 4 half-lives take 20 hours.

Question 7

Suppose you view the solar system from high above Earth's North Pole. Which of the following statements about planetary orbits will be true?
A) All the planets orbit counterclockwise around the Sun.
B) The inner planets orbit the Sun counterclockwise while the outer planets orbit the Sun clockwise.
C) All the planets except Uranus orbit the Sun counterclockwise; Uranus orbits in the opposite direction.
D) The inner planets orbit the Sun clockwise while the outer planets orbit the Sun counterclockwise.

Accepted Answer

When viewed from above Earth's North Pole, all the planets in the solar system orbit the Sun counterclockwise. This is due to the direction of the solar system's formation from a rotating disk of gas and dust.

Question 8

Which of the following is not true of Mercury?
A) It has been studied closely by several NASA spacecraft.
B) At any given time, about half the planet is colder than Antarctica.
C) Its surface is heavily cratered.
D) Mercury has essentially no atmosphere.

Accepted Answer

The answer of Which of the following is not true...

Question 9

Which of the following lists the planets of our solar system in the correct order from closest to farthest from the Sun?
A) Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
B) Mercury, Earth, Venus, Mars, Jupiter, Saturn, Neptune, Uranus
C) Mercury, Venus, Mars, Earth, Saturn, Jupiter, Neptune, Uranus
D) Earth, Mars, Mercury, Venus, Jupiter, Saturn, Uranus, Neptune

Accepted Answer

This is the correct order of planets from closest to farthest from the Sun.

Question 10

Observations vs. Explanations. Which of the following statements is an explanation?
A) The farther a galaxy is, the faster it is moving away from us.
B) The inner planets of the solar system are rocky and the outer planets are gas giants.
C) The orderly orbits of planets arose from their formation in a rotating cloud of gas.
D) Hydrogen and helium are important constituents of stars.
E) All planets orbit the Sun in the same direction and nearly the same plane.

Accepted Answer

The orderly orbits of planets arose from their formation in a rotating cloud of gas.

Question 11

If the proto star that became our Sun had been hotter and more luminous when it formed, what changes (if any) might have been experienced by our Solar System?
A) Terrestrial planes could only have formed closer to the Sun.
B) No comets could have formed.
C) The Moon would not exist.
D) Mars would be a gas giant.
E) Jupiter would now be farther from the Sun.

Accepted Answer

The answer of If the proto star that became our...

Question 12

Which of the following hypothetical discovery would force us to modify or discard our most current nebular theory?
A) A star with 5 planets, orbiting in different directions
B) A star with 1 planet, rotating in a direction opposite to its orbital direction
C) A star with a disk of gas and zero planets
D) A star with 9 planets, and none of them have moons

Accepted Answer

The answer of Which of the following hypothetical discovery would...

Question 13

You are observing the wobble of a star caused by the orbit of a planet around that star. Which property of this system listed below most signiﬁcantly affects the period of that wobble?
A) Both the planet's orbital radius and its mass
B) Neither the planet's orbital radius or its mass
C) The planet's orbital radius
D) The planet's mass

Accepted Answer

The period of the wobble caused by the planet's orbit around the star is related to the planet's distance from the star. This means that the planet's orbital radius has the most significant effect on the wobble period. The planet's mass does have an effect on the wobble amplitude but not on the wobble period itself. Therefore, choice C is the best answer.

Question 14

Which of the following statements does NOT apply to the formation of gas giants like Jupiter, compared to terrestrial planets?
A) Caused icy planetesimals to slingshot away from the Sun, to become Oort cloud comets
B) Formed in a region with lower orbital speeds
C) Accreted from icy planetesimals
D) Surface dramatically altered during bombardment
E) Formed in regions cold enough for water to freeze

Accepted Answer

Gas giants like Jupiter did not have their surfaces dramatically altered during bombardment in the same way terrestrial planets did, as they are primarily composed of gas and lack a solid surface.

Question 15

You are measuring how velocity changes with time of two stars like the Sun in order to detect their planets. Both stars have a velocity curve with a periods of 2 years, but the maximum size (peak-to-peak amplitude) of the velocity curve of star A is 100 km/s, and for star B it is 200 km/s. What causes this difference? Assume the planets are named after their stars.
A) Planet A is less massive than Planet B.
B) Planet A is closer to Star A than Planet B is to Star B.
C) Planet A is more massive than Planet B.
D) Planet A is farther from Star A than Planet B is to Star B.
E) Not possible to say, since you're measuring the velocity curve of the stars, not the planets.

Accepted Answer

The larger amplitude of the velocity curve for star B suggests that Planet B is more massive than Planet A, causing a greater gravitational effect on its star.

Question 16

All of the following hypothetical planets orbit a star with the same mass as the Sun (one solar mass). Which one has the shortest orbital period? (If two objects would have the same orbital period to within a difference of less than 1% consider them as having identical periods.)
A) Planet A: one Earth mass and 1 AU from the star
B) Planet B: two Earth masses and 1 AU from the star
C) Planet C: two Earth masses and 2 AU from the star
D) Planets A and B
E) Planets B and C F) All of them have the same period.

Accepted Answer

According to Kepler's third law, the orbital period of a planet depends only on the semi-major axis of its orbit, not its mass. Therefore, Planets A and B, both at 1 AU, have the same shortest orbital period.

Question 17

Consider two main sequence K-stars. Each star has been measured for a periodic wobble in its velocity curve. Which star has the closest planet (the planet with the smallest orbit)?
A) The planet orbit sizes can't be determined from the information provided.
B) The star with a period of 1 month
C) The star with a period of 2 months

Accepted Answer

The star with a period of 1 month has a smaller orbit because the shorter the period of a planet's orbit, the closer it is to its star. Therefore, it is likely that this star has the closest planet.

Question 18

How do we know the mass of Neptune?
A) The orbital speed of Neptune moving around the Sun
B) The periods and sizes of the orbits of the moons around Neptune
C) The size and density of Neptune
D) The period and size of Neptune's orbit around the Sun
E) The distance of Neptune from the Earth and its rotation period

Accepted Answer

The mass of Neptune can be determined by measuring the orbital speed and distance of its moons. By using Kepler's laws and the measured periods and sizes of the moons, the mass of Neptune can be calculated through the application of Newton's laws of motion. Therefore, option B is the correct choice. The other options, such as option A (orbital speed of Neptune around the Sun) and option D (period and size of Neptune's orbit around the Sun) can also provide information but are not as direct as option B. Option C (size and density of Neptune) is not sufficient on its own to determine the mass of Neptune as there could be objects with similar size and density but different masses. Option E (distance of Neptune from the Earth and its rotation period) is also not sufficient to calculate Neptune's mass.

Question 19

Suppose that the temperature of the solar nebula had been much colder. How might the Solar System look different today?
A) More planets would have formed.
B) Terrestrial planets may have formed at a larger distance from the Sun.
C) The gas giant planets might be bigger and closer to the Sun.
D) The gas giant planets might be bigger and farther from the Sun.

Accepted Answer

The answer of Suppose that the temperature of the solar...

Question 20

Which of the following statements best explains why the planets orbit in nearly a single plane and in the same direction around the Sun?
A) The planets formed from a disk of rotating gas.
B) The Sun rotates in the same direction, and spun out the planets as it formed.
C) The planets all rotate in same direction as they orbit.
D) It's a mysterious coincidence: the planets form randomly, so it's a puzzle how they orbit that way.

Accepted Answer

The planets orbit in nearly a single plane and in the same direction around the Sun because they formed from a disk of rotating gas, called the protoplanetary disk, around the young Sun. This disk was flattened and slowly rotated, causing the planets to form in nearly the same plane and in the same direction of rotation.

Quiz 6: Formation of Planetary Systems: Our Solar System and Beyond

Which of the following discoveries would cause us to re-evaluate the nebular theory for forming planets?

Hot Jupiters were a surprise to astronomers. What is the current explanation for their existence?

Which of the following statements about our Sun is not true?

You have observed the wobble in the velocity curves of two otherwise identical stars. Star A has a period of 6 months and Star B has a period of 1 year. What can you say about these stars?

Which of the following statements about Mars is not true?

If a radioactive isotope that was injected into your bloodstream has a half life of 5 hours, how many hours do you have to wait before the amount of this isotope in your body is $\frac{1}{16}$ its original amount?

Suppose you view the solar system from high above Earth's North Pole. Which of the following statements about planetary orbits will be true?

Which of the following is not true of Mercury?

Which of the following lists the planets of our solar system in the correct order from closest to farthest from the Sun?

Observations vs. Explanations. Which of the following statements is an explanation?

If the proto star that became our Sun had been hotter and more luminous when it formed, what changes (if any) might have been experienced by our Solar System?

Which of the following hypothetical discovery would force us to modify or discard our most current nebular theory?

You are observing the wobble of a star caused by the orbit of a planet around that star. Which property of this system listed below most signiﬁcantly affects the period of that wobble?

Which of the following statements does NOT apply to the formation of gas giants like Jupiter, compared to terrestrial planets?

All of the following hypothetical planets orbit a star with the same mass as the Sun (one solar mass) . Which one has the shortest orbital period? (If two objects would have the same orbital period to within a difference of less than 1% consider them as having identical periods.)

Consider two main sequence K-stars. Each star has been measured for a periodic wobble in its velocity curve. Which star has the closest planet (the planet with the smallest orbit) ?

How do we know the mass of Neptune?

Suppose that the temperature of the solar nebula had been much colder. How might the Solar System look different today?

Which of the following statements best explains why the planets orbit in nearly a single plane and in the same direction around the Sun?