Deck 7: The Formation of Planetary Systems

Question 1

What is the ratio of the orbital angular momentum of Earth compared to its spin angular momentum? Note that Earth has a radius of 6 * 10⁶ m, and 1 AU is 1.5 *10¹¹ m.

A) 1
B) 70
C) 640
D) 25,000
E) 4.3* 10⁶

Answer 1

4.3* 10⁶

Question 2

What is a protostar?

A) a planet like Jupiter
B) a hot star
C) a large ball of gas not yet hot enough at its core to be a star
D) a large ball of gas too hot at its core to be a star
E) a star with too much angular momentum

Answer 2

a large ball of gas not yet hot enough at its core to be a star

Question 3

Conservation of angular momentum slows a cloud's collapse

A) equally in all directions.
B) only when the cloud is not rotating initially.
C) mostly along directions perpendicular to the cloud's axis of rotation.
D) mostly at the poles that lie along the cloud's axis of rotation.
E) to a complete stop.

Answer 3

mostly along directions perpendicular to the cloud's axis of rotation.

Question 4

Consider a small parcel of gas in the cloud out of which the Sun formed that initially was located in the accretion disk at a distance of 10 AU from the Sun and rotating around it with a speed of 10 km/s.If this parcel of gas eventually found its way to a distance of 1 AU from the Sun without changing its orbital angular momentum, what would be its new rotation speed?

A) 100 km/s
B) 0.1 km/s
C) 0.001 km/s
D) 10 km/s
E) 1,000 km/s

Question 5

That fact that all major Solar System objects orbit the Sun in the same direction, and mostly with the same direction of spin, is the original evidence for

A) the Big Bang theory.
B) the nebular hypothesis.
C) brown dwarfs.
D) primary atmospheres.
E) exoplanets.

Question 6

Approximately how much mass was there in the protoplanetary disk out of which the planets formed, compared to the mass of the Sun?

A) 1000 percent
B) 200 percent
C) 100 percent
D) 50 percent
E) ( $\lt$ 1 percent)

Question 7

If you are spinning in a chair and then you spread your arms out wide, you should expect

A) your rotation rate to slow.
B) your rotation rate to increase.
C) to heat up.
D) to cool down.
E) none of these

Question 8

What have astronomers and geologists studied to arrive at the same conclusions about Earth's origins?

A) volcanism in the solar system
B) comets
C) meteorites
D) the Moon
E) the oceans

Question 9

Once a planetesimal is large enough, it grows by

A) electric charges attracting other charged material.
B) generating new mass within itself.
C) passing close to its star or protostar.
D) attracting more material through gravitation.
E) heating up and sticking to encountered material.

Question 10

Consider the figure shown below.At which point in time does the collapsing cloud have the greatest angular momentum?

A) point 1
B) point 2
C) point 3
D) points 1 and 2, because the protostar has not yet formed
E) The cloud has the same angular momentum at each point in time.

Question 11

According to the conservation of angular momentum, if an ice-skater who is spinning with her arms out wide slowly pulls them close to her body, she will

A) spin faster.
B) spin slower.
C) maintain a constant rate of spin.
D) fall down.
E) stop spinning entirely.

Question 12

If an interstellar cloud having a diameter of 10¹⁶ m and a rotation period of 1 million years were to collapse to form a sphere that had the diameter of our Solar System (approximately 40 AU), what would its rotation period be? Assume the cloud's total mass and angular momentum did not change.

A) 1 million years
B) 600 years
C) 1 year
D) 6 years
E) 4 months

Question 13

In order for two clumps of dust to stick together in an accretion disk, they must collide at roughly

A) 100 m/s.
B) 10 m/s.
C) 1 m/s.
D) 0.5 m/s.
E) 0.1 m/s or less.

Question 14

The smallest grains of dust stick together in an accretion disk by which force?

A) gravitational force
B) electrostatic force
C) magnetic force
D) quantum mechanical force
E) strong force

Question 15

In the figure shown below, the direction of the disk's rotation is indicated.What is the direction of the protostellar Sun's rotation?

A) It's impossible to tell.
B) in the opposite direction as the disk's rotation
C) in the same direction as the disk's rotation
D) perpendicular to the disk's rotation
E) It will not rotate.

Question 16

Because energy must be conserved, a collapsing cloud of gas must

A) eventually expand again.
B) rotate more slowly with time.
C) always be at the same temperature.
D) heat up.
E) cool down.

Question 17

Jupiter's radius is contracting at a rate of 1 mm per year, which will result in

A) Jupiter's rotation rate slowing down with time.
B) Jupiter's shape being noticeably oblate.
C) Jupiter moving slightly farther from the Sun with time.
D) Jupiter's temperature being higher than expected otherwise.
E) Jupiter having a strong magnetic field.

Question 18

What is the ratio of the orbital angular momentum of Jupiter to its spin angular momentum? Jupiter's orbit has a semimajor axis of 5 AU and period of 12 years, and Jupiter has a rotation period of 0.4 days and a radius of 70,000 km.

A) 650,000
B) 26,000
C) 920
D) 38
E) 4.5

Question 19

If the entirety of a collapsing interstellar cloud went into forming a single protostar,

A) the forming protostar would be significantly less massive than it would have been otherwise.
B) the forming protostar would be rotating too fast to hold itself together.
C) the protostar would eventually capture free-floating planets to form a normal planetary system.
D) the protostar would be too massive to hold itself together, and would explode before becoming a star.
E) the protostar would become so massive that it would collapse into a black hole.

Question 20

The object shown in the figure below is a ________ and the dark circles, or "lanes," are mostly likely due to ________.

A) protoplanetary disk; planets in the process of formation
B) galaxy; star formation
C) protoplanetary disk; infalling gas
D) a single forming planet; moon formation
E) galaxy; infalling gas

Question 21

Which of the following is a terrestrial planet?

A) Saturn
B) Jupiter
C) Venus
D) Pluto
E) Neptune

Question 22

Which is the best description of a moon?

A) any small, icy body in the solar system
B) any small, rocky body in the solar system
C) any natural satellite of a planet or asteroid
D) a captured asteroid
E) a captured comet

Question 23

Comets and asteroids are

A) other names for moons of the planets.
B) primarily located within 1 AU of the Sun.
C) all more massive than Earth's Moon.
D) material left over from the formation of the planets.
E) other names for meteors.

Question 24

What is the most important factor in determining whether or not a planet will be rocky like terrestrial planets or gaseous like giant planets?

A) the time at which the planet forms
B) the planet's radius
C) the planet's distance from the Sun
D) whether the planet has moons
E) the planet's internal temperature

Question 25

What is a secondary atmosphere?

A) the atmosphere that escapes
B) the gas captured during the planet's formation
C) the gas farthest from the surface
D) the atmosphere that remains after the planet has formed
E) the gas closest to the planet's surface

Question 26

The icy planetesimals that remain in the Solar System today are called

A) asteroids.
B) moons.
C) meteorites.
D) comet nuclei.
E) dwarf planets.

Question 27

We expect a planet that forms close to its star to be

A) rocky in composition like terrestrial planets.
B) a comet or asteroid.
C) rich in volatile ices.
D) composed primarily of hydrogen and helium.
E) similar in mass to Earth.

Question 28

The atmosphere of which of these Solar System bodies is primary (as opposed to secondary) in origin?

A) Venus
B) Earth
C) Saturn's moon Titan
D) Saturn
E) Mars

Question 29

Which of the following is a giant planet?

A) Mercury
B) Jupiter
C) Venus
D) Earth
E) Pluto

Question 30

When you push your palms together and rub them back and forth, you are demonstrating one way of converting ________ energy into ________ energy.

A) potential; thermal
B) kinetic; potential
C) thermal; kinetic
D) kinetic; thermal
E) potential; total

Question 31

Why do the terrestrial planets have a much higher fraction of their mass in heavy chemical elements than the giant planets?

A) Terrestrial planets are low in mass and high in temperature, thus their lighter chemical elements eventually escaped to the outer reaches of the Solar System.
B) The heavier elements in the forming solar nebula sank to the center of the Solar System, thus the inner terrestrial planets formed mostly from heavy chemical elements.
C) The giant planets were more massive than terrestrial planets, and the giant planets preferentially pulled the lighter elements from the inner to the outer Solar System.
D) Terrestrial planets formed much earlier than giant planets, before the hydrogen and helium had a chance to cool and condense onto them.
E) Terrestrial planets are colder and thus more massive chemical elements condensed on them than on the giant planets.

Question 32

The solid form of a volatile material is generally referred to as a(n)

A) metal.
B) silicate.
C) ice.
D) rock.
E) refractory material.

Question 33

A refractory material is a material that

A) can withstand high temperatures without melting or vaporizing.
B) will melt or vaporize at high temperatures.
C) is transparent, and bends light passing through it.
D) will vaporize when exposed to light.
E) makes up a protostar.

Question 34

Which of the following would be considered to have a secondary atmosphere?

A) Jupiter
B) Mars
C) Saturn
D) Uranus
E) Neptune

Question 35

The primary atmospheres of the planets are made mostly of

A) carbon and oxygen.
B) hydrogen and helium.
C) oxygen and nitrogen.
D) iron and nickel.
E) nitrogen and argon.

Question 36

What happens to the kinetic energy of gas as it falls toward and eventually hits the accretion disk surrounding a protostar?

A) It is immediately converted into photons, giving off a flash of light on impact.
B) It is converted into thermal energy, heating the disk.
C) It is converted into potential energy as the gas plows through the disk and comes out the other side.
D) It becomes the kinetic energy of the orbit of the gas in the accretion disk around the protostar.
E) It disappears into interstellar space.

Question 37

Why do the outer giant planets have massive gaseous atmospheres of hydrogen and helium whereas the inner planets do not?

A) These gases were more abundant in the outer regions of the accretion disk where the outer planets formed.
B) The outer planets grew massive quickly enough to hold on to these gases through gravity before the solar wind dispersed the accretion disk.
C) The inner planets "used up" all of the rocky materials.
D) Frequent early collisions by comets with the inner planets caused most of their original atmospheres to dissipate.
E) They were most likely captured by the Sun after our Solar System formed.

Question 38

What is a primary atmosphere?

A) the atmospheres that all planets have today
B) the gas captured during the planet's formation
C) the gas captured after the planet's formation
D) the oxygen and nitrogen in Earth's atmosphere
E) the gas closest to the planet's surface

Question 39

If you want to find naturally occurring volatile materials that formed with the Solar System, you should look

A) near the Sun.
B) in the asteroid belt.
C) near Earth's orbit.
D) around other stars.
E) on the outer parts of the Solar System.

Question 40

Based on the figure shown below, which planet(s) is (are) most likely to have the largest fraction of its (their) mass made of highly volatile materials such as methane and ammonia?

A) Venus, Earth, and Mars
B) Earth
C) Saturn
D) Jupiter
E) Uranus

Question 41

Astronomers have used radial velocity monitoring to discover

A) extrasolar planetary systems that are similar to our own Solar System.
B) Mercury-sized planets around other stars.
C) Earth-sized planets at distances of 10 AU from their parent stars.
D) extrasolar planetary systems that contain more than one planet.
E) all of the above

Question 42

Detecting a planet around another star using the transit method is difficult because the

A) planet must pass directly in front of the star.
B) planet must have a rocky composition.
C) star must be very dim.
D) star must be moving with respect to us.
E) planet's orbital period is usually longer than 1 month.

Question 43

The figure below shows data from the transit study of a star in which three different planets (A, B, and C) repeatedly transit in front of the star.Which dip is (are) caused by the transit of the planet with the smallest radius?

A) A
B) B
C) C
D) They are all equally small.
E) It's impossible to tell from these data.

Question 44

Which method can be used to determine the radius of an extrasolar planet?

A) Doppler shift
B) transit
C) microlensing
D) direct imaging
E) none of these

Question 45

In the figure below, which of the dips in the brightness of the star is (are) caused by the transit of the planet with the largest orbital period?

A) A
B) B
C) C
D) A and B
E) B and C

Question 46

The Moon probably formed

A) out of a collision between Earth and a Mars-sized object.
B) when Earth's gravity captured a planetesimal.
C) when the accretion disk around Earth fragmented.
D) when planetesimals collided to form a more massive object.
E) when a piece of Earth broke off and entered orbit.

Question 47

The difference in composition between the giant planets and the terrestrial planets is most likely caused by the fact that

A) the giant planets are much larger.
B) only the terrestrial planets have iron cores.
C) the terrestrial planets are closer to the Sun.
D) the giant planets are made mostly of carbon.
E) only small differences in chemical composition existed in the solar nebula.

Question 48

From the data shown in the figure below, which property of an extrasolar planet can be determined?

A) atmosphere thickness
B) orbital distance
C) mass relative to central star.
D) axial tilt
E) None of these properties can be determined from the graph.

Question 49

Why have astronomers using the radial velocity method found more Jupiter-sized planets at a distance of 1 AU around other stars than Earth-sized planets?

A) A Jupiter-sized planet occults a larger area than an Earth-sized planet.
B) A Jupiter-sized planet exerts a larger gravitational force on the star than an Earth-sized planet, and so the Doppler shift of the star is larger.
C) A Jupiter-sized planet shines brighter than an Earth-sized planet.
D) Earth-sized planets are much rarer than Jupiter-sized planets.
E) Actually, the planets found at these distances all have been Earth-sized.

Question 50

What is the most accurate method to detect Earth-sized exoplanets with the telescopes and instrumentation that exist today?

A) Doppler shift
B) transit
C) microlensing
D) direct imaging
E) astrometry

Question 51

An observer located outside our Solar System, who monitors the velocity of our Sun over time, will find that the Sun's velocity varies by $\pm$ 12 m/s over a period of 12 years, due mainly to

A) Jupiter's gravitational pull.
B) Earth's gravitational pull.
C) variations in its brightness.
D) convection on the Sun's surface.
E) the sunspot cycle.

Question 52

How many exoplanets are known (that is, have been confirmed) to exist?

A) 8
B) 9
C) 150
D) 1,000-2,000
E) more than 3,000

Question 53

Two competing models of the formation of giant gaseous planets suggest they form either from gas accreting onto a rocky core or from

A) fragmentation of the accretion disk that surrounds the protostar.
B) the merger of two large planetesimals.
C) planets stolen from another nearby protostar.
D) materials condensing out of the solar wind.
E) an eruption of material from the protostar.

Question 54

Earth-sized planets have been found using the ________ method(s).

A) Doppler shift
B) transit and Doppler shift
C) microlensing
D) direct imaging
E) transit

Question 55

Was it ever possible (or is it currently possible) for Jupiter to become a star?

A) Yes, it is in the process of becoming a star in the near future.
B) Yes, but it cooled off before it could become a star.
C) No, it would have to be at least 13 times more massive.
D) No, its composition is too different from stars for it to become one.
E) No, it used to be massive enough, but the solar wind has blown off too much of its mass.

Question 56

Which of the following is true?

A) Radial velocity surveys have yet to find any extrasolar planets.
B) The most common types of extrasolar planets found to date have masses more than 10 times the mass of Jupiter and lie within 5 AU of their parent star.
C) Our Solar System is the only known planetary system to contain more than one planet.
D) A star can brighten significantly because of gravitational lensing when a planet that orbits it passes directly in front of the star.
E) The Kepler Mission has not yet found terrestrial planets similar in size to Earth.

Question 57

How much material in an accretion disk goes into forming the planets, moons, and smaller objects?

A) most of it
B) roughly half of it
C) none; these objects were not formed in the accretion disk
D) a small amount of it
E) all of it; the star forms separately

Question 58

The Kepler Mission is designed to search for extrasolar planets using the ________ method.

A) Doppler shift
B) transit
C) microlensing
D) direct imaging
E) radial velocity

Question 59

Using the Doppler effect data shown in the figure below, what is the approximate orbital period of the extrasolar planet?

A) 1 year
B) 3 years
C) 6 years
D) 8 years
E) 12 years

Question 60

Using the Doppler effect data for a particular star shown in the figure below, and assuming the star is about the same mass as our Sun, what is the approximate orbital distance of its exoplanet?

A) 1.1 AU
B) 6.4 AU
C) 18 AU
D) 36 AU
E) 3.3 AU

Question 61

Explain the nebular hypothesis, and describe two observations that support it.

Question 62

Hot Jupiters were the first exoplanets to be discovered, and have since been found to be

A) extremely common.
B) erroneous detections of smaller planets.
C) more likely to exist far from their star.
D) brown dwarfs.
E) relatively rare.

Question 63

What is the habitable zone?

A) the distance from a star where liquid water can exist
B) the location on the sky where planets can be found
C) the distance from a star where liquid can exist
D) the distance from a star where planets have oxygen in the atmosphere
E) 1 AU from any star

Question 64

Why does an accretion disk heat up?

Question 65

If an astronomer on a planet orbiting a nearby star observed the Sun when Neptune was transiting in front of the Sun, how would the Sun's brightness change? Note that the radius of Neptune is 2.5 * 10⁷ m.

A) The Sun's brightness would decrease by 0.1 percent.
B) The Sun's brightness would increase by 0.1 percent.
C) The Sun's brightness would increase by 1 percent.
D) The Sun's brightness would decrease by 1 percent.
E) The Sun's brightness would not change at all.

Question 66

What evidence do we have that the accretion disk that formed the Solar System was initially much denser near its center?

Question 67

Compare the orbital angular momentum of Earth and Jupiter.Which is larger and by how much? (Note that Jupiter's mass is 318 times that of Earth, the semimajor axis of Jupiter's orbit is 5.2 AU, and Jupiter's orbital period is 12 years.)

Question 68

If you detect an exoplanet that is orbiting a star that is 8 times as massive as the Sun with an orbital period of 1 (Earth) year, you would expect the semimajor axis of its orbit to be

A) 8 AU.
B) 6 AU.
C) 4 AU.
D) 2 AU.
E) 1 AU.

Question 69

Explain why an accretion disk forms around a protostar when an interstellar cloud collapses.

Question 70

Explain the primary reasons why the inner solar nebula was hotter than the outer solar nebula.

Question 71

What happens to the rotation speed of a slowly rotating cloud as it collapses to form a stellar system? Why does this occur?

Question 72

The borderline between the most massive planet and the least massive brown dwarf is thought to occur at around

A) 4 Jupiter masses.
B) 13 Jupiter masses.
C) 120 Jupiter masses.
D) 80 Jupiter masses.
E) 45 Jupiter masses.

Question 73

Explain why astronomers believe that the formation of planets is a natural by-product of star formation.

Question 74

Astronomers believe that the "hot Jupiters" found orbiting other stars must have migrated inward over time

A) by slowly accreting large amounts of gas and increasing their gravitational pull.
B) by losing their gas because of evaporation.
C) by losing orbital angular momentum.
D) after colliding with another planet.
E) after a close encounter between their star and another star.

Question 75

The figure shown below illustrates the changing brightness of a star due to a planet transiting in front of it.Which of the following can be directly measured from the information provided?

A) the mass of the planet
B) percentage reduction in light
C) size of the planet
D) orbital radius of the planet
E) distance of the star

Question 76

What does conservation of angular momentum mean?

Question 77

How do meteorites tell us about how the solar system formed?

Question 78

When astronomers began searching for extrasolar planets, they were surprised to discover Jupiter-sized planets much closer than 1 AU from their parent stars.Why is this surprising?

A) These planets must have formed at larger radii where temperatures were cooler and then migrated inward, which is thought to be a rare phenomenon.
B) Jupiter-sized, rocky planets were thought to be uncommon in other solar systems.
C) These planets must be the remnants of failed stars.
D) Earth-like planets must be rarer than Jupiter-sized planets in other solar systems.
E) Jupiter-sized planets so close to the star are common and difficult to explain in our Solar System.

Question 79

As the radius, r, of extrasolar planets increases, we expect the amount of light they block from their parent star to change by a factor of ________.

A) 1/r²
B) 1/r
C) r
D) r²
E) There will be no change.

Question 80

Astronomers have discovered other stars with planets that are more massive than Earth, but less massive than Neptune, that are called

A) dwarf giants.
B) super-Earths or mini-Neptunes.
C) planetesimals.
D) hot Jupiters.
E) asteroids or comets.