The Origin of the Solar System

Solar –Nebular Hypothesis

Our Solar SystemOur solar system consists of eight planets only excluding Pluto.

The inner four planets are called terrestrial and the outer four planets are Jovian planets.

(i) What is the difference in the formation of

the inner and outer planets?

(i) By what criteria are the planets placed

into either the terrestrial or Jovian groups

• After the big bang, matter in the universe separated into galaxies.

• Gas and dust spread throughout space in our galaxy. Where the solar system is now, there was only cold, dark gas and dust.

• About 5 billion years ago, a giant cloud of gas and dust or nebula form a spinning disk.

• As gravity pulled some of the gas into the centre of the disk, the gas become hot and dense enough for nuclear fusion to begin.

• The Sun was born.

Formation of the Solar system

• The remaining gas and dust form solid spheres smaller than the Sun. The spheres closest to the Sun lost most of their gases and became the inner planets Mercury, Venus, Earth and Mars.

• The spheres farthest from the Sun became the gas giants Jupiter, Saturn, Uranus and Neptune.

• Between the inner planets and the gas giants the asteroid formed.

• Beyond the gas giants, a huge cloud of ice and other substances formed, Kuiper belt (short-orbital comets) and Oort Cloud (long-orbital comets).

• This cloud is probably the main source of comets.

Formation of the Solar system

Evolutionary hypothesis.

Catastrophic hypotheses

Nebular hypothesis

Solar-Nebula hypothesis

Rene Descartes (1596-1650)

Georges-Louis de Buffon (1707-1788)

Pierre –Simon de Laplace (1749-1827)

Through careful observations of astronomers.

He believed that the entire universe was filled with vortices of whirling invisible particles.The sun and planets formed when a large vortex contracted and condensed

A passing comet pulled matter out of the sun to form the planets.Later astronomers replaced the comet with a star to produce the passing star hypothesis.

(combined Descartes vortex & Newton’s gravity to produce a model of a rotating cloud of matter (nebula- clouds of dust and gas) that contracted under its own gravitation and flattened into a disk.

Gradually part of the nebula contracted into a large, tightly pack spinning disk. The disk‘s centre was so hot and dense that nuclear fusion reactions began to occur and the Sun was bornEventually, the remaining gas and dust in the disk cooled enough to clump into scattered solids forming the planets. Finally these clumps collided and combined to become the eight planets that make up the solar system today.

Most stars should have planets!

Only few stars should have planets!

Early Hypotheses- Evolutionary hypotheses

The first theory for Earth’s origin proposed by French philosopher and mathematician Rene Descartes (1596-1650)

He believed that the entire universe was filled with vortices of whirling invisible particles. He proposed that the sun and planets formed when a large vortex contracted and condensed

Evolutionary hypotheses predict: Most stars should have planets!

Early Hypotheses- Catastrophic hypotheses

In 1745, the French naturalist Georges-Louis de Buffon (1707-1788) suggested that a passing comet pulled matter out of the sun to form the planets—a catastrophic hypothesis. (passing star hypothesis)

Later astronomers replaced the comet with a star to produce the passing star hypothesis. (no longer considered) Why?

Catastrophic hypotheses predict: Only few stars should have planets!

• Material pulled out of the Sun would be too hot to condense.

• Planetary systems are common, whereas nearby star collisions are rare.

Quiz Questions

1. Why do we reject the formation of planets as proposed by Buffon (the passing star hypothesis)?

a. Material pulled out of the Sun would be too hot to condense.b. Planetary systems are common, whereas nearby star collisions are rare.c. The angular momentum of the Sun is too low.d. Both a and b above.e. All of the above.

Quiz Questions

1. Why do we reject the formation of planets as proposed by Buffon (the passing star hypothesis)?

a. Material pulled out of the Sun would be too hot to condense.b. Planetary systems are common, whereas nearby star collisions are rare.c. The angular momentum of the Sun is too low.d. Both a and b above.e. All of the above.

Condensation is the building of larger particles one atom (or molecule) at a time, whereas accretion is the sticking together of larger particles.

Early Hypotheses

The modern theory of the origin of solar system begin with Pierre –Simon de Laplace (1749-1827) French astronomer and mathematician (combined Descartes vortex & Newton’s gravity to produce a model of a rotating cloud of matter (nebula- clouds of dust and gas) that contracted under its own gravitation and flattened into a disk – nebular hypothesis

Evolutionary hypotheses predict: Most stars should have planets!

Catastrophic hypotheses predict: Only few stars should have planets!

Nebular Hypothesis-Pierre Simon de Laplace

As the disk (clouds of dust and gas) grew smaller, it had to conserve angular momentum and spin faster and faster.

When the disk spin faster, it will shed its outer edge to leave behind a ring of matter. Then the disk could contract further, speed up again and leave another ring.

Rings of material separate from the spinning cloud, carrying away angular momentum of the cloud (become a planet) cloud could contract further (forming the sun)

According to nebular hypothesis the sun should be spinning very rapidly ( have most of the angular momentum) . As astronomers studied the planets they found that the sun rotated slowly and that the planets moving in their orbits had most of the angular momentum in the solar system. Because the nebular hypothesis could not explain the sun’s low angular momentum (angular momentum problem), they keep refining the details on the origin of the solar system.

Quiz Questions

2. What was the major problem for the solar nebula hypothesis that was proposed by Pierre-Simon Laplace?

a. It did not predict that inner planets orbit the Sun more quickly than outer planets.b. The Sun contains little of the angular momentum of the Solar System.c. It called for a catastrophic event to produce the Solar System.d. The Sun spins more rapidly than is expected.e. All of the above.

Quiz Questions

2. What was the major problem for the solar nebula hypothesis that was proposed by Pierre-Simon Laplace?

a. It did not predict that inner planets orbit the Sun more quickly than outer planets.b. The Sun contains little of the angular momentum of the Solar System.c. It called for a catastrophic event to produce the Solar System.d. The Sun spins more rapidly than is expected.e. All of the above.

Quiz Questions

3. How do astronomers believe the Sun came to have less angular momentum than its system of planets?

a. The solar wind mass outflow carries angular momentum away from the Sun.b. The Sun's magnetic field drags material out in the Solar System, transferring angular momentum outward.c. A large planetesimal impacted the Sun on its leading hemisphere.d. The planets gain angular momentum from passing stars.e. Both a and b above.

Quiz Questions

3. How do astronomers believe the Sun came to have less angular momentum than its system of planets?

a. The solar wind mass outflow carries angular momentum away from the Sun.b. The Sun's magnetic field drags material out in the Solar System, transferring angular momentum outward.c. A large planetesimal impacted the Sun on its leading hemisphere.d. The planets gain angular momentum from passing stars.e. Both a and b above.

The Solar Nebula Hypothesis

About 4.6 billion years ago, the solar system was a vast, swirling cloud of gas, ice and dust.

Gradually part of the nebula contracted into a large, tightly pack spinning disk. The disk‘s centre was so hot and dense that nuclear fusion reactions began to occur and the Sun was born

Eventually, the remaining gas and dust in the disk cooled enough to clump into scattered solids forming the planets.

Finally these clumps collided and combined to become the eight planets that make up the solar system today.

The Solar Nebula Hypothesis

Basis of modern theory of planet formation is the solar nebula theory

Planets form at the same time from the same cloud as the star.

Example:

Planet formation sites observed today as dust disks of T Tauri stars.

In 1940, astronomers begin to understand how stars form and how stars generate their energy

The solar nebula theory proposes that the planets formed in a disk of gas and dust around the protostar that became the sun. Observations show that these disks are common.

Quiz Questions

4.(a) How may gravity have affected the formation of the solar system?

(b) How would the solar system have been different if the disk’s centre had not been as hot and dense as it was.

Quiz Questions

4(a) How may gravity have affected the formation of the solar system?

Gravity pulled the cloud of gas, ice and dust together causing it to spin faster and then form the Sun and the planets.

(b) How would the solar system have been different if the disk’s centre had not been as hot and dense as it was.

Nuclear fusion reaction might not have occurred to form the Sun. Without light and heat energy, life would not have been possible anywhere in the solar system.

Quiz Questions

5. How is the solar nebula theory supported by the motion of Solar System bodies?

a. All of the planets orbit the Sun near the Sun's equatorial plane.b. All of the planets orbit in the same direction that the Sun rotates.c. Six out of seven planets rotate in the same direction as the Sun.d. Most moons orbit their planets in the same direction that the Sun rotates.

Quiz Questions

5. How is the solar nebula theory supported by the motion of Solar System bodies?

a. All of the planets orbit the Sun near the Sun's equatorial plane.b. All of the planets orbit in the same direction that the Sun rotates.c. Six out of seven planets rotate in the same direction as the Sun.d. Most moons orbit their planets in the same direction that the Sun rotates.

The Solar Nebula Hypothesis

SIMULATION -refer to GEOSYSTEMS

According to the solar nebula theory, our Earth, and the other planets of the solar sysytem formed billions of years ago as the sun condensed from a a cloud of gas and dust.

Sun and our Solar system formed ~ 5 billion years ago.

This means that planet formation is a natural part of star formation, and most stars should have planets

The End Origin of Solar System

Concept map of the Solar system

Survey of the Solar SystemRelative Sizes of the Planets

Assume, we reduce all bodies in the solar system so that the Earth has diameter 0.3 mm.

Mercury, Venus, Earth, Mars: ~ size of a grain of salt.

Sun: ~ size of a small plum.

Jupiter: ~ size of an apple seed.

Saturn: ~ slightly smaller than Jupiter’s “apple seed”.

Pluto: ~ Speck of pepper.

ACTIVITY 1 & 2

To see how widely scattered the planets are:-

• Act 1: Solar system distances and sizes• Act 2: Solar system distances• Act 3: Relative size and distance of the planets

from the sun

General view of the Solar SystemSolar system is almost entirely empty space. The planets are small and are scattered far apart in a large disk around the sun

There are 8 planets in the solar system. Five planets are visible to the naked eyes – Mercury, Venus, Mars, Jupiter and Saturn but the other three are so distant- seen through telescopes

Humans have never set foot on any planet. Some day! But we have reached the Moon. Unmanned space vehicles have visited all of the planets

From the research, there is a home truth we should remember – the Earth is just a small, isolated planet in orbit around an ordinary, middle-aged star

Planetary Orbits

Ura

nusSaturn

Jupi

terM

ars

Earth

VenusMercury

All planets in almost circular (elliptical) orbits around the

sun, in approx. the same plane

(ecliptic).

Sense of revolution: counter-clockwise

Sense of rotation: counter-clockwise (with exception of

Venus, and Uranus)

Planets’s orbits generally inclined by no more than 3.4o

Venus rotates backwards, Uranus rotates on its side – equator almost perpendicular to its orbit

(Distances and times reproduced to scale)

Exceptions: Mercury is tipped (7o) to the plane of earth’s orbit

Two Kinds of PlanetsPlanets of our solar system can be divided into two very different kinds:

Terrestrial (earthlike) planets: Mercury,

Venus, Earth, Mars Jovian (Jupiter-like) planets: Jupiter, Saturn, Uranus,

Neptune

Terrestrial Planets

Four inner planets Four inner planets of the solar systemof the solar system

Relatively small in Relatively small in size and mass size and mass

(Earth is the largest (Earth is the largest and most massive)and most massive)

Surface of Venus cannot be seen directly from Earth because of its

dense cloud cover.

Terrestrial planets - Terrestrial planets - small, rocky, dense small, rocky, dense Earthlike worlds.Earthlike worlds. The terrestrial planets have no visible rings and few moons.

Quiz Questions

6. Which of the following is NOT a property associated with terrestrial planets?

a. They are located close to the Sun.b. They are small in size.c. They have low mass.d. They have low density.e. They have few moons.

Quiz Questions

6. Which of the following is NOT a property associated with terrestrial planets?

a. They are located close to the Sun.b. They are small in size.c. They have low mass.d. They have low density.e. They have few moons.

The Jovian Planets

All have rings (not only Saturn!) and large families of moons

Mostly gas; no solid surface

Jovian planets are large and have much lower average density.

Craters on Planets’ Surfaces

Craters (like on our Moon’s surface) are common throughout the Solar System.

Not seen on Jovian planets because they don’t have a solid surface.

Differences between Terrestrial & Jovian Planets

• Location

• Size

• Density

• Rate of rotation

• Chemical makeup

• Craters

• Rings and moons

• Thickness of atmosphere

Quiz Questions

7. How does the solar nebula theory account for the drastic differences between terrestrial and Jovian planets?

a. The temperature of the accretion disk was high close to the Sun and low far from the Sun.b. Terrestrial planets formed closer to the Sun, and are thus made of high-density rocky materials.c. Jovian planets are large and have high-mass because they formed where both rocky and icy materials can condense.d. Jovian planets captured nebular gas as they had stronger gravity fields and are located where gases move more slowly.

Quiz Questions

7. How does the solar nebula theory account for the drastic differences between terrestrial and Jovian planets?

a. The temperature of the accretion disk was high close to the Sun and low far from the Sun.b. Terrestrial planets formed closer to the Sun, and are thus made of high-density rocky materials.c. Jovian planets are large and have high-mass because they formed where both rocky and icy materials can condense.d. Jovian planets captured nebular gas as they had stronger gravity fields and are located where gases move more slowly.

Quiz Questions

8. What is the difference between the processes of condensation and accretion?

a. Both are processes that collect particles together.b. Condensation is the building of larger particles one atom (or molecule) at a time, whereas accretion is the sticking together of larger particles.c. Accretion is the building of larger particles one atom (or molecule) at a time, whereas condensation is the sticking together of larger particles.d. Both a and b above.e. Both a and c above.

Quiz Questions

8. What is the difference between the processes of condensation and accretion?

a. Both are processes that collect particles together.b. Condensation is the building of larger particles one atom (or molecule) at a time, whereas accretion is the sticking together of larger particles.c. Accretion is the building of larger particles one atom (or molecule) at a time, whereas condensation is the sticking together of larger particles.d. Both a and b above.e. Both a and c above.

Jadual Data Sistem Suria

Solar System Data

9. Self-Test1. Which of these planet’s orbits is farthest from

Earth’s orbit?

a. Mars b. Jupiter c. Uranus d. Neptune

2. Which planet has a “day” that is most similar in length to a day on Earth?

a. Mars b. Jupiter c. Uranus d. Neptune

3. Light takes about 8 minutes 20 seconds to travel from the Sun to the Earth, 150 million km away. About how long does it take light to travel from the Sun to Jupiter?

a. 10 mins b. 25 mins c. 43 mins d. 112 mins

9. Self-Test4. Which of the following conclusions about planets is

supported by the information in the Table?

A.As distance from the sun increases, period of rotation

increases

B. As distance from the sun increases, period of revolution

increases

C. As distance from the sun increases, period of revolution

decreases

D. There is no relationship between distance from the sun

and period of revolution

Space Debris (details in Chap.25)

In addition to planets, small bodies orbit the sun:- Asteroids, comets and meteoroids

Asteroid Eros, imaged by the NEAR spacecraft-34km long

Area about 11km from top to bottom

-irregular rocky body pocked by craters

Impacts from collisions with other asteroids

Asteroids

• Are small irregular rocky bodies, most of which orbit the sun in a belt between the orbits of Mars and Jupiter.

• Diameter can range from a few hundred kilometers to less than a kilometer.

• They have orbital periods of three to six years.• Common misconception that asteroids are the

remains of a planet that broke up.• In fact planets are held together very tightly by

their gravity and do not break up.

Quiz Questions

10. Where are most of the asteroids located?

a. Inside the orbit of Mercury.b. Between the orbits of Earth and Venus.c. Between the orbits of Earth and Mars.d. Between the orbits of Mars and Jupiter.e. Between the orbits of Jupiter and Neptune.

Quiz Questions

10. Where are most of the asteroids located?

a. Inside the orbit of Mercury.b. Between the orbits of Earth and Venus.c. Between the orbits of Earth and Mars.d. Between the orbits of Mars and Jupiter.e. Between the orbits of Jupiter and Neptune.

Irregular orbits of asteroids

Comets

• Comets are icy bodies that fall into the inner solar system along long elliptical orbits. As the ices vaporize and release dust, the comet develops a tail that points approximately away from the sun.

• Since the passage of Comet Halley in 1986, astronomers found evidence that comet nuclei are made of icy dirt not dirty ice. (at least 50 % rock and dust) –icy mudball model

• The nuclei of comets are ice-rich bodies left over from the formation of planets.

• These ices were important in the formation of the Jovian planets.

Comets eg Hyakutake, Hale-Bopp, Halley

Mostly objects in highly elliptical orbits, occasionally coming close to the sun.

Icy nucleus, which evaporates and gets blown into space by solar wind and solar radiation

Quiz Questions

11. How do asteroids and comets differ?

a. Asteroids orbit in the opposite direction that the Sun rotates.b. Comets are younger than asteroids.c. Asteroids have lower reflectivity.d. Comets contain ices.e. All of the above.

Quiz Questions

11. How do asteroids and comets differ?

a. Asteroids orbit in the opposite direction that the Sun rotates.b. Comets are younger than asteroids.c. Asteroids have lower reflectivity.d. Comets contain ices.e. All of the above.

MeteoroidsSmall (m – mm) sized dust, grains of sand or tiny pebbles throughout the solar system - meteoroid

If they collide with Earth, they evaporate in the atmosphere -Visible as streaks of light in the sky as meteors.

and any part that reach the earth’s surface is called meteorite

The Kuiper Beltafter Dutch –American astronomer Gerard Kuiper

Second source of small, dark, icy bodies in the outer solar system beyond Neptune discovered since 1992

Kuiper belt, at ~ 30 – 100 AU from the sun.

• Few Kuiper belt objects could be observed directly by Hubble Space Telescope.

• Some over 1000 km in diameter but most are smaller.

•Pluto and Charon may be captured Kuiper belt objects.

Can this belt generate short-period comets?

Objects from the Kuiper belt that fall into the inner solar system can become short-period comets.

Kuiper belt• Kuiper belt, at ~ 30 – 100 AU from the sun. • Second source of small, dark, icy bodies in the outer

solar system beyond Neptune discovered since 1992• Origin of short –period comet (< 200 years)

• The Kuiper belt is composed of small, icy bodies that orbit the sun beyond the orbit of Neptune.

• The icy Kuiper belt objects appear to be ancient planetesimals that formed in the outer solar system but were never incorporated into a planet.

56

More to come!• Half a million Kuiper belt objects with

diameters greater than 30 kilometers.• Beyond Neptune there are estimated to

be more than 100000 icy objects with diameters over 100km.

• Are rich in ices & have similar physical properties of comets

• With new telescopes (e.g PanStarrs) coming on line more and more of these will be discovered.

Oort Cloud –named after Dutch astronomer Jan Oort Spherical cloud of several trillion icy bodies, ~ 10,000 – 100,000 AU from the sun. (1 AU = 150 million km

10,000 – 100,000 AU

Oort Cloud

Gravitational influence of occasional passing stars may perturb some orbits and draw them towards the inner solar system.

Interactions with planets may perturb orbits further, capturing comets in short-period orbits.

A few short-period comets have been produced when long-period comets passed near Jupiter and had their orbits changed.

The long period comets appear to originate in the Oort cloud. Objects that fall into the solar system from this cloud arrive from all directions.

Kuiper Belt and Oort Cloud

58

Kuiper Belt and Oort Cloud

• Oort Cloud – spherical cloud enveloping solar system; (named after Dutch astronomer Jan Oort) source of many comets.

• Sedna comes from Oort Cloud. (origin of long-period comets (10,000 X Earth-Sun distances)

The Age of the Solar SystemSun and planets should have about the same age.

Ages of rocks can be measured through radioactive dating:

Measure abundance of a radioactively decaying element to find the time since formation of the rock

Dating of rocks on Earth, on the Moon, and meteorites all give ages of ~ 4.6 billion years.

Half-life

• The half-life of a radioactive element is the time it takes for half of the atoms to decay.

• The age of an object can be found by analyzing the abundance of radioactive elements with long half-lives. The oldest rocks from Earth, the moon, and Mars have ages approaching 4.6 billion years.

• The oldest objects in our solar system are the meteorites, which have ages of 4.6 billion years. This is taken to be the age of the solar system.

Quiz Questions

12. Radiometric dating of rock samples indicates that the Solar System formed about 4.56 billion years ago. Which rock samples have this age?

a. Earth rocks.b. Moon rocks.c. Meteorites.d. Both a and b above.e. Both b and c above.

Quiz Questions

12. Radiometric dating of rock samples indicates that the Solar System formed about 4.56 billion years ago. Which rock samples have this age?

a. Earth rocks.b. Moon rocks.c. Meteorites.d. Both a and b above.e. Both b and c above.

Radioactive Decay

(SLIDESHOW MODE ONLY)

Our Solar System

Explaining the characteristics of the solar system – read Pg 431

The Story of Planet Building

Planets formed from the same protostellar material as the sun, still found in the Sun’s atmosphere.

Rocky planet material formed from clumping together of dust grains in the protostellar cloud.

Mass of less than ~ 15 Earth masses:

Planets can not grow by gravitational collapse

Mass of more than ~ 15 Earth masses:

Planets can grow by gravitationally attracting

material from the protostellar cloud

Earthlike planetsJovian planets (gas

giants)

The Condensation of SolidsTo compare densities of planets, compensate for compression due to the planet’s gravity:

Only condensed materials could stick together to form planets

Temperature in the protostellar cloud decreased outward.

Further out Protostellar cloud cooler metals with lower melting point condensed change of chemical composition throughout solar system

Formation and Growth of Planetesimals

Planet formation starts with clumping together of grains of solid matter: Planetesimals

Planetesimals (few cm to km in size) collide to form planets.

Planetesimal growth through condensation and accretion.

Gravitational instabilities may have helped in the growth of planetesimals into protoplanets.

The Growth of Protoplanets

Simplest form of planet growth:

Unchanged composition of accreted matter over time

As rocks melted, heavier elements sink to the center

differentiation

This also produces a secondary atmosphere

outgassing

Improvement of this scenario: Gradual change of grain composition due to cooling of nebula and storing of heat from potential energy

The Jovian Problem

Two problems for the theory of planet formation:

1) Observations of extrasolar planets indicate that Jovian planets are common.

2) Protoplanetary disks tend to be evaporated quickly (typically within ~ 100,000 years) by the radiation of nearby massive stars.

Too short for Jovian planets to grow!

Solution:

Computer simulations show that Jovian planets can grow by direct gas accretion without forming rocky planetesimals.

Clearing the NebulaRemains of the protostellar nebula were cleared away by:• Radiation pressure of the sun

• Solar wind• Sweeping-up of space debris by planets

• Ejection by close encounters with planets

Surfaces of the Moon and Mercury show evidence for heavy bombardment by asteroids.

passing star hypothesisevolutionary hypothesiscatastrophic hypothesisnebular hypothesisangular momentum problemsolar nebula hypothesisextrasolar planetsterrestrial planetJovian planetGalilean satellitesasteroidcometmeteormeteoroidmeteoritehalf-lifegravitational collapse

uncompressed densitycondensation sequenceplanetesimalcondensationaccretionprotoplanetdifferentiationoutgassingheat of formationradiation pressureheavy bombardment

New Terms

1. In your opinion, should all solar systems have asteroid belts? Should all solar systems show evidence of an age of heavy bombardment?

2. If the solar nebula hypothesis is correct, then there are probably more planets in the universe than stars. Do you agree? Why or why not?

Discussion Questions

Quiz Questions

1. What was the major problem for the solar nebula hypothesis that was proposed by Pierre-Simon Laplace?

a. It did not predict that inner planets orbit the Sun more quickly than outer planets.b. The Sun contains little of the angular momentum of the Solar System.c. It called for a catastrophic event to produce the Solar System.d. The Sun spins more rapidly than is expected.e. All of the above.

Quiz Questions

2. Why do we reject the formation of planets as proposed by Buffon (the passing star hypothesis)?

a. Material pulled out of the Sun would be too hot to condense.b. Planetary systems are common, whereas nearby star collisions are rare.c. The angular momentum of the Sun is too low.d. Both a and b above.e. All of the above.

Quiz Questions

3. How do astronomers believe the Sun came to have less angular momentum than its system of planets?

a. The solar wind mass outflow carries angular momentum away from the Sun.b. The Sun's magnetic field drags material out in the Solar System, transferring angular momentum outward.c. A large planetesimal impacted the Sun on its leading hemisphere.d. The planets gain angular momentum from passing stars.e. Both a and b above.

Quiz Questions

4. What is the origin of the atoms of hydrogen, oxygen, and sodium in the perspiration that exits your body during an astronomy exam?

a. All of these elements were synthesized inside stars more than 4.6 billion years ago.b. All of the elements were produced in the first few minutes after the Big Bang event.c. The hydrogen nuclei were produced few minutes after the Big Bang event 13.7 billion years ago, and the oxygen and sodium nuclei were synthesized inside stars more than 4.6 billion years ago.d. They were all fused deep inside Earth.e. None of the above.

Quiz Questions

5. What evidence do we have that planets form along with other stars?

a. At radio wavelengths, we detect cool dust disks around young stars.b. At Infrared wavelengths, we detect large cool dust disks around stars.c. At visible wavelengths, we see disks around the majority of single young stars in the Orion Nebula.d. Both a and b above.e. All of the above.

Quiz Questions

6. How do we know that extrasolar planets are orbiting other stars?

a. We see a star's light dim as a planet passes in front of the star.b. We detect alternating Doppler shifts in the spectra of some stars.c. We see a series of small faint points in line with stars, much like Galileo's discovery of the moons of Jupiter.d. Both a and b above.e. All of the above.

Quiz Questions

7. What are the general characteristics of the extrasolar planets discovered so far?

a. They have low mass and orbit close to their stars.b. They have low mass and orbit far from their stars.c. They have high mass and orbit close to their stars.d. They have high mass and orbit far from their stars.e. These extrasolar planetary systems are much like the Solar System.

Quiz Questions

8. Why haven't we detected low-mass planets close to their stars and high-mass planets far from their stars?

a. Our techniques are not yet sensitive enough.b. We have not been observing for a long enough time.c. We have not been looking at stars similar to our Sun.d. Such systems cannot form, as the material in dust disks is densest close to their stars.e. Both a and b above.

Quiz Questions

9. How is the solar nebula theory supported by the motion of Solar System bodies?

a. All of the planets orbit the Sun near the Sun's equatorial plane.b. All of the planets orbit in the same direction that the Sun rotates.c. Six out of seven planets rotate in the same direction as the Sun.d. Most moons orbit their planets in the same direction that the Sun rotates.e. All of the above.

Quiz Questions

10. Which of the following is NOT a property associated with terrestrial planets?

a. They are located close to the Sun.b. They are small in size.c. They have low mass.d. They have low density.e. They have few moons.

Quiz Questions

11. How do asteroids and comets differ?

a. Asteroids orbit in the opposite direction that the Sun rotates.b. Comets are younger than asteroids.c. Asteroids have lower reflectivity.d. Comets contain ices.e. All of the above.

Quiz Questions

12. Where are most of the asteroids located?

a. Inside the orbit of Mercury.b. Between the orbits of Earth and Venus.c. Between the orbits of Earth and Mars.d. Between the orbits of Mars and Jupiter.e. Between the orbits of Jupiter and Neptune.

Quiz Questions

13. Radiometric dating of rock samples indicates that the Solar System formed about 4.56 billion years ago. Which rock samples have this age?

a. Earth rocks.b. Moon rocks.c. Meteorites.d. Both a and b above.e. Both b and c above.

Quiz Questions

14. According to the solar nebula theory, why are Jupiter and Saturn much more massive than Uranus and Neptune?

a. Jupiter and Saturn formed earlier and captured nebular gas before it was cleared out.b. Jupiter and Saturn contain more high-density planet building materials.c. Uranus and Neptune have suffered more interstellar wind erosion.d. Both a and b above.e. All of the above.

Quiz Questions

15. How does the solar nebula theory account for the drastic differences between terrestrial and Jovian planets?

a. The temperature of the accretion disk was high close to the Sun and low far from the Sun.b. Terrestrial planets formed closer to the Sun, and are thus made of high-density rocky materials.c. Jovian planets are large and have high-mass because they formed where both rocky and icy materials can condense.d. Jovian planets captured nebular gas as they had stronger gravity fields and are located where gases move more slowly.e. All of the above.

Quiz Questions

16. What is the difference between the processes of condensation and accretion?

a. Both are processes that collect particles together.b. Condensation is the building of larger particles one atom (or molecule) at a time, whereas accretion is the sticking together of larger particles.c. Accretion is the building of larger particles one atom (or molecule) at a time, whereas condensation is the sticking together of larger particles.d. Both a and b above.e. Both a and c above.

Quiz Questions

17. Which of the following is the most likely major heat source that melted early-formed planetesimals?

a. Tidal flexing.b. The impact of accreting bodies.c. The decay of long-lived unstable isotopes.d. The decay of short-lived unstable isotopes.e. The transfer of gravitational energy into thermal energy.

Quiz Questions

18. How does the solar nebula theory explain the formation of an asteroid belt between Mars and Jupiter, rather than a planet at this location?

a. A single planet formed here and was disrupted by an impact with a large comet from the outer Solar System. b. Jupiter swept up so much material that not enough was left to form a planet.c. Mars was once larger and collided with a large planetesimal from the inner Solar System that sent debris outward.d. Jupiter formed early, and its gravitational influence altered the orbits of nearby accreting planetesimals such that their collisions became destructive rather than constructive.e. The asteroids were originally moons of the planets that were perturbed by Jupiter's gravity, and now reside in the zone between Mars and Jupiter.

Quiz Questions

19. Which of the following accurately describes the differentiation process?

a. High-density materials sink toward the center and low-density materials rise toward the surface of a molten body.b. Low-density materials sink toward the center and high-density materials rise toward the surface of a molten body.c. Only rocky materials can condense close to the Sun, whereas both rocky and icy materials can condense far from the Sun.d. Both rocky and icy materials can condense close to the Sun, whereas only rocky materials can condense far from the Sun.e. Small bodies stick together to form larger bodies.

Quiz Questions

20. How did the solar nebula get cleared of material?

a. The radiation pressure of sunlight pushed gas particles outward.b. The intense solar wind of the youthful Sun pushed gas and dust outward.c. The planets swept up gas, dust, and small particles.d. Close gravitational encounters with Jovian planets ejected material outward.e. All of the above.