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HNRS 227 Fall 2007Chapter 13

The Solar Systempresented by Dr. Geller

23 October 2007

Key Points of Chapter 13

• Planets– Mercury, Venus, Earth, Mars, Jupiter, Saturn,

Uranus, Neptune• Dwarf Planets

– Pluto, Ceres and Eris• Asteroids and Comets• Meteors and Meteorites• Origin of the Solar System

What is a Planet?IAU RESOLUTION 5Definition of a Planet in the Solar SystemContemporary observations are changing our understanding of planetary systems, and it

is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation "planets". The word "planet" originally described "wanderers" that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information. The IAU therefore resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:

• (1) A planet is a celestial body that– (a) is in orbit around the Sun,– (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a

hydrostatic equilibrium (nearly round) shape, and– (c) has cleared the neighbourhood around its orbit.

• (2) A "dwarf planet" is a celestial body that– (a) is in orbit around the Sun,– (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a

hydrostatic equilibrium (nearly round) shape,– (c) has not cleared the neighbourhood around its orbit, and– (d) is not a satellite.

• (3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

What is Pluto?

IAU RESOLUTION 6PlutoThe IAU further resolves:• Pluto is a "dwarf planet" by the above

definition and is recognized as the prototype of a new category of Trans-Neptunian Objects.

There are two broad categories of planets: Terrestrial and Jovian

• All of the planets orbit the Sun in the same direction and in almost the same plane

• Most of the planets have nearly circular orbits

Tycho Brahe’sastronomical observations (unaided eye)

provided evidence for heliocentric model of the solar system

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Kepler’s Laws (no longer in textbook, but you should be aware of them)

• Using data collected by TychoBrahe, Kepler deduced three laws of planetary motion:– the orbits are ellipses

– with Sun at one focus– Planets sweep out equal

areas in equal times• a planet’s speed varies as

it moves around its elliptical orbit

– The period squared equals the semi-major axis cubed• the orbital period of a

planet is related to the size of its orbit

» P2 = a3

Galileo’s observations with a telescope supported the heliocentric model

• Galileo’s observations reported in 1610– the phases of Venus*– the motions of the

moons of Jupiter*– “mountains” on the

Moon– Sunspots on the Sun

*observations supporting heliocentric model

Density

VmD =

• The average density of any substance depends in part on its composition

• An object sinks in a fluid if its average density is greater than that of the fluid, but rises if its average density is less than that of the fluid

• The terrestrial (inner) planets are made of rocky materials and have dense iron cores, which gives these planets high average densities

• The Jovian (outer) planets are composed primarily of light elements such as hydrogen and helium, which gives these planets low average densities

The Terrestrial Planets

• The four inner planets are called terrestrial planets– Relatively small (with diameters of 5000 to 13,000 km)– High average densities (4000 to 5500 kg/m3)– Composed primarily of rocky materials

Cratering on planets and satellites is the result of impacts from interplanetary debris

• When an asteroid, comet, or meteoroid collides with the surface of a terrestrial planet or satellite, the result is an impact crater

• Geologic activity renews the surface and erases craters, so a terrestrial world with extensive cratering has an old surface and little or no geologic activity

• Because geologic activity is powered by internal heat, and smaller worlds lose heat more rapidly, as a general rule smaller terrestrial worlds are more extensively cratered

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Picture of Moon taken with GMU telescope and CCD by H. Geller

Venus has a hot, dense atmosphere and corrosive

cloud layers• Spacecraft measurements

reveal that 96.5% of the Venusian atmosphere is carbon dioxide

• Most of the balance of the atmosphere is nitrogen.

• Venus’s clouds consist of droplets of concentrated sulfuric acid.

• The surface pressure on Venus is 90 atm, and the surface temperature is 460°C

• Both temperature and pressure decrease as altitude increases

iClicker Question

Venus is very bright in the skyA due to highly reflective rocks on the surface.B due to the lightening discharges in the

atmosphere.C largely due to the highly reflective cloud cover.D due to being closer to the sun than any other

planet.E because of the accumulative effects of all of

the above factors.

iClicker Question

The Venus atmosphereA is almost completely water.B is almost completely carbon dioxide.C is almost completely nitrogen.D is almost completely oxygen.E is almost completely methane.

iClicker Question

The greenhouse effect on Venus has causedA little or no effect on the temperature of Venus.B the surface temperature to be much higher

than what might be expected otherwise.C slow rotation rates of clouds of Venus.D the same effect on Mercury.E reduction of the surface temperature.

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iClicker Question

Venus has been explored best byA spacecraft and radio observations.B spacecraft and visual (visible light)

observations.C spacecraft only.D radio and visual (visible light)

observations.E none of the above techniques.

iClicker QuestionVenus may have had an ocean of waterA but is all frozen at the poles of Venus now.B but it is now trapped in the subsurface of the

planet.C but it was all lost to space.D which now exists as water vapor in the

atmosphere.E but the water broke up into its constituents and

the hydrogen escaped and the oxygen was absorbed by the surface rocks.

iClicker Question

Venus is hot becauseA of its closeness to the sun.B of its dense atmosphere.C its atmosphere is almost completely

CO2.D all of the above factors are true.E None of the above.

iClicker Question

Venus has craters thatA are all due to meteoritic impacts.B are all volcanic since no meteor

penetrated the thick atmosphere.C are mostly volcanic in nature, but there

are some meteoritic.D origins are not known.E are all different than any others known.

The Changing Face of Mars

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iClicker Question

Among the following, which discovered the most information about Mars?

A The Pioneer spacecraft.B The Galileo spacecraft.C The Voyager spacecraft.D The Viking spacecraft and its lander.E The spacecraft Magellan using Synthetic

Aperture Radar.

iClicker Question

Mars' two moons, probably captured asteroids, are called

A Valles and Marineris.B Phobos and Deimos.C Chryse and Planitia.D Olympus and Mons.E Romulus and Remus.

iClicker QuestionPart of the Martian surface is higher in altitude and

has a higher crater density. This tells us thatA dust storms destroyed the surface of Mars in

other regions.B sulfuric acid rain destroyed the surface of

Mars.C this surface is older and has not seen the

erosion that other portions experienced.D volcanic ash is a form of grounded up rock.E the atmosphere was denser and of different

composition in that region.

iClicker Question

Mars volcanoes are generally higher above the surface than Earth's volcanoes because

A its material is less dense than Earth rock.B it has a thin crust.C it has a thick crust.D it is further from the Sun.E largely because of lower gravity.

iClicker Question

Ultimately, Viking's search for lifeA gave no definitive answer as to the

existence of life on Mars.B proved that there was life on Mars.C proved that there was no life on Mars.D proved that there was no organic life on

Mars.E discovered microscopic life remains in

the rocks.

Jovian Planets

• The four giant outer planets are called Jovianplanets– Large diameters (50,000 to 143,000 km)– Low average densities (700 to 1700 kg/m3)– Composed primarily of hydrogen and helium.

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Seven large satellites are almost as big as the terrestrial planets

• Comparable in size to the planet Mercury• The remaining satellites of the solar system are much smaller

Spectroscopy reveals the chemical composition of the planets

• The spectrum of a planet or satellite with an atmosphere reveals the atmosphere’s composition

• If there is no atmosphere, the spectrum indicates the composition of the surface.

• The substances that make up the planets can be classified as gases, ices, or rock, depending on the temperatures at which they solidify

• The terrestrial planets are composed primarily of rocky materials, whereas the Jovian planets are composed largely of gas

Pluto•Pluto is a special case

– Now called a “dwarf planet”

– Smaller than any of the terrestrial planets

– Intermediate average density of about 1900 kg/m3

– Density suggests it is composed of a mixture of ice and rock

iClicker Question

How can we know the composition of the atmosphere of Pluto?

A We cannot know, it is all just a theory.B We can use spectral analysis.C We can use pyschokinesis.D We sent a spacecraft to Pluto.E We use gravitational perturbations.

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iClicker Question

Pluto's surface and interiorA consists of partially hydrated rock, organics

and water ice.B consists of partially hydrated rock and layers of

water ice.C either A or B above are feasible.D can never be determined.E cannot be determined until we land on Pluto.

iClicker Question

In terms of size and mass, Pluto is most similar to which of the following:

A IoB TitanC PhobosD DeimosE Triton

Hydrogen and helium are abundant on the Jovianplanets, whereas the terrestrial planets are

composed mostly of heavy elements

A planet with a magnetic field indicates a fluid interior in motion

• Planetary magnetic fields are produced by the motion of electrically conducting liquids inside the planet

• This mechanism is called a dynamo

• If a planet has no magnetic field, that is evidence that there is little such liquid material in the planet’s interior or that the liquid is not in a state of motion

• The magnetic fields of terrestrial planets are produced by metals such as iron in the liquid state

• The stronger fields of the Jovian planets are generated by liquid metallic hydrogen or by water with ionized molecules dissolved in it

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The diversity of the solar system is a result of its origin and evolution

• The planets, satellites, comets, asteroids, and the Sun itself formed from the same cloud of interstellar gas and dust

• The composition of this cloud was shaped by cosmic processes, including nuclear reactions that took place within stars that died long before our solar system was formed

• Different planets formed in different environments depending on their distance from the Sun and these environmental variations gave rise to the planets and satellites of our present-day solar system

Planetary Observations

• Planets formed at same time as Sun• Planetary and satellite/ring systems are

similar to remnants of dusty disks such as that seen about stars being born

• Planet composition dependent upon where it formed in solar system

Other Observations• Radioactive dating of solar system rocks

– Earth ~ 4 billion years– Moon ~4.5 billion years– Meteorites ~4.6 billion years

• Most orbital and rotation planes confined to ecliptic plane with counterclockwise motion

• Extensive satellite and rings around Jovians• Planets have more of the heavier elements than

the sun

A Linear View of AbundanceLinear Plot of Chemical Abundance

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

H He C N O Ne Mg Si Si Fe

Chemical Species

Rel

ativ

e ab

unda

nce

Log Abundance of ElementsLogarithmic Plot of Chemical Abundance of Elements

1

10

100

1000

10000

100000

H He C N O Ne Mg Si Si Fe

Chemical Species

Rel

ativ

e A

bund

ance

Planetary Summary

PlanetMass

(Earth=1)Density(g/cm3)

MajorConstituents

MercuryVenusEarthMars

0.060.821.000.11

5.45.25.53.9

Rock, IronRock, IronRock, IronRock, Iron

JupiterSaturn

31895

1.30.7

H, HeH, He

UranusNeptune

1417

1.31.7

Ices, H, HeIces, H, He

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Nebular Condensation (protoplanet) Model

• Most remnant heat from collapse retained near center

• After sun ignites, remaining dust reaches an equilibrium temperature

• Different densities of the planets are explained by condensation temperatures

• Nebular dust temperature increases to center of nebula

Nebular Condensation Physics

• Energy absorbed per unit area from sun = energy emitted as thermal radiator

• Solar Flux = Lum (Sun) / 4 x distance2

• Flux emitted = constant x T4 [Stefan-Boltzmann]

• Concluding from above yields

–T = constant / distance0.5

Nebular Condensation Chemistry

Molecule Freezing Point Distance fromCenter

H2 10 K >100 AUH2O 273 K >10 AUCH4 35 K >35 AUNH3 190 K >8 AU

FeSO4 700 K >1 AUSiO4 1000 K >0.5 AU

Nebular Condensation Summary• Solid Particles collide, stick together, sink

toward center– Terrestrials -> rocky– Jovians -> rocky core + ices + light gases

• Coolest, most massive collect H and He• More collisions -> heating and

differentiating of interior• Remnants flushed by solar wind• Evolution of atmospheres

Thought Questions

• Describe the surface and atmospheric conditions on Mars.

• What evidence exists that Mars at one time had abundant liquid water?

• If Mars did have liquid water at one time, what happened to it and why?

• Describe the internal structure of Jupiter and Saturn.

Surface features indicate that water once flowed on Mars

• Flash-flood features and dried riverbeds on the Martian surface indicate that water has flowed on Mars at least occasionally

• No liquid water can exist on the Martian surface today– Check phase

diagram

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Jupiter and Saturn Interior Jupiter and Saturn Atmosphere

Jupiter Atmosphere

Details

iClicker Question

Jupiter is believed to have a massive coreA where fusion takes place.B consisting of liquid hydrogen.C consisting of gaseous hydrogen and

helium.D consisting of metallic hydrogen.E consisting of rocky material.

iClicker Question

Jupiter emits radio wavesA caused by charged particles moving in its

magnetic field.B caused by metallic hydrogen in the

mantle.C massive gravitational forces.D caused by the Great Red Spot.E large Coriolis forces on the atmosphere.

iClicker Question

• Saturn has a magnetic fieldA caused by rapid rotation of methane clouds.B caused by rapid rotation of nitrogen clouds.C caused by rapid rotation of metallic hydrogen.D caused by rapid rotation of molecular

hydrogen.E caused by rapid rotation of water ice.

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iClicker Question

• The rings of SaturnA are solid rings around Saturn.B lie within the Roche limit of Saturn.C lie outside the Roche limit of Saturn.D lie precisely at the Roche limit of Saturn.E are not visible from Earth-bound

telescopes.

iClicker Question

• Voyager 1 and 2 made major discoveries about Jupiter including

A the fact that Jupiter has a ring.B the fact that Jupiter's red spot has complex

eddies, like a hurricane on Earth.C the fact that Jupiter's moons are as varied as

the planets themselves.D All of the above.E None of the above

iClicker Question

• Saturn gives off more heat than it absorbsA because of its enormous mass.B because its methane is a greenhouse gass.C because its thick clouds contribute to heat

generation.D because of helium rain that gives off heat as it

falls to center.E because it is radiating heat left over from its

formation.

iClicker Question

Jupiter is noticeably oblateA mainly because of its strong magnetic

field.B mainly because of its distance from the

Sun.C mainly because of rapid rotation.D mainly because of the tidal effects of its

moons.E mainly because of its large mass.

iClicker Question

Jupiter is believed to have a massive coreA where fusion takes place.B consisting of liquid hydrogen.C consisting of gaseous hydrogen and

helium.D consisting of metallic hydrogen.E consisting of rocky material.

iClicker Question

Jupiter emits radio wavesA caused by charged particles moving in its

magnetic field.B caused by metallic hydrogen in the

mantle.C massive gravitational forces.D caused by the Great Red Spot.E large Coriolis forces on the atmosphere.

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iClicker Question

• Saturn has a magnetic fieldA caused by rapid rotation of methane clouds.B caused by rapid rotation of nitrogen clouds.C caused by rapid rotation of metallic hydrogen.D caused by rapid rotation of molecular

hydrogen.E caused by rapid rotation of water ice.

iClicker Question

• The rings of SaturnA are solid rings around Saturn.B lie within the Roche limit of Saturn.C lie outside the Roche limit of Saturn.D lie precisely at the Roche limit of Saturn.E are not visible from Earth-bound

telescopes.

Thought Questions

• Describe some unusual features found on the moons of Jupiter, Saturn and Neptune.

• What are the similarities and differences between the Sun and Jupiter?

• What evidence exists today that the number of rocks and rock particles floating around in the solar system was much greater in the past soon after the planets formed?

Thought Questions

• Explain why oxygen is a major component of Earth’s atmosphere but not the atmospheres of Venus or Mars.

• Using the properties of the planets other than Earth, discuss the possibilities of life on each.

• What are “shooting stars”? Where do they come from? Where do they go?

Comets and AsteroidsSmall chunks of rock and ice also

orbit the Sun• Asteroids are small, rocky

objects, while comets and Kuiper belt objects are made of dirty ice

• All are remnants left over from the formation of the planets

• The Kuiper belt extends far beyond the orbit of Pluto

• Pluto can be thought of as the largest member of the Kuiper belt

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Thought Questions

• What is a meteorite? What is the most likely source of meteorites?

iClicker QuestionWhich of the following is true of comets and

asteroids?A Earth is just as much at risk now, of an impact,

as it was in the distant past.B All impacts are detrimental to life.C Every mass extinction on Earth was caused by

an impact.D All of the above.E None of the above.

iClicker Question

Which of the following meteor showers are linked to cometary debris?

A OrionidsB LeonidsC GeminidsD All of the above.E None of the above.

iClicker Question

The orbits of most asteroidsA lie beyond the orbit of Mars.B cross the orbit of Mars.C lie beyond the orbit of Jupiter.D cross the orbit of Earth.E bring them near the Sun.

iClicker Question

Comets are thought to reside mainly inA the inner solar system.B an orbit between Mars and Jupiter.C the solar nebula.D an orbit parallel to Earth.E the Oort Cloud and Kuiper Belt.

iClicker Question

Comets are made ofA silicates.B dust particles.C methane, ammonia and water ice.D all of the above.E None of the above.

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iClicker Question

Meteor showers are caused byA a small constellation of dying stars, called

shooting stars.B Earth crossing the orbit of a comet's debris.C Earth crossing the orbit of the asteroid belt.D Earth crossing the orbit of an asteroid.E a large number of iron filings.

iClicker Question

The Oort Cloud is considered to beA a cloud of debris between Mars and Jupiter.B a cloud of comets surrounding the solar

system.C a cloud of comets near Pluto.D a cloud of comets in the inner solar system.E a cloud of comets in the Jovian neighborhood.

iClicker Question

• Jupiter emits more energy than it absorbsA due to the helium rain falling in.B due to the escape of gravitational energy

released during its formation.C due to the decay of radioactive elements.D due to a small amount of fusion in its core.E due to the generation of heat from tidal forces.

iClicker Question

• Saturn's famous rings areA composed of complex carbohydrates.B composed of a solid thin disk of material.C composed mostly of rocky boulders.D composed of a disk of liquid helium.E composed mostly of icy particles moving

about Saturn.

iClicker Question• The Roche limit is an important conceptA that defines the maximum brightness a moon

be be.B that defines the maximum mass a moon can

possess.C that defines the maximum density of a planets'

ring system.D that defines the critical distance from a planet

inside of which a moon can be tidally destroyed.

E that defines the critical distance from a planet to its moon.

iClicker Question

• The most geologically active moon isA Io.B Ganymede.C Europa.D Callisto.E Almathea.

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iClicker Question

• Volcanic activity on the geologically active moon of Jupiter is caused by

A Jupiter's enormous mass.B tidal stresses from Jupiter alone.C tidal stresses from all other moons.D tidal stresses from Jupiter and Europa.E Jupiter's enormous gravity.

iClicker Question• In general what can be said about Jupiter's

moons?A That all the moons were formed with Jupiter.B That some formed with Jupiter and some were

captured.C That all the moons were captured by Jupiter.D That some moons formed in the inner solar

system.E That all the moons are larger that the terrestrial

planets.

iClicker Question

• Saturn's moon Titan is most interestingA because it possess an atmosphere like that of

today's Earth.B because it possesses a thick atmosphere that

may be like primordial Earth's atmosphere.C because it has ice volcanism.D because it is a large moon.E because it demonstrates the Roche critical

limit.

iClicker Question

• Titan's atmosphereA consists mostly of hydrogen.B consists mostly of carbon dioxide.C consists mostly of sulfur.D consists mostly of methane.E consists mostly of nitrogen.