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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.