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Lecture PowerPoint Chapter 6 Astronomy Today, 5 th edition Chaisson McMillan. © 2005 Pearson Prentice Hall

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Lecture PowerPoint

Chapter 6

Astronomy Today,

5th edition



© 2005 Pearson Prentice Hall

This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials.


Chapter 6

The Solar System

learning goals
Learning Goals
  • What is comparative planetology?
  • Describe the scale & structure of our solar sytem
  • Summarize the basic differences between the terrestrial & jovian planets
  • Identify & describe the major non-planetary components of our solar system
  • Describe some important solar system exploration spacecraft missions
  • Cosmogony – theories of solar system formation

Units of Chapter 6

An Inventory of the Solar System

Planetary Properties

Computing Planetary Properties

The Overall Layout of the Solar System

Terrestrial, Jovian & Dwarf Planets

Interplanetary Debris (asteroids, comets & meteors)


Units of Chapter 6, cont.

Spacecraft Exploration of the Solar System

Gravitational “Slingshots”

How Did the Solar System Form?

The Concept of Angular Momentum


6.1 An Inventory of the Solar System

Early astronomersknew the Moon, stars, Mercury, Venus, Mars, Jupiter, Saturn, comets, and meteors

Now known: Solar system has 166 moons, one star, eight planets (added Uranus & Neptune), many objects in the new class called dwarfplanets (Pluto, Ceres, Eris, …), asteroids, comets, and meteoroids


6.2 Planetary Properties

  • Distance from Sun known by Kepler’s laws
  • Orbital periodcan be observed
  • Radius known from angular size
  • Masses from Newton’s laws
  • Rotation period from observations
  • Density can be calculated knowing radius and mass

6.3 The Overall Layout of the Solar System

All orbits paths are close to the ecliptic plane

Pluto’s orbit does not (17° tilt)


6.4 Terrestrial and Jovian Planets

Relative sizes of the Sun & Planets

It would take 109

Earths to span the



6.4 Terrestrial and Jovian Planets

Terrestrial planets:

Mercury, Venus, Earth, Mars

Jovian planets:

Jupiter, Saturn, Uranus, Neptune

Pluto is neither but a new class called the

Dwarf planets


6.4 Terrestrial and Jovian Planets

  • Differences (Comparative Planetology) between the terrestrial planets:
  • Atmospheres and surface conditionsare very dissimilar
  • Only Earth has oxygen in atmosphere and liquid water on surface
  • Earth and Mars rotate at about the same rate; Venus and Mercury are much slower, and Venus rotates in the opposite direction
  • Earth and Mars have moons; Mercury and Venus don’t
  • Earth and Mercury have magnetic fields; Venus and Mars don’t

6.5 Interplanetary Debris

Asteroids and meteoroids have rocky composition; asteroids are bigger

Asteroid Eros is 34 km long:


6.5 Interplanetary Debris

Comets are icy, with some rocky parts.

Comet Hale–Bopp


ion tail

dust tail


6.6 Spacecraft Exploration of the Solar System

Mariner 10: flew by Mercury, 1974–75

MESSENGER: it’s there now!


Mariner 10


6.6 Spacecraft Exploration of the Solar System

Soviet Venera probes landed on Venus from 1970–1978:


6.6 Spacecraft Exploration of the Solar System

Viking landers arrived at Mars in 1976:


Spacecraft Exploration of the Solar System

TheSojourner Rover was deployed on Mars in 1997 as part of the Pathfinder Mission


6.6 Spacecraft Exploration of the Solar System

Pioneer 10 & 11 and Voyager 1 & 2 flew through the outer solar system. This is Voyager:


6.6 Spacecraft Exploration of the Solar System

The Cassini mission is now orbiting around Saturn, the ring system and its many moons; it used many gravity assists to get there:


6.6 Spacecraft Exploration of the Solar System

Gravitational “slingshots” can change the trajectories of spacecraft, and also accelerate them:


6.7 How Did the Solar System Form?

Nebular contraction:

Cloud of gas and dust contracts due to gravity; conservation of angular momentum means it spins faster and faster as it contracts


6.7 How Did the Solar System Form?

Condensation theory:

Interstellar dust grains help cool cloud, and act as condensation nuclei


6.7 How Did the Solar System Form?

Conservation of angular momentum says that product of radius and rotation rate must be constant:

L = mvr

Lbefore = Lafter

m1 v1r1 = m2 v2r2

Think ice skaters, divers

& gymnasts


6.7 How Did the Solar System Form?

Temperature in nebular clouddetermines where various materials condense out:


Summary of Chapter 6

  • Solar system consists of Sun and everything orbiting it
  • Asteroids are rocky, and most orbit between orbits of Mars and Jupiter
  • Comets are icy, and are believed to have formed early in the solar system’s life
  • Major planets orbit Sun in same sense, and all but Venus rotate in that sense as well
  • Planetary orbits lie almost in the same plane

Summary of Chapter 6, cont.

  • Four inner planets – terrestrial planets – are rocky, small, and dense
  • Four outer planets – jovian planets – (omitting Pluto) are gaseous and large
  • Nebular theory of solar system formation: cloud of gas and dust gradually collapsed under its own gravity, spinning faster as it shrank
  • Condensation theorysays dust grains acted as condensation nuclei, beginning formation of larger objects