March 28, 2006Astronomy 20101 Chapter 6 Other Worlds: An Introduction to the Solar System What are the basic properties of the solar system? What are some

March 28, 2006 Astronomy 2010 1

Chapter 6

Other Worlds: An Introduction to the Solar System

What are the basic properties of the solar system?

What are some of the general patterns in the solar system?What do these patterns tell us

about the how the solar system formed?

Is (was) there life beyondEarth?


6.1 Overview of Our Planetary System

• We have sent spacecraft to every planet except Pluto.– Also to moons, comets, and an

asteroid.

• We’ve learned much about the planets and the solar system.

• We want to get an overview of the solar system, and then discuss in more detail in chs. 7 to 13.


Our Planetary System is the Solar System


6.1.1 An Inventory

Object Percentage of Total Mass

Sun 99.80%

Jupiter 0.10%

Comets 0.05%

All other planets 0.04%

Satellites and rings 0.00005%

Asteroids 0.000002%

Cosmic dust 0.0000001%

Most of the mass of the solar system is in the Sun.In this chapter we are discussing everything else.


The Nine Planets


The Nine Planets• The masses of the Sun, Earth, Jupiter, and other

objects are measured by observing the effect of their gravity.

• All the planets orbit the Sun in the same directions.

• All the orbits lie (almost) in the same plane.

• All the planets rotate (spin) about an axis.– Most rotate in the same direction as they orbit.– Venus rotates backwards– Pluto and Uranus spin “on their sides”


The Orbits of the Planets


Terrestrial Planets• The four innermost

planets:– Mercury– Venus– Earth– Mars

• Small, composed of rock and metal, with solid surfaces.

Mars


Jovian Planets• The next four planets are

called Jovian or giant planets– Jupiter

– Saturn

– Uranus

– Neptune

• Mostly liquids and gases• No solid surface we can

stand on.


6.1.2 Smaller Members of the Solar System

• Satellites or moons– All the planets except Mercury and Venus have

moons (small “m”)

• Rings– All the giant planets have rings

• Asteroids– Rocky metallic objects, mostly in the asteroid belt

• Comets– Chunks of ice, mostly beyond the orbit of Pluto


A Scale Model of the Solar SystemDiameter Distance from Sun

Sun 5cm 0m

Mercury 0.17mm 2.0m

Venus 0.43mm 3.9m

Earth 0.46mm 5.3m

Mars 0.24mm 8.1m

Jupiter 5.1mm 28m

Saturn 4.3mm 51m

Uranus 1.8mm 100m

Neptune 1.8mm 160m

Pluto 0.08mm 210m


6.2 Composition and Structure of Planets

• Three groups by composition– Giant planets: Jupiter, Saturn, Uranus, Neptune– Terrestrial planets: Mercury, Venus, Earth, Mars– Pluto

• The different compositions and locations can help us understand how they formed.


6.2.1 The Giant Planets• Core of metal, rock, and ice• Surrounded by hydrogen

and helium• Strong gravity holds and

compresses the hydrogen and helium into liquid form

• The pressure at the core is so great that any material will be crushed no solid surface to land on.


6.2.2 The Terrestrial Planets• Composed primarily of

rocks and metals– Silicon, oxygen, nickel,

iron

• Densest metals in the central core

• Differentiated– Interior of the planets

are or were molten long enough to allow the heavier elements to settle to the core


6.2.3 Moons, Asteroids, and Comets• Earth’s Moon is like the

terrestrial planets• Mars’ moons look like

captured asteroids• Other moons more

similar to the cores of the giant planets they orbit -- differentiated

• Asteroids and comets are probably unchanged since they formed.


6.2.4 Temperatures: Going to Extremes

• Generally, the farther something is from the Sun, the colder it is.– Mercury: 500K– Pluto: 50K

• Venus breaks this rule, since at 700K it is hotter than Mercury but further from the Sun.

• Earth is the only planet at about the right place to have liquid water


6.2.5 Geological Activity• Planetary crusts are

modified by both internal and external forces.

• Good evidence that all the planets have seen considerable number of impacts.

• Impacts more frequent in the early history of solar system

• Volcanos and seismic quakes produced by internal heat.


6.3 Dating Planetary Surfaces• We’d like to know the

age of a planet’s surface

• Two techniques:– Counting the craters– Radioactive rocks


6.3.2 Radioactive Rocks• Relies on the natural

abundances of certain radioactive isotopes

• Used to determine the age of the Earth and Moon– 4.5 billion years

• Radioactive isotopes are atoms that decay and transform into a different atom.– In a half-life, half of the

radioactive isotopes decay.


6.4 Origin of the Solar System

• Where did the solar system come from?

• How did it form?

• Look at the patterns in the solar system as a whole to get a clue.


6.4.1 Looking for Patterns• All the planets revolve around the Sun in the same

direction, and in nearly the same plane

• The Sun rotates in the same direction

• Hypothesis: the Sun and planets formed from a spinning system called the solar nebula. (discuss angular momentum)


6.4.2 The Evidence from Far Away

• In cool gas clouds, like the one pictured on the cover of the book, we find evidence for new star formation.

• In some instances we see evidence of a disk of material around the star, a stellar nebula.


Recent Photo from Spitzer Space Tele.


The Search for Life Beyond Earth

• We are searching for evidence of life within our solar system.

• Advantages: we can send probes or humans to the locations to perform direct tests

• Disadvantages: limited possible locales

• The search is concentrated on Mars and Europa, one of Jupiter’s moon’s.


Dear Professor Robert Harr Good morning, I like to present for you these lines of our recently published book about Astronomy, that I have translated, and which you can see at our website. Your brother E. A. Nassir The Mistake of Astronomers about Mars Mars is bigger than Earth; it is about one and a half times (less than! two times) that of Earth.Click here - [The Wrong Calculations of Astronomers Concerning Mars]: If it were smaller than Earth, it would be nearer than Earth to Sun.Click on: the cause of a planet being near the sun and another being far , and see- at our website- the diagram 3 of a simple experiment. Mars is inhabited: having rivers, seas, deserts, plains, mountains, day and night, and the plant, the animal and intelligent human beings to whom God has sent their apostles a! nd prophets, out of themselves. Click here The Planets Are Inhabited There will be an anticipated meeting between the people of Earth and the people of Mars, which may be a fruitful one. Click here An Anticipated Meeting between the Inhabitants of Earth and some other Planets The circumstances and conditions on Earth will become bad in the future (when Earth will stop its axial rotation; like what happened to Venus and Mercury before, on which life was exterminated), then there will be a migration from Earth to Mars. Click here The Traveling to Mars Is Successful

http://www.universeandquran.741.com/new_page_3.htm#Calculations%20concerning%20Mars

http://www.universeandquran.741.com/My%20Webs/new_page_2.htm#A%20!%20Planet%20Being%20Near%20Sun

http://www.universeandquran.741.com/new_page_1.htm#Planets%20Inhabited

http://www.universeandquran.741.com/new_page_1.htm#Planets%20Inhabited

http://www.universeandquran.741.com/new_page_4.htm#Meeting%20Between%20Inhabitants

http://www.universeandquran.741.com/new_page_4.htm#Meeting%20Between%20Inhabitants

http://www.universeandquran.741.com/new_page_2.htm#Traveling%20to%20Mars


Discussion Question• Here is planet Earth

• Which other object in the solar system do you think is most interesting for the next NASA mission, and why?

Documents

March 28, 2006Astronomy 20101 Chapter 6 Other Worlds: An Introduction to the Solar System What are the basic properties of the solar system? What are some