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General Properties of the Solar System … continued. Announcements. Reading for next class 8-4, 8-5, 8-6 (pp. 171-180) Quiz today Closed book, closed note, no electronic devices (like it will be for the exam) First Exam Next Thursday (2/15) - PowerPoint PPT Presentation
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PTYS/ASTR 206 Solar System2/8/07
General Properties of the Solar System …
continued
PTYS/ASTR 206 Solar System2/8/07
Announcements
• Reading for next class– 8-4, 8-5, 8-6 (pp. 171-180)
• Quiz today– Closed book, closed note, no electronic devices (like it will be for the
exam)
• First Exam Next Thursday (2/15)– Brief review and discussion of the exam format on Tuesday– Come prepared with questions– Make use of study groups, instructor and TA office hours to help
you prepare
PTYS/ASTR 206 Solar System2/8/07
Next Week’s Preceptor-led Study Group
• Monday – 10:30AM-12:00PMPreceptors: Chris Dockins, Maggie Jahn, Katie Landon, and Jared MosleyRoom 330 of Kuiper Space Sciences
– We encourage you to attend and study for the exam with a group of students from the class
PTYS/ASTR 206 Solar System2/8/07
• Most massive object in the solar system
• Formed at about the same time as all of the planets, and from the same material
• The source of energy that keeps is shining for billions of years is thermonuclear fusion
Solar-system inventory continued…The Sun
PTYS/ASTR 206 Solar System2/8/07
Solar-system inventory continued… The Solar Wind
• The solar corona is in a constant state of expansion and continues off into space, creating the Solar Wind
• The Solar Wind is a plasma – the 4th state of matter (solid, liquid, and gas are the other 3)
• Its existence was predicted based on observations of comet tails (the blue ion tail in the picture is directed along the solar wind)
PTYS/ASTR 206 Solar System2/8/07
Solar-system inventory continued…Small 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 (or icy dirt?)
• All are remnants left over from the formation of the planets
• Some of them contain the primordial material from which the solar system is made
PTYS/ASTR 206 Solar System2/8/07
• Asteroid belt
– Between the orbits of Mars and Jupiter
– Probable origin of Near-Earth objects
• Kuiper Belt Objects– Beyond the orbit of Neptune– Distributed loosely along the
ecliptic plane– Pluto is a large KBO
PTYS/ASTR 206 Solar System2/8/07
Solar-system inventory continued… The outer reaches of the Solar System
• The Heliosphere– The cavern carved out of the
interstellar gas by the solar wind
• The Oort Cloud– contains billions of comet nuclei in a
spherical distribution that extends out to 50,000 AU from the Sun
– Intermediate period and long-period comets are thought to originate in the Oort cloud
– As yet no objects in the Oort cloud have been detected directly
PTYS/ASTR 206 Solar System2/8/07
Structure of a Terrestrial Planet
• Metallic core in center
• Rocky mantle
• Crust of some sort?
• All are differentiated– But the proportions of the
core, mantle, crust, differ
Look up its definition !
PTYS/ASTR 206 Solar System2/8/07
Will a planet have active volcanoes?
• Requires Heat – After the planets formed, they
were very hot– Big planets cool slower – Small planets cool more rapidly
• Big terrestrial planets are active longer– Fewer craters– More likely to have active
volcanoes• Earth and Venus for example –
both of these worlds also have very few visible craters
PTYS/ASTR 206 Solar System2/8/07
• Another important tool for “probing” the interior of a planet
• Magnetic fields of terrestrial planets are produced by metals such as iron in the liquid state (molten core) and in motion (dynamo action) – moving electrically conducting material
• The stronger fields of the Jovian planets are generated by liquid metallic hydrogen or by water with ionized molecules dissolved in it
• Earth, Mercury, and all Gas Giants have magnetic fields – Mars and Venus do not
Planetary Magnetic Fields
PTYS/ASTR 206 Solar System2/8/07
Impact Cratering
• When an asteroid or comet strikes the surface of a terrestrial planet or moon, 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 geological activity is powered by internal heat, and smaller worlds lose heat less rapidly than larger ones … as a loose general rule … the
smaller a world is, the more heavily cratered it will be
PTYS/ASTR 206 Solar System2/8/07
Will a planet have an atmosphere?
• Requires a gas– The gas must be cool
enough to not escape– The planet must have
enough gravity to prevent the escape of gasses
• Big, cool, planets are more likely to have atmosphere
PTYS/ASTR 206 Solar System2/8/07
To understand the retention of an atmosphere, we need to understand the motion of particles in a gas
• Kinetic Energy associated with an object of mass m in motion with a speed v
• SI unit of energy– Joule (kg m2/s2)
PTYS/ASTR 206 Solar System2/8/07
Kinetic Energy and Temperature
• Kinetic Energy of a gas with temperature T
k = Boltzmann constant
= 1.38 x 10-23 J/K
PTYS/ASTR 206 Solar System2/8/07
Average speed of atoms in a gas
• Equate kinetic energy of motion to that of the gas at a given temperature, and solve for the velocity, v
This is the AVERAGE SPEED of atoms in a gas having a
temperature T
PTYS/ASTR 206 Solar System2/8/07
To understand whether the gas is gravitationally bound to a planet, we need to understand the
concept of Escape velocity
• The speed that an object must have in order to escape the pull of gravity of a planet of mass M and radius R is:
PTYS/ASTR 206 Solar System2/8/07
As a loose, general rule of thumb:
• A Planet can retain a gas if the escape speed is at least 6 times greater than the average speed of molecules in the gas
PTYS/ASTR 206 Solar System2/8/07
Tableobject Escape
speed (km/s)
Avg. temp. (K)
Oxygen speed (km/s)
Hydrogen speed (km/s)
Sun 618 5800 - 12
Earth 11.2 293 0.5 1.9
Mars 5.0 240 0.4 1.7
Jupiter 59.5 125 0.3 1.2
Pluto 1.3 40 0.2 0.8
Atmosphere?
Yes / expanding
yes
yes - thin
yes
yes/no(comes and
goes)
PTYS/ASTR 206 Solar System2/8/07
The diversity of the solar system is a resultof its origin and evolution
• The planets, satellites, comets, asteroids, and the Sun itself formed from the same cloud of interstellar gas and dust
• This material came from cosmic processes that took place within stars that died long before our solar system was formed
• Different planets formed in different environments depending largely on their distance from the Sun
PTYS/ASTR 206 Solar System2/8/07
How Old is the Solar System ?
• How can we determine this ?– Radioactive dating– Need to find the right material to
date !– Because of plate tectonics and
geological activity, Earth rocks are not a good indicator of the age of the Solar System
– Meteorites!
PTYS/ASTR 206 Solar System2/8/07
Today’s quiz• Be sure to fill in the ovals for your name
(last name first!!!)
• Closed book, closed notes, no electronic devices
• The quiz has 15 questions (front and back)– Fill in the oval corresponding to your answer on the scantron sheet
using a #2 pencil
• Only turn in the scantron sheet – you may take the quiz itself with you when you leave
• You may leave when you are finished – but please do so as quietly as possible and leave through the North Entrance (upper right door)