Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
General Properties of the Solar System … continued PTYS/ASTR 206 Solar System 2/8/07 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 System 2/8/07 Next Week’s Preceptor-led Study Group • Monday – 10:30AM-12:00PM Preceptors: Chris Dockins, Maggie Jahn, Katie Landon, and Jared Mosley Room 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 System 2/8/07 Solar-system inventory continued… The Sun • 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 PTYS/ASTR 206 Solar System 2/8/07 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 System 2/8/07 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 System 2/8/07 • Asteroid belt – Between the orbits of Mars and Jupiter – Probable origin of NearEarth objects PTYS/ASTR 206 • Kuiper Belt Objects – Beyond the orbit of Neptune – Distributed loosely along the ecliptic plane – Pluto is a large KBO Solar System 2/8/07 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 System 2/8/07 Structure of a Terrestrial Planet • Metallic core in center • Rocky mantle • Crust of some sort? • All are differentiated Look up its definition ! – But the proportions of the core, mantle, crust, differ PTYS/ASTR 206 Solar System 2/8/07 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 System 2/8/07 Planetary Magnetic Fields • 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 PTYS/ASTR 206 Solar System 2/8/07 • 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 will206 be PTYS/ASTR Solar System 2/8/07 Impact Cratering 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 System 2/8/07 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 System 2/8/07 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 System 2/8/07 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 System 2/8/07 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 System 2/8/07 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 System 2/8/07 Table object Escape speed (km/s) Avg. temp. (K) Oxygen speed (km/s) Hydrogen speed (km/s) Sun 618 5800 - 12 Yes / expanding Earth 11.2 293 0.5 1.9 yes Mars 5.0 240 0.4 1.7 yes - thin Jupiter 59.5 125 0.3 1.2 yes Pluto 40 0.2 0.8 yes/no (comes and goes) PTYS/ASTR 206 1.3 Solar System 2/8/07 Atmosphere ? 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 • 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 System 2/8/07 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 System 2/8/07 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 PTYS/ASTR 206 Solar System (upper right door) 2/8/07