Introductory AstrSolar System
Introductory AstrSolar System ASTR 111
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C mparative Planetology I U 39 Our Solar Sygem ASTR 111 003 Fall 2006 Lecture 07 Oct 16 2006 Introduction To Modern Astronomy Ch7 Comparative Planetology I Introducing Astronomy Chap39 1396 Ch8 Comparative Planetology II Ch9 The Living Earth Cth Our Barren Moon Chl l SunScorched Mercury Planets and Moons Ch12 Cloudcovered Venus chap 717 Ch13 Red Planet Mars Chl4 Jupiter and Saturn ChlS Satellites of Jup amp Saturn Chl6 Outer World Chl7 Vagabonds of Solar System DJ 809 Guiding Questions Are all the other planets similar to Earth or are they very different Do other planets have moons like Earth s Moon How do astronomers know What the other planets are made of Are all the planets made of basically the same material What is the difference between an asteroid and a comet Why are craters common on the Moon but rare on the Earth Why do interplanetary spacecraft carry devices for measuring magnetic elds Do all the planets have a common origin Solar System lew o the solar ystem from above Pluto There are 8 planets in the solar system In 2006 Pluto is disquali ed as a regular planet Sun All of the planets orbit 53quot Jupiter the Sun in the same direction and in almost the same plane Neptune Uranus Mercury Saturn Planets have elliptical Mercur orbits but nearly Venls circular 5quotquot 7 Ems Jupiter View of the solar system from the side Planets Physical properties of planets Diameter Mass Average Density Chemical Composition Planets are divided into two broad categories Terrestrial planets the four inner planets resembling the Earth Jovian planets the four outer planets resembling the Jupiter Mercury 39 Earth Q Q a l L Mars Venus Jupiter 39 Uranus V w Neptune Pluto Terrestrial Planets Terrestrial planets Relatively small in size with diameters of 5000 to 13000 km Relatively small in mass 1024 kg Relatively high average densities 4000 to 5500 kgm3 Composed primarily of rocky materials Characteristics of the Planets Mercury Venus Earth Mars Average distance from Sun 106 km 579 1082 1496 2279 Average distance from Sun AU 0387 0723 1000 1524 Orbital period years 0241 0615 1000 188 Orbital eccentricity 0206 0007 0017 0093 Inclination of orbit to the ecliptic 700 339 000 l85 Equatorial diameter km 4880 12104 12756 6794 Equatorial diameter Earth 1 0383 0949 1000 0533 Mass kg 3302 X 1013 4868 X 1024 5974 X1024 6418 X 1023 Mass Earth 1 00553 08150 10000 01074 Average density kgm3 5430 5243 5515 3934 Jovian Planets Jovian planets Large diameters 50000 to 143000 km Large in mass 1026 kg Low average densities 700 to 1700 kgm3 Composed primarily of hydrogen and helium gas objects Jupiter Saturn Uranus Neptune Pluto Average distance from Sun 106 km 7783 1429 2871 4498 5915 Average distance from Sun AU 5203 9554 19194 30066 39537 Orbital period years 1186 2946 8410 16486 24860 Orbital eccentricity 0048 0053 0043 0010 0250 Inclination of orbit t0 the ecliptic 130 248a 077 1770 1715 Equatorial diameter km 142984 120536 51118 49528 2300 Equatorial diameter Earth 1 11209 9449 4007 3883 0180 Mass kg 1899 X 1027 5685 X 1026 8682 X 1015 1024 X 1026 13 X 1022 Mass Earth 1 3178 9516 1453 1715 00021 Average density kgm3 1326 687 1318 1638 2000 Pluto Why not a planet Pluto is a special case An outer planet but smaller than any of the terrestrial planets Intermediate average density of about 1900 kgm3 Density suggests it is composed of a mixture of ice and rock Its orbit has large eccentricity and inclination angle It is now called a dwarf planet possibly a member in the family called in Kuiper Belt Objects Seven large satellites Comparable in size to the planet Mercury 0 The remaining satellites of the solar system are much smaller ldbiQ 72 The Seven Giant Satellites Moon 10 Europa Ganymede Callisto Titan Triton Parent planet Earth Jupiter Jupiter Jupiter jupirer Saturn Neptune Diameter km 3476 3642 3 ISO 5268 4806 5150 2706 Mass kg 735 X1013 893 X 11 480 X1031 148 gtltl013 08 X1013 134 X 013 215 X1 31 Average density kg1113 3340 3530 2970 940 1850 1880 2050 Substantial atmosphere No No No Nn No Yes Nn Europa Ganymede Callisto Triton JPLNASA R m U X G Planets Chemical composition Spectroscopy observations reveal the chemical composition of a planet or satellite 0 If there is no atmosphere the spectrum indicates the composition of the surface For example Titan s atmosphere is made of methane CH4 0 For example Europa s surface is made of ice not rock The spectrum of Europa is almost identical to that of ice indicating that the surface of Europa is mostly ice not rock The absorption lines of methane CH4 Tit an are produced in Titan s atmosphere Saturn x a quot quot The abSDfP m quot5 I The absorption line of of hydrogen H oxygen 02 is produced is Pmdu ed iquot S quot395 quot in Earth s atmosphere atmosphere Ear h Fraction of incident light that is reflected uuuuuuuuuuuiuyuuuuu 10 15 20 b Interpreting Titan s spectrum WaVelength Mm Planets Chemical composition Terrestrial planets are made mostly of heavy elements such as iron oxygen silicon magnesium nickel and sulfur Terrestrial planets are solid or rocky because these elements remain solid except at very high temperature gtlOOO K Jovian planets are composed mainly of light elements hydrogen and helium Jovian planets are gaseous in the outer layers or liquid in the interior because hydrogen and helium are gaseous except at extremely low temperature and extraordinary high pressure Ice in the solar system substance such as water H20 carbon dioxide C02 methane CH4 and ammonia NH3 solidify at low temperature 100 K to 300 K Asteroids Asteroids are small and rocky objects orbiting the Sun also called minor planets Asteroids belt most asteroids orbit the Sun at distance between 2 to 35 AU between the orbits between Mars and Jupiter They are thousands of kilometersized asteroids and millions of metersized asteroids The largest asteroid Ceres is about 900 km Eros 33 km long and 13 km wide NEAR Shoemaker spacecraft landed on it in March 2000 Comets Comets are chunks of dirty ice 0 They have highly elongated orbit thus occasionally bring them close to the Sun When close to the Sun solar radiation vaporizes some of the ice material forming a bluish tail of gas and a white tail of dust both tails can extend for tens of million of kilometers Comets are thought to come from the Kuiper Belt a region of the solar system extends from around the orbit of Neptune to about 500 AU from the Sun quot Bluish39tail of gas White tail of clust i ASTR 111 003 Fall 2006 Lecture 08 Oct 23 2006 Introduction To Modern Astronomy Ch7 Comparative Planetology I Introducing Astronomy Chap39 1396 Ch8 Comparative Planetology II Ch9 The Living Earth Cth Our Barren Moon Chl l SunScorched Mercury Planets and Moons Ch12 Cloudcovered Venus chap 717 Ch13 Red Planet Mars Chl4 Jupiter and Saturn ChlS Satellites of Jup amp Saturn Chl6 Outer World Chl7 Vagabonds of Solar System Craters Impact craters the result when meteoroid collides with the surface of a terrestrial planet or satellite Meteoroids small objects in space ranging from a few centimeters to a few hundred meters They are mainly the result of collisions between asteroids Craters Why is the Moon heavily cratered Answer Moon is geologically inactive Why is the Earth rarely cratered Earth is geologically active Craters are erased with time Plate movement Volcano Water and Wind Geologic activity is powered by internal heat Which keeps the interior is at least partially molten The smaller the object the easier it loses heat the less internal heat it is likely to have retained For instance the Moon The larger the more dif cult it loses heat the more internal heat it is likely to have retained For instance the Earth Magnetic eld of Planets A planet with magnetic eld indicates that it has liquid material in its interior The liquid material eg molten iron conducts electricity The liquid material is in motion generating magnetic eld through a process similar to electric dynamo f u magmas Geographic north pole Magnetic north pole Geographic south pale Bar Mag et39 Earth s Magnetic Field Diversity of the Solar System Sun Planets satellites comets asteroids and meteoroids The diversity is a result of its origin and evolution lille 7 l Comparing Terrestrial and Jovian Planets lu39u a39 lquot139r Distance from the Sun Less than 2 AU More than 5 AU Size Small Large Composition Mostly rocky materials containing iron oxygen Mostly hydrogen and helium silicon magnesium nickel and sulfur Densrty High Low