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A Guide to the Solar System Solar System on a shoe string budget Earth, as viewed by the Voyager spacecraft Reading: Chapter 12 Relative Sizes of the Sun and Planets 1 The Sun • • • • Radius: 108 x radius of Earth Mass: 333,000 x mass of Earth Over 99.9% of solar system’s mass Surface temperature 5800 K The Sun • Composition: 98% hydrogen and helium, 2% other elements • In 1 second the Sun produces a million times the total energy used in the US in 1 year ! 2 Mercury 0.4 AU from sun 0.38 x radius of Earth 0.055 x mass of Earth • Made of metal and rock; large iron core, no atmosphere • Desolate, cratered • Very hot and very cold: 425°C (day), –170°C (night) • Rotates 3 times in every 2 orbits around the Sun Venus 0.7 AU from sun 0.95 x radius of Earth 0.82 x mass of Earth • Extreme greenhouse effect: Hotter than Mercury: 470°C, day and night • Atmospheric pressure like 1km underwater! • No oxygen or water 3 Earth • An oasis of life • The only surface liquid water in the solar system • A surprisingly large moon Mars 1.5 AU from sun 0.53 x radius of Earth 0.11 x mass of Earth • Looks almost Earth-like, but don’t go without a spacesuit! • Giant volcanoes, a huge canyon, polar caps, more… • Water flowed in the distant past; could there have been life? • Dramatic Mars movies and simulations: maasdigital.com/gallery.html esa.int/SPECIALS/Mars_Express/SEMINCO7BTE_0.html 4 Jupiter 5.2 AU from sun 11.2 x radius of Earth 318 x mass of Earth • Much farther from Sun than inner planets • Mostly H/He; no solid surface • 300 times more massive than Earth • Many moons, rings … Jupiter Jupiter’s moons can be as interesting as planets themselves, especially Jupiter’s four Galilean moons • Io: Active volcanoes all over • Europa: Possible subsurface ocean • Ganymede: Largest moon in solar system • Callisto: A large, cratered “ice ball” 5 Jupiter Jupiter's Ring System Jupiter's Ring System Saturn 9.5 AU from sun 9.4 x radius of Earth 95.2 x mass of Earth • • • • Giant and gaseous like Jupiter Spectacular rings made of ices and rocks Many moons, including cloudy Titan Cassini spacecraft currently studying it 6 Saturn Cassini’s view of Saturn with the Sun behind it Can you spot Earth ? Saturn Cassini’s view of Saturn with the Sun behind it Now can you spot Earth ? Check out saturn.jpl.nasa.gov/home/index.cfm for more 7 Uranus 19.2 AU from sun 4 x radius of Earth 14.5 x mass of Earth • Smaller than Jupiter/Saturn; much larger than Earth • Made of H/He gas & hydrogen compounds (H2O, NH3, CH4) • Extreme axis tilt • Moons & rings Neptune 30.1 AU from sun 3.9 x radius of Earth 17.1 x mass of Earth • Similar to Uranus (except for axis tilt) • Many moons (including Triton) • Has rings 8 Pluto: A Dwarf Planet 39.5 AU from sun 0.18 x radius of Earth 0.0022 x mass of Earth • • • • • Much smaller than other planets: Dwarf planet Icy, comet-like composition Its moon Charon is similar in size The plane of its orbit is tilted Other dwarf planets: Eris, Ceres 9 Motion of Planets • All planets in the solar system orbit in the same direction and in nearly the same plane • Most also rotate in that direction Two Main Planet Types • Terrestrial planets are rocky, relatively small, and close to the Sun • Jovian planets are gaseous, larger, have rings and are farther from Sun 10 Notable Exceptions • Several exceptions to the normal patterns need to be explained Small Bodies in the Solar System • Small bodies, the leftover “scraps” from the formation of the Solar System, fall into three distinct groups: 1 asteroids • rocky or metallic in composition • most are located between the orbits of Mars and Jupiter http://www.nasa.gov/mission_pages/WISE/multimedia/pia12469.html 11 Small Bodies in the Solar System 2 Kuiper belt comets • made mostly of ice • orbit the Sun beyond Neptune • orbit in same direction and plane as the planets 3 Oort cloud comets • made mostly of ice • orbit at the outer fringe of the Solar System • spherically distributed about the Sun Properties of Asteroids • They are small in size. • the largest one, Ceres, (now a dwarf planet) is only 1,000 km across • They are not spherical in shape. • shaped more like “potatoes” • gravity not strong enough to compress rocky material • odd shapes imply that some are fragments from asteroid collisions • Small asteroids are more common than large asteroids. • All the asteroids in the solar system wouldn’t add up to even a small terrestrial planet. 12 Rocks Falling from the Sky • meteor – a trail of light caused by a particle which enters Earth’s atmosphere. • most of these particles are the size of a pea • they completely burn up in Earth’s atmosphere • meteorite – a rock which is large enough to have survived its fall to Earth • they caused a brighter meteor…sometimes called a fireball • How can you tell that you have a meteorite? – they have a higher metal content than terrestrial rocks – they contain Iridium and other isotopes not found in terrestrial rocks Comets • Comets are icy counterparts to asteroids. • Unlike planets, they are not confined to the ecliptic and disappear after several weeks • Most comets remain perpetually frozen in the outer solar system. • Only comets that enter the inner solar system grow tails. 13 Composition and Structure of Comets • Comets are “dirty snowballs”…ice mixed with rock and dust. • ices are H2O, CO2, CO, NH3 , CH4 • nucleus • the “dirty snowball” • how the comet appears far from the Sun • coma • surrounds nucleus when near the Sun • sublimated gas & dust • plasma tail • ionized gas swept back by Solar wind • dust tail • dust particles swept back more slowly by radiation A Comet’s Journey 14 Meteor Showers • Earth is impacted by an estimated 25 million small particles each day which cause meteors. • When the Earth passes through the trail of a comet, the number of particles impacting the Earth’s atmosphere increases. We call this a meteor shower. Perseid meteor shower against the backdrop of an aurora, (2000). Meteor Showers • Showers occur on the same dates each year, corresponding to when the Earth crosses a given comet’s orbit. • The meteors appear to emanate from one point in the sky. 15