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ES 023 Planet Earth: Shaken and Stirred •Quick review of last class •Hertzsprung-Russell diagram (star classification) •A tour of the solar system •How did the solar system form? •Are we alone? ES 123 The Dynamic Earth Mendeleev’s Periodic Law • Periodic variations in the properties of elements led Dimitri Mendeleev to organize the elements into the Periodic Table Atomic Isotopes Mass number (A) Number of protons (Z) Number of neutrons Hydrogen (1H) Deuterium (2H) Tritium (3H) 1 2 3 1 1 1 0 1 2 Uranium-235 (235U) Uranium-238 (238U) 235 92 143 238 92 146 Composition of the universe Helium (7.8%) Hydrogen (92%) Carbon (.03%) and Oxygen (.06%) All other elements (.11%) Interior of the Sun • The sun has multiple layers (like an onion) • The sun’s energy source is generated by H fusion at the core • Heat escapes the core by radiation • In the outer part of the sun, heat is transferred by convection Evolution of a 15 solar-mass star Element fused Hydrogen Helium Carbon Neon Fusion product Helium Carbon O, Ne, Mg O, Mg Oxygen Silicon Si, S Iron Time Temp. (K) 1010 years > 106 years 1000 years A few years 1 year A few days 4x106 1x108 6x108 1x109 Source: In Quest of the Universe, Kuhn, 1998 2x109 3x109 Star Classification: Hipparchus of Rhodes 190 BC to 120 BC •Created a catalog of 850 stars, classified by brightness • His brightness scale counts backwards, from 1st magnitude (brightest) to 6th magnitude (dimmest) Apparent Stellar Magnitude (m) • In 1856, Oxford astronomer Norman R. Pogson invented an apparent magnitude scale based on Hipparchus’ visual magnitudes • According to this scale, an increase of 5 units corresponds to an object that is 100 times brighter • An increase of 10 units corresponds to 10,000 times brighter (100x100) Absolute Magnitude • Definition: Absolute stellar magnitude (M) is the apparent magnitude that a star would have if it were 32.6 light years from the Earth. • Absolute magnitudes for stars generally range from -10 to +17. • The Sun has an absolute magnitude of 4.83, quite average Hertzsprung-Russell diagram •Classification chart for stars •Shows absolute magnitude versus temperature (colour) •Developed in the early 20th century by Danish astronomer Ejnar Hertzsprung and American Astronomer Henry Russell Hertzsprung-Russell diagram Super Giants Giants Sun White Dwarfs Stellar Evolution •Stars on the main sequence are fueled by H fusion •Near the end of its life, a star gets hotter and bigger (i.e., main -> giant), as it switches to He fusion, etc. •Ultimately, a star may explode (nova) then become a white dwarf, a neutron star or a black hole A tour of the solar system The inner solar system http://seds.lpl.arizona.edu/nineplanets/nineplanets/ A tour of the solar system The outer solar system http://seds.lpl.arizona.edu/nineplanets/nineplanets/ A tour of the solar system Pluto Jovian planets Neptune Uranus Saturn Mars Jupiter Earth Venus Mercury Terrestrial planets http://seds.lpl.arizona.edu/nineplanets/nineplanets/ Terrestial planets vs. Jovian planets Terrestrial Jovian Diameter < 13000 km Diameter > 48000 km Two or fewer satellites 8 or more known satellites No rings All have ring systems Density > 3.9 g/cm3 Density < 1.8 g/cm3 Solid surface Primarily liquid Mercury •Smallest planet •Heavily cratered surface, like the moon’s. • Studied by Mariner 10 spacecraft (1974 and 1975). • Each day lasts 1.5 years • Surface temperature variations are most extreme in the solar system (90 K to 700 K*) *To get degrees Celsius from degrees Kelvin, subtract 273.15. http://seds.lpl.arizona.edu/nineplanets/nineplanets/ Venus • Most similar to Earth in size (95% of diameter, 80% of mass) •Surface temperature 740 K, pressure = 90 bars • Studied by Mariner 2 in 1962, and more than 20 spacecraft since • Each day lasts longer than one year, retrograde rotation http://seds.lpl.arizona.edu/nineplanets/nineplanets/ Mars • Surface area is about the same as the land surface area of Earth •Most spectacular topography in the solar system • Olympus Mons: 24 km high • Valles Marineris: canyons 2 to 7 km deep •Mariner 4 (1965), Viking (1976), Mars Pathfinder (1997), Mars Expedition (2004), 3 orbiters currently. http://seds.lpl.arizona.edu/nineplanets/nineplanets/ Jupiter • More massive than the rest of the planets combined • In 1994, Comet ShoemakerLevy 9 collided with Jupiter •Great red spot has persisted for > 300 years •16 known moons •Since Pioneer 10 (1973) visited by 5 missions including Galileo probe (1995-2003). http://seds.lpl.arizona.edu/nineplanets/nineplanets/ Saturn • 2nd largest planet in the solar system •Rings are > 250,000 km in diameter, but only 1 km thick •Less dense than water •18 known moons •Pioneer 11 (1979), then Voyager 1 and Voyager 2. Cassini (20042008) http://seds.lpl.arizona.edu/nineplanets/nineplanets/ Formation of the solar system Two theories: 1. Solar system evolved from a nebula (dust cloud) 2. Solar system formed by catastrophic event Orion nebula - “stellar nursery” Catastrophic theories for the formation of the solar system Georges de Buffon (1745) – A comet collided with the Sun, expelling matter which accreted to form planets. Forest Moulton & Thomas Chamberlin (1900) – A star passed close to Sun, pulling away huge filaments of material. Problems: such events are extremely rare. Also material is so hot that it would dissipate into space and not accrete. Formation of the solar system Nebular theory is more consistent with observations e.g., All planets rotate in same direction and almost in the same plane (plane of the ecliptic) The Best Prospects for Life Name Why Earth Mars Europa Titan Io Jupiter :-) most Earth-like; more so in the past may have liquid water atmosphere like early Earth, liquids likely complex chemistry, warmer than most long shot: warm, plenty of organic material http://seds.lpl.arizona.edu/nineplanets/nineplanets/gif/NinePlanets.jpg