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CORNELL ASTRO 202 - Lecture 1 – Geography of the Solar System

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ASTRO 202Lecture 1 – Geography of the Solar SystemJanuary 22, 2008Policy and philosophical issues:Human vs Robotic exploration of space. Should we be spending money on space exploration at all given the other needs of the world?Are there higher life forms including intelligent life on other planets in our galaxy? What is the likelihood?Should we be concerned about the threat to Earth from near-earth asteroidsHow should we address the issue of climate warming?What are the necessary conditions for life to form? Evolution, the age of the universe and religious belief."The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors, so that, in glory and triumph, they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light."-- Carl SaganFrom "Pale Blue Dot: A Vision of the Human Future in Space," Random House, 1994The Earth as a “pale blue dot”taken from the Voyager I spacecraft at a distance of 4 billion miles in 1991.Galaxy cluster Abell 2218 Hubble Space Telescope photo"The Earth is a very small stage in a vast cosmic arena.” Carl SaganIt is estimated that the Milky Way is one of over 100 billion galaxies in the Universe.A model of our Milky Way galaxy~100,000 light years acrossAbout 400 billion starsSun is about 28,000 light years from the centerStars separated by about 5 light years. Voyager 1 now 14 light hours away after 20 yearsA spiral galaxy similar to the model of our own galaxy39 AU30 AU19 AU9.5 AU5.2 AUAU = Astronomical Unit = distance from Earth to Sun = 150 million km or 90 million milesCOMETSSUN –4. 108more luminous than Jupiter, the biggest planet.99.8% of solar systemmassRadius 700,000 kmTemp 6,000KMass 2 1030kgDensity 1.4 g/ccSOHO 3-color UV imageJupiter: Radius 71,500km; 0.1 radius of the Sun; 11 times radius of EarthMass 0.1% mass of the Sun; 318 times mass of Earth.Saturn: Radius 60,300 kmDensity 0.69 g cm-3Cassini OrbiterCassini around Saturn – artists imageSaturn from Cassini as it crosses the ring planeCassini orbiter image of Saturn and its rings looking back to Earth – the “pale blue dot” at upper left in the rings. The Sun is behind Saturn illuminating the rings.Neptune: Radius 24,800 km~17 x mass of EarthDensity ~ 1.6 g/ccUranus: Radius 25,600 km~14 x mass of EarthDensity ~ 1.3 g/ccEarth from GalileoRadius 6,378 kmMass 1/300,000 of SunVenus optical imageRadius 6052 kmYmir – the creature from Venus, 1957 movie “Twenty Million Miles to Earth”Venus showing cloudsCornell MayerCarl Sagan(1934 – 1996)Realistically assessed all the data and concluded:HOT - about 8650F (4600C)Carbon dioxide atmosphere (96%)Pressure 90 times Earth’s atmosphere - Equivalent to being 3,000 ftdown in the ocean.White clouds are sulphuric aciddropletsVERY STRONG GREENHOUSE EFFECTVenus – Radar image from the Magellan orbiterRadius 6,052 kmInterior structure of EarthTube worms in Galapagos rift at 2,500mBlack smoker on mid-ocean riftMercury from Mariner 10 outbound 1974Radius 2,440 kmMars – Two images showing effects of dust stormsRadius 3,396 kmMars Rovers, Mars Reconnaissance orbiter, Mars Express orbiter (ESA), Odyssey orbiter, Phoenix lander (soon)Messenger MissionHarmon et al, Icarus, 149, 1-15, 2001Ice at the poles of MercurySurface temperature at equator can be 4000CMars – Schiaparelli’smapPercival’s Lowell’s mapViking I lander image of surface of Mars 1976Mars topography from MOLA – the Mars Orbiting Laser Altimeter on the Odyssey OrbiterMars roverImage of Cape Verde in Victoria crater from Mars Opportunity RoverThe Opportunity Mars Rover imaged by the HiRISE camera on the Mars Reconnaissance Orbiter. Resolution of the camera is ~30 cm.Phoenix Mars landerLaunch August 2007Arrival at Mars May 25 2008The solar-powered lander will robotically dig to underground ice at a northern latitude landing site and will run laboratory tests assessing whether the site could have ever been hospitable to microbial life. The instruments will also look for clues about the history of the water in the ice. They will monitor arctic weather as northern Mars' summer progresses toward fall, until solar energy fades and the mission ends.Pluto and CharonRadii 1,150 and 625 kmTwo small recently discovered moonsPluto now a minor planetNEW HORIZONSLaunch - January 2006Jupiter Gravity Assist – Feb 2007Cruise – 2007 to 2015Pluto/Charon flyby – July 2015Kuiper Belt object flybys – 2016 to 2020CASSINI-HUYGENS at SATURNCassini image of TitanWent into orbit about Saturn on June 30, 2004Titan surface observations with:Imaging systemVisible and Infra-red mapping spectrometerRadar systemHuygens probeHuygens Lander Simulation Huygens landed on January 14, 2005European Space Agency/NASASurface of Titan from HuygensRadar image of probable lakes of liquid methane in the northern hemisphere of TitanHubble Space Telescope image of Ceres~1,000 km in diameterDAWN mission to largest main belt asteroids Ceres and Vesta –launched Sept 28 2007Positions of all known asteroids projected onto the plane of the Earth’s orbit on Jan 20, 2008Red ones (Apollo and Alten) cross the orbit of Earth so are potentially hazardous. Yellow ones (Amors) don’t cross Earth’s orbit now but could in the future if their orbits are


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