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What’s New on the Planets? Small Bodies of the Solar System • Asteroids: within the orbit of Jupiter • Centaurs: Between Jupiter and Neptune • Kuiper Belt Objects (KBO’s): Beyond Neptune • Scattered Disk: Extreme KBO’s • Comets: Icy bodies with elongated orbits • Meteoroids: Small objects – Meteors: vaporize in Earth’s atmosphere – Meteorites: survive to reach surface The Asteroid Belt, 2001 The Asteroid Belt, 2010 Asteroid Discoveries Asteroids Year 1 1801 100 1867 500 1902 1,000 1921 2,000 1942 5,000 1972 10,000 1981 20,000 1993 50,000 1999 100,000 2000 200,000 2003 Recent Progress • 2010 September 2 – 535789 – 251651 – 16154 Minor planets catalogued Officially numbered Named • 2013 February 1 – 604344 – 353926 – 17698 Minor planets catalogued Officially numbered Named Can we predict impacts? • Incomplete inventory of objects – May be a million km-sized objects • Initial observations don't permit completely accurate predictions • Comets vent gases and change orbits • The meaning of probability of impact – Planets don’t “wander” – Observational uncertainty Example, Measuring A Lot • You measure the lot 5 times, getting 99.7, 99.9, 100.1, 100.0 and 100.3 feet. • Average = 100 • Best estimate but might not be true value • Any random measurement has even odds of being too high or low • P All 5 too high or low = (1/2)5 = 1/32 • P 4 too high or low = 5/32 • P 3 too high or low = (5*4/2)/32 = 10/32 Impact Probability Impact Probability Meteorite Peekskill, NY 1992 Chondrite Stony-Iron Meteorite Iron Meteorite Meteo-Wrongs • Meteorites Never: – Have internal cavities – Have layers – Have veins – Flatten on impact – Mold around objects – Almost never light in color outside • If you “think” it’s magnetic, it’s not magnetic Nope Nope Uh-uh No Way Nope Nope Nope Tunguska, 1908 Tunguska, 1908 Sikhote-Alin Fall, February 12, 1947 Mass = 100,000 Kg Sikhote-Alin Crater Sikhote-Alin Crater Sikhote-Alin Crater Near Miss, August 10, 1972 1972 Near Miss • Object was about the size of a bus • Entered Atmosphere over Utah, travelling north, exited over Canada • Velocity 15 km/sec • Missed by 58 km Returning to Space Carangas, Peru, 2007 Carangas, Peru, 2007 Averting Impact Hazards • Simplest Strategy: Detection + Diversion • Destruction too unpredictable – Can object be destroyed? – “Cookie crumbs have no calories” – In real life, the pieces matter • The longer the lead time, the easier diversion becomes • Only need a close miss • Detection is cheap and off-the shelf Diversion “The question is: how to do it? These things must be done … delicately.” • • • • • • Nukes? Thrusters? Space tug? Gravitational? Solar Sail Laser? Asteroid Itokawa Space Tug What is a Planet? • Ancient: 7 (including sun and moon) • Copernicus: Sun and moon out, Earth in (6) • Uranus, 1781 (7) • Ceres 1801 (8); 12 by 1850 • Asteroids Out, back to 7 • Neptune 1846 (8) Pluto 1930 (9) • Kuiper Belt, 1990’s; Pluto out • This is not over yet. What is a Planet? • Current Definition: – Hydrostatic Equilibrium – Clears its vicinity • Will certainly need adjustment in the future Hydrostatic Equilibrium Hydrostatic Equilibrium Clearing the Vicinity Two Coming Comets • Comets are like cats; they have tails, and they do precisely what they want. –David Levy • PANSTARRS – March-April 2013 – Near Moon on March 12 – Faintly visible to unaided eye? • ISON – 800,000 miles from Sun in November 2013 – May be very bright in December – January 8, 2014, only 2° from Polaris Ceres and Vesta Dawn to Vesta and Ceres • First Mission to use ion propulsion • First Mission to main belt asteroids • First Mission to orbit two different bodies Getting There Vesta’s Huge Crater Rocket Science Dropping the Heat Shield Curiosity Landing Where Things Landed Mount Sharp Layeerd Rocks Conglomerate Layered Rocks Self Portrait Drill Holes Meteorite from Mercury? Finding Other Solar Systems The Sample Bias Problem The Exoplanet Zoo • Hot Jupiters – Must have migrated inward • • • • Highly eccentric orbits Super-Earths Waterworlds? 861 as of February 19, 2013 Kepler • Monitor 100,000 stars continuously for 4+ years • Views an area about 10 degrees across • Detects transits • Star dims by 1/10,000