Transcript 28 comets asteroids
Agenda Short practice test Asteroids Comets Pluto Get a review sheet! Thursday is a review, but is not “optional.” Phobos Warm up exercise for final exam Only answer questions 1-22 Include last and first name only Solar system “minor bodies” Asteroids Comets Asteroids Asteroids Some are differentiated Range in size: less than 1 km to almost 1000 km Near Earth objects are being tracked by NASA Asteroids http://apod.nasa.gov/apod/ap060328.html Eros flyby NEAR Shoemaker landing site on Eros (Feb 1, 2001) Composition of Eros Meteors fall to Earth sometimes They are then called Meteorites. 4.55 billion yrs old Similar to moon oldest Earth rocks helioseismic age of Sun Can contain amino acids and water 2 kinds: Stony meteorites and... ...Iron meteorites Very dense Iron and nickel Get out your planner, and schedule PERSEID METEOR SHOWER for the night of August 12. That would be a good night to invite some friends over, put out the lawn chairs, and spend a relaxed evening in the back yard. How are rocks dated? Radiometric dating! Some elements naturally decay into lighter elements Half life – when half of the original element is left Time Amount of parent element Siberian mystery: Tunguska 1908 explosion 1000 times more powerful than Hiroshima bomb Comets Made of ice and solids Small solid nucleus Much larger head, or coma Large, very elliptical orbits Meteor showers are caused by debris in cometary orbits! Comet Halley, 1985 (AAT) Elliptical orbit, 2 tails Tails point away from the Sun (like a wind sock!). Wikipedia Nucleus of Halley’s comet! (10 km long) Coma is larger than Mercury! Nucleus is smaller than one pixel on this image! Halley’s period is 75 years. How much of the time can we see it with unaided eyes? A. 37 years, or about half its period. B. 65 years (that is, most of the time!) C. About a year or less. D. Not enough information. Reason: Kepler’s laws. Comets spend most of their time in the outer solar system. Ions pushed by stellar winds Dust tail, often curved Deep Impact July 4, 2005 Impact probe of Comet Tempel-1 to see what would happen! Tempel-1 (time lapse) Brightens on impact! Bursts during approach QuickTime™ and a YUV420 codec decompressor are needed to see this picture. Approach movie from the impact probe itself! QuickTime™ and a Sorenson Video 3 decompressor are needed to see this picture. Approach movie What did it teach us? Website: deepimpact.umd.edu Kuiper belt and Oort cloud Pluto “Kuiper belt” object Discovered 1930 by Clyde Tombaugh Frozen nitrogen & methane, –220˚C Pluto is little. Pluto’s moons Charon Nix & Hydra discovered mid-2005 Pluto Demoted to “dwarf planet” (2006) IAU definition of a planet Which of the following is NOT part of the official definition of a planet? A. In orbit around the Sun B. Has an atmosphere C. Massive enough to be round D. Has cleared the neighborhood around its orbit Pluto Bye bye, Pluto! Summary Asteroids Live in asteroid belt Made of terrestrial material Comets Live in Kuiper belt and Oort cloud Pluto is a Kuiper belt object too! Very elliptical orbits Made of ice, dirt 3 parts: coma, nucleus, tails Time to evaluate my teaching Pass out review sheets I need a volunteer to collect them Return to the physics office (EPS 264) after class. Back in 15 min.!