Primordial Matter in the Solar System Solar system formed out of cold, dense hydrogen gas cloud, but containing ALL other heavy elements Sun too young to have synthesized any other elements, still in the H He production stage (about half-way) Planetesimals or Minor Planets In addition to the Sun and 8 planets and we have -- Asteroid Belt, rocky/metallic bodies (also called minor planets or planetesimals ) up to 1000 Kms in diameter, -- Planet never formed, or broken up by Jupiters tidal effect -- Pluto and Kuiper Belt Objects (KBOs) Debris of the Solar System The ice/rock dichotomy is most starkly evident in comets and asteroids Meteoroids in space; meteors or meteorites when they enter the Earths atmosphere Comets/Meteors are mainly ice(snow) balls, and Asteroid/Meteorites are rocky/metallic objects Comets would have been a source of water on the Earth Comets originate in either (i) the Oort Cloud at the edge of the solar system, or (ii) the Kuiper Belt beyond the orbit of Pluto Planetesimals etc. Minor planets or asteroids, comets, and other objects orbiting the Sun obey Keplers laws Kuiper Belt Objects (KBOs) are planetesimals beyond Plutos orbit Recently discovered (at least) two planets comparable to Pluto, named Xena and Sedna Asteroids Over 5000 found between AU Keplerian orbits, e.g. P 2 = a 3 Gaps, such as the Kirkwood Gap, due to orbital resonance with Jupiter and other asteroids (like the Cassini Division in Saturns rings) Jupiter maintains the asteroid belt, although may have prevented planet formation Families of asteroids: Floras, Trojans, and the AAA objects -- Amors Appolos, Atems that could come close to Earth (Dinosaurs !) Asteroids (Contd.) Small albedo ~ Masses: Largest about 1/20,000 of the mass of the Earth; all asteroids combined would still be only about 1/1000 of M(E) Composition of Asteroids Meteorites; metallic and silicates mixed with organic carbon compounds Meteorites Stones from Heaven Excalibur, Kaaba (black) stone, etc.; survive atmospheric friction and land on Earth) Metallic ones with pure iron; surprising ? Extraterrestrial origin since Iron never occurs in pure form on the Earth but as iron ore compounds Stones (silicates), Irons (iron and nickel), Stony-irons (silicates and metals) Largest meteorite (Namibia): 7m 3, 60 tons Ages from radioactivity 4.6 Gyrs Typical asteroids Meteorite damage! Barringer Crater (Flagstaff, AZ) Stony Carbonaceous chondrites (Allende Meteorite) Stony Iron Meteorite Glassy nodules on exterior. Why? Iron Meteorite (Interlocking crystal pattern) Comets Comets: Head and Tail Where is the Sun (which direction) ? Orbits of comets Altering orbits of comets Long-period comet Short-period comet The Tale of Two Tails! Gaseous and Ionic Tails ice/dust tail (white) Ion tail (blue) Ice/dust tail: Evaporating mattter as the comet approaches the Sun Ion tail: charged particles Electrons, protons, ions pushed directly away by charged particles in the Solar Wind Structure of comets The vaporizing nucleus Cometary Orbit Around the Sun Comets Ancient remnants of the Solar nebula Long period comets from the Oort Cloud; short period ones from the Kuiper Belt Total number about 10 trillion ! Structure Nucleus, Coma, H-cloud, Tail Tail(s): Gaseous and Ionic Nucleus ~ 5-10 Kms diameter, less than ten billionth of the mass of the Earth Total mass in comets about 1000 times Earths mass (all the planets combined) Comets (Contd.) Formed out of the building blocks of the Solar System: Ices (H2O, CO2), like the outer planets Large eccentricity Evaporate while approaching the Sun; the tail gets longer Sometimes break up, e.g. Comet Shoemaker-Levy in 1993 Meteor Showers, e.g. Leonid shower in 2001 Meteors Shooting Stars Icy/Dusty pieces like cometary material, or small pieces from comets Burn up completely in the atmosphere Meteor showers appear to originate at a common point optical illusion like parallel rail tracks meeting in the distance