CometsComets l Small dusty/icy chunk of material few kms size (often characterized as “dirty snowball”) l Originally condensed out of Solar nebula and still orbit Sun - primitive material l Orbits often elliptical, large aphelion l Partially vaporized when close to Sun - material (gases) then pushed by sunlight makes long tail (gases) then pushed by sunlight makes long tail l Gas tail always points away from Sun l Also dust tail along orbit

COMET IKEYA-SEKI

COMET WEST

COMET HALE-BOPP

PARTS of a COMET Pushed by Sun Dust along comet’s orbit

COMET TAIL ORIENTATION Ion trail Dust trail Comet Hale-bop Dust trail Ion trail

RECIPE for a COMET l Ingredients ä Frozen methane ä Frozen water ä Frozen ammonia ä Dust grains (dirt) ä Traces of organic compounds and other chemicals l Directions ä Mix into a ball about 10 km across containing 100,000,000,000,000, (10 14 ) kg of this mixture About the mass of Mt. Baker

COMET HALLEY

COMET HALLEY’S ORBIT

COMET HALLEY’S PATH 1910 and

Returns to Perihelion of Halley’s Comet 239 BCMarch 30989September BCOctober 51066March BCAugust 21145April BCOctober 51222October 1 AD 66January October March November 9 218May June 9 295April August February October June September September March May November February April July 91986February

BAYEUX TAPESTRY

Giotto-Adoration of the Magi

ORIGIN of LONG PERIOD COMETS Originate in Oort Cloud -a huge reservoir ancient Solar System material far from Sun -likely produced by planetesimals ejected by Jupiter and Saturn Early on from inner Solar System. Passing star perturbes Cloud sends lumps inward - see as comets when near Sun.

KUIPER BELT Planetesimals ejected from inner Solar System by strong gravitational fields of Giant Planets - some interact Jupiter and Saturn flung far out to Oort Cloud, interactions Uranus and Neptune pushed them out to Kuiper Belt Kuiper Belt

KUIPER BELT OBJECT

KUIPER BELT OBJECTS Sedna e =0.86 Perihelion 76 A U Aphelion 975 AU! P =12,000 years Pluto + 3 Moons

METEORS AND METEORITES Meteors are parts of comets that pass through Earth’s orbit - burn up in Earth’s atmosphere Meteorites are ground up pieces of asteroids - off orbit - enter Earth’s atmosphere and survive passage

Meteor Shower Comet breakup near perihelion Material spread out along orbit If Earth passes through comet debris - shower

A METEOR STORM 1833 Wood Cut Leonid Shower

LEONID METEOR SHOWER Long Exposure

Dates Some Meteor Showers

ANTARCTIC METEORITE Easiest to find meteorites against snow. Most found in Arctic or Antarctic Primitive material - planetesimals - useful for dating Solar System Many varieties - stony, metallic, often contain organic material