Ceres largest asteroid and 30% mass of all asteroids

Only ceres, Pallas, and Vesta have diameters greater than 300km (everything else is tiny!)

Not enough mass to make up a planet-smaller than Pluto

gaps in asteroid belt created by Jupiter’s gravitational attraction—they occur in simple fractions like 1/3, 2/5, 3/7, 1/2 ) at Jupiter’s orbital period. Similar to Cassini division with Saturn

Asteroid belt contains millions of asteroids-but each about 10 million kilometers apart –huge spacing

Still sometimes crash into each other-if the pieces can’t escape the gravitational force (not going fast enough) they reassemble

Otherwise they orbit one another

Average rotation period for an asteroid is between 5-20 hours (one rotates every 10.7 minutes-fastest rotation object in solar system)

Eros and Mathilde-neared our planet and sent NEAR shoemaker to look at them

Mathilde-only 1.3 x denser than water—darker than charcoal (only ½ density of other asteroids)

Eros-3x dense as water, rotates every 5.25 hours; made of rock and metal and was never heated enough to separate rock from metal (differentiate)

made of ice (either water, carbon dioxide, methane, ammonia)

Comets formed in outer reaches distant from Uranus, Neptune etc. so cold enough for ice to form solid chunks km across—gravitational tug from Uranus and Neptune sent them flying everywhere

Two reservoirs of comets in universe-first is doughnut shaped and beyond orbit of Pluto, the Kupier belt extends 500 AU from the sun-comets are called Plutinos there

Classical Kuiper belt objects roughly circular orbits and form between 30 and 50 AU

Scattered Kuiper belt objects-elliptical orbit range from 35 to 200 AU

Comets head inward as result of collision or near misses with other comets

Second mass of comets found even farther from the sun and believed to have a spherical distribution around the sun called Oort cloud

Passing star’s gravitational force will nudge comet towards inner solar system

-Because these belts are far from the solar system, comets are completely frozen (solid comet bodies called nuclei)

when comet nucleus comes within 20 AU of sun, solar radiation vaporizes ice on surface created gases that form an atmosphere (coma)

Comet tails-form from coma gas and dust pushed outward from the sun (doesn’t flow behind comet, always points away from the sun regardless of the comets rotation)

positively charged ions from coma are swept from comet directly away from sun by the solar wind to form the gas tail

-often appears blue (scatters blue light)

when photons strike dust particles that have been freed from comet’s evaporating nucleus-pushed away from comet and forms tail

-color of sunlight

rocky and metallic debris smaller than asteroids scattered throughout solar system

glowing gas trail we see

Most of meteor will vaporize completely, but if any part of it survives will create an impact crater

occur when Earth moves through orbit of debris left behind by a comet

About 30 meteor showers each year, named after constellation they appear in

Moon has too thin an atmosphere to protect it from meteor showers

pieces of debris left from meteors that make it through the Earth’s atmosphere

-help astronomers determine age of things—oldest meteorite ever found was 4.57 billion years old

Three types of meteorites:

Stony Meteorites-composed of stone and look like rocks---95% of meteorites on Earth

Iron Meteorites-

Iridium is common in Iron meteorites but rare in ordinary rock on Earth

Stony-Iron-roughly equal amounts of stone and iron