Small Bodies in the Solar System

Small Planetary Bodies In addition to planets & moons, the solar system contains many other types of objects: including comets, asteroids, and meteoroids.

Comet Structure Nucleus gas and dust released & form atmosphere around the comet called the coma

Comet’s Tail Dust Tail Usually white Ion Tail (ionized gas) Usually blue

Comet’s Tail A comet's tail points away from the Sun due to solar wind Tail gets longer when it is closer to the Sun.

Kuiper Belt Short-period < 200 years Oort cloud not actually seen, billions to 2 trillion objects, made out of water, ammonia & methane 2000 AU ~ 1 ly thick

Oort Cloud Long-period > 200 years Oort cloud not actually seen, billions to 2 trillion objects, made out of water, ammonia & methane 2000 AU ~ 1 ly thick

Comet’s Orbit Eccentricity How “oval shaped” 0 = circle 1 = very long oval Speed ~ 40 km/s (86,400 miles/hr)

Halley’s ~76 years Tempel ~5.5 years Hyakutaka ~17,000 years

Comet’s Orbit Perihelion – nearest sun Aphelion – furthest sun

Asteroid Belt

Asteroids Size Meters – 900 km (too small to be planet) Shape Irregular Larger ones are more spherical Content Lighter – more rock Darker – more metal

Asteroids > 200 asteroids > 60 miles (100 km) in diameter. Sometimes considered planetoids or minor planets Most located in asteroid belt (between Mars & Jupiter) > 200 asteroids > 60 miles (100 km) in diameter. > 750,000 asteroids > .6 mile (1 km) in diameter and 1,000,000 of smaller ones. Speed ~ 25 km/s (54,000 miles/hr)

Asteroids Ceres – largest asteroid in asteroid belt 580 miles across Considered dwarf planet

Asteroids A large asteroid may have hit the Earth when the dinosaurs were alive. ~65 million years ago.

Asteroids Many will drop out of orbit Collision w/ other asteroid & may head toward Earth. < 10 km across, burn up in atmosphere. > 10 km across, will hit surface of planet. Hundreds of millions of years ago, collisions with asteroids more often.

Meteoroids… Meteoroid - A small particle from an asteroid or comet orbiting the Sun.  Meteor - A meteoroid that is observed as it burns up in the Earth's atmosphere – a shooting star. Meteorite - A meteoroid that survives and impacts the Earth's surface

Meteoroids… Size Pebble to boulder (smaller than asteroids, most weigh < 1g) Shape Irregular Content From asteroids & comets, so likely metal & rock

Meteor Heats up to > 2,000˚C. Creates a streak of light called a “shooting star”. Fireballs - larger meteors -> brighter flash On average, 1/ 10 minutes, or about 6/hour Speed ~ 11-72 km/s (~ 20 – 155,000 miles/hr)

Meteor Showers Usual rate = 6/hour Meteor Shower = rate may be as high as 60/hour Occur when Earth passes through the tail or debris of a comet Perseids (mid-August) Leonids (mid-November)

Meteorite Meteorites could be fragments from collisions involving asteroids. weigh few pounds & cause little damage. Impact craters Earth – not many, thick atmosphere Moon & Mercury – lots, no atmosphere Where to find – Antarctica & Desert

Meteorites 3 Types Iron – chunks of iron and nickel Stony – silicate masses that resemble Earth rocks Stony-iron – iron–stone mixtures

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