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Solar System Solar System DebrisDebris

Asteroids, Comets, Meteors, Oh My!

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Asteroids• Asteroids are small,

irregular, rocky bodies that orbit the sun

• Most are located between he orbits of Mars and Jupiter in the asteroid belt

• Some are located in the same orbit as Jupiter, but are separated by 60º - Trojans

• Some asteroids are in highly elliptical orbits that pass earth – Earth-crossing asteroids, Near-earth asteroids (NEAs), Near-earth objects (NEOs)

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What do asteroids look like?

• Too small to be seen with the naked eye – need large telescopes

• Appear as streaks because of their motion

• Three fly-bys of asteroids:– Gaspra by Galileo in 1998– Ida by Galileo in ????– Mathilde by NEAR in 1999

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What are asteroids made of?• Asteroids are classified into a number of types

according to their spectra (and hence their chemical composition) and albedo:1. C-type, includes more than 75% of known

asteroids:– extremely dark (albedo 0.03)– approximately the same chemical

composition as the Sun minus hydrogen, helium and other volatiles

2. S-type, 17%– relatively bright (albedo .10-.22)– metallic nickel-iron mixed with iron- and

magnesium-silicates3. M-type, most of the rest

– bright (albedo .10-.18)– pure nickel-iron

4. There are also a dozen or so other rare types

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Asteroids

• How many are there?– Some 5000 with

well-determined orbits– Probably >500,000 larger

than 1 km

• How big are they?– Largest (Ceres) is 940 km in diameter– Three larger than 500 km– About a dozen larger than 250 km– Number increases rapidly with decreasing

size

• Total mass of all asteroids ~ 5% of the moon

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Eros

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More Eros

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Eros Landing

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Comets• Comets are small

bodies of ice and dust that form tails as they near the sun.

• What way is this comet moving?

• Recall Kepler’s second law. Where do comets spend most of their time?

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What are comets made of?

• When they are near the Sun and active, comets have several distinct parts: – nucleus: relatively solid and stable,

mostly ice and gas with a small amount of dust and other solids;

– coma: dense cloud of water, carbon dioxide and other neutral gases sublimed from the nucleus;

– hydrogen cloud: huge (millions of km in diameter) but very sparse envelope of neutral hydrogen;

– dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye;

– ion tail: as much as several hundred million km long composed of plasma and laced with rays and streamers caused by interactions with the solar wind.

                                     

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Comet Parts

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Where do comets live?

• Short period comets come from the Kuiper belt

• Long period comets from the Oort cloud

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What happens when comets loose their

tails?• Meteor showers

   

                                       

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MeteoritesThree main types:• Stony

– Look like ordinary earth rocks at first glance. If you were to look closely, you would see that the outsides of the rocks look melted. Most meteorites (93%) striking the earth are stony

• Irons– These dark grey, metallic, and very

dense meteorites are unlike any earth rocks that you have ever seen. Five percent of meteorites striking the earth are irons

• Stony-Irons– These meteorites have clumps of both iron

and stone

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Asteroid – Meteorite Connection

• Iron– similar to type M asteroids

• Stony Iron– like type S asteroids

• Stony– Chondrite

• by far the largest number of meteorites fall into this class;similar in composition to the mantles and crusts of the terrestrial planets

– Carbonaceous Chondrite• similar to type C asteroids

– Achondrite• similar to terrestrial basalts

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Finding Meteorites

• Finds– Found on earth, often long after they landed– usually noticed because of their unusual appearance

or their unusual location

• Falls– These meteorites are seen falling, making a fireball

in the sky. By following the trail, the landing site and meteorite can be found. Most of these are stony meteorites

Peekskill, NY 1994

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Impacts

• What happens when a meteor hits the ground?– Usually

nothing– Occasionally,

large pieces make it to the ground and create impact craters

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Impact craters

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Impact Hazards• No person has ever been killed by a

meteorite hitting earth• However, a large impact killed the

dinosaurs• A smaller impact in remote Russia in 1908

knocked down trees and could have caused severe damage in a populated area

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Earth Sterilizing Impact

Mass Extinction Impact

Civilization Threatening Impact

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Terrestrial Impact Frequency

year

century

million yr.

billion yr.

ten thousand yr.

100 millionmillion10,00010010.01

Hiroshima

Tunguska

K/T

TNT equivalent yield (MT)

Global catastrophe

Tsunami danger