asteroids and comets debris of the solar system chapter 9

Asteroids and Comets

Debris of the Solar System

Chapter 9

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Asteroids• Small, rocky objects

– like terrestrial planets– size much smaller

• shape not round• no atmosphere

– little volatile material

• Also called “Minor Planets”• Early solar system remnants • Four largest:

– Ceres, Pallas, Vesta, Hygeia

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Discovery of Asteroids

• Ceres discovered in 1801– by Piazzi

– thought it was “missing planet”

– more discovered later• 300 known by 1890

• today >10,000 known

• Most in asteroid belt – between Mars and Jupiter

(2.2-3.3 AU)


Composition & Classification

• Three main types:• C-type (carbon-rich):

– silicates mixed with dark carbon compounds – “primitive” (unchanged since formation of solar system)

• S-type (stony):– mostly silicates, no dark carbon compounds– “primitive”

• M-type (metallic): – rare– fragments from core of differentiated asteroid– potential mining resource

Comets• Observed from earliest recorded times

– frequently interpreted as “harbingers of doom”, or bad omens

• Primordial remnants of early solar system

• Three main components:– nucleus

– coma

– tail (often two parts)• gas (ion) tail

• dust tail


Comet Nucleus

• Small, solid body (few km)– “dirty snowball” model

• nucleus made of ices• mixed with rocks and dust

• When heated (near sun) – ices vaporize– release gas & dust

• Gas released in “jets”– not steady

– like geysers



Comet Atmosphere (Coma)

• Escaping gases– forms “cloud” around nucleus

• Coma mostly water vapor

Comet Tails

• Sunlight pushes gas & dust • Gas & dust flows away from nucleus• Forms tail• Tail points away from Sun

– gas (ion) tail straighter, bluer– dust tail curves, yellower QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.


Comet Orbits

• Orbits highly elongated– most have aphelion well beyond Pluto

• 50,000 AU!

– perihelion near sun

Origin of Comets

• Comets come from large distances • Jan Oort (1950)

– proposed “cloud” (reservoir) of ancient icy bodies

• Oort Cloud– extends half way to nearest star

– contains 10 trillion (1013) comets• total mass: 1000 Earth masses

• more mass than all the planets

– Occasionally comets fall into inner solar system


The Kuiper Belt

• Second source of comets – in plane of solar system– beyond the orbit of Pluto– proposed by Kuiper

• Pluto probably largest Kuiper belt object


Meteors

• Rocks from space falling to Earth– vaporized by air friction– glow from heat– produces “shooting stars”

• Typical size < 1 gram (pea-sized)– 100 tons/day fall to Earth

• Occasional larger objects– produce fireballs (bolides)



Meteor Showers

• Comets leave debris in their orbits

• Meteor showers – occur when Earth passes through

comet debris– produces large number of meteors– meteors appear to come from a

point in the sky (called the radiant)• shower named for location of radiant

(Leonids come from Leo)


Meteorites

• Meteors that land on Earth called meteorites

• Origin– early solar system debris

(asteroids / comets)– planets (e.g. Mars)– the Moon






Meteorites

• Three types:– iron (almost pure nickel-iron)

• clearly extraterrestrial

• easy to identify

– stony (silicate or rocky)• difficult to find, look like rocks

– stony-iron (mixture)

• Age ~ 4.5 billion years

asteroids and comets debris of the solar system chapter 9

Documents

solar systemchapter

plane of solar systembeyond

gas dust gas dust flows

tail curves

ctype carbonrich

earth massesmore mass

sungas ion tail straighter

planetsoccasionally