Asteroids and Comets Debris of the Solar System Chapter 9.
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Transcript of Asteroids and Comets Debris of the Solar System Chapter 9.
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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
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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)
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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
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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
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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
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Comet Atmosphere (Coma)
• Escaping gases– forms “cloud” around nucleus
• Coma mostly water vapor
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Comet Tails
• Sunlight pushes gas & dust • Gas & dust flows away from nucleus• Forms tail• Tail points away from Sun
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Comet Orbits
• Orbits highly elongated– most have aphelion well beyond Pluto
• 50,000 AU!
– perihelion near sun
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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
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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
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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)
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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)
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Meteorites
• Meteors that land on Earth called meteorites
• Origin– early solar system debris
(asteroids / comets)– planets (e.g. Mars)– the Moon
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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