Remnants of Rock and Ice
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Transcript of Remnants of Rock and Ice
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Remnants of Rock and Ice
• Asteroids
• Meteoroids (meteorites, meteor)
• Comets
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Remnants of the Solar Nebula•Small bodies remain virtually unchanged since their formation 4.5 billion years ago•They carry history of the Solar system in their compositions, locations, and numbers.
Asteroid means starlike, a rocky leftoverMeteoroid – small rocky material in space Meteor – in the atmosphere (falling star)Meteorite – any piece of rock than fell to the ground from the skyComet means hair (Greek), an icy leftover
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Asteroids (minor planets)• Most abundant between
the orbits of Mars and Jupiter
• Largest is Ceres, 800 km diameter
• Most are much smaller, irregular
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Asteroids
The first asteroid Ceres was discovered by Piazzi on January 1, 1801 in an attempt to find the missing planet between Mars and Jupiter
Ceres has a diameter of half of Pluto
There are more than 100,000 asteroids larger than 1 km in diameter
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Asteroid Eros
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Asteroids (minor planets)
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Evolution of the BeltEarly in the history of the Solar system, the belt contained enough planetesimals to form a planet.
Gravitational tugs from Jupiter created the gaps.
Two stable zones along Jupiter’s orbit host two families of asteroids (Trojans).
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Jupiter’s Trojan Asteroids
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Meteorites
Meteorites are pieces of rock that fell from the sky.
Seen as fireballs (sometimes with sound)
May cause damage, but most fall into oceans
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MeteoritesMeteor showers – result of the Earth’s passing through a comet orbit
Meteors are single pieces of comet dust
25 million meteoroids enter Earth’s atmosphere every day
Meteor showers get their names after constellations from which they appear to radiate
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Meteor
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Meteor Showers
(These occur when earth passes through cloud of debris along a comet’s orbit.)
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Leonid Meteor Shower
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Meteor Trail Recorded During Leonid Meteor Shower, 1998
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Ionized Trail Generation by Meteor Crossing Eastern US,
1992
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The Origin of Meteorites
Primitive meteorites may be either rocky or carbon-rich
Processed meteorites can be removed from the surface of a planet by an impact.
There are meteorites from Moon and Mars found on Earth.
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Primitive Meteorites
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Processed Meteorites
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Comets• Chunks of rock and ice in highly eccentric orbits
• Near sun, ice sublimates to produce “tail”
• A couple have been visited by robotic craft
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Comet StructureComets are basically dirty snowballs where ice mixes with rocky dust.
Their mean size is a few kilometers across.
The comet body is called nucleus.Sublimating ices create coma.A tail pointing away from the Sun appears.There are two tails: plasma tail and dust tail.
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Nucleus of Comet Borrelli
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Comets
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Comet Orbits
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CometsComets contain information about the outer solar system
Most of them visit the inner part only once, a few are regular guests
One of the most famous comets is Halley’s comet. It was discovered by Edmund Halley in 1682. Its orbital period is 76 years. The last appearance in 1986.
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Halley’s Comet
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Comet Halley
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Comet Hale-Bopp
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Comet Hale-Bopp
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Sun Grazing Comets
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Comet Shoemaker-Shoemaker-Levy 9
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Earth impacts
• Do we ever get hit?• Yes! The questions are when and by
what?• Classify events by size
–Small–Medium–Large
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ImpactsThe larger the impactor, the more rare the impact
In 1908, an unusual explosion occurred in Siberia.
Meteor crater in Arizona formed 50,000 years ago.
A large impact occurred 65 million years ago perhaps caused the dinosaur extinction.
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Earth impacts: small
• Small: less than 50 m across at top of atmosphere– Happening all the time– Will burn up or break up in the atmosphere– Most are very tiny (‘pea’ sized)– Meteors! (“Shooting stars”, “Falling stars”)
• Can see 3 - 5 per hour on a typical night• 25 million every day!• 100 tons per day
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Earth impacts: medium
• Medium: 50 m - 1 km across at top of atmosphere
–Only ~ one every century or millennium
–Causes “severe local damage”
–Two great examples from ‘recent’ history
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Earth impacts: medium• The Tunguska event - Siberia, Russia
–Happened in 1908 –Flattened a forest–Knocked people over 200 km (140
miles) away–No crater (exploded just above
ground)
• The impactor?–A stony meteorite (?) Size: 30 m
across
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The Tunguska event
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The Tunguska event
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Earth impacts: medium
• The Berringer Crater, in Arizona
–Happened 50,000 years ago
–The crater:
•1,200 m across
•200 m deep
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Earth impacts: medium
• The impactor?–An iron meteorite–100 m across (50 m on impact)–Going 40,000 mph!–Explosion = 20 million tons of TNT
•A moderate atomic bomb•2 Mt. Saint Helens
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The Berringer crater, Arizona
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Meteor Crater in Arizona
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Earth impacts: large
• Large: more than 1 km across at top of atmosphere–One every few million years–Severe global effects–More than 2 km can cause mass
extinction–Most recent: 65 million years ago
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Earth impacts: large• The K/T extinction event
–Some history…
• ‘K/T’ = ‘Cretaceous / Tertiary’
• 60 % of all species on Earth disappeared, including the dinosaurs
• One explanation (there are several): Earth was hit by a large impactor
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Earth impacts: large
• The K/T extinction event
–Evidence for an impact:
• Iridium found at that geologic level
•A crater near the Yucatan, in Mexico
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The K/Textinctionevent
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Earth impacts: large• The K/T extinction event
–The impactor:• Probably a comet• Size: ~ 10 km across• Energy released:
–100 million million tons of TNT–5 million atomic bombs–10 million Mt. Saint Helens
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How often is there an impacted?
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How often do impacts occur?
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http://astro1.panet.utoledo.edu/~anatoly/astr1010/materials/324,41,Slide 41
http://campus.pari.edu/sara/arecibo/presentations/fields/294,13,Meteor Trail Recorded During Leonid Meteor Shower, 1998
http://departments.weber.edu/physics/schroeder/astro/lectureslides/356,8,Kuiper Belt objects (other stuff near Pluto)
http://www.phys-astro.sonoma.edu/people/faculty/carico/A100/367,2,Earth impacts