Download - Meteorites: rocks from Outer Space
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Meteorites: rocks from Outer Space
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Nature cooperates with us….the meteor last night
Youtube video of meteor from Iowa
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Meteorites…when the piece of solid matter causing the meteor makes it to the ground
• Were noticed in deep antiquity
• There is probably one in the Kaaba Shrine in Saudi Arabia
• A knife made of meteoric iron was found in the tomb of Pharaoh Tutankhamun
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Types of meteorites
• Stony meteorites (about 94%), usually chondrites
• Iron-nickel (about 5 %)
• Relatively rare but extremely important carbonaceous chondrites (“objects that have the consistency of dirt clods”) Tagish Lake meteorite
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A piece of the Tagish Lake meteorite
Best preserved carbonaceous chondrite found
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Orbits of meteorites: where do they come from?
A powerful hint as to the nature of meteorites: stay tuned
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Ages of meteorites
• Age of formation (how determined?): almost all around 4.60 Gyr
• Cosmic ray exposure ages (how long they were out in outer space unshielded): millions to tens of millions of years.
• Last number suggests they were broken off a bigger object fairly recently
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Things you should be thinking about
• How do meteorites fit into the other objects we have discussed all semester?
• Are they pieces broken off of planets? Which planets?
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Presentation of the hagioliths
A picture is worth a thousand words, and a real thing is worth a
thousand pictures
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The next type of small solar system object: asteroids
There is a big gap between the orbits of Mars and Jupiter. Shouldn’t there be a
planet in there?
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First such object was found on Jan. 1, 1801…Ceres
• Others found in following years:• Vesta• Pallas• Juno• The fact that it took so long to find them
means that they are much smaller than major planets
• They are called minor planets or asteroids
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What the solar system looks like without asteroids
Seems a big jump between Mars and Jupiter
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Include the asteroids and it looks like this
Each dot is an asteroid
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A description of asteroids
• Little worlds (minor planets)• Big rocks (largest 600 miles in
diameter)• Red things on previous plot: near-
Earth asteroids (scary name, isn’t it?)
• What do they look like? No idea before 1993
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Gaspra: our first view of an asteroid
Not spherical; why not?
20km
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“Family picture” of several asteroids
52 km
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Eros…an asteroid with a lander (NEAR)
33 km
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The big asteroids (none visited yet by spacecraft)
• Ceres 930 km• Vesta 520 km• Pallas 520 km• Juno 480 km
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Vesta as seen by the HST
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Aspects of Vesta
• At opposition is almost naked eye brightness (was at opposition in February)
• Go visit it at the Smithsonian Museum of Natural History (!#*)
• HST has observed it rotating• rotation of Vesta
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The Dawn spacecraft…mission to Vesta and Ceres
Mission timeline:Launch: September 27, 2007Arrival at Vesta: August 2011Arrival at Ceres: February 2015
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Classes of asteroids (hey, this is a science course, you’ve got to have classes!)
• S type; albedo of 7-23 percent; main class in inner and middle belt
• C type; albedos of 2-7 percent (or less); main type in outer belt
• M type: metallic (mainly in central belt)• V for Vesta; albedo of 38 percent,
reflectance spectrum of pyroxine
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Geology of asteroids determined by collisions
• Surfaces are cratered, but not as much as would be expected for an unaltered object
• Images show stress fractures on the object• Collisional fracturing of a differentiated object
could account for the different classes• There are lots of double asteroids
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The orbits of asteroids
What do we see if we study the distribution of semimajor axes of
asteroids
Think about what we might Expect to see
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What we do see
Kirkwood’s Gaps: orbital resonances with Jupiter
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The physics of orbital resonance…like Cassini’s Division in Saturn’s ring
Remember demo with forced oscillator
What happens to the asteroids which were In resonant orbits?