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- Yesterday, Thursday, January 17, 2013, at 5:21 AM you could have witnessed an early morning meteor that flew over northern California. I was up but must have been looking the wrong direction. Darn! It was a fireball traveling east to west from Reno to San Francisco at 10 miles per second, 36,000 miles per hour, faster than a speeding bullet.
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- 50 witnesses reported it to the American Meteor Society. Witnesses said it “ lit up the ground like daylight.” It was a “long streak of light, the front part a huge , square- ish shape”. “It left a trail of smaller , glowing particles.”
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- It was likely the size of a small car, disintegrating 5 to 50 miles above the Earth. ( See Review # 1540 Sutter’s Mill Meteorite that happened April, 2012.)
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- What can we learn from these asteroids that enter the Earth’s atmosphere?
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- We have 8 planets, well 9 if you count Pluto. But, Pluto should probably be counted as a large asteroid. There are even larger ones. But, if you count up all sizes of asteroids orbiting the Sun you get trillions of these bodies in our Solar System. Comets, are simply asteroids that formed beyond the “ frost line” where they are far enough from the Sun for water to freeze. Greater than 3 astronomical units ( 1 AU is Earth-Sun distance.) Inside the frost line all the water evaporated during our Solar System formation. How Earth got its water is another story.
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- The majority of asteroids are orbiting between Mars and Jupiter. These asteroids would have become another planet except for the gravitational resonance, tidal forces, created by the immense gravity pull of Jupiter. Resonance occurs when gravity tugs at an object in the same direction at each orbital alignment. These resonances pull objects apart and even toss them out of orbit. Sometimes to the outer Solar System and sometimes to the inner Solar System where we live.
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- If an asteroid hits Earth’s atmosphere it can become a “ shooting star”. The word “ asteroid” means “star-like”. If an asteroid makes it into the atmosphere it is a “ meteor” . If makes it to the surface of Earth it is a “ meteorite”.
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- All asteroids are really just remnants of the birth of the Solar System. Not all of the accretion disk that formed the planets became planets and moons. Some of the debris was left over after multiple mergers and collisions as the matter circled the Sun in a flat disk, much like the rings of Saturn. These asteroids are 4.5 billion years old. By studying them we can learn a lot about the birth of our Solar System.
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- Over 150,000 asteroids have been catalogued and numbered, some are named, but only 10% have enough data to be tracked, determining their orbits.
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- The largest asteroid in the inner Solar System is Ceres, 1,000 kilometers in diameter. It is large enough to have attained a spherical shape due to the pull of gravity. The asteroids that are smaller have all sorts of shapes, most look like potato-shapes.
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----------------- Pallas is 540 kilometers long
----------------- Vesta is 510 kilometers long
----------------- Gaspra is 16 kilometers long
----------------- Ida is 40 kilometers long
----------------- Mathilde is 50 kilometers long
----------------- Eros is 25 kilometers long
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- Astronomers measure asteroids with the brightness of their reflected light. Infrared brightness depends on the asteroid’s temperature. Comparing the two spectrum measurements tells astronomers the ratio between reflected light and absorbed light. Then, a measurement of brightness and distance can calculate the size of the asteroid. Radar measurements of a rotating asteroid can reveal its shape. Spectroscopy measurements of reflected light can determine its composition.
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- Asteroid composition varies from water to sand to iron. To measure the mass astronomers need a second object to be able to measure gravitational force effects. Some spacecraft have come close enough in a fly-by to measure gravitational effects. Some asteroids have “ moons” that can be measured for orbit velocities and separations. From these we can calculate mass. Mass and volume we can calculate density.
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- Mathilde asteroid has a density of 1.5 grams / cubic centimeter. It is likely an empty bile of rubble.
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- Eros asteroid has a density of 2.4 grams / cubic centimeter. It must be a solid rock.
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- Science fiction movies depict the asteroid belt as a minefield of flying rocks. Actually the Asteroid Belt between Mars and Jupiter has asteroids separated by millions of kilometers on average. That would be like grains of sand separated by kilometers.
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- Meteorites are asteroids that make it to the surface of Earth. The best way to study them is with a microscope not just telescopes. They are often identified due to their rare earth content, like the element iridium. Over 20,000 meteorites have been found and analyzed in this way.
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- There are 2 basic types of meteorites:
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--------------------------------- Primitive
--------------------------------- Processed
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- Primitive meteorites are 4.6 billion years old. They are categorized in 2 basic types:
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-------------------------------- Stony - with rocky minerals
-------------------------------- Carbon-rich - rocky minerals plus carbon compounds.
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- Processed meteorite were part of a larger asteroid that suffered an impact. They come in 2 types:-
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------------------------------ Metal rich - made of high density iron or nickel. Represents the core of a larger asteroid.
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------------------------------ Rocky - less dense composition representing the terrestrial mantles or crusts of larger planets or asteroids. Some of the rock is like basalt that comes from volcanoes on Earth. Some meteorites have been identified as coming from the surface of the Moon or from Mars.
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- Astronomers studying asteroid fragments cut them in slices thinner than 30 microns. Under a microscope they become transparent to a bright light The tiny fragments are called Chondrites and they contain tiny beads of melted material called chondrules. The optical properties of each material can be studied to determine where in the early Solar System the asteroid first formed.
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------------------ Between Mercury and Earth < 1 AU -------- Enstatite Chondrites
------------------ Beyond Mars > 2 AU ------------ “ Ordinary” Chondrites
----------------- 3 AU ---------------------------------”Rumuruti” Chondrites
----------------- > 3 AU ----------------------------- Carbonaceous Chondrites.
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- Enstatite Chondrites are 2% of the meteorites found and they contain the mineral MgSiO3, which is enstatite. These minerals are formed inside the orbit of Mars.
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- Ordinary Chondrites represent 74% of the meteorites found and they were formed around the belt 2.4 AU between Mars and Jupiter.
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- Rumunti Chondrites are meteorites found in Kenya, Africa. They have an abundance of oxygen isotopes indicating that they must have formed farther from the Sun than Ordinary Chondrites.
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- Carbonaceous Chondrites have the presence of organic compounds indicating they must have formed far from the Sun. They were not evaporated by the Sun’s intense heat.
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- How ere these chondrules, little beads, originally created? The process required repeated melting and cooling. One theory is that they were hit by a shockwave from a supernovae or a Gamma Ray burst. This seems unlikely. Maybe lightning bolts occurred in space? Maybe there were others sources of shockwaves, density waves, that traveled through the accretion disk? To learn more see: http://meteorites.wustl.edu/id/ordinary_chondrites.htm.an announcement will be made shortly, stay tuned.
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RSVP, please reply with a number to rate this review: #1- learned something new. #2 - Didn’t read it. #3- very interesting. #4- Send another review #___ from the index. #5- Keep em coming. #6- I forwarded copies to some friends. #7- Don‘t send me these anymore! #8- I am forwarding you some questions? Index is available with email upon request. Some reviews are at http://jdetrick.blogspot.com Please send feedback, corrections, or recommended improvements to: jamesdetrick@comcast.net. ---- “Jim Detrick” -- www.facebook.com, -- www.twitter.com, -- 707-536-3272 Saturday, January 19, 2013
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