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Impacts with Space Objects (Meteoroid Influx (At speeds of 11 to 30km/sec,…
Impacts with Space Objects
Distinguishing Extraterrestrial Debris
2 main origins
Fragmented asteroids (primarily)
Comets (secondarily)
Meteoroids: pieces of asteroids or comets revolving around the sun
Shooting Stars or Meteors: Meteoroids blazing through Earth's Atmosphere
Meteorites: Meteors that hit Earth's surface and they can be of two types
Iron-rich meteorites, which are metallic
Stony meteorites, which are rocky
Cosmic Dust: refers to the smallest meteoroids; they settle on the earth's surface as gentle rain
Asteroids
Rocky fragments , diameter of 10 m to 1000km, which failed to consolidate into a planet or are remnants of a planet
Some are metallic (stony) strong and hard and may hit the earth
Some are weak and friable and explode in atmosphere
Most located in asteroid belt between Mars and Jupiter
Most meteorites come from asteroid belt
Comets
Come from outer solar system
Consist of frozen water, Carbon dioxide, or both with small rock fragments and dust
"dirty icebergs". or "dirty snowballs"
Highly elongated, elliptical orbits, which bring them close to the sun
Long period: if orbit is more than 200 years
Short period: if orbit is less than 200 years
Most have eccentric orbits, perihelion (near the sun), and aphelion(far away beyond outermost planet)
When a comet passes Saturn toward the sun it undergoes sublimation and releases gas and dust to form a tail
Meteoroid Influx
Add 100 to 1000 tons of material to earths surface each day
115km above: atmosphere is dense enough to heat them into glowing
Typically visible 100km above ground, but vaporized by 60km above ground
Meteoroids of 1 gram or more can pass through eh atmosphere to reach the surface
Frictional resistance melts away exterior, protecting interior, giving them a glazed, blackened crust
Frictional resistance also creates a mini-sonic boom
Atmospheric frictional heat may raise surface temperature to 3000 C, feeding the tail of a fireball
At speeds of 11 to 30km/sec, the atmosphere behaves like a solid
Most meteoroids are destroyed on impact, deflected back into space, or slowed down by friction
Meteors larger than 350 tons are unaffected by the atmosphere
Shooting stars can be described as sand grain-sized debris, flashing at 35km
Cosmic dust is unaffected by the atmosphere
Impact Scars: indirect evidence of meteorite impacts
meteoroids more than 350 tons can explode and excavate craters
Craters are destroyed by plate tectonics and erosion, buried under young sediments, some preserved on old regions (shields)
The Cratering Process
Very rapid dure to the mass and travel speed of meteorites
meteorites from asteroids impact the ground at 14km/sec; meterorites from comets impact at 70km/sec
Large energy transfer upon impact
Blanket of ejecta is dispersed around the crater as rock is fractured, crushed and broken
In large impact events the rock can even be vaporized
High pressure result in rock compression, then decompression which causes the rock to melt
Simple Craters
Simple bowls
With time, the ejecta blanket outside the crater is eroded
Meteor Crater, Arizona; Lac Cratere, Quebec
Complex Craters
Central uplifts and collapsed and fractured outer rims
Very hot and very high pressure at impact
New minerals created (diamonds) and the ground is pushed downward and outwards
A
Release Wave
deflects the material upward and outward which forms the central uplift
Chicxulub crater, Yucatan peninsula; Manicougan crater, Quebec
Hazards associated with Space -objects impacts
Base Surge: generated by the impact, similar to a volcanic pyroclastic flow
Earthquakes with Mw 11.3 can be generated with lots of aftershocks
Volcanism(flood basalts) can occur on the opposite side of the globe as a result of shock waves
Terrestrial Impact: rock is pulverized ot vaporized, sending up dust into the stratosphere
Oceanic impact: huge amounts of water vaporized, global tsunamis up to 300m tall can be generated
Short-term: global wildfires , sending more dust and soot into the air. This can cause global darkness and global winter , acid rain, and blocking of sunlight, reducing photosynthesis, failing crops
Long-Term: Dust settles but water vapour and CO2 remain in the atmosphere, leading to global warming, worst case scenario: mass extinction
Frequency and Classification
Frequency: 2400 impacts of > 25km diameter should be found on earth, 720 on land, but only 160 have been found
Classification: the Torino Scale is used to communicate risk to the public. It assesses the impact threat on a scale of 0 to 10
90% near-Earth Asteroids and short period comets, 10% long period comets
Mitigation Efforts
Problem: little to no warning before an impact occurs
Options currently studied to alter an NEO's collision course
Blowing it apart with a nuclear explosion
Attaching a rocket engine to drive it away
Using a big mirror to focus sunlight and vaporize it
Scooping the NEO rock mass and tossing it away