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Impacts with Space Objects. Moon shows many impact scars though most are prior to 3.8 billion years ago. Earth destroys most evidence over time. Why?. ASTEROIDS Originate in the asteroid belt between Mars and Jupiter. Mostly pieces of rock and metals that never coalesced to form a planet.

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Asteroids originate in the asteroid belt between mars and jupiter
ASTEROIDS billion years agoOriginate in the asteroid belt between Mars and Jupiter


Mostly billion years agopieces of rock and metals that never coalesced to form a planet



Comets
COMETS billion years ago

Short-period comets

They are part of the Kuiper belt, a flattened disk of comets made up of icy debris left over from the formation of the outer planets.


Make a complete orbit in <200 years. billion years ago

Haley’s Comet every ~75 years


Comet orbits
Comet Orbits billion years ago

  • http://www.st-andrews.ac.uk/~bds2/ltsn/ljm/JAVA/COMETORB/COMET.HTM


Long-period comets billion years ago

They are part of the Oort cloud, a vast diffuse envelope of encircling comets. Period may thousands of years of more.


Comet hale bopp visible for 18 months in 1996 1997
Comet Hale billion years agoBopp – visible for 18 months in 1996 - 1997



Impacts
IMPACTS billion years ago

Energy release depends on speed and size.

Asteroids may impact at >30,000mph.

Long-period comets >150,000mph.

M-16 rifle ~2250 mph.



Atmosphere may heat the asteroid to 3,000 that of a comet.oC.

Impact instantly released enormous heat and energy, melting and vaporizing not only rock but also much of the asteroid itself.

Crater may end up filled with crushed and shattered rock.


Comet shoemaker levy 9 impact with jupiter july 16 22 1994
Comet Shoemaker Levy 9 impact with Jupiter that of a comet.July 16-22, 1994



Meteor crater arizona 1km wide 4 000 ft impact crater created 50 000 years ago
Meteor Crater Arizona fragments up to 2km diameter.>1km wide (4,000 ft.) impact crater created ~50,000 years ago.


Meteor crater arizona
METEOR CRATER, ARIZONA fragments up to 2km diameter.

Impact from nickel-iron metallic meteorite (asteroid).

Diameter ~40m (120ft.).

Speed at impact ~27,000mph.

Crater floor holds 365m (870ft.) of shattered rock.


Tektites fragments up to 2km diameter.– glassy spherules formed by in-air-cooling of impact melted rock.

Happens with large asteroid impacts.


Wolfe creek australia age 300 000 years
Wolfe Creek Australia – age ~300,000 years fragments up to 2km diameter.


Manicouagan impact site 215 5 million years b p
Manicouagan Impact Site ~215.5 million years B.P. fragments up to 2km diameter.

~5km (3mi) diameter asteroid

~70km (40mi) diameter crater


Extinction of Dinosaurs fragments up to 2km diameter.

~65 Million Years B.P.


Kt boundary clay layer and iridium
KT boundary clay layer and iridium fragments up to 2km diameter.


Kt boundary layer raton basin
KT boundary layer Raton Basin fragments up to 2km diameter.


Figure 17.25 fragments up to 2km diameter.


Tunguska june 30 1908
Tunguska, June 30, 1908 fragments up to 2km diameter.


Tunguska
TUNGUSKA fragments up to 2km diameter.

Probably a stony meteorite or comet possibly smaller than 40m in diameter.

Exploded 5 – 10km (3 – 6mi.) above the earth’s surface.


Flattened trees over 2 150km 2 830mi 2
Flattened trees over 2,150km fragments up to 2km diameter.2 (830mi2)


Figure 17.26 fragments up to 2km diameter.



Near earth objects neos project
NEAR-EARTH OBJECTS (NEOs) PROJECT similar impacts every ~2,000 years.

Monitors and identifies near earth-objects for potential impact of objects >1km (.62mi.) diameter.

Average time interval between impacts of this size >100,000 years.


However, objects 40m(or less) – 100m in diameter can cause devastating local effects (like Tunguska).

Smaller potentially damaging events occur perhaps every couple of centuries.


Would we have warning before an impact? devastating local effects (like Tunguska).

Maybe, maybe not.


November 2011 asteroid
November 2011 Asteroid devastating local effects (like Tunguska).

http://neo.jpl.nasa.gov/news/news171.html

Near Earth Objects Tracking

http://neo.jpl.nasa.gov/risk/#legend


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