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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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slide6

200 asteroids with diameters >100km

  • ~1000 asteroids >30km diameter
  • ~1,000,000 >1km diameter
comets
COMETS

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.

slide8

Make a complete orbit in <200 years.

Haley’s Comet every ~75 years

comet orbits
Comet Orbits
  • http://www.st-andrews.ac.uk/~bds2/ltsn/ljm/JAVA/COMETORB/COMET.HTM
slide10
Long-period comets

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

impacts
IMPACTS

Energy release depends on speed and size.

Asteroids may impact at >30,000mph.

Long-period comets >150,000mph.

M-16 rifle ~2250 mph.

slide15

Atmosphere may heat the asteroid to 3,000oC.

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.

meteor crater arizona
METEOR CRATER, ARIZONA

Impact from nickel-iron metallic meteorite (asteroid).

Diameter ~40m (120ft.).

Speed at impact ~27,000mph.

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

slide21

Tektites – glassy spherules formed by in-air-cooling of impact melted rock.

Happens with large asteroid impacts.

manicouagan impact site 215 5 million years b p
Manicouagan Impact Site ~215.5 million years B.P.

~5km (3mi) diameter asteroid

~70km (40mi) diameter crater

slide24
Extinction of Dinosaurs

~65 Million Years B.P.

tunguska
TUNGUSKA

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

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

slide37
Tunguska originally thought to be ~60m in diameter. If so, similar impacts every ~2,000 years.
  • But, with new estimate of 40m or less, once every ~300 years.
  • Total potential hazard from impacts has increased.
near earth objects neos project
NEAR-EARTH OBJECTS (NEOs) PROJECT

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.

slide39

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.

november 2011 asteroid
November 2011 Asteroid

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

Near Earth Objects Tracking

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

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