Impacts with space objects
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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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Impacts with Space Objects

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Impacts with space objects

Impacts with Space Objects


Moon shows many impact scars though most are prior to 3 8 billion years ago

Moon shows many impact scars though most are prior to 3.8 billion years ago


Impacts with space objects

Earth destroys most evidence over time. Why?


Asteroids originate in the asteroid belt between mars and jupiter

ASTEROIDSOriginate in the asteroid belt between Mars and Jupiter


Impacts with space objects

Mostly pieces of rock and metals that never coalesced to form a planet


Impacts with space objects

  • 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.


Impacts with space objects

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


Impacts with space objects

Long-period comets

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 Bopp – visible for 18 months in 1996 - 1997


Impacts with space objects

  • All comets are mainly made of ice and rocky debris.


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.


Impacts with space objects

Given equal size, the mass of an asteroid is greater than that of a comet.


Impacts with space objects

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.


Comet shoemaker levy 9 impact with jupiter july 16 22 1994

Comet Shoemaker Levy 9 impact with Jupiter July 16-22, 1994


Impacts with space objects

Fragment Q impacts on Jupiter. There were 21 discernable fragments up to 2km diameter.


Meteor crater arizona 1km wide 4 000 ft impact crater created 50 000 years ago

Meteor Crater Arizona>1km wide (4,000 ft.) impact crater created ~50,000 years ago.


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.


Impacts with space objects

Tektites – 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


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


Impacts with space objects

Extinction of Dinosaurs

~65 Million Years B.P.


Kt boundary clay layer and iridium

KT boundary clay layer and iridium


Kt boundary layer raton basin

KT boundary layer Raton Basin


Impacts with space objects

Figure 17.25


Tunguska june 30 1908

Tunguska, June 30, 1908


Tunguska

TUNGUSKA

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 2,150km2 (830mi2)


Impacts with space objects

Figure 17.26


Impacts with space objects

  • 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.


Impacts with space objects

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.


Impacts with space objects

Would we have warning before an impact?

Maybe, maybe not.


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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