Earth Sciences 240A Lecture 5
Part B: Space Objects and Impacts: Introduction
Zhamanshin Impact
1 million years ago; Crater 13.5 km
diameter (~1 km asteroid)
Sufficient to end modern
civilization; Should expect one per 1 million years
Definitions: asteroid,
meteoroid, meteorite, meteor, etc.
Asteroid Belt
Location; Series of belts; Collisions
common
Asteroids (many differentiated)
NEOs (Apollos); Amors
Impact craters
PHAs and the
Comets
Oort cloud main source; examples: Halley’s;
Hale Bopp
Dust
Daily: approx. 100-1000 tonnes
1mm size = ‘shooting stars’
Impact!
Atmosphere’s influence: no
influence on dust or on objects >350 tonnes
Objects >1 gm will pass through
and land
Friction
Possible 3000oC
‘skin’; Slows descent
Fireball effect; Sonic
boom
Meteorite
Classification
Aerolites (‘Stones’): 92.8% finds
Chondrites
and Achondrites
Siderolites (‘Stony-irons’): 1.5%; About
50% Ni-Fe alloy; 50% silicates
Fragments of
differentiated asteroids
Siderites (‘Irons’): 5.7% of finds;
Primarily Ni-Fe alloys
Chondrules
Partly to completely molten
Almost completely silicate
Suggested precursor: Solar nebula
dust
Note importance of carbonaceous
chondrites
Historical Falls
Most never found (fall into oceans)
Watch webpage:
http://miac.uqac.ca/MIAC/MIAC.html
Next lecture: Meteor
Crater and some impact/crater properties
http://www.unb.ca/passc/ImpactDatabase/CINameSort.html
Check above for complete crater database.
Our class site: