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 Torino Scale

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

 

Tagish Lake: Later lecture

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:

http://instruct.uwo.ca/earth-sci/240a/