ESYS 150 LECTURE 18: IMPACTS WITH SPACE OBJECTS
When was the last major space object impact?
Are we likely to have a catastrophic rendezvous with a space object in the near future?
IMAPCT SCARS AND SPACE OBJECTS (ABBOTT Ch 17) (F1)
Introduction Earth moves through space occupied by comets and asteroids on different paths.
Could a comet or asteroid destroy the human race? (F2 17.1)
Impact Scars Earth dynamic so scars wiped out. Not a good place to look.
Moon dead. Huge Number impact scars. By 3.9 Ba impacts died down (F3 17.2)
Lunar Maria – dark colored, flood basalts 3.8 -3.2 Ba, few impact scars
Sources of Extraterrestrial Debris
Meteoroids Pieces of asteroids or comets orbiting the Sun. (F4)
Meteor Debris fragmented asteroids/comets hits atmosphere creates meteor in Atmosphere.
Meteorite becomes meteorite on ground, two types
Irons – metallic, stones – made of rocks
Stony more common entering atmosphere but more irons found
Asteroids 9 planets orbit around sun, 4 inner rocky, 5 outer gaseous hydrogen and helium
Asteroids rocky and metallic. Max diameters 933 km.
Form in belts in space between Mars and Jupiter (F5 17.5)
When asteroids collide, major collision, debris goes into gap
Attraction from Jupiter that gives eccentric orbit. (F6 17.8)
Clusters of asteroids have orbits that intersect the orbits of Earth and Mars
Comets Divided into short and long period (F7)
Short period in Kuiper Belt – a flattened disc from near Neptune to 50 Astronomical
Units beyond sun and earth have orbits < 200 years.
Long period in Oort cloud (dirty snowballs) – a spherical cloud of objects going out far
beyond solar system, many millions of them.
Comets essentially dirty snowballs.
Have wildly eccentric orbits and a few come near to sun. (F8)
Tail from sublimation to vapor, gives off gases. Gases pushed out by solar wind.
Most only 15 km diameter. Have to be > 350 tons to burst through atmosphere
Halley’s Comet comes every ~ 76 years. (F9 17.10 & 17.11)
Ices contain carbon products and C, H, O and N in same ratio as human body
Rates of Meteoroid Influx
Meteoroids 100,000 enter earth’s Atmos. every day. Atmos. protects earth. Burn up. (F10 17.12)
Cosmic dust Smallest meteorites 0.001 mm settle as cosmic dust.
Shooting stars Incoming debris with 1mm diameter flame out as shooting stars
Meteorites Debris weighing more than 1 gm falls onto earth’s surface. Outer surface burned off.
Creates sonic boom
KNOWN IMPACTS ON EARTH
