Meteors and Meteorites
“Meteoroids” - still in space…
“Shooting Stars” Size of a pea velocities of 10’s km/sec ~ 6/hour sporadic rate (any night)
“Bolides” or “fireballs”
Sometimes seen in daytime
Sometimes break up
Meteor “train” can persist
If hit: “meteorites”
Meteor showers occur when we cross paths of a broken up comet Here the “Persieds” named …
… named for constellation containing the radiant point Leonids shown here or plotted…
…plotted back to radiant in Leo
Caused by perspective – the artist’s “vanishing point” Driving in snow
Major showers Handout
Leonids spectacular every 33 years Due to lumpiness in distribution of old comet within orbit This woodcut from 1833 – 100,000/hour My first chance – 1966 Most recent who saw?
Meteors better after midnight But…
Meteorites: types Carbonaceous Stony Iron-nickel Iron
Iron most commonly found but more stony meteorites more common!
Widmanstatten patterns
Stony meteorites – 93% of all meteorites
Show chondrules (round stones) when cut and polished
Stony-irons show a mix
Carbonaceous chondrites this at right from 1969 Allende’ fall in Mexico Primordial in content Contain volatiles Organics Radioactive nuclei – 26 Al may be from supernova that sparked the formation of our solar system
Model to explain the variety
Barringer crater in Arizona 1.2 km diameter, 25,000 years ago, 11 km/s = 20 Mton bomb
Drilling found the rock
41-mile diameter crater in Quebec
Tunguska Heard for 1000 km. Small comet? What if had happened 60 – 70 years later?
Walter and Luis Alvarez found iridium clay layer at Cretacous-Tertiary boundary (65My ago) Traced impact to …
Chicxulub Impact structure A bad day for dinosaurs Expect such hits every ~ 8 million years May find a kilometer within years Need to look for 100-m objects Need a wakeup call?
That’s all. Have a nice day!