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 2000-2002-who saw?

Meteors better after midnight

But…

Meteorites: typesCarbonaceous

Stony

Iron-nickel

Iron

Iron most commonly found but more stony meteorites more common!

Widmanstatten patterns

these crystals take several millions of years to grow

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 – 26Al 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 10-20 years

• Need to look for 100-m objects

• Need a wakeup call?

That’s all. Have a nice day!