Meteorites and Cosmic Collisions Notes

Meteorites:
- How are meteorites found?
- Main types
- Where do they come from?
- Meteorites as time capsules
Cosmic Collisions:
- Role of cosmic collisions in evolution of Solar System
- History of collisions
- Collision of Comet Shoemaker-Levy 9 with Jupiter
- Effects of impacts
- Prospects for future giant collisions with Earth

Asteroids:
- Rocky or metallic bodies in outer space not classified as moons, planets, or comets.
- Usually orbit stars at great distances.
Comets:
- Icy objects that orbit their star in highly elliptical paths, often far from the Sun.
Meteorites:
- Pieces of rock from outer space that survive atmospheric entry and strike Earth.
- Collectible physical evidence of extraterrestrial matter.
Meteors:
- Glowing trails (shooting stars) created by matter burning upon atmospheric entry.
- Larger meteors may become meteorites if they survive the fall.
Meteoroids:
- Meteors before they hit Earth's surface, generally small asteroids.
Fireballs:
- Extremely bright meteors.
Meteor Showers:
- Occur when Earth passes through a belt of debris, resulting in numerous meteors in a short time.
Bolides:
- Bright meteors often causing craters on impact.
Craters:
- Round impact holes from collisions with large objects.

Earth collects about 80,000 tons of extraterrestrial matter annually:
- Comes in varying sizes from dust to large rocks (up to 200 tons/day).
- Most are pieces of asteroids; some are from the Moon, Mars, or Vesta.
Chondrites:
- Oldest meteorites containing interstellar dust and tiny diamonds from supernovae.
- Provide insights into solar system formation and materials prior to its existence.
How to Identify a Meteorite:
- Magnetism: Many meteorites are magnetic.
- Nickel-Iron Composition: Often contain native iron with 1-11% nickel.
- Fusion Crust: Freshly fallen meteorites have a black outer layer due to atmospheric entry heat.
- Interior: Typically gray with metallic flecks.
- Chemical Analysis: Higher metal content (like nickel) and unique isotopes compared to terrestrial rocks.

Primitive Meteorites:
- About 4.6 billion years old, unchanged since originating in the Solar nebula.
Processed Meteorites:
- Younger, showing differentiation, often from larger bodies subjected to impacts.
Main classifications:
- Chondrites: Variant types include carbonaceous (rich in organic molecules) and non-carbonaceous.
- Achondrites: Fragmented materials from Mars and the Moon.
- Iron Meteorites: Primarily composed of nickel-iron, often with distinct crystallization patterns.
- Stony-Iron Meteorites: Contain both silicate minerals and metallic components.

Cosmic collisions significantly influenced the evolution of the Solar System:
- Aggregation of planets from planetesimals, formation of the Moon, and defining the axial tilt of Venus and Uranus.
- Historical data derived from crater patterns and isotope analysis.
Major impacts on Earth lead to mass extinctions, including the one responsible for the dinosaurs' demise (Chicxulub impact).
Near Earth Objects (NEOs) are being actively tracked as potential threats to our planet.

Notable Annual Meteor Showers:
- Quadrantids: January 3,
- Lyrids: April 22,
- Eta Aquarids: May 5,
- Perseids: August 12,
- Orionids: October 22,
- Geminids: December 14,
- Ursids: December 23.

On rare occasions, meteorites have caused damage on Earth, though human injuries are extremely rare.
The Chelyabinsk meteor of 2013 illustrates the potential impact of such objects, highlighting real dangers associated with large cosmic impacts.

The likelihood of future collisions remains a concern with estimates of major impacts occurring every 100 million years.
Various projects are underway to better detect and mitigate threats from NEOs, with the use of observational techniques and potential diversion methods being explored.