Asteroids Astronomy 311 Professor Lee Carkner Lecture 15

Quiz #2 Friday  Quiz 2 same format as quiz 1  ~20 multiple choice/matching  ~4 short answer  Covers lectures 9-15  bring pencil and calculator

Rocks in Space  Asteroid --  Meteoroid --  Meteor -- the flash of light when a meteor hits the Earth’s atmosphere   sometimes called a falling or shooting star  Meteorite --

Types of Meteorites  Meteorites are classified based on their composition  Two major types are irons and chondrites    Chondrites are the most common type of meteorite   But, irons are much easier to find    What are the properties of chondrites and irons and how can you identify them?

Iron Meteorites  Composed of iron and nickel   Often show Widmanstatten patterns when etched with acid  

Widmanstatten Paterns

Chondrite (Stony) Meteorites  Composed of silicates   Contain chondrules, small glassy inclusions of material that were heated and quickly cooled    Carbonaceous chondrites

Chondrules

Impacts  Most meteoroids are small enough to burn up completely in the atmosphere  Occasionally a very large asteroid hits the Earth   Large impacts can put large amounts of material into the atmosphere causing global climate change  

Impacts and Mass Extinction   Evidence for impact    The mass extinctions at the Cretaceous/Tertiary (KT) boundary are probably due to a 15 km diameter impactor

Meteor Crater

The Chicxulub KT Impactor

The Missing Planet  In the 18th century astronomers noticed that there was a gap between Mars and Jupiter with no planets  In 1801 G. Piazzi found a faint moving star in the gap    This is the asteroid belt

The Asteroid Belt

Asteroid Myths  Are the asteroids debris from a planet that exploded?   Is the asteroid belt dangerous to travel through?  

Asteroid Facts  Size:  Orbit: Asteroid Belt AU, some have eccentric Earth crossing orbits  Description:

Formation of the Asteroid Belt  If Jupiter did not exist, a fifth terrestrial planet might have formed at 2.8 AU  Jupiter’s gravity:   

Trojans and NEOs  Many asteroids are found outside of the asteroid belt  Trojan asteroids have been captured in Jupiter’s Lagrange points    Some asteroids cross the Earth’s orbit and are called Near Earth Objects (NEO) 

Studying Asteroids  Four asteroids have been observed at close range    The best studied asteroid is now Eros, which the NEAR mission orbited and studied at close range in 2000

Gaspra

Ida and Its Moon

Asteroid Features  Only Ceres, Pallas and Vesta (the 3 largest asteroids) have enough gravity to form a sphere   Asteroids show many craters   During the heavy bombardment period asteroid collisions must have been frequent

Composition of Asteroids  Asteroids are divided into three major groups based on composition  S Type   C Type   M type 

Formation of Asteroids  M and S type asteroids are found in the inner asteroid belt where temperatures are higher  

Formation of Meteoroids  Some asteroids became large enough to differentiate    These asteroids were then broken up by collisions    Asteroids that never differentiated formed chondrites

What Use is an Asteroid?  Mining   Space Habitats   Spaceships   Providing Material for Life in Space 

Summary  Asteroids are small bodies that orbit the Sun  Most are in the asteroid belt between Mars and Jupiter (2-3.5 AU)  Jupiter’s gravity prevented the asteroids from forming a planet  Description:  Small (most less than 1 km)  Max size is few hundred km  Irregularly shaped  Heavily cratered

Summary: Meteoroids  Iron  made of metal  formed from core of asteroids (M type)  Achondrites (Stony)  made of rock with no inclusions  made from crust of asteroids (S type)  Chondrites (Stony)  made of rock with small inclusions  made from undifferentiated asteroids (S and C type)