ASTR 3 Chapter Notes - Chapter 9: Radiometric Dating, Silt, Kuiper Belt
ASTEROIDS, COMETS AND METEORITES
Asteroids are rocky leftovers of planet formation
• Largest asteroid is Ceres, diameter of ~1000km
• 150,000 asteroids known in catalogs, ad probably over a million with diameter >1km
o Small are more common than larger
o All asteroids in solar system wouldn't add up to even a small terrestrial planet
Most asteroids orbit in a belt between Mars and Jupiter
• Trojan Asteroids follow Jupiter's orbit
• Orbits of near-Earth Asteroids cross Earth's orbit
Which explanation seems to be the most plausible?
• The belt is where all asteroids seemed to survive
Orbital Resonances
• Asteroids in orbital resonance with Jupiter experience periodic nudges
• Eventually those nudges move asteroids out of resonant orbits, leaving gaps in the belt
• The gravity of Jupiter is KEY
Origin of Asteroid Belt - Rocky planetesimals survived in the asteroid belt between Mars and Jupiter
because they did not accrete into a planet
Jupiter's gravity through the influence of orbital resonances, stirred up asteroid orbits and
prevented their accretion into a planet
Meteorites are pieces of asteroids, or sometimes planets or the Moon, that reaches Earth's surface
intact
Meteor is a bright visible tail of hot debris from the rock as it burns up due to friction with Earth's
atmosphere; a "Shooting star" but has nothing to do with stars
**UCLA meteorite collection 3697 Earth and Space Sciences EC OPPORTUNITY**
Two types of Meteorites:
1. Primitive: unchanged in coposition since they first formed 4.6 billion years ago
a. Age of primitive meteorites tell us when solar system formation began
b. Simple, all ingredients mixed together
2. Processed: younger, have experienced processes like volcanism
a. Shattered fragments of larger objects
Comets are icy counterparts to asteroids, which formed beyond the Frost Line
• Nucleus is like a "dirty snowball"
• Most comets do not have tails
• Most remain perpetually frozen in outer solar system; only a few enter the inner where they can
grow tails
• The tail is caused by solar heating which results in sublimation of the ices to gases
o The tail always points away from the sun; the plasma tail (ionized gas) points directly away,
but dust tail is pushed by sunlight into a different angle
