23 4 Minor Members of the Solar System

Minor Members of the Solar
Chapter 23, Section 4
Asteroid – small rocky bodies that have been
likened to “flying mountains”
Most asteroids lie between the orbits of Mars
and Jupiter. They have orbital periods of 3 to 6
Some have very eccentric orbits, a few regularly
pass Earth and our moon
Many asteroids have irregular shapes, and
some planetary geologists believe the asteroids
are fragments of a broken planet (pulled apart
by the immense gravity of Jupiter)
Asteroid Orbits
Comets – pieces of rocky and metallic materials
held together by frozen gases
Most comets travel in elongated orbits, taking
them past Pluto and take hundreds of thousands
of years to go around the sun.
Coma – glowing head of a comet, caused by the
solar energy vaporizing frozen gases
A small glowing nucleus with a diameter of only
a few kilometers can sometimes be detected
within a coma. As comets approach the sun,
some develop a tail that extends for millions of
The tail of the comet always points away from
the sun, this is accounted for by the solar wind
and radiation pressure
Comet’s Tail Orientation
Beyond the Planets
Kuiper Belt – where most short-period
comets are thought to originate from, it is a
belt of material orbiting outside the orbit of
Oort Cloud – Unlike the Kuiper Belt
comets, these comets have longer orbital
periods and aren’t confined to the plane of
the solar system. The Oort Cloud appears
as a spherical shell of comets and other
materials surrounding our solar system.
Beyond the Planets
Meteoroid – a small solid particle that travels through
Most meteoroids originate from any one of the
following sources: (1) interplanetary debris that was
not gravitationally swept up during the formation of the
solar system, (2) material from the asteroid belt, or (3)
the solid remains of comets that once traveled near
Earth’s orbit
Meteor – meteoroids that enter Earth’s atmosphere
and burn up, a “shooting star”
The light that we see is caused by the friction between
the meteor and the air
Meteorite – a meteoroid that reaches Earth’s surface
A few meteorites have blasted out craters on Earth’s
World Map of Major Impact
The Age of the Solar System
How did scientists determine the age of the
Solar System?
They use radiometric dating to determine that
the oldest meteorites found on Earth formed
more than 4.54 billion years ago
Scientists believe that the composition of these
meteorites is similar to the composition of other
materials in the inner solar system during its
The oldest moon rocks are believed to be ~4.5
billion years old
The oldest known Earth rocks are found in
Canada ~4 billion years old
Age of the Solar System
Read Chapter 23, Section 4 (pg. 660-664)
Do Section 23.4 Assessment #1-6 (pg. 664)