Minor members of the
Solar System
Asteroids, Meteors, Comets
Formation
• We have already seen how the solar
system formed
• Some planetesimals were left over when
the solar system formed
• These became the asteroids, meteoroids
and comets
• Many of the asteroids are in the asteroid
belt.
• What is an asteroid belt like?
Link
The Asteroid Belt
• The asteroid belt occurs in orbit between Mars and Jupiter
• The combined left over mass was not quite large enough to
form another planet, especially due to the large disruptive
force of gravity from nearby Jupiter, with its great mass.
• Had the left over mass been larger, we might have had
another planet there
Ida and Dactyl
Asteroids
• So, asteroids are
remnants from the
formation of the solar
system
• They are therefore 4.5
billion years old and
when we find pieces of
them they give us
information about the
origins of the solar
system
• That is why we send
probes to comets and
asteroids
Eros
Asteroids
• Asteroids occur in 3 types
– Stony
– Iron
– Stony-iron
• These actually are parts of asteroids that
differentiated as shown in the link below
Meteoroids, meteors,
meteorites
Leonid Meteor
• These are actually all the same thing
• They are named differently depending on
their location
• Small asteroid pieces are meteoroids
• When they fall towards earth, burning up,
they are called meteors. We get some of
these all the time
• If they actually hit the surface, then they
are meteorites
Comets
• Comets are icy remnants of the solar
system, with a small hard nucleus core
and the surrounding gaseous coma
• They reside in two regions, the Oort
cloud and the Kuiper Belt
Hale-Bopp
• They orbit the sun in long period elliptical
orbits
• They begin to heat and vaporize as they
approach the sun, forming a tail. The tail
always points away from the sun, being
pushed there by solar wind and radiation
pressure
Meteor showers
• Many comets are periodic, visiting the sun regularly
• When comets go around the sun, they leave many small
pieces in their orbital paths
• When the earth intersects this comet debris, we get
meteor showers – many small meteors giving us a great
light show as they burn up – rarely touching the ground
• We can predict when we get these since we cross these
orbital paths periodically, like the Perseids every August
• The complete breakup of comet Shoemaker-Levy 9 in
1994 produced this spectacular telescopic image below
After colliding with Jupiter
Collisions
• This is worrisome since the earth periodically also
gets hit by larger solar system remnants – asteroids
or comets
• The mass extinction at the end of the Mesozoic was
probably due to an impact in the Yucatan
• There is a small government program that searches
for asteroids on collision paths with earth.
• If a large one hits, it would be very bad for us
Review
•
•
•
•
•
•
How old are asteroids
Where are most asteroids located
Where do you find a meteorite?
Where are comets located?
Which way does the tail of a comet point?
Why do metoer showers occur?
How likely is a large collision?
• The map below shows major impact sites
around the world. There are many of them.
Craters
• Most craters have been
weathered and are not
visible anymore
• But they give evidence that
we have been visited many
times by these fragments
from space
• And it has happened before
• What if a collision sent new
asteroids our way. Could
this happen?
The End?