Transcript OAT Asteroids:Comets

Asteriods
• “Minor planets”, ranging in size from several hundred km to
boulders (most less than 10 km)
• Orbits are fairly circular, most between Mars and Jupiter; some
orbits in resonance with Jupiter; some Earth-crossing
Production of Asteroids (and meteors)
(Such bodies are icy in the
outer solar system.)
Visiting the Asteroids
Gaspra
Ida and Dactyl
Eros and the NEAR mission
Eros appears to be a solid object,
apparently formed near the
beginning of the solar system. It is
thus a “planetesimal”.
Craters large and small
Impacts clearly play a role in Eros’ history.
Since there is little mass and the rock is
tumbling, the apparent gravity acts very
strangely.
Landing on an asteroid
Icy Planetesimals :
Comets
Of similar size and shape,
the comets turn out to be
icy versions of the
asteroids. Despite their
bright appearance, they
are actually much darker,
covered with
carbonaceous “tars”. As
they approach the Sun,
the ices vaporize, blowing
off gas and dust and
giving a kick to the
comet’s orbit.
Parts of a Comet
The actual nucleus is tiny compared to
the tails (which contain almost
nothing). They always point away
from the Sun. The comet does not
rush through the sky although it looks
like it might be doing that.
Bright Comets
Halley’s Comet 1986
Hyukatake
1998
Hale-Bopp
1997
Comets can be beautiful
Ikeya-Seki 1965
Meteor Showers :
Remnant Comets
A comet leaves a trail of debris.
Convergent point
Some parts can be
thicker than others.
Some passages make
“meteor storms”.
The Leonid Meteor Shower
November 18, 2001
Great view from the Bay Area
Several bright meteors per minute
Meteors and Meteorites
A meteor is commonly called
a shooting star. Most burn up
completely and never hit the earth’s
Surface.
A meteor that
makes it all the way
to the ground is called a
Meteorite.
Types of Meteors
• “Carbonaceous”: lighter elements (C, Si, Mg), can
be covered with dark organic compounds or rocky
material
– Source: unformed planet or planetesimal
• “Metallic”: dominantly nickel/iron
– Source: differentiated body broken up later
• “Basaltic”: like lava; must have been melted rock
– Source: differentiated body or large collision
Many meteors are chunks from asteroids (some sources
are known), others are pieces from comets
Inside Meteorites
Many meteors contain spherical “chondrules”.
The formation of these has been mysterious,
but a recent Berkeley theory shows how they
might have been melted by the young Sun.
The Sources of Meteors
and Comets
Jupiter and the other giants are
responsible for the asteroids
and the Oort cloud comets.
The Kuiper Belt is simply the
outer remnant of the solar
nebula.
Sometimes they hit us…
Some meteors are large enough to survive passage through the
atmosphere and strike the ground with enough force to be vaporized
and release large amounts of energy. They hit at 50 km/s, so a rock
the size of a building can make a hole a mile across.
The Shoemaker-Levy Impact
A comet which broke up inside
Jupiter’s Roche limit also found
itself on an orbit which intersected
the surface…
Like a machine gun burst, the
fragments struck at the same latitude,
one after the other...
Deep Impact…
It’s a good thing it wasn’t us…
The Dinosaurs weren’t so lucky…
It is widely accepted that the discovery of iridium
in a clay layer at the end of the Cretaceous marks
a mass extinction caused by the impact of a large
comet (the “K-T” impact).
Boom!!!!
How likely is it?
The end of all surface life on the Earth
Too large an impactor (> 50 mi) would replace our entire atmosphere
with rock vapor for a few centuries. Only life in the deepest oceans
would survive. Maybe this happened near the beginning…