Transcript ASR - GEOCITIES.ws

ASTEROID
• An asteroid is any of numerous small planetary bodies that revolve
around the sun. Asteroids are also called minor planets or planetoids.
Most of them are located in the asteroid belt between the orbits of
Mars and Jupiter. The belt contains more than 1,150 asteroids with
diameters greater than 30 kilometers. The average temperature of the
surface of a typical asteroid is -73 degrees C.
• One theory is that a planet located between the orbits of Mars and
Jupiter broke up, forming the asteroids. According to the other theory,
there was enough material for a planet between the two orbits, but no
planet formed. Instead, the material simply became a belt of rocky
objects.
• One group of asteroids dominates the outer part of the belt. These
asteroids are rich in carbon. Asteroids in the second group, which are
located in the inner part of the belt, are rich in minerals. These
asteroids formed from melted materials.
METEORITE
• A meteorite is a chunk of metallic or stony material from space
that strikes the surface of Earth. There are three kinds of
meteorites, stony, iron, and stony-iron. Stony meteorites consist of
minerals rich in silicon and oxygen, with smaller amounts of iron,
magnesium, and other elements. One group of stony meteorites,
called chondrites, are pieces of the same material from which the
planets formed.
• Another group of stony meteorites, the achondrites, that was large
enough to have melted and separated into an iron-rich core and a
stony crust. Achondrites come from the outer crust; stony-iron
meteorites, from the inner crust; and iron meteorites, from the
metallic core. Iron meteorites consist mostly of iron and nickel.
Stony-iron meteorites have nearly equal amounts of silicon-based
stone and iron-nickel metal.
METEOR
• A meteor is a bright streak of light that appears briefly in
the sky.
• Shooting stars or falling stars.
• A meteor appears when a particle or chunk of metallic or
stony matter called a meteoroid enters Earth's atmosphere
from outer space. Air friction heats the meteoroid so that
it glows and creates a shining trail of gases and melted
meteoroid particles. The gases include vaporized meteoroid
material and atmospheric gases that heat up when the
meteoroid passes through the atmosphere. Most meteors
glow for about a second.
• Most meteoroids disintegrate before reaching the earth.
But some leave a trail that lasts several minutes. Millions of
meteors occur in Earth's atmosphere every day.
FIREBALL
• A fireball is a meteor that burns brightly as it
plunges through Earth's atmosphere. If the
fireball explodes at the end of its path, it is
generally called a bolide. Some pieces may
survive the explosion and fall to the earth. Only
brightness makes a fireball different from an
ordinary meteor. A fireball is as bright as Jupiter
or Venus. In rare cases, it may be as bright as a
full moon. A sound like thunder occasionally
accompanies the passage of a fireball.
METEOR SHOWER
COMET
• A comet is an icy body that normally travels around the sun in a long,
oval orbit.
• A comet consists of a solid nucleus (center), a cloudy atmosphere
called a coma, and one or two tails. The nucleus resembles a dirty
snowball. It is made of ices of various kinds and of rocky dust
particles that are stuck in the ices. When the comet approaches the
sun, some of the surface ices vaporize. The resulting gases and the
particles that were stuck in the ices fly away from the sun, forming the
coma and the tails.
• As a comet gets closer to the sun, increased heat vaporizes ices on the
surface of the nucleus, and the solar wind causes the resulting gases
and dust particles that were stuck in the ice to fly away from the sun in
tails.
COMET
Impact Crater and Basin
• When large bodies such as asteroids and comets strike a planet,
they produce an impact crater or impact basin. Impact craters are
bowl-shaped depressions that measure up to about 25 kilometers
in diameter. They have shallow, flat floors and uplifted centers.
Impact basins are larger, and inside their rims there are one or
more rings on the planet's surface.
• Scientists have found more than 120 impact craters and basins on
Earth. One of the most famous, the Meteor Crater in Arizona, is
about 1,275 meters across and 175 meters deep. It formed nearly
50,000 years ago when an iron meteorite weighing 300,000 metric
tons struck the earth.