Transcript Comets, Asteroids, and Meteorites

(5) Earth in space and time. The student
understands the solar nebular accretionary
disk model. The student is expected to:
(C) contrast the characteristics of comets,
asteroids, and meteoroids and their positions
in the solar system, including the orbital regions
of the terrestrial planets, the asteroid belt,
gas giants, Kuiper Belt, and Oort Cloud;
In addition to the Sun and planets, our Solar
System contains many small bodies known as
asteroids, comets, and meteoroids.
Although these bodies often have distinguishing
characteristics, the classification of them can
sometimes cause controversy. For example, some
moons may actually be asteroids that were
trapped by the planet's gravity.
In order to classify celestial
bodies,
all theirnatural
Himalia;
one of Jupiter’s
to be a moon?
characteristics must besatellites…too
taken intosmall
consideration.
These characteristics include their composition,
location, orbit, and origin.
This is a picture of Asteroid 951
Gaspra. Gaspra has an irregular
shape with dimensions of about 19
x 12 x 11 kilometers. (Courtesy
USGS/NASA/JPL)
Actual
Distance
from Sun
(Astronomic
al Units)
.387
.723
1.00
1.52
In the eighteenth century, a German
Bode
Bode
Planet
astronomer, Johann Bode, found a
Equation
Number
mathematical sequence
representing the distances of the
(0+4)/10
.4
planets from the Sun. The sequence, Mercury
Venus
(3+4)/10
.7
known as Bode's Law, works by
Earth
(6+4)/10
1.0
starting with 0, then 3, and doubling
the number each time until you
Mars
(12+4)/10
1.6
reach 192 (for Uranus) . Then, by
None
(24+4)/10
2.8
1.46 - 5.71
adding four to each number and
(Asteroids)
dividing the result by 10, the
Jupiter
(48+4)/10
5.2
5.20
numbers give the approximate
Saturn
(96+4)/10
10.0
9.54
distance of each planet from the Sun
Uranus
(192+4)/10
19.6
19.18
in astronomical units (AU).
In 1801, Giuseppe Piazzi discovered an object between
Scientists noticed that the law worked
flawlessly from Mercury to Uranus with
Mars and Jupiter and gave it the name Ceres. Although
one exception… between the orbits of
Ceres is the largest known asteroid it is still very small
Mars and Jupiter where there was no
compared to the planets, with a diameter of only 1,003
known planet.
kilometers.
Scientists
notthat
satisfied
discovery of Ceres, so they continued to search
It became were
obvious
therewith
was the
no planet
for
a planet.
They
realized
that countless asteroids orbited where they had once
between
Mars
andsoon
Jupiter.
Astronomers
expected
to findtheories
a planet.
Let’s givethe
them
some perspective…
began to make
explaining
origins
of the many small bodies called asteroids.
Some suggested that asteroids were the
remnants of a planet that had been shattered
by an explosion.
The most commonly accepted theory,
however, states that asteroids are pieces of
Ceres
matter that never coalesced to form a planet.
The fact that the combined mass of all the
asteroids in this area is far less than the mass
of most planets led scientist to believe
asteroids lack the gravity necessary to
coalesce into a planet.
Vesta
Pallas
Hygiea
The
Asteroid
Belt liesclassified
between
the orbits of Mars and Jupiter and
Asteroids
are commonly
into
contains
millions
of asteroids.
Over 6,000 asteroids have been named
types
according
to their
spectra.
and 70,000 have been identified.
• Type C asteroids are extremely
dark carbonaceous objects and
Some
asteroids even cross Earth's orbit. The unusually eccentric orbits
comprise more than 75% of all
of these
asteroids are a result of collisions in the Asteroid Belt that sent
asteroids.
asteroids on a new path.
• Type S asteroids are relatively light
asteroids composed of metallic
nickel-iron and make up 17% of all
asteroids.
• Type M, which are bright asteroids
composed of pure nickel-iron. There
are a few other rare types of
asteroids.
Comets are cosmic snowballs of frozen
gases, rock and dust roughly the size of
a small town.
As you can see, comets come in many
forms…some are even tailless.
Comets
Comets are large bodies rich in ices along with dust grains, gravel and
small rocky bodies embedded in the ice. When the ices evaporate as
they get closer to the Sun, they grow tails and we see them as 'comets'.
They leave behind in their orbits, gravel and rocky debris that Earth
may encounter from time to time as orbits cross. We see these
encounters as 'meteor showers'.
Because they orbit the Sun, we
can see them come back from
time to time. Halley's Comet
appears about every 76 years,
for example. We had a visit
from this comet in 1986, and
we won’t see it again until mid2061
Comets are in long elliptical orbits around
the Sun from beyond Uranus. These objects
are found in the Kuiper Belt between Uranus
and Neptune and the Oort Cloud from way
out beyond Pluto.
Short period comets originate from the
Kuiper Belt, while long-period comets come
from the Oort Cloud.
The name "comet" comes from the Greek
meaning "long-haired" because of their tails.
Comets throughout history have been
thought to bring bad luck but these are just
natural phenomena of the solar system.
Meteorites are small rocky bodies, from micron-sized up to perhaps a
meter across that impact Earth after a brilliant atmospheric display.
• Cometary debris
• Space junk (never got
incorporated into cometary
bodies, planets or asteroids)
A meteor is a small body, usually
the size of a pebble or sand grain,
that enters the atmosphere and
burns up, but some of the larger
ones a foot or more across can
reach the ground and are called
meteorites when their fragments
are recovered.
As the meteor enters the Earth's
atmosphere it becomes very hot due
to friction. They become bright and
seem to streak across the sky.
When the Earth enters a meteoroid
stream left by a comet it produces a
meteor shower. These showers can be
predicted and come every year or so.
They are named after the constellation
that the meteors appear to be coming
from.
Common Meteor Showers
Name
Date Seen
Lyrids
April and June
Perseids
August
Orionids
October
Taurids
November
Leonids
November
The inner-most planets,
composed of mainly rock and
some metal and have high
densities. They have solid
surfaces and rotate slowly.
The four terrestrial planets
in our solar system are
Mercury, Venus, Earth and
Mars.
Venus is the largest of the
terrestrial planets.
Some,
like Jupiter,
maymainly
have a solid
rocky core,
a thick
Thesehowever,
are the giant
planets,
composed
of with
gas and
not
atmosphere
and matter,
helium, whereas
Uranus
and Neptune
of any rockoforhydrogen
other solid
examples
of Jovian
planetare
composed mainly of frozen water, methane, and ammonia.
would be Jupiter, and Saturn, Uranus and Neptune.
Frost Line: Also known as the snow line is an
imaginary line that refers to a specific spot in the
solar nebula where it is cold enough for hydrogen
compounds to freeze. This line separates the
terrestrial planets from the Jovian planets. Inside
the frost line, these gases would not be frozen
and therefore could not form planets.
Accretion is the formation of a planet, small
particles of gas and dust stick together, as they
get larger they start to attract particles and their
growth speeds up. Once they grow large enough
gravity forces it into a sphere shape, and when
the planet grows to a certain size it
gravitationally dominates everything near it.