Ch. 14 - Astro1010

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Debris in the Solar System
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Rocks are Asteroids. Dirty Snowballs are
Comet Nuclei
Asteroids are quite
small, and most
have eccentric
orbits in the asteroid
belt between
Mars and Jupiter.
Two other families
are Apollo Asteroids
and Trojan Asteroids
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The Titus-Bode Rule
predicted that there was a
Planet at 2.8 AU from the
Sun. It was tentatively named
Aster. When the field of rocks
instead of a Planet was
discovered at that distance
the tiny objects were called
Asteroids. Now all rocks in
space are called Asteroids.
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Belt Asteroids are rocky; about 200,000 have
been identified so far.
Belt Asteroids are classified in types:
C-type: carbonaceous
S-type: silicate
M-type: metallic; iron and nickel
The three largest Belt Asteroids are Ceres (940
km), Pallas (580 km) and Vesta (540 km)
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This is an artist’s concept of Dawn
at Vesta
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Dawn is a robotic NASA spacecraft tasked with the exploration
and study of the asteroid Vesta and
the dwarf planet Ceres, two of the
largest members of the Asteroid
Belt. The spacecraft was
constructed with some European
partners.
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Two small S-type asteroids, Gaspra and Ida,
were visited by the Galileo. Gaspra (left) is in
false color; it is really gray. Note that Ida
(right) has a small moon, Dactyl.
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A 2nd family of asteroids have orbits so
eccentric that they cross Earth’s orbital plane.
They are called Apollo Asteroids, or Near Earth
Asteroids, and raise the concern of a possible
collision. These are survivors left over from
creation and were not picked up during the
Early Intense Bombardment.Over 2600 such
asteroids have been discovered so far, of which
about 600 have been designated as potentially
hazardous, due to their size, over one mile.
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The NEAR –Shoemaker
spacecraft visited the Ctype asteroid Mathilde, on
its way to its main target,
Eros. Mathilde, like many
other asteroids, has a very
low density, and is
probably not solid, but is
rather like a compact
gravel pile.
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Eros does seem to be solid. It
is covered with craters, as
expected, but it also has free
rocks sitting on it, not
expected.
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The NEAR program
presented an
interesting challenge.
Not only did we need
to go to a new orbit
but we had to go to a
new orbital plane. The
maneuver was
successful and we also
landed on the Asteroid.
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The Trojan
Asteroid Family
is located at the
LaGrangian
points for
Jupiter at L4
and L5
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Comet Nuclei are described as “Dirty
Snowballs”. They reside in the Oort
Cloud which is a spherical cloud
surrounding the Sun. It came from
the Tsunami caused when the Sun
went nuclear. The nuclei are
Irregular shaped objects of ices
laced with dust and rock
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The spherical Oort Cloud of
Comet Nuclei is very large but
not densely populated. The
trajectories go in every direction.
The Kuiper Belt Objects are
more in the plane of the planets
and are closer to the orbit of
Neptune. They are roughly the
same composition as the Comet
Nuclei but many are much larger.
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The Kuiper Belt begins around 40 AU from the
Sun but continues out until it finally blends in with
the Oort Cloud. The KBO orbits are irregular but
move roughly in the
prograde direction.
Some of these
Objects are quite
large, larger even
than Pluto.
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Comets have a very small
Nucleus, a Coma of gas and
dust that is the most visible
part that can be very large,
a Hydrogen Envelope, a
dust tail, and an gas
(ionized) tail.
The Nucleus and the
Hydrogen Envelope are
not normally seen.
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Comets have very eccentric
orbits.
The comet’s tail always points
away from the sun, due to the
sunshine and the solar wind. The
ion tail is straighter than the dust
tail.
Long-period comets; over 2000
years
Short-period comets; less
common, and have periods of
less than 200 years.
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The theory of
Jupiter adjusting
the orbit of an
incoming comet
would be much
less viable if we
had not seen
Jupiter capture an
incoming comet.
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Halley’s comet is one of the most famous; it has a
period of 76 years and has been observed since
antiquity. Its most recent visit, in 1986, was not
spectacular.
Left: The comet in 1910, as seen with the naked eye.
Right: the comet in 1986, seen through a telescope.
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Halley’s comet has a short period, just 76 years. Its
orbit is not in the plane of the solar system so as it
revolves around the Sun it passes through the plane
of the Earth’s orbit at a spot closer to the Sun than
the Earth. Some passes it is closer to the Earth than
on other passes.
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This close up image was made by a Japanese
spacecraft in 1986. It shows how the gas
Coma is developed from the Sun side of the
Nucleus as it rotates on its axis.
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Occasionally the Earth passes
through a debris cloud left behind in
the path of Comets. The interaction
of the Atmosphere with these tiny
particles looks like a
Shower of Meteors.
Meteor Showers repeat every year
as the Earth passes through that
part of the sky. [The + shown simply
marks the apparent location of the
radiant and is not seen in the sky]
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Here are some of the best known Meteor Showers
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Meteorites are defined as any
particle from space that survives
to reach the surface.
Most matter from space falls in
slowly and does not make a crater.
These come mostly from the
asteroid belt.
Meteorites are mostly very old –
4.4 to 4.6 billion years – and carry
valuable information about the
early stages of the solar system.
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Rarely does a
meteorite strike near
humans. This one hit a
car.
This one arrived in
New England before
the Whites did.
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Most meteorites are rocky
and often have a polished
look from passing through
the atmosphere They are
distinguishable from Earth
rock by their internal
structure.
A few are made of iron and
can be identified by their
grain structure, Iron like this
can not be duplicated on
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Barringer Crater
Some large objects impact the earth when their
orbits intersect the Earth’s orbit. These are
often larger, from the Apollo (Near Earth)
asteroids, and their impact velocity can be very
large and their impact craters also large.
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The event called Cretaceous-Tertiary
Extinction likely resulted from a giant
meteorite impact near Mexico 65 million
years ago. It caused a 10 year long “Nuclear
Winter” that probably killed the dinosaurs
along with 90% of the living things on Earth
and from which only 25% of the species
recovered. The event was likely due to an
impact of a Near Earth Asteroid
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End Chapter 14
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