Transcript Chapter 2

Chapter 2
The Solar System
Part 2
Planets
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Planets are bodies of considerable mass
that orbit a star like the sun.
The solar system is officially comprised of
nine planets.
A comparison of the planets reveals the
following:
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they seem to divide into rocky, dense, inner
planets (called the terrestrial planets) and
large outer gas giants.
The Planets
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The orbits of the planets are ellipses though all
except Mercury and Pluto are very nearly circular.
The further away from the sun, the slower a planet
travels around the sun.
Venus rotates very slowly and in the opposite
direction of most of the other planets. Uranus and
Pluto seem to have been knocked over their axis.
All the planets except for Pluto rotate nearly on the
same plane (called the ecliptic) around the sun.
Inner Terrestrial Planets
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The inner terrestrial planets (Mercury, Venus,
Earth, and Mars) are relatively smaller and
denser.
They contain a much higher percentage of metal
elements. Terrestrial planets all have roughly the
same structure: a central metallic core made up
of mostly iron with a surrounding silicate mantle.
Terrestrial planets have canyons, craters,
mountains, and volcanoes.
Terrestrial planets have few moons if any.
Outer Gas Giants (Jovian
Planets)
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Jovian planets (Jupiter, Saturn, Uranus,
Neptune) are composed primarily of hydrogen
and helium just like the Sun but lack the size to
be able to start a fusion reaction.
All Jovian planets generally have low densities,
rapid rotation, and deep atmospheres.
All Jovian planets have rings (ie. Jupiter) and
numerous moons.
Pluto … is it a Planet?
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It has a moon, Charon, which is half its size.
Very similar to Neptune’s largest moon Triton.
Pluto's orbit is highly eccentric. At times it is closer to the
Sun than Neptune (as it was from January 1979 thru
February 11 1999).
Pluto’s orbit is quite inclined compared to the other
planets.
The size and composition of Pluto resemble the sizes
and composition of Kuiper Belt objects.
Officially Pluto is a planet and for historical reasons that
may not change.
Moons (Natural Satellites)
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A moon is a natural object that orbits
another object.
Up to date 140 planetary moons (orbiting
planets) have been discovered:
Earth
1
Mars
2
Jupiter Saturn
63
33
Uranus Neptune Pluto
27
13
1
Planetary Moons
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Mars’ moons Phobos and Deimos are
irregular shaped and believed to be
captured asteroids. Phobos is the larger
inner moon that’s in a doomed course. In
the next 50 million years it is expected to
either collide with Mars or break up and
form a planetary ring.
Galilean Moons
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They are by far the 4 largest moons of Jupiter. They
were discovered by Galileo in 1610 when he pointed a
telescope at Jupiter thus providing solid evidence that all
objects did not orbit around the Earth.
Io is the innermost of the Galilean moon best known for
being the most volcanically active body in the Solar
System. The high activity is believed to be caused by
Jupiter and the other moons gravitational effect on Io.
They squeeze and stretch the moon heating up its
interior to very high temperatures. Eruptions resulting in
plumes hundreds of kilometers high are then inevitable
to relieve the pressure. Because of Io’s low gravitation, a
lot of this material is ejected into space.
Galilean Moons
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Europa, the next moon, has an outer layer of
water 60 miles thick. The upper 12 miles are
believed to be in the form of ice. This ocean is
salty and holds a tantalizing possibility of life.
Europa and Io are somewhat similar in bulk
composition to the terrestrial planets: primarily
composed of silicate rock below the outer layer
of water.
Galilean Moons
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Ganymede is the largest moon in the Solar
System. It is larger than Mercury and Pluto.
Callisto's surface is covered entirely with craters.
It has the oldest, most cratered surface of any
body yet observed in the solar system; having
undergone little change other than the
occasional impact for 4 billion years.
Titan
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Saturn’s largest moon is nearly the size of
Ganymede.
Titan has a considerable atmosphere composed
of mostly nitrogen but with traces of organic
compounds.
Recent Huygens data shows that there is
geological evidence for precipitation, erosion,
and other fluvial activity. There processes are
much the same as those shaping Earth.
Titan
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These events are carried out in Titan a little
differently. Instead of liquid water, Titan has
liquid methane. Instead of silicate rocks, Titan
has frozen water ice. Instead of dirt, Titan has
hydrocarbon particles settling out of the
atmosphere, and instead of lava, Titanian
volcanoes spew very cold ice.
Titan's organic chemicals are thought by many
to be the constituents that marked early Earth
and that combined into complex forms to launch
the long journey toward life itself.
Triton
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It is the largest of Neptune’s moons.
It is volcanically active like Io and Titan.
Strangely it orbits the moon in the
opposite direction of any other large
moon.
Main Asteroid Belt
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Located between Mars and Jupiter
It contains most of the asteroids (rocky and
metallic objects that orbit the Sun but are too
small to be considered planets).
The Belt is continuously disrupted by Jupiter
causing asteroids within to change orbits. Many
are believed to have been thrown out of the belt.
Some have wondered inward passing near
Earth.
The Kuiper Belt
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The Kuiper Belt is a disk-shaped region past
the orbit of Neptune extending roughly from 30
to 50 AU from the Sun containing many small icy
bodies. (An AU or Astronomical Unit is the mean
distance from the Earth to the Sun).
The Kuiper Belt has a large population (over
70,000) of small bodies. It is likely that the
Kuiper Belt Objects are extremely primitive
debris from the formation of the solar system.
It is considered to be the source of the shortperiod comets.
The Oort Cloud
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The Oort Cloud is a hypothetical spherical cloud
of comets approximately 50,000 AU to 100,000
AU from the Sun.
The Oort cloud is a remnant of the original
nebula that collapsed to form the Sun.
No Oort Cloud objects have been detected, the
existence of this classification is only inferred
from indirect evidence.