Transcript Now known: Solar system has 166 moons, one star, eight planets

The Solar System
© 2011 Pearson Education, Inc.
An Inventory of the Solar System
Now known: Solar system has 166 moons, one
star, eight planets (added Uranus and
Neptune), eight asteroids, and more than 100
Kuiper belt objects more than 300 km in
diameter (smaller asteroids, comets, and
meteoroids)
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An Inventory of the Solar System
More than 400 extrasolar planets have been
found
Understanding planetary formation in our
own solar system helps understand its
formation as well as formation of other
systems
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The Overall Layout of the Solar System
All orbits but
Mercury’s are close
to the same plane
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The Overall Layout of the Solar System
Because the planet’s
orbits are close to
being in a plane, it is
possible for them to
appear in a straight
line as viewed from
Earth. This
photograph was
taken in April 2002.
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Terrestrial and Jovian Planets
In this picture of the eight planets and the Sun,
the differences between the four terrestrial and
four jovian planets are clear.
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Terrestrial and Jovian Planets
Turn to your neighbor an list all the
differences you see between the
Terrestrial and Jovian planets.
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Terrestrial and Jovian Planets
Terrestrial planets:
Mercury, Venus, Earth, Mars
Jovian planets:
Jupiter, Saturn, Uranus, Neptune
Terrestrial planets are small and rocky, close to
the Sun, rotate slowly, have weak magnetic
fields, few moons, and no rings
Jovian planets are large and gaseous, far from
the Sun, rotate quickly, have strong magnetic
fields, many moons, and rings
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Terrestrial
Differences among the terrestrial planets:
• All have atmospheres, but they are very
different; surface conditions vary as well
• Only Earth has oxygen in its atmosphere and
liquid water on its surface
• Earth and Mars spin at about the same rate;
Mercury is much slower, Venus is slow and
retrograde
• Only Earth and Mars have moons
• Only Earth and Mercury have magnetic fields
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Interplanetary Matter
Asteroids and meteoroids have rocky
composition; asteroids are bigger
Asteroid Eros is 34 km long
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Interplanetary Matter
Comets are icy, with some rocky parts
Comet Hale-Bopp
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Interplanetary Matter
Pluto, once classified as one of the major
planets, is the closest large Kuiper belt object
to the Sun
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Turn to your neighbor
Discuss your theory of how the solar system formed.
Why do you think that? What characteristics of the solar
system might your theory address?
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How Did the Solar System Form?
Solar system properties show it has a
high degree of order
1.
2.
3.
4.
5.
6.
7.
8.
Each planet is relatively isolated in space
The orbits of the planets are nearly circular
All planets but Mercury lie in the same plane
Rotational direction around the sun is the same
direction as the sun rotates
Planets are differentiated between terrestrial and Jovian
Asteroids are very old
The Kuiper belt is asteroid-sized icy bodies
The oort cloud comets are icy fragments that do not orbit
on the plane of the ecliptic
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How Did the Solar System Form?
Nebular contraction:
Cloud of gas and dust contracts due to gravity;
conservation of angular momentum means it spins
faster and faster as it contracts
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How Did the Solar System Form?
Nebular contraction
is followed by
condensation around
dust grains, known to
exist in interstellar
clouds such as the
one shown here.
Accretion then leads
to larger and larger
clumps; finally
gravitational
attraction takes over
and planets form.
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Aug. 24, 2006
Demotion of Pluto
“Plutoed” -meaning to demote or devalue
someone
Dr. Mike Brown and Neil Degrase Tyson
to “blame”
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Eris is at fault
• Found large asteroids by 1851
(including Ceres) between Mars and
Jupiter
• Pluto not in the asteroid belt but in the
Kuiper belt
• Then we discovered Eris, which is in the
Kuiper belt
• However Eris is classified Pluto would
be classified (both have large
inclinations)
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2006 IAU meeting
Planet Criteria
1. Must orbit the sun
2. Enough gravity to shape itself into a
sphere
3. Big enough to clear its neighborhood
around its orbit
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Dwarf planet criteria
1-2 are the same
3. Not cleared its neighborhood around
its orbit
4. Not a moon
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Plutoid criteria
Same criteria as dwarf planet
except
5. Must orbit beyond Neptune
Known Plutoids:
Pluto, Haumea, Makemake,Eris
“Pluto Heard ME”
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