Transcript 08_moons, rings, and plutoids

Chapter 8
Moons, Rings, and Plutoids
https://www.youtube.com/watch
?v=PTE08qZz7MM nice Cassini
images
You should be
asking about
Dwarf Planets
as well.
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The “systems” of our solar
system
•
•
•
•
•
Sun
Terrestrial planets
Jovian planets
The Jovian moons
The asteroid and Kuyper belts
– Kuyper belt objects = Plutoids
• A whole bunch more
– Gas, dust, ions, magnetic fields, Oort Cloud
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Small solar systems with
much happening
• Jupiter and Saturn are so big
• With so many moons
• And with a few big (Mercury sized)
moons
• Some with liquid water, more than Earth
• Some with volcanic activity, more than
Earth
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Units of Chapter 8
The Galilean Moons of Jupiter
The Large Moons of Saturn and Neptune
The Medium-Sized Jovian Moons
Planetary Rings
Beyond Neptune
Plutoids and the Kuiper Belt
Summary of Chapter 8
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What are the various white dots?
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Learning goals for chapter 8
1. Understand the general properties of Galilean
moons, the only other moons we can see with
binocs.
2. Discuss composition and origin of the Titan’s
atmosphere.
3. Explain the evidence for Triton to be captured by
Neptune
4. Understand the new Cassini data on Enceladus
5. Describe structure and origin of Saturn’s rings
6. Explain the Kuyper belt relative to the origin of the
solar system
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Projects groups of 3
1. Diagram with color the general properties of the 4
Galilean moons;
2. Diagram the composition and origin of the Titan’s
atmosphere;
3. Diagram the Cassini data on Enceladus;
4. Diagram the structure and origin of Saturn’s rings;
5. Diagram how the Kuyper belt formed and why it is
stable;
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The list is too big to know them all
•
http://www.windows2universe.org/our_solar_system/moons_table.html
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8.1 The Galilean Moons of Jupiter
All four Jovian planets have extensive moon
systems, and more are continually being
discovered. Why?
The Galilean moons of Jupiter are those observed
by Galileo G in 16th c: Io, Europa, Ganymede, and
Callisto.
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8.1 The Galilean Moons of Jupiter
This image shows Jupiter with two of its Galilean
moons.
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8.1 The Galilean Moons of Jupiter
The Galilean
moons and their
orbits
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8.1 The Galilean Moons of Jupiter
Their interiors
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8.1 The Galilean Moons of Jupiter
Io is the densest of Jupiter’s moons, and the
most geologically active object in the solar
system.
• It has many active volcanoes, some quite
large.
• Io can change surface features in a few
weeks.
• Io has no craters; they fill in too fast – Io has
the youngest surface of any solar system
object.
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Why is Io so geologically
active?
•
•
•
•
It’s close to a huge planet.
Gravity is huge.
Tidal forces are huge, 100m lift!
So why doesn’t it get tidally locked?
– Europa, nearby, tugs it every pass, few
days
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8.1 The Galilean Moons of Jupiter
Io is very close to Jupiter, and
also experiences gravitational
forces from Europa. The tidal
forces are huge, and provide
the energy for the volcanoes.
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8.1 The Galilean Moons of Jupiter
Europa has no craters;
surface is water ice, possibly
with liquid water below.
Tidal forces stress and crack
ice; water flows, keeping
surface relatively flat.
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8.1 The Galilean Moons of Jupiter
Ganymede is the largest
moon in the solar
system – larger than
Pluto and Mercury.
It has a history similar
to Earth’s Moon, but
with water ice instead
of lunar rock.
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8.1 The Galilean Moons of Jupiter
Callisto is similar to Ganymede; no evidence
of plate activity.
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Jan 26: 8.2 The Large Moons of
Saturn and Neptune
Titan has been known for many years to have an
atmosphere thicker and denser than Earth’s;
mostly nitrogen and argon.
Makes surface
impossible to see; the
picture at right was
taken from only 4000 km
away.
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Titan’s interior
• Look at figure 8.13.
• What is unusual about Titan’s interior?
• How can silicates (rock) sink to the core
when usually iron does?
• Where did Titan’s iron core go?
• How was Titan formed?
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8.2 The Large Moons of Saturn
and Neptune
Infrared image of Titan,
showing detail, and
possible icy volcano
Few craters, consistent
with active surface
Complex
chemical
interactions in
atmosphere
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8.2 The Large Moons of Saturn
and Neptune
The Huygens
lander took
these images
of the surface
of Titan.
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8.2 The Large Moons of Saturn
and Neptune
Trace chemicals in
Titan’s atmosphere
make it chemically
complex.
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8.3 The Medium-Sized Jovian Moons
Densities of these moons suggest that they are
rock and water ice.
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30 jan: 8.3 The Medium-Sized Jovian Moons
Moons of Saturn, in natural color
Note the similarities,
as well as
the large
crater on
Mimas.
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Multiple plume jets erupting from the four tiger-stripe fractures near
Enceladus’s south pole are visible in this Cassini image. The jets appear
not only on the edge of Enceladus’s disk but also where they rise up into
sunlight from sources on the night side of the moon
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Enceladus makes its own ring
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My favorite Jovian moon: Enceladus
• http://dx.doi.org/10.1063/PT.3.1331
• Finding liquid water is a fundamental quest of planetary
science.
• Because H2O is the simplest stable compound of the first and
third most cosmically abundant elements, it is one of the
commonest molecules in the universe.
• Our solar system is no exception: During its formation,
temperatures in the protosolar nebula were low enough that
water ice could condense in most places beyond what is now
the asteroid belt.
• The solid worlds of the outer solar system thus tend to be rich
in water ice, and the moons of the giant planets typically
comprise roughly equal parts rock and ice.
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• From our parochial point of view as biological entities,
however, H2O is most interesting in its liquid form, which is
essential for the maintenance of life on Earth.
• If life exists elsewhere, the best places to look for it are
those with liquid water. Compared with ice and water vapor,
liquid water is stable over a narrow range of temperature
and pressure. So it is relatively rare in the solar system.
• But Jupiter’s large moon Europa has been a center of
attention for planetary scientists since the late 1990s, when
the Galileo orbiter discovered evidence for a global water
ocean beneath Europa’s icy surface.
• More recently, the Cassini orbiter has revealed a place that
not only probably hosts liquid water but also is obligingly
launching fresh samples of that water into space for analysis
by spacecraft instruments. That place is Enceladus—a
moon of Saturn 500 km in diameter.
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Enceladus facts
• Dead center E ring of saturn
• E ring is mostly water ice and is constantly
replenished
• Heat at tiger stripes
• Geysers of water ice from stripes
• Constant snowfall, young craters, high albedo
• Cassini is the major probe to find chemical
information
• Theory is tidal heating centered at south pole
• Ongoing geological activity according to Daniel’s
book
• Possibility of life in liquid water with salts
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The current model for how Enceladus makes
water guysers What body creates
the tidal tug ?
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8.3 The Medium-Sized Jovian Moons
Moons of
Uranus and
Neptune
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8.3 The Medium-Sized Jovian Moons
Miranda shows evidence
of a violent past, although
the origin of the surface
features is unknown.
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8.4 Planetary Rings
The ring system
of Saturn is
large and
complex, and
easily seen from
Earth. The other
Jovian planets
have ring
systems as well.
https://www.youtube.com/watch?v=AyFMP
dHU1n0 start
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at 6:00min to 10:15
8.4 Planetary Rings
The rings are not solid; they are composed of
small rocky and icy particles.
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8.4 Planetary Rings
Our view of Saturn’s
rings changes as the
planets move in their
orbits.
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8.4 Planetary Rings
Why are there rings?
The Roche limit
is where the
tidal forces of
the planet are
too strong for a
moon (held
together by
gravity) to
survive; this is
where rings are
formed.
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8.4 Roche Limit
All observed ring systems are within this limit.
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8.4 Planetary Rings
Voyager probes showed Saturn’s rings to be
much more complex than originally thought.
Earth is shown
on the same
scale as the
rings.
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8.4 Planetary Rings
“Shepherd” moons
define the edges of
some of the rings.
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8.4 Planetary Rings
Jupiter has been found to have a small, thin ring.
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8.4 Planetary Rings
The rings of
Uranus are more
complex.
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8.4 Planetary Rings
Two shepherd
moons keep the
epsilon ring
from diffusing.
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8.4 Planetary Rings
Neptune has five rings, three narrow and two
wide.
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This Exoplanet’s Ring System
Puts Saturn to Shame
• Chapter_08, moons, rings, plutoids\This Exoplanet.docx
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Why don’t terrestrial planets
have rings?
1. Roche Limit is very low
2. Not enough ices around to form the
rings
3. Rings are short lived and jovian
planets are grabbing all the stuff that
wanders into the solar system.
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Quiz: ring formation
• Explain how rings form around a planet
– Include a description of tidal forces
– Include a description of the Roche Limit
– Include a description of shepherd moons
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The formation process for
moons and rings
• Draw a picture
• Notice how these are the same 3 mechanisms, either
inside or outside the Roche Limit
• How are moons made?
– Accretion, like the planets
– Capture of a wandering body
– Impact with the planet and capture
• How are rings made?
– Capture of dust and debris from early SS
– Debris from moon-asteroid or planet-asteroid or moon-planet
impact
– Debris from moon that wandered into the roche limit.
• The origin of Saturn’s rings. 1:49
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8.5 Beyond Neptune
Pluto was discovered
in 1930. It was
thought to be needed
to explain
irregularities in the
orbits of Uranus and
Neptune, but it turned
out that there were no
such irregularities.
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8.5 Beyond Neptune
Pluto’s moon, Charon, was discovered in 1978.
It is orbitally locked to Pluto, and about a sixth
as large.
Pluto also has two smaller
moons, Nix and Hydra,
discovered in 2005.
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What a difference a space
probe makes in our learning!
http://apod.nasa.gov/apod/ap15
0918.html
https://twitter.com/NASANewHor
izons?ref_src=twsrc%5Egoogle
%7Ctwcamp%5Eserp%7Ctwgr
%5Eauthor
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8.5 Beyond Neptune
Charon’s orbit is at a large angle to the plane of
Pluto’s orbit.
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8.6 Plutoids and the Kuiper Belt
The first Kuiper belt
objects were observed
in the 1990s, and more
than 700 are now
known. Some of them
are comparable in size
to Pluto.
These images show
Eris and its moon
Dysnomia.
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8.6 Plutoids and the Kuiper Belt
This figure shows several of the largest known
trans-Neptunian objects, now collectively called
plutoids.
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Where do dwarf planets fit in?
• Is a dwarf planet the same as a plutoid?
• P237
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The ninth planet?
•
http://www.nytimes.com/2016/01/21/science/space/ninth-planet-solar-system-beyondpluto.html?rref=collection%2Fsectioncollection%2Fscience&action=click&contentCollection=science&region
=rank&module=package&version=highlights&contentPlacement=1&pgtype=sectionfront&_r=1
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Summary of Chapter 8
• Outer solar system has 6 large moons, 12
medium ones, and many smaller ones.
• Titan has a thick atmosphere and may have
flowing rivers of methane.
• Triton has a fractured surface and a retrograde
orbit.
• Medium-sized moons of Saturn and Uranus are
mostly rock and water ice.
• Saturn’s rings are complex, and some are
defined by shepherd moons.
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Summary of Chapter 8, cont.
• The Roche limit is the closest a moon can
survive near a planet; inside this limit rings
form instead.
• Jupiter, Uranus, and Neptune all have faint
ring systems.
• Pluto has three moons, Charon, Nix, and
Hydra.
• Dwarf planets beyond Neptune (including
Pluto) are now known as plutoids.
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Supporting views
• Look at videos on support files for
review
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Final check/quiz
• Solar walk movie on size comparison,
without subtitles
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More video
• Rings of the Jovian Planets 43 min,
360p, History Channel
overexaggeration
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What if the planets were as
close as our moon….
• https://www.youtube.com/watch?v=usY
C_Z36rHw
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Recent Titan pictures
• In Dec 2012,
http://www.esa.int/Our_Activities/Space_Science/Cassini_spots_mini_Nile_River_on_Saturn_moon
shows rivers and seas of methane and
ethane
• In 2005, Huygens gave surface pictures
before it froze.
http://www.esa.int/Our_Activities/Space_Science/Cassini-
Huygens/New_images_from_Titan
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quiz
• On a new page, sketch and describe
the three ways that a moon can be
made.
• On the flip side, sketch and describe the
three ways that rings can be formed
around a planet. Define the Roche limit,
and describe why it exists.
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