A1 11 Moons

Moons of the Gas Giants
LACC §11.1,2,3

• Understand the conditions and processes that shaped
the outer planets’ moons

• Know the following moons in some detail: Io, Europa,
Ganymede, Callisto, Titan, Triton

• Understand a moon’s history by its surface

An attempt to answer the “big questions”: what is out
there? Are we alone?

Wednesday, March 24, 2010

http://spaceplace.nasa.gov/en/kids/
sse_ﬂipﬂop2.shtml


Jupiter: Galilean Moons

http://oursun.open.ac.uk/11-14/
SunFamily.htm#Moons


Galilean Moons:
Gravitational Resonances

(CALLISTO 1:9.43)

http://en.wikipedia.org/wiki/File:Galilean_moon_Laplace_resonance_animation.gif


Galilean Moons: Interiors

Data recently obtained
from the Galileo
spacecraft has revealed
the surprising result that
Callisto might have a
salty ocean lying
beneath its icy crust....
Beneath the ocean...data
suggests that the
interior is composed of
compressed rock and
ice with the percentage
of rock increasing as
depth increases.
The interiors of Io, Europa, Callisto, and Ganymede, clockwise from http://
upper left. All except Callisto have metallic (iron/nickel) cores, shown www.solarviews.com
in gray, surrounded by rock in brown. The rock shells in Europa and /cap/jup/calint.htm
Ganymede are surrounded by liquid water (blue) and ice (white).
http://ircamera.as.arizona.edu/NatSci102/lectures/jupmoon.htm


Jupiter’s Io: Active Volcanoes

The reddish materials may be associated with very recent fragmental volcanic deposits (pyroclastics)
erupted in the form of volcanic plumes. Dark materials appear in flows and on caldera floors. Bright white
materials correspond to sulfur dioxide frost, and bright yellow materials appear to be in new flows such as
those surrounding Ra Patera. The red material may be unstable since the color appears to fade over time.
This fading appears to occur most rapidly in the equatorial region and more slowly over the polar regions;
surface temperature may control the rate of transformation. Comparisons of these images to those taken
by the Voyager spacecraft 17 years ago have revealed that many changes have occurred on Io. Since that
time, about a dozen areas at least as large as the state of Connecticut have been resurfaced.
http://solarsystem.nasa.gov/multimedia/gallery.cfm?Page=29

Io: Volcanic Eruption
Explanation: Io's surface is active.
Geyser-like eruptions from volcanoes on
this Jovian moon were seen by both
Voyager spacecraft in 1979 and were also
spotted this year in late June by Galileo's
camera from a distance of about 600,000
miles. The blue plume seen at the moon's
edge (magniﬁed in the inset) arises from
Ra Patera, a large shield volcano, and
extends about 60 miles above the surface.
The blue color is attributed to
condensing and freezing sulfur dioxide
gas. Galileo images have also revealed
that the plume glows in the dark - perhaps
due to ﬂuorescence of excited sulfur and
oxygen ions. Io's surface is cold, its
temperature averages about -230°F, so
why is it so active? The most likely cause
is the gravitational tug of war over Io
between Jupiter and the other Galilean
moons which perturbs Io's orbit. The
orbital changes would result in tidal
force variations heating Io's interior and
and generating the sulfurous volcanic
activity.

http://apod.nasa.gov/apod/ap960815.html

Io: Volcanic Eruption
...taken February 22 [2000] came from
Galileo's closest pass ever of Io.
From Galileo's vantage point, a scant
124 miles (200 kilometers) above the
surface, the probe could discern features
as small as a house.
Galileo also took new pictures of a
strange volcanic region called Tvashtar
Catena, which was seen to be erupting
last fall.
The images show that Tvashtar's mile-
high volcanic plume -- gasses and lava
-- has shifted directions and its
temperature has reached almost
1,900° F (1,038° C). That's hotter than
any eruption on Earth.
Io is the most volcanically active body
in the solar system. Until Galileo,
scientists were aware of only about 20
volcanic regions, fleetingly photographed
during the two Voyager-probe flybys two
decades ago.
With the new data, scientists now have
confirmed the existence of 80 active
volcanoes and suspect Io is riddled with
at least 200 more.
http://www.space.com/scienceastronomy/solarsystem/galileo_new_io_000601.html

Jupiter’s Europa: Oceans?
Speculation is rampant that
oceans exist under these
tortured ice-plains that could
support life. Europa, the smallest
of Jupiter's Galilean moons, was
photographed last month in natural
color by the robot spacecraft
Galileo, now in orbit around Jupiter.
The brown patches are what one
might think: dirt -- tainting an
otherwise white ice-crust.
Europa, nearly the same size as
Earth's Moon, similarly keeps one
face toward its home planet. The
hemisphere of Europa shown
above is the one that always trails.
Why is Europa's surface the
smoothest in the Solar System?
Where are Europa's craters?


Jupiter’s Ganymede: Largest
Explanation: If Ganymede orbited the
Sun, it would be considered a planet.
The reason is that Jupiter's moon
Ganymede is not only the largest
moon in the Solar System, it is
larger than planet Mercury. The
robot spacecraft Galileo currently
orbiting Jupiter has been able to
zoom by Ganymede several times
and snap many close-up pictures.
Ganymede, shown above in its
natural colors, sports a large oval
dark region known as Galileo Regio.
In general, the dark regions on
Ganymede are heavily cratered,
implying they are very old, while
the light regions are younger and
dominated by unusual grooves. The
origin of the grooves is still under
investigation.


Jupiter’s Callisto: Oldest
Callisto is the most heavily
cratered object in the solar
system. It is thought to be a
long dead world, with a nearly
complete absence of any
geologic activity on its surface.
In fact, Callisto is the only body
greater than 1000 km in
diameter in the solar system
that has shown no signs of
undergoing any extensive
resurfacing since impacts have
molded its surface. With a
surface age of about 4 billion
years, Callisto has the oldest
landscape in the solar system.

http://solarsystem.nasa.gov/planets/proﬁle.cfm?Object=Jup_Callisto

Other Large Moons

http://www.astronomynotes.com/solarsys/s15.htm


Titan’s: Internal Structure

...graphic illustration of
Titan's internal structure....
Methane is locked in the
methane-rich water ice that
forms a crust above an
ocean of liquid water mixed
with ammonia.

http://www.solarviews.com/eng/titan.htm


Saturn’s Titan: Atmosphere
Although Titan is classiﬁed as a
moon, it is larger than the planet
Mercury. It has a planet-like
atmosphere which is more dense
than those of Mercury, Earth, and
Mars. The atmospheric pressure
near the surface is about 1.6 bars,
60 percent greater than Earth's.
Titan's air is predominantly made
up of [92% N2, 6% Ar, 2% CH4]
and trace hydrocarbon elements
which give Titan its orange hue.
These hydrocarbon rich elements
are the building blocks for amino
acids necessary for the formation
of life. Scientists believe that
Titan's environment may be
similar to that of the Earth's
before life began putting oxygen
http://www.solarviews.com/eng/titan.htm into the atmosphere.


Saturn’s Titan: Atmosphere

-170°F

-170°F

-245°F
-330°F
-290°F

http://www.jpl.nasa.gov/media/cassini-102504/visuals.html

Saturn’s Titan: Huygens Pic
Methane rain, evaporating lakes,
flowing rivers, and water ice-
volcanoes all likely exist on
Saturn's moon Titan, according to
preliminary analyses of recent
images taken by the successful
Huygens lander. A snaking and
branching riverbed is identified with
the dark channel near the top of the
above image, while a dark lakebed is
identified across the image bottom.
Both the riverbed and lakebed were
thought to be dry at the time the
image was taken but contained a
flowing liquid - likely methane - in the
recent past. Titan's surface ... is so
cold that methane flows and water
freezes into rock-hard ice.

Saturn’s Titan: Surface!
This color view from Titan gazes across a
suddenly familiar but distant landscape on
Saturn's largest moon. The scene was
recorded by ESA's Huygens probe after a 2
1/2 hour descent through a thick
atmosphere of nitrogen laced with
methane. Bathed in an eerie orange light at
ground level, rocks strewn about the scene
could well be composed of water and
hydrocarbons frozen solid at an
inhospitable temperature of [-290°F]. The
light-toned rock below and left of center is
only about 15 centimeters across and lies 85
centimeters away. Touching down ... the
saucer-shaped probe ... into a surface with
the consistency of wet sand or clay.
Huygen's ... transmitted data for more than
90 minutes after landing.


Huygens Probe lands on Titan

http://video.google.com/videoplay?
docid=-287238877012213463&ei=c0BGSobjPIHaqAPG3PDABg&q=Titan&hl=en&client=
safari


Saturn’s Enceladus
Remarkably high temperatures, at least 180 Kelvin (minus 135°F) were registered along
the brightest fracture. For comparison, surface temperatures elsewhere in the south
polar region of Enceladus are below 72 Kelvin (minus 330°F).

...a mass spectrum that shows the
chemical constituents sampled in
Enceladus' plume by Cassini's Ion and
Neutral Mass Spectrometer during its ﬂy-
through of the plume on Mar. 12, 2008.
http://spacespin.org/article.php/80344-cassini-organic-material-enceladus


Enceladus: H2O Ice Geysers
Cassini scientists infer that the temperature of
the ice in the south polar region must be close
to its melting point (shown in red).

A layer of liquid water (dark blue) might exist between the
ice and the silicate core (brown), allowing the ice to deform
independent of the rock, providing even more mechanical
energy and more ﬂexing of the icy shell for extreme tidal
heating. Tidal heating could also cause friction in faults
near the surface, leading to pockets of partially melted ice.
http://photojournal.jpl.nasa.gov/target/Enceladus


Neptune’s Triton: Volcanoes
[Triton] shares many similarities with
Pluto, the best known world of the
Kuiper Belt.

Triton's thin atmosphere is composed
mainly of nitrogen with small amounts
of methane. This atmosphere most
likely originates from Triton's volcanic
activity which is driven by seasonal
heating by the Sun.

Triton is one of the coolest objects in
our solar system.... (38 K, about -391°
Fahrenheit); it is so cold that most of
Triton's nitrogen is condensed as
frost.... The dark streaks ... are believed
to be an icy and perhaps carbonaceous
dust deposited from huge geyser-like
plumes...

...it is the only large moon in our solar
system that orbits in the opposite
direction of its planet's rotation - a
http://solarsystem.nasa.gov/planets/proﬁle.cfm? retrograde orbit.
Object=Triton

Moons on Parade

http://starryskies.com/The_sky/events/lunar-2003/multimedia.html


Large Moons: Composition
and Evolution
The three moons to the left illustrate three possible stages in the history
of an icy satellite. The satellite can be cold and so have no internal
activity. In that case, the surface is unchanged, old, and heavily
cratered. This case may be illustrated by Callisto, the top moon in the
picture. The craters are left over from the formation of the moon itself, 4
billion years ago. Nothing has happened to this moon to ever change
its surface appearance.

If there was some internal heating, then the surface may show some
changes and will not be as heavily cratered. This case may be
illustrated by Ganymede, the moon in the middle of the picture.
Ganymede has many craters but also trenches and grooves which
indicate that the surface ﬂowed at some point in time.

If the heating took place over a long time, then the surface may
show many changes, and in fact may still be evolving. This case may
be illustrated by Europa, the third moon in the picture. The surface of
Europa is lightly cratered with evidence of cracks and fractures.

Many moons in the solar system exhibit features of evolution somewhere
between those of Ganymede and those of Europa. Examples of these
moons include Dione, Rhea, Enceladus, Tethys, Ariel, Umbriel, Miranda,
Titania, Oberon, and Triton.
http://www.windows.ucar.edu/tour/link=/jupiter/moons/general_evolution.icy.html

Small Moons

Composition and Evolution
...not much is known about the [small moon’s] surface features or composition. With
no knowledge of the composition, and no clues from the surface, little can be
determined about the course of their evolution. Nevertheless, from the location of
some of the moons, as well as their shape, it can be determined that some
moons are fragments of a larger moon, or are captured asteroids. Examples of
moons such as these are Epimetheus, Janus, and Hyperion.
[Based on their densities,] It is thought that most small moons are icy.
http://www.windows.ucar.edu/tour/link=/jupiter/moons/general_evolution.small.html&edu=high


Moons of the Gas Giants
LACC §11.1,2,3
• Understand the conditions and processes that shaped
the outer planets’ moons: formed outside the frost line
w/ ices (CH4, NH3, H2O)

• Know the following moons in some detail: Io
(volcanoes), Europa (ocean under ice), Ganymede
(largest), Callisto (oldest), Titan (atmosphere), Triton
(retrograde, geysers)

• Understand a moon’s history by its surface: Light =
icy and young, Dark = dusty and old; fresh cracks =
geological activity, more craters = older

An attempt to answer the “big questions”: what is out
there? Are we alone?


HW Ch 11: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.

• Ch 11, pp. 263-264: 1.

• Ch 12: Image Analysis Quiz accessible from:
http://www.brookscole.com/cgi-brookscole/course_products_bc.pl?
ﬁd=M20b&product_isbn_issn=9780495017899&discipline_number=19
Must Know: 1, 3
Important: 4, 5

Due at the beginning of next class period.
Be working your Solar System project.


A1 11 Moons

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