Moons of the Gas Giants
LACC §11.2, 11.3
• Understand what conditions and processes
shaped the gas giant planets’ moons
• Know the following moons in some detail: Io,
Europa, Ganymede, Callisto, Titan, Triton.
• Light = icy and young; Dark = dusty and old
An attempt to answer the “big questions”: what is
out there? Are we alone?

Solar System Moons
http://spaceplace.nasa.gov/en/kids/sse_flipflop2.shtml

Gas Giant Moons
http://www.astro.rug.nl/%7Eetolstoy/ACTUEELONDERZOEK/JAAR2000/moons/aoz.html

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

Galilean Moons:
Gravitational Resonances
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.
http://
The interiors of Io, Europa, Callisto, and Ganymede, clockwise
from upper left. All except Callisto have metallic (iron/nickel) www.solarviews.com/cap/
cores, shown in gray, surrounded by rock in brown. The rock jup/calint.htm
shells in Europa and 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 degrees Fahrenheit,
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 degrees
Fahrenheit (1,038 degrees Celsius). 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?
http://apod.nasa.gov/apod/ap961120.html

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.
http://apod.nasa.gov/apod/ap000620.html

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

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 into the
atmosphere.
http://www.solarviews.com/eng/titan.htm

Saturn’s Titan: Atmosphere
...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
-170°F
-170°F
-245°F
-330°F
-290°F
http://www.jpl.nasa.gov/media/cassini-102504/visuals.html

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.
http://apod.nasa.gov/apod/ap050117.html

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

Neptune’s Triton: Volcanoes
Triton is one of only three objects in the
Solar System known to have a
nitrogen-dominated atmosphere (the
others are Earth and Saturn's giant
moon, Titan). Triton has the coldest
surface known anywhere in the Solar
System (38 K, about -391° Fahrenheit);
it is so cold that most of Triton's
nitrogen is condensed as frost, making
it the only satellite in the Solar System
known to have a surface made mainly
of nitrogen ice. The pinkish deposits
constitute a vast south polar cap
believed to contain methane ice, which
would have reacted under sunlight to
form pink or red compounds. The dark
streaks overlying these pink ices are
believed to be an icy and perhaps
carbonaceous dust deposited from
huge geyser-like plumes, some of
which were found to be active during
the Voyager 2 flyby.
http://solarsystem.nasa.gov/planets/profile.cfm? Also, Triton orbits backwards.
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

Enceladus: H2O Geysers
March 9, 2006: NASA's
Cassini spacecraft may have
found evidence of liquid
water reservoirs that erupt in
Yellowstone-like geysers on
Saturn's moon Enceladus.
http://science.nasa.gov/headlines/
y2006/09mar_enceladus.htm

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