Objective
To examine images of a sampling of the moons of the giant planets and
summarize the major features;
to distinguish these features from those of the Moon; to examine the atmosphere
of Saturn's moon Titan.
Materials
Exercise
The standard for comparative planetology of the moons:
LUNA
JUPITER'S moon Io
Io is the most geologically active world in our solar system. In fact, the
surface of Io is so active that it is the only solid surface in our solar system
without any impact craters. Io is resurfaced in under a million years and the
entire crust is recycled in about 10 million years. That means that over the age
of the solar system, the crust of Io has been completely recycled over 400
times.
The mechanism for this intense amount of resurfacing is volcanism. Io's
volcanism dwarfs all other worlds in our solar system. Volcanoes were first
discovered on Io when the Voyager spacecrafts flew past in 1979 and detected
eight volcanoes in eruption. The Galileo spacecraft now in orbit around Jupiter
has discovered more volcanoes and continues to monitor the eruptions on Io. The
size of the eruptions is immense, some hurtling material higher and farther than
any terrestrial volcano. Part of the reason for the difference is the lower
gravity of Io, plus the fact that it does not have an atmosphere.
The first image that follows was taken by Voyager 2 of the volcano
Prometheus. The second image is of the Pillan Patera volcano taken by the Galileo
spacecraft. To simplify our calculations, we assume that the volcanoes are
right on the limb of Io and we ignore any projection effects resulting from
putting a 3-D sphere onto a 2-D page.
Calculations
For each of the images determine the maximum height of the
volcano shown (Prometheus and Pillan Patera)
from the surface of Io. To do this, you must first calculate the scale
of the pictures. (Each picture has a different scale.)
The radius of Io is 1820 km. For the image of
Prometheus, you may assume that 1/4 of the disk is being shown; that is, the lower
left hand corner of the red-dashed line represents the center of IO.
For Pillan Patera, you should note that "complete the circle" has been done.
Determine the scale factor by finding the diameter and then the radius.
Please show all calculations.
| Prometheus (click on the image) |
Pillan Patera (click on the image) |
Additional information on Io and
Prometheus
[Calvin Hamilton] Voyager I Spacecraft
|
Additional information on Io and
Pillan Patera and
this image.
[JPL/NASA] Galileo Spacecraft
|
| Note: your values should be between 50 and 250 km;
otherwise, you've made an error. |
- From the height
of the volcano's plume, you can approximate the velocity that the material left
the volcano by the equation:
 | or |  |
where the
height is measured in meters, the velocity in meters per second, and g
is the acceleration due to gravity for the surface of Io. Values of g
are given for Io and the Earth in the table that follows.
| Name |
g (m/s2) |
| Io |
1.81 |
| Earth |
9.81 |
Determine the velocity that material is being ejected from the surface of Io
for these two volcanoes. Show all work on the answer sheet.
Questions:
Explain why the volcanoes on Io spew material so much higher than
similar volcanoes on Earth.
You should use "the force of gravity" somewhere in your explanation.
Another reason material is shot so much higher on Io is the
fact that this moon has no atmosphere. Theorize
as to why the presence of an atmosphere makes such a difference
Satellites of SATURN
Saturn has 28 moons, the most of any planet.
Following are the best images we have from the Voyager spacecraft
for two of the largest satellites of Saturn, Enceladus and Dione.
We are going to assume that processes we see as having occurred on these two
moons are representative of processes on most of the other moons.
In order to access a photograph of a particular satellite just click on the name
from the list below.
Enceladus |
Dione |
Comparative Planetology: Saturn's Satellites and our Moon
Mentally note the amount of cratering, unusual terrain,
coloring, etc. Is it uniform? Envision what the probable evolution has
been for each of these moons, then answer the following questions.
- Has either moon experienced resurfacing? Describe the evidence.
- Are there areas of saturation cratering? How do you know? (This is
meant to be an easy question.)
- Is the surface young or old compared to the surface of the Moon? Explain
your reasoning (and make sure you indicate whether you are talking about
the lunar highlands or mare).
- Based on the physical characteristics of your satellites
(see data table), what
would you conclude they are made of? How do the data support this?
(Hint: recall the fundamentals of density and albedo from earlier
in the quarter.)
Saturn's Majestic Moon: Titan
- Look at the image of Titan. Do you see any
surface features? What might be an explanation for this?
- Look at the comparison between the Earth's
atmosphere and Titan's.
Do you think there is liquid water on Titan's surface? Why or why not?
- If Titan's atmosphere is only a little thicker than Earth's, and made of
nitrogen (which we know we can see through), how would you explain why we cannot
see through Titan's atmosphere? Name a US city that has a similar atmospheric
composition.
MIRANDA, the strange moon of Uranus
In The Tempest, Miranda was the beautiful daughter of Prospero.
In the solar system, it is one of the most interesting moons around.
Miranda [mih-RAN-dah] is not one of the larger satellites of Uranus; however, it
was the one that was approached the closest by Voyager 2. This was not the
satellite scientists would have chosen to get close to if they had a choice, but
they had no choice. Voyager 2 had to fly close to the planet in order to get the
boost it needed to go to Neptune. The resolution at which the larger satellites
were photographed was around 2 to 3 kilometers (1.2 to 1.9 miles). On the other
hand, details on the order of a few hundred meters can be seen on Miranda.
Fortunately, Miranda turned out to be the most remarkable of all the satellites.
Miranda is a small satellite with a diameter of 470 kilometers (290 miles).
Its surface is unlike anything in the solar system with features that are
jumbled together in a haphazard fashion. Miranda consists of huge fault
canyons as deep as 20 kilometers (12 miles), terraced layers and a mixture of
old and young surfaces. The younger regions might have been produced by incomplete
differentiation of the moon, a process in which upwelling of lighter material
surfaced in limited areas. Alternatively, scientists believe that Miranda may
have been shattered as many as five times during its evolution. After each
shattering the moon would have reassembled from the remains of its former self
with portions of the core exposed and portions of the surface buried.
Miranda's
appearance can be explained by theories, but the real reason is still unknown.
Mapping Miranda
- Examine this high-resolution image of Miranda.
On your answer sheet, make a geological map of Miranda. Find examples of each of
the following geological features and label them on your map. (You should include
enough detail to adequately represent Miranda's features without taking an excessive
amount of time to do this part of the lab.)
- Scarp (a line of cliffs produced by faulting or erosion; a relatively
straight, clifflike face or slope of considerable linear extent)
- Old, heavily cratered surface
- Young, lightly cratered terrain
- Dark, grooved terrain
- Craters
- Faults
- Our Moon is about 7 times larger than Miranda. List two features that are similar,
and two that are very different.
- If our Moon looked like Miranda, the Apollo missions
would have had a difficult time deciding where to land first. Where would you choose to
land for "Miranda Mission 1" (mark it with a big "X" on your map) and why?
- Two scenarios for the formation of Miranda's characteristics are given in the
introduction for Miranda. Which one do you think
was the "most likely" one? Support your decision based on your knowledge of the
history of the solar system.
TRITON, largest moon of Neptune
In mythology, Triton was a sea god with the head and upper body of a man and the
tail of a fish. The moon Triton is similarly "made in two parts."
The orbit of Triton is currently circular, but it probably was not so early on.
The fact that the orbit is retrograde suggests that Triton did not form in a disk
around Neptune. Rather, it is speculated that Triton was originally a small planet
similar to Pluto. Triton was captured by collision with a primordial regular moon of
Neptune several billion years ago. The collision would have extracted a small amount
of energy from the orbit of Triton, leaving it on a large, highly eccentric orbit
around Neptune rather than around the sun. The high eccentricity was then rapidly
reduced by tides on Triton raised by Neptune. The energy extracted from the orbit
was dumped into Triton, melting it. Voyager found evidence for such a process in
the form of a very young surface on Triton.
The two parts of Triton
Shown here is a
high-resolution (false-color) image of Triton.
Examine the image closely,
and answer the following questions.
In your own words, describe the two different regions of Triton.
How do we know that Triton has been resurfaced (has a very young surface)?
South pole of Triton
This
high-resolution image of Triton's south pole was obtained
by Voyager 2 in 1989. One of the unusual aspects of this image is the dark
streaks in the images. Perhaps they were made by geyser-like eruptions of nitrogen.
The geyser eruptions could have carried darker materials from the crust.
The light regions probably consist of layers of nitrogen.
- How many geysers do you count?
- Yellowstone National Park lies over a hot-spot on the Earth. Could these
geysers be the result of a "hot-spot" on Triton? Why or why not?
- Name two other geological features you see on in this image of Triton.
Triton up close
This image of Triton shows a
plain of ice.
The plain was probably formed by eruptions of water or a water-ammonia slurry.
It seems to fill the remains of an ancient impact basin.
- What region(s) on our Moon would be similar in origin?
- What is one major difference between the formation of this plain and those
similar features on the Moon?
- How does the age of this plain on Triton compare to the similar features on
the Moon? (Recall the cratering lab and the principle of superposition.) Explain
your answer.
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