The Jupiter System

The Jupiter System
Io passing in front of Jupiter
Overview
1. Jupiter overview
2. Io: Volcanic Activity & Composition
3. Callisto: Geology of an old icy body
4. Ganymede: Ocean on an icy world?
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Jupiter: Composition
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Jupiter does not have a solid surface but is
instead dominated by H and He. Trace
amounts of methane and ammonia are also
present.
The bulk composition of Jupiter is thus very
similar to the Sun, but it is not quite massive
enough to ignite (does not cause fusion).
The atmosphere increases in density with
depth, and at some point (though we don’t
know exactly where) the material must
become a fluid in which H behaves as an
electrically conducting metal.
Beneath this, there may lie a core composed of
heavier elements.
Together, these properties somehow produce
a very intense magnetic field, though the exact
process is unknown.
Jupiter: Internal Structure
The upper atmosphere contains ammonia
(NH3) crystals and clouds, whereas ice
clouds and water droplets are present
below.
At some depth, the hydrogen starts to
behave like fluid metallic hydrogen.
The amount of water in Jupiter is unknown, but
this will be measured by an upcoming mission.
In addition, we know the general aspects of the
interior structure of Jupiter (as shown in these
diagrams), but we need more information on
the details (where do phase transitions take
place, where/how is the magnetic field
generated, etc.).
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Jupiter: Magnetic Field
The magnetic poles of Jupiter are shifted by
about 10° from the rotational pole, similar to
Earth.
In addition to the strong magnetic field, Jupiter
also exhibits a plasma torus.
This plasma torus is produced by Io; volcanic
activity on Io releases S, Cl, O, and Na in to the
atmosphere, and some of this escapes and
interacts with Jupiter’s magnetic field, where it
is ionized and produces the torus.
The plasma torus is in the same rotational
plane as the magnetic field, thus Io actually goes
above the plasma torus at some points in its
orbit and below it at others.
The magnetic field of Jupiter is ~14 times
stronger than that of Earth, and it is the
strongest in our Solar System.
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Jupiter: Magnetic Field
Aurorae on Jupiter are 10-100 times brighter than the ‘northern lights’ seen on Earth.
They are always present on Jupiter and are caused by interaction of charged particles from
the Sun (solar wind) with the strong magnetic field of Jupiter, and this interaction causes
gases in the upper atmosphere to fluoresce near the magnetic poles
The image to the right shows the aurorae as
seen in ultraviolet images captured by the
Hubble Space Telescope. The background image
was acquired at a visible wavelength of light.
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The Juno Mission to Jupiter
The Juno mission launched August 5, 2011 and will arrive at Jupiter in July 2016.
It will be only the 2nd spacecraft to orbit Jupiter.
Some of the questions that this mission will try to answer are:
- How did the giant planets form? (get better estimates of core mass)
- Does Jupiter have a rock-ice core, and if so how large is it?
- Is the composition of Jupiter different from the original solar nebula? If so, why?
- How deep into the atmosphere do atmospheric features (e.g., great red spot) go?
- How does the dynamo on Jupiter work?
- What is the abundance of water on Jupiter?
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The Moons of Jupiter
Galileo Galilei, 1610
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The Moons of Jupiter
Io
Europa
Jupiter has 63 moons, though the 4 largest moons
are the most well known. Several dozen of these
were only discovered in the past 10 years.
The 4 largest moons are believed to have been
first observed by Galileo Galilei in 1610, thus they
are often called the ‘Galilean moons’.
Io is a volcanically active moon, whereas the other
3 large moons are dominated by ice and may
contain liquid water oceans beneath their icy
crust.
Ganymede is the largest moon and is actually
larger than Mercury!
Ganymede
Callisto
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These 4 moons are spheroidal and would be
considered dwarf planets if they orbited the Sun
directly (like Ceres).
The Galilean moons are believed to have formed
by accretion of dust and gas in a disk surrounding
Jupiter, similar to a protoplanetary disk. They are
not consistent with captured objects.
Galilean Moons
Io
All 4 appear to be differentiated, and
several likely have distinct cores.
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Europa
Three are believed to have significant
amounts of water beneath the outer
crust...liquid or ice??
This has opened up the possibility that
these moons may be good places for
life beyond Earth.
Io
Europa
Ganymede
Ganymede
Callisto
Callisto
Galilean Moon Surfaces
The Galilean satellites are each unique with respect to their geologic
histories, as evident from even visible images of their surfaces.
Ganymede & Callisto exhibit numerous impact craters (surfaces are ‘older’).
Io and Europa lack impact craters (surfaces are ‘younger’).
Io Europa
Ganymede Callisto
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Io: A Volcanically Active Moon
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Io is perhaps one of the most fascinating moons in the outer solar system because of its extreme
volcanic activity. This means that the surface is continuously being covered with new material and that
it is a geologically young surface (impact craters are extremely rare).
Io is one of only several objects in the solar system that exhibits current volcanic activity.
To the naked eye, Io would have a yellowish hue marked with red and black spots.
‘True’ Color Image of Io
Voyager image of Pele region on Io
showing an active eruption.
Io: Tidal Heating
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Io exhibits an orbital resonance with Jupiter and gravitational pull from Europa, Ganymede, and
Callisto, and this causes the orbit of Io to be elliptical.
The elliptical orbit means that the gravitational pull on Io from Jupiter changes depending on where Io
is in its orbit.
This causes the moon to flex in and out (kind of like squeezing a tennis ball).
This flexing produces internal friction, which releases energy in the form of heat.
This continual tugging by Jupiter has kept
the moon warm its entire life, and this
has sustained volcanic activity on Io.
If Io had a more circular orbit and less
tidal heating, then it would likely be
volcanically dead today, more like Earth’s
moon.
Color Variations on Io
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The diversity of surface
compositions is more
striking in false-color images
such as this one, where the
circular features surround
volcanic sources and the red/
yellow tones indicate sulfurrich compounds.
Most of the lava flows are
mafic or ultramafic (Mg/Fe
rich), but large amounts of
sulfur are released during
the volcanic eruptions.
The gases and particles from
the eruptions can reach
heights of 100s of kilometers
and form large umbrella
shaped plumes. This spreads
the sulfur-rich material over
the surface.
Sulfur on Io
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Sulfur gas consisting of pairs of sulfur atoms (S2) is ejected from the hot vents of Io's volcanoes (green
arrow). The sulfur gas lands on the cold surface, where the sulfur atoms rearrange into molecules of
three or four atoms (S3, S4), which give the surface a red color. Eventually the atoms rearrange into
their most stable configuration, rings of eight atoms (S8), which form ordinary pale yellow sulfur.
Io:Volcanic Eruptions
Galileo images also captured active lava flows, and it was shown that these are sometimes
preceded by fire fountain eruptions.
In the image on the left, the red/yellow colors are actually a sketch of where the fire fountain is; the
image on the right shows the actual lava flow that followed.
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Io: Tohil-Culann Region
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This region on Io (Tohil-Culann region) exhibits
interconnected mountains and volcanoes, and it is
also one of the more colorful regions on Io.
The center of the volcano (the patera, seen at the
top center) is associated with bright orange/red
deposits.
Just to the
south are the
Tohil
mountains.
The volcanoes
produce both
reddish sulfurrich lavas and
dark silicaterich lavas, and
the white
regions are
likely cooler
flows rich in
SO2.
Mountains on Io
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Io also has mountains, as shown in this image acquired by the Galileo spacecraft in 2000.
The mountain ridge along the left side of the image rises ~7 km above the plains.
Most of the mountains on Io are not related to volcanoes but are instead believed to result from
tectonic activity, likely from uplifting of the crust along thrust faults.Younger mountains are more
jagged and angular, whereas older mountains have subdued topography (top middle of image).
Uplifting and compressional stresses
can lead to thrust faults, which can in
turn lead to mountain ridges.
The fault may not always be visible at
the surface, in which case it is called a
‘blind’ thrust fault.
Icy Moon Surfaces
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When we examine the icy satellites at higher resolution, we see that even though they may have
experienced roughly similar geologic processes they have very different surface features.
Callisto contains hills, numerous craters, and appears more ‘rugged’.
Ganymede has a complex surface of ridges, grooves, and craters.
Europa has a very complex surface of intersecting ridges/grooves
and has clearly been affected by tectonic processes.
Europa
Ganymede
Callisto
Cratering Record on Icy Moons
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While all three moons are believed to be nearly as old as the solar system (4.5 billion years), the age of the
surfaces is still subject to debate. Without having surface samples in hand, the only method to roughly
determine the geologic surface age is by crater counting. However, assumptions about the impactor fluxes must
be made based on theoretical models and possible observations of candidate impactors: asteroids and
comets.
Asteroids should have been very common in the early days of the solar system, but this source should have
been largely exhausted by ~3.8 billion years ago. For comets, the impactor flux is believed to be rather constant
throughout the whole lifetime of the solar system, meaning that the probability of an impact of a large comet is
similar today as it was even 4 billion years ago.
If asteroids have been the dominant bodies that impacted the Galilean satellites (which is believed to be the
case on the Moon, the Earth, and other inner solar system bodies as well as within the asteroid belt itself), the
surfaces of Ganymede and Callisto must be roughly 4 billion years old whereas Europa’s surface is only several
hundred million years old. Low-level geologic activity on Europa might be possible today, but Ganymede and
Callisto should be geologically dead.
In contrast, if we assume that comets have been the main impactors in the Jovian system, Callisto's surface
would still be determined to be old (4 billion years), but Ganymede's youngest large craters would have been
created only ~1 billion years ago. In this model, Europa's surface should be very young, and it would be quite
geologically active even today.
or
?
Callisto
Callisto is the 2nd largest of the Galilean moons and is almost the same size as Mercury.
As with Ganymede, the low mean density (1.83 g/cm3) implies the presence of water/ice.
It is tidally locked such that the same side always faces Jupiter.
As with Europa & Ganymede, Callisto may have a liquid ocean beneath the crust.
It may have a small solid core, but this is not
clear. Callisto accreted relatively slow and it
may not have had time to fully differentiate.
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Callisto
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The surface of Callisto is covered with dark material (only reflects 20% of light) that is relatively smooth and
seems to fill in topographic lows and small craters.
The darker regions likely contain silicates, possibly organics, and other non-ice phases; the brighter regions are
dominated by water and other ices.
Unlike Ganymede & Europa, the surface seems to be dominated by impact events and not tectonics; it also
appears that Callisto did not experience significant tidal heating.
Global Map of Callisto
Callisto: Surface Features
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These images are some of the highest-resolution views ever obtained of Callisto. The bright knobby
terrain seen in the top image is unusual for any of Jupiter's moons. The spires are very icy but also
contain some darker dust. As the ice erodes, the dark material apparently slides down and collects in
low-lying areas. The knobs are about 80-00 m tall and may consist of material thrown outward from a
major impact billions of years ago (theses areas lie to the south of the large Asgard impact basin).
Over time, as the
surface continues to
erode, the icy knobs
will likely disappear,
producing a scene
similar to the bottom
image.
The numerous
impact craters in the
bottom image
indicates that erosion
has essentially ceased
in the dark plains in
that location.
Callisto: Surface Features
This large multi-ring basin on Callisto was imaged by the Voyager spacecraft in 1979. The complicated
circular structure seen at left center is similar to the large circular impact basins that dominate the
surface of our Moon and Mercury. The inner parts of such large basins are generally surrounded by
radial ejecta and several concentric mountainous ring structures formed during the impact event.
This multi-ring basin consists of lighttoned on the floor of the central basin
(~300 km in diameter), surrounded by
at least eight to ten discontinuous
rhythmically spaced ridges.
No radially lineated ejecta can be seen.
The great number of rings observed
around this basin on Callisto is
consistent with its low planetary
density and probable low internal
strength (lots of ice, not just rock!).
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Callisto: Surface Features
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Callisto also exhibits ‘domed’ craters (left image), which may represent impacts into a slushy material.
Other craters exhibit bright rays from ejecta, similar to typical craters seen on other planetary
surfaces.
Of all the icy satellites of Jupiter, Callisto exhibits the most craters and is likely the oldest surface.
Callisto: Surface Features
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Here, Callisto is in approximate natural color (left) and in false color to enhance subtle color variations (right). The the ancient, multi-ring
impact structure Valhalla is just above the center of the image.Valhalla, possibly created by a large asteroid or comet which impacted
Callisto, is the largest surface feature on this moon.Valhalla consists of a bright inner region, about 600 kilometers in diameter
surrounded by concentric rings 3000 to 4000 kilometers in diameter. The bright central plains were possibly created by the excavation
and ejection of "cleaner" ice from beneath the surface, with a fluid-like mass (impact melt) filling the crater bowl after impact.
The false color image on the right highlights ejecta from relatively recent craters, which are often not apparent in the natural color
image. The colors also reveal a gradual variation across the moon's hemisphere, perhaps due to implantation of materials onto the surface
from space. The ‘color’ data were obtained with the 1 um (infrared), green, and violet filters of the Solid State Imaging (SSI) system on the
Galileo spacecraft.
Liquid Oceans?
How do you test for a liquid ocean?
http://www.youtube.com/watch?v=30oPZO_z7-4
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Ganymede
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The surface of Ganymede consist of bright & dark terrain. The bright terrain is dominated by water
ice and the dark terrain is silicate-rich (though the exact composition is unknown).
Ganymede also contains sulfate salts, possibly originating from a salty ‘ocean’ beneath the surface.
Ganymede is the largest satellite in the solar
system & is larger than Mercury.
However, it only has a mean density of 1.9 g/
cm3, implying a significant component of ice.
It appears to have an Fe or Fe-S core, a
silicate mantle, and an outer ice mantle.
Ganymede
Color-enhanced images reveal frosty polar caps in
addition to the two predominant terrains on
Ganymede (bright, grooved terrain and older, dark
furrowed areas).
Many craters with diameters up to several dozen
kilometers are visible.
Ganymede's intrinsic magnetic field was detected
by the magnetometer on the Galileo spacecraft in
1996, and it may be partly responsible for the
appearance of the polar terrain.
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Ganymede: Surface Features
The dark regions retain more craters than the bright regions and the bright regions clearly crosscut the dark
regions; thus the dark regions are the older terrain.
The exact origin for the ridges and grooves that cover the surface of Ganymede is not clearly known,
but they seem to result from tectonic forces, not cryovulcanism.
Large fracture/crack systems developed at one point and new, fresh surface material was formed, possibly
sourced form the potential ocean beneath the frozen surface.
Global Map of Ganymede
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Ganymede: Surface Features
The ancient, dark terrain of Nicholson Regio (left) shows many large impact craters, and zones of
fractures oriented generally parallel to the boundary between the dark and bright regions. In
contrast, there are fewer craters in the bright terrain of Harpagia Sulcus (right) and it is smoother.
The bright and dark regions are the two principle terrain types on Ganymede, and the nature of the
boundary between ancient, dark terrain and younger, bright terrain, was explored in detail by the
Galileo spacecraft. Subtle parallel ridges and grooves show that Harpagia Sulcus's land has been
smoothed out over the years by tectonic processes.
Dark Terrain
Bright Terrain
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Ganymede: Surface Features
The ridges/grooves on Ganymede are similar to what is observed during extensional faulting on
Earth (and other terrestrial planets).
As the crust is pulled apart,
large sections can drop down
to form grabens.
In some cases a series of blocks
drop down and rotate,
sometimes referred to as halfgrabens (image below).
This is a possible process that
forms ridges on Ganymede
(image to the left).
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Ganymede: Surface Features
Imaging the surface several times from different viewing angles can allow us
to create models of the surface topography. This ‘stereo imaging’ can then
be used to determine relative differences in elevation between different
types of terrains, as in the image below.
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Ganymede: Surface Features
In these images, the bright region cuts across the
dark region, thus the bright region is younger.
The bright region that runs north-south is
younger than the dark terrain, but it is then cut
by the bright band that runs east-west near the
bottom. Therefore, the east-west band is even
younger than the north-south band of bright
material.
The bottom image shows the topography (blue
tones are lower elevation) draped on top of the
visible image. It then becomes clear that the
bottom, east-west bright band is lower in
elevation than the surrounding terrain to the
north.
Be examining cross-cutting relationships and
topography, we can try to piece together the
relative ages of different geologic units.
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Ganymede: Surface Features
Similar to the previous figure, these data also exhibit cross-cutting relationships and topography.
In addition, this image covers several major types of terrain on Ganymede: grooved, smooth, &
reticulate terrain. The simple geologic map inset in (b) shows the location of each type of terrain.
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Ganymede: Surface Features
These are some of the
highest resolution images of
Ganymede ever acquired.
They show several important features:
- even ‘smooth’ terrain is rough at
small scales
- there are numerous craters that have
retained their shape
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Ganymede: Surface Features
Unlike Europa, the surface of Ganymede (and Callisto) exhibits numerous impact craters.
In these Voyager images, bright material appears as rays that can be traced back to an impact crater.
The infrared data (right) show this icy ejecta in blue tones, providing a different view of the ejecta
pattern and information on its composition.
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Ganymede: Internal Structure
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from Steve Vance, JPL