Transcript DTU 8e Lecture PPT Chap 8 The Outer Planets v2

Neil F. Comins • William J. Kaufmann III
Discovering the Universe
Eighth Edition
CHAPTER 8
The Outer Planets
Jupiter as Seen from a Spacecraft
This view was sent back from Voyager 1 in 1979. Features as small as
600 km across can be seen in the turbulent cloud tops of this giant
planet. The complex cloud motions that surround the Great Red Spot
are clearly visible. Also, clouds at different latitudes have different
rotation rates. The inset image of Earth shows its size relative to
Jupiter.
Close-ups of Jupiter’s Atmosphere
The dynamic winds, rapid rotation, internal heating, and complex
chemical composition of Jupiter’s atmosphere create its beautiful
and complex banded pattern. (a) A Voyager 2 southern hemisphere
image showing a white oval that has existed for over 40 years. (b) A
Voyager 2 northern hemisphere image showing a brown oval. The
white feature overlapping the oval is a high cloud.
Jupiter Unwrapped
Cassini images of Jupiter combined and opened to give a
map like representation of the planet. The banded
structure is absent near the poles. The Web link will take
you to a movie version of this and related images. In
them, you will see that the light and dark regions slide by
one another, continually moving eastward or westward.
The Great Red Spot
This true color image of the Great Red Spot, taken by Galileo in
1996, shows what this giant storm would look like if you were
traveling over it in a spacecraft. The counterclockwise circulation
of gas in the Great Red Spot takes about 6 days to make one
rotation. The clouds that encounter it are forced to pass around it,
and when other oval features are near it, the entire system
becomes particularly turbulent, like the batter in a two-bladed
blender.
Jupiter’s and Saturn’s Upper Layers
These graphs display temperature profiles of (a) Jupiter’s and (b) Saturn’s
upper regions, as deduced from measurements at radio and infrared
wavelengths. Three major cloud layers are shown in each, along with the
colors that predominate at various depths. Data from the Galileo spacecraft
indicate that Jupiter’s cloud layers are not found at all locations around the
planet; there are some relatively clear, cloud-free areas.
Original Model of Jupiter’s Belts and Zones
The light-colored zones and dark-colored belts in Jupiter’s atmosphere were
believed, until recently, to be regions of rising and descending gases,
respectively. In the zones, gases warmed by heat from Jupiter’s interior were
thought to rise upward and cool, forming high-altitude clouds. In the belts, cooled
gases were thought to descend and undergo an increase in temperature; the
cloud layers seen there are at lower altitudes than in the zones. Observations by
the Cassini spacecraft on its way to Saturn suggest that just the opposite may be
correct! In either case, Jupiter’s rapid differential rotation shapes the rising and
descending gas into bands of winds parallel to the planet’s equator. Differential
rotation also causes the wind velocities at the boundaries between belts and
zones to move predominantly to the east or west.
Jupiter’s Four Largest Moons
Io
This true-color view was taken by the Galileo spacecraft in
1999. The range of colors results from surface deposits of
sulfur ejected from Io’s numerous volcanoes. Plumes from the
volcano Prometheus rise up 100 km. Prometheus has been
active in every image taken of Io since the Voyager flybys of
1979.
Io
Galileo image of an
eruption of
Pilan Patera on Io.
Io
Photographed in 1999 and then 2000
(shown here), the ongoing lava flow from
this volcanic eruption at Tvashtar Catena
has considerably altered this region of
Io’s surface.
Europa
Imaged by the Galileo spacecraft, Europa’s ice
surface is covered by numerous streaks and cracks
that give the satellite a fractured appearance. The
streaks are typically 20 to 40 km wide.
Surface Features on Europa
This false color Galileo image of Europa combining
visible and infrared observations shows smooth plains
of ice, mineral ridges deposited by upwelling water,
and numerous fractures believed to be caused by tidal
stresses.
Surface Features on Europa
This region of Europa’s surface shows the jumbled,
stressed features common to the surface, as well as
direct indications of liquid water activity underground.
Surface Features on Europa
Lenticulae attributed to rising warmed ice and debris
travel up from the moon’s interior by convection,
arriving at and then leaking out at the surface. The
white domes are likely to be rising material that has not
yet reached the surface.
Ganymede
This side of Ganymede is dominated by the huge, dark, circular
region called Galileo Regio, which is the largest remnant of
Ganymede’s ancient crust. Darker areas of the moon are older;
lighter areas are younger, tectonically deformed regions. The light
white areas in and around some craters indicate the presence of
water ice. Large impacts create white craters, filled in by ice from
below the surface.
Callisto
The outermost Galilean
satellite is almost exactly the
same size as Mercury.
Numerous craters pockmark
Callisto’s icy surface. (a) The
series of faint, concentric rings
that cover much of this image is
the result of a huge impact that
created the impact basin
Valhalla. Valhalla dominates the
Jupiter-facing hemisphere of this
frozen, geologically inactive
world.
Callisto
The two insets in this Galileo mission image show spires that contain
both ice and some dark material. The spires were probably thrown
upward as the result of an impact. The spires erode as dark material in
them absorbs heat from the Sun.
Saturn
Combined visible and ultraviolet images from the Hubble
Space Telescope reveal spiral arcs of aurora near Saturn’s
south pole. The image of Earth shows its size relative to
Saturn. Note that there is much less contrast between
Saturn’s clouds than those of Jupiter.
Merging Storms on Saturn
This sequence of Cassini images shows two
hurricane-like storms merging into one on Saturn in
2004. Each storm is about 1000 km (600 mi) across.
Numerous Thin Ringlets Constitute Saturn’s Inner Rings
This Cassini image shows that Saturn’s rings contain
numerous ringlets. Inset: As moons orbit near or between
rings, they cause the ring ices to develop ripples, often
like the grooves in an old-fashioned record.
Saturn’s Outer Ring System
Another view of the inner and intermediate
rings, where subtle color differences are
indicated.
Saturn’s Outer Ring System
Superimposed on this Cassini image are labels that indicate
how far the rings extend into the moon system of Saturn.
Titan (off image on right) is 1.2 million km (750, 000 mi)
from the center of Saturn.
Spokes in Saturn’s Rings
Believed to be caused by Saturn’s magnetic field
moving electrically charged particles that are lifted
out of the ring plane, these dark regions move
around the rings like the spokes on a rotating
wheel.
Surface Features on Titan
Voyager images of Titan’s smoggy atmosphere.
Surface Features on Titan
Cassini image of Titan of lighter highlands, called Xanadu,
and dark, flat, lowlands that may be hydrocarbon seas.
Resolution is 4.2 km (2.6 mi).
Surface Features on Titan
Riverbeds meandering across the Xanadu
highlands of Titan. These are believed to have
formed by the flow of liquid methane and ethane.
Surface Features on Titan
Lake likely filled with liquid methane and ethane found at Titan’s
north pole, with Lake Superior, a Great Lake on Earth, for
comparison.
Surface Features on Titan
The Huygens spacecraft took
this image at Titan’s surface
on January 14, 2005. What
appear like boulders here are
actually pebbles strewn
around the landscape. The
biggest ones are about 15
cm (6 in.) and 4 cm (1.5 in.)
across.
Enceladus
(a) Cassini view of the two distinct landscapes on Enceladus, one
heavily cratered, the other nearly crater-free. The blue “Tiger Stripes”
are believed to be due to upwelling of liquid that froze at the surface.
(b) The crater-free region near the south pole. The ridges are thought
to be created by tectonic flows. Inset shows ice boulders.
Enceladus
Icy particles leaving Enceladus.
Uranus, Earth, and Neptune
Images of Uranus, Earth, and Neptune are to the same scale. Uranus
and Neptune are quite similar in mass, size, and chemical
composition. Both planets are surrounded by thin, dark rings, quite
unlike Saturn’s, which are broad and bright. The clouds on the right of
Uranus (false color pink) are each the size of Europe.
Exaggerated Seasons on Uranus
Uranus’s axis of rotation is tilted so steeply that it lies nearly in
the plane of its orbit. Seasonal changes on Uranus are thus
greatly exaggerated. For example, during midsummer at
Uranus’s south pole, the Sun appears nearly overhead for
many Earth years, during which time the planet’s northern
regions are subjected to a long, continuous winter night. Half
an orbit later, the seasons are reversed.
Cutaways of Uranus and Neptune
The interiors of both Uranus and Neptune are believed to have
three regions: a terrestrial rocky core surrounded by a liquid
water mantle, which is surrounded, in turn, by liquid hydrogen
and helium. Their atmospheres are thin layers at the top of their
hydrogen and helium layers.
The Magnetic Fields of Five Planets
This drawing shows how the magnetic fields of Earth, Jupiter,
Saturn, Uranus, and Neptune are tilted relative to their rotation
axes. Note that the magnetic fields of Uranus and Neptune are
offset from the centers of the planets and steeply inclined to their
rotation axes. Jupiter, Saturn, and Neptune have north magnetic
poles on the hemisphere where Earth has its south magnetic pole.
Miranda
The patchwork appearance of Miranda in this mosaic of Voyager 2
images suggests that this satellite consists of huge chunks of rock and ice
that came back together after an ancient, shattering impact by an asteroid
or a neighboring Uranian moon. The curious banded features that cover
much of Miranda are parallel valleys and ridges that may have formed as
dense, rocky material sank toward the satellite’s core. At the very bottom of
the image—where a “bite” seems to have been taken out of the satellite—
is a range of enormous cliffs that jut upward as high as 20 km, twice the
height of Mount Everest.
Neptune
This view from Voyager 2 looks down on the southern hemisphere of
Neptune. The Great Dark Spot’s longer dimension at the time was
about the same size as Earth’s diameter. It has since vanished.
Note the white, wispy methane clouds.
Neptune’s Rings
Two main rings are easily seen in this view alongside overexposed
edges of Neptune. In taking this image, the bright planet was hidden
so that the dim rings would be visible, hence the black rectangle
running down the center of the figure. Careful examination also reveals a
faint inner ring. A fainter-still sheet of particles, whose outer edge is
located between the two main rings, extends inward toward the planet.
Triton’s South Polar Cap
Approximately a dozen high-resolution Voyager 2 images were
combined to produce this view of Triton’s southern hemisphere. The
pinkish polar cap is probably made of nitrogen frost. A notable scarcity of
craters suggests that Triton’s surface was either melted or flooded by icy
lava after the era of bombardment that characterized the early history of
the solar system.
A Frozen Lake on Triton
Scientists think that the feature in the center of this
image is a basin filled with water ice. The flooded
basin is about 200 km across.
The Outer Planets: A Comparison