Download Lecture09_2012 Giant Planets Satellites

Lecture 9. Giant planets satellites
Anton B. Ivanov
Monday, January 14, 13
Top 4 themes in planetary science
• The First Billion Years of Solar System History.
- Formative period that features the initial accretion and development of Earth and its sibling planets,
including the emergence of life on our globe. This pivotal epoch in the solar system’s history is only
dimly glimpsed at present.
• Volatiles and Organics: The Stuff of Life.
- Life requires organic materials and volatiles, notably, liquid water. These materials originally
condensed in the outer reaches of the solar nebula and were later delivered to the planets aboard
organic-rich comets and asteroids.
• The Origin and Evolution of Habitable Worlds.
- The third theme recognizes that our concept of the “habitable zone” has been overturned, and
greatly broadened, by recent findings on Earth and elsewhere throughout our galaxy. Taking
inventory of our planetary neighborhood will help to trace the evolutionary paths of the other planets
and the eventual fate of our own.
• How Planetary Systems Work.
- The fourth theme seeks deeper understanding of the fundamental mechanisms operating in the solar
system today. Comprehending such processes—and how they apply to planetary bodies—is the
keystone of planetary science. It will provide deep insight into the evolution of all the worlds within
the solar system and of the multitude of planets being discovered around other stars.
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Galilean Satellites
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Io, Europa, Ganymede, Callisto
IO
Three volcanic plumes are visible. Most conspicuous
is the enormous 300-kilometer (190-mile) -high
plume from the Tvashtar volcano at the 11 o'clock
position on Io's disk. Two much smaller plumes are
barely visible: one from the volcano Prometheus, at
the 9 o'clock position on the edge of Io's disk, and
one from the volcano Amirani, seen between
Prometheus and Tvashtar along Io's terminator (the
line dividing day and night). The plumes appear
blue because of the scattering of light by tiny dust
particles ejected by the volcanoes, similar to the
blue appearance of smoke. In addition, the
contrasting red glow of hot lava can be seen at the
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Europa
As seen by Voyager
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Tidal heating
• Tidal heating occurs on a celestial body when rotational,
orbital or gravity energies are dissipated through internal
heat inside a body
• Examples:
- Io
‣ Io’s highly eccentric orbit causes raises of up to 100m during perihelion of an
orbit
‣ friction is causing internal heat
- Enceladus
‣ tidal heating is causing water to heat inside the satellite, evidenced through
water vapor geysers
‣ this process is observed currently by Cassini spacecraft
✦ The flyby on Nov. 30, 2011 will bring Cassini to within about 48 kilometers (30 miles) of the
surface of Enceladus.
✦ During the closest part of the Nov. 30 flyby, Cassini's radio science subsystem made gravity
measurements. The results will be used to understand the moon's interior structure. Cassini's
fields and particles instruments will sample the charged particle environment around
Enceladus. Other instruments captured images in visible light and other parts of the light
spectrum after Cassini makes its closest approach.
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Tidal force
ˆr - is a unit vector from M to m
G - gravitational constant
M, m - masses of two bodies
R - distance between the two
Consider a small particle at a distance of Δr
use series to expand acceleration
first term is gravity at the center of mass
on Earth tides are the pulls by both Sun
(0.54x10-7g) and the Moon (1.1x10-7g)
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Tidal force
ˆr - is a unit vector from M to m
G - gravitational constant
M, m - masses of two bodies
R - distance between the two
Consider a small particle at a distance of Δr
use series to expand acceleration
first term is gravity at the center of mass
on Earth tides are the pulls by both Sun
(0.54x10-7g) and the Moon (1.1x10-7g)
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The view combines images taken in violet,
green and near-infrared filters in 1998 and
1995. The colors have been stretched to
show the subtle differences in materials that
cover the icy surface of Europa. Reddish
linear features are some of the cracks and
ridges, thousands of kilometers long, which
are caused by the tides raised by the
gravitational pull of Jupiter. Mottled, reddish
"chaotic terrain" exists where the surface has
been disrupted and ice blocks have moved
around. The red material at the ridges and
chaotic terrain is a non-ice contaminant and
could be salts brought up from a possible
ocean beneath Europa's frozen surface.
Europa
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Also visible are a few circular features, which are
small impact craters. Europa's surface has very
few craters, indicating that recent or current
geologic activity has removed the traces of older
impacts. The paucity of craters, coupled with
other evidence, has led scientists to surmise that
there could be an ocean of liquid water beneath
Europa's surface. (NASA/Photohournal/
PIA02590)
The image on the left shows a region of Europa's crust made up of blocks which are thought to have broken apart and
"rafted" into new positions. These features are the best geologic evidence to date that Europa may have had a
subsurface ocean at some time in its past. Combined with the geologic data, the presence of a magnetic field leads
scientists to believe an ocean is most likely present at Europa today. In this false color image, reddish-brown areas
represent non-ice material resulting from geologic activity. White areas are rays of material ejected during the formation of
the 25-km diameter impact crater Pwyll (see global view). Icy plains are shown in blue tones to distinguish possibly
coarse-grained ice (dark blue) from fine-grained ice (light blue). Long, dark lines are ridges and fractures in the crust,
some of which are more than 3,000 kilometers (1,850 miles) long. These images were obtained by NASA's Galileo
spacecraft during September 7, 1996, December 1996, and February 1997 at a distance of 677,000 kilometers (417,489
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IO
Ganymede
Europa
Callisto
Cutaway views of the possible internal structures of the Galilean satellites. The surfaces of the satellites are
mosaics of images obtained in 1979 by NASA's Voyager spacecraft, and the interior characteristics are
inferred from gravity field and magnetic field measurements by NASA's Galileo spacecraft. With the
exception of Callisto, all the cores are surrounded by rock (shown in brown) shells. Io's rock or silicate shell
extends to the surface, while the rock layers of Ganymede and Europa (drawn to correct relative scale) are
in turn surrounded by shells of water in ice or liquid form (shown in blue and white and drawn to the correct
relative scale). PIA01082
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Europa Tidal Heating
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This artist concept illustrates two possible cut-away views through Europa's ice shell. In both, heat escapes, possibly volcanically,
from Europa's rocky mantle and is carried upward by buoyant oceanic currents. If the heat from below is intense and the ice shell is
thin enough (left), the ice shell can directly melt, causing what are called "chaos" on Europa, regions of what appear to be broken,
rotated and tilted ice blocks. On the other hand, if the ice shell is sufficiently thick (right), the less intense interior heat will be
transferred to the warmer ice at the bottom of the shell, and additional heat is generated by tidal squeezing of the warmer ice. This
warmer ice will slowly rise, flowing as glaciers do on Earth, and the slow but steady motion may also disrupt the extremely cold,
brittle ice at the surface. Europa is no larger than Earth's moon, and its internal heating stems from its eccentric orbit about Jupiter,
seen in the distance. As tides raised by Jupiter in Europa's ocean rise and fall, they may cause cracking, additional heating and even
venting of water vapor into the airless sky above Europa's icy surface. Nasa/Photojournal/PIA10131
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Titan
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Huygens Descent
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Titan atmosphere
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Titan: Methane lakes
This image covers the south pole of Titan, which
can be seen as a region of broad smooth
valleys surrounded by rugged terrain. Also seen
in this image are two features interpreted as
lakes Their very dark appearance in the radar
image indicates that they are probably filled
with liquid methane. Other apparently empty
lake basins are seen elsewhere in the radar
swath. Since Titan is currently in its late summer
season in the southern hemisphere, this
interpretation is consistent with a previously
proposed theory that methane fills the lakes
during the winter and evaporates during the
summer, leaving them dry until the next fall.
Intensity in this colorized image is proportional
to how much radar brightness is returned The
colors are not a representation of what the
human eye would see. The lakes, darker than
the surrounding terrain, are emphasized here
by tinting regions of low backscatter in blue.
Radar-brighter regions are shown in tan.
Credit: NASA/JPL
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Titan: lakes/ liquid hydrocarbons
The images on the left (unlabeled at top and labeled
at bottom) were acquired July 3, 2004. Those on the
right were taken June 6, 2005. In the 2005 images,
new dark areas are visible and have been circled in
the labeled version. The very bright features are
clouds in the lower atmosphere (the troposphere).
Titan's clouds behave similarly to those on Earth,
changing rapidly on timescales of hours and
appearing in different places from day to day.
During the year that elapsed between these two
observations, clouds were frequently observed at
Titan's south pole.
It is likely that rain from a large storm created the
new dark areas that were observed in June 2005.
Some features, such as Ontario Lacus, show
differences in brightness between the two
observations that are the result of differences in
illumination between the two observations. These
mosaics use images taken in infrared light at a
wavelength of 938 nanometers. Image resolutions
are several kilometers per pixel.
Credit: NASA/JPL/Space Science Institute
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Titan: sand dunes
Cassini radar sees sand dunes on
Saturn's giant moon Titan (upper photo)
that are sculpted like Namibian sand
dunes on Earth (lower photo). The
bright features in the upper radar photo
are not clouds but topographic features
among the dunes. Image credit: NASA/
JPL - upper photo; NASA/JSC - lower
photo
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Summary
• Europa
- icy satellite
- tidal heating due to an eccentric orbit around Jupiter
- surface features contain evidence that subsurface is heated, leading to two hypothesis:
‣ warm ice subsurface
‣ liquid subsurface
• Titan
- thick atmosphere
‣ no data on its surface prior to Cassini
‣ composed mostly of nitrogen, with methane and ethane clouds
- liquid lakes
‣ hydrocarbons, rained out of the atmosphere
- life?
‣ possibly Titan is similar to Earth in its early days
‣ conditions necessary prior to life flourishing?
‣ conditions will change in distant future, when Sun will become red giant.
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