soaring whistle and hissing static
Polar caps are composed of a light covering of water ice or frost.
Fine Details
of the Icy Surface of Ganymede
Ganymede
The bulk of the satellite is believed to be about half water-ice and half rock. Portions of its surface are relatively bright, clean ice while the other regions are covered with darker "dirty" ice. The darker areas appear to be ancient and heavily cratered, while the lighter regions display evidence of tectonic activity that may have broken up the icy crust. A
thin layer of ozone has been found in Ganymede's surface by Earth (Sw Tellus/Jordan)-based astronomers.Ganymede
sounds of Ganymede
soaring whistle and hissing static
BIG ICY MOON OF JUPITER FOUND TO HAVE
A 'VOICE' AFTER ALL
Jupiter's big moon Ganymede is not only the size of a
planet -- it sounds like one too, as heard in audio
recordings made from data returned by NASA's Galileo
spacecraft released today.
Characterized by a soaring whistle and hissing static,
Ganymede's song reveals that the Solar System's largest moon
is also the only one known to possess a planet-like, self-
generated magnetic cocoon called a magnetosphere, which
shields the moon from the magnetic influence of its giant
parent body, Jupiter (Sw Jupiter).
Using extremely precise data from tracking the
spacecraft, investigators on Galileo's celestial mechanics
team also have been able to confirm that Ganymede's interior
is differentiated, probably having a three-layer structure.
"These data show clearly that Ganymede has differentiated
into a core and mantle, which is in turn enclosed by an ice
shell," said JPL planetary scientist Dr. John Anderson, team
leader on the Galileo radio science experiment.
"At Ganymede, the magnetic field is strong enough to
carve out a magnetosphere with clearly defined boundaries
within Jupiter's magnetosphere, making it the only
'magnetosphere within a magnetosphere' known in the Solar
System," Kivelson said.
http://www.jpl.nasa.gov/galileo
FROSTED RIMS ON GANYMEDE
Bright white areas seen around the circular rims of
high-latitude impact craters on Ganymede in new Galileo
images of that moon are likely water-ice frosts, Galileo
scientists report. Even though the Sun is shining from the
south, the north-facing walls of the ridges and craters are
brighter than the walls facing the Sun. Images of regions
elsewhere on Ganymede show more details of the remarkable
juxtaposition of newer and older fractured and faulted
terrain that characterizes so much of this big moon's
surface. A stereoscopic view of Ganymede has also been
produced with two images of the Galileo Regio region (one was
taken during the first Ganymede flyby in June and the second
was acquired in the September flyby). The image, which was
computer-reconstructed by imaging scientists at JPL, shows
new topographic information about the moon.
Ganymede
frost
On Callisto and Ganymede, the near-infrared mapping
spectrometer found surface features indicating the presence
of hydrated materials, or possibly carbon dioxide frost.
WET AND WILD
Apparently
water ice, from Galileo.
The first midday temperature for Europa, -229
Fahrenheit has allowed the radiometer instrument team to
determine that the moon has a more porous or "fluffy" ice
surface than the other moons. Researchers said that such
porosity indicates Europa's surface is covered with finely
powdered ice grains.
Scientists were surprised by the lack of small craters
visible in the images. Some small craters appear to have been
softened or modified by downslope movement of debris,
revealing ice-rich surfaces.
spacecraft makes its first close approach to Europa, the moon
thought to harbor a liquid ocean beneath its icy surface.
Results from that flyby will be radioed to Earth (Sw Tellus/Jordan) starting in
the last half of December through early February.
The Europa image received from the spacecraft earlier
this week shows the cracked surface of this moon in greater
detail than it has been seen before. The new image shows an
area 150 miles by 140 miles that has been highly disrupted by
fractures and ridges.
Arizona State University planetary scientist Dr. Kelly
Bender of Galileo's imaging team said that symmetric ridges
in the dark bands suggest that Europa's surface crust was
separated and filled with darker material, somewhat analogous
to spreading centers in the ocean basins of Earth (Sw Tellus/Jordan). Although
some impact craters are visible, their general absence
indicates a youthful surface, she said.
The youngest ridges, such as the two features that cross
the center of the picture, have central fractures, aligned
knobs, and irregular dark patches. These and other features
could indicate cryovolcanism, or processes related to
eruption of ice and gases.
Europa
Apparently
RESHAPE EUROPA'S CHAOTIC SURFACE
Ice-spewing volcanoes and the grinding and tearing of
tectonic plates have reshaped the chaotic surface of Jupiter's
frozen moon Europa, images from NASA's Galileo spacecraft reveal.
The images, captured when Galileo flew within just 430 miles
(692 kilometers) of Europa on Dec. 19, were released at a news
briefing today at NASA Headquarters, Washington, DC.
Although the images do not show currently active ice
volcanoes or geysers, they do reveal flows of material on the
surface that probably originated from them, said Galileo imaging
team member Dr. Ronald Greeley of Arizona State University, Tempe.
"This is the first time we've seen actual ice flows on any of
the moons of Jupiter," said Greeley. "These flows, as well as
dark scarring on some of Europa's cracks and ridges, appear to be
remnants of ice volcanoes or geysers."
The new images appear to enhance Europa's prospects as one of
the places in the Solar System that could have hosted the
development of life, said Greeley.
"There are three main criteria to consider when you are
looking for the possibility of life outside the Earth (Sw Tellus/Jordan) -- the
presence of water, organic compounds and adequate heat," said
Greeley. "Europa obviously has substantial water ice, and organic
compounds are known to be prevalent in the Solar System. The big
question mark has been how much heat is generated in the interior.
"These new images demonstrate that there was enough heat to
drive the flows on the surface. Europa thus has a high potential
to meet the criteria for exobiology," Greeley added.
"This doesn't prove that there is an ocean down there under
the surface of Europa, but it does demonstrate that it is a
scientifically exciting place," said Galileo imaging team member
Dr. Robert Sullivan, also of Arizona State University.
The images also reveal a remarkable diversity in the
geological age of various regions of Europa's surface. Some areas
appear relatively young, with smooth, crater-free terrain, while
others contain large craters and numerous pits, suggesting that
they are much older.
The icy crust bears the signs of having been disrupted by the
motion of tectonic plates. "There appear to be signs of different
styles of tectonism," said Greeley. "In many areas we see that
the crust was pulled apart in a spreading similar to the processes
on the sea floor on Earth (Sw Tellus/Jordan). This is different from the tectonic
processes at work on, say, Jupiter's moon Ganymede. This suggests
that Europa's interior may be different from Ganymede's."
Galileo scientists will have a better chance to understand
Europa's interior when the spacecraft gathers gravity data on
another flyby next November. The gravity field is measured by
tracking how the frequency of Galileo's radio signal changes as it
flies past the moon. This was not possible during the recent
flyby because radio conditions were degraded as Jupiter passed
behind the Sun from Earth's point of view.
Europa is crisscrossed by an amazingly complex network of
ridges, according to Sullivan. "Ridges are visible at all
resolutions," he explained. "Closely paired ridges are most
common. With higher resolution, ridges seen previously as
singular features are revealed to be double."
Some of the ridges may have formed by tension in the icy
crust: as two plates pull apart slightly, warmer material from
below might push up and freeze to form a ridge. Other ridges may
have been formed by compression: as two plates push together, the
material where they meet might crumple to form the ridge.
In addition to ice flows and tectonics, Greeley and Sullivan
noted that some areas on Europa seem to have been modified by
unknown processes that scientists are still debating. Greeley
said that some areas, for example, seem to have been modified by
"sublimation erosion" -- the evaporation of water and other
volatiles such as ammonia and methane into the vacuum of space.
"Something is destroying the topography," said Greeley, "and this
sublimation erosion is a good candidate for what is at work."
During last month's encounter, Galileo flew more than 200
times closer to Europa than the Voyager 2 spacecraft did in 1979.
After a swing past Jupiter next week in what mission engineers
call a "phasing orbit," Galileo's next targeted flyby will take it
again past Europa as it passes within 364 miles (587 kilometers)
on Feb. 20.
Europa
Apparently
LATEST IMAGES OF ICY EUROPA AND DEBATE OVER SURFACE
AGE TO BE FEATURED IN APRIL 9 GALILEO BRIEFING
New images of Europa from NASA's Galileo mission
and related animation supporting the theory that the
icy moon of Jupiter may have a subsurface ocean will
be presented at a press briefing on Wednesday, April
9, at 2 p.m. EDT. The briefing will originate from
NASA's Jet Propulsion Laboratory, Pasadena, CA, and
will be carried live on NASA Television.
The latest images were taken during Galileo's
closest flyby of Europa on Feb. 20, 1997, when the
spacecraft came within 363 miles of the Jovian moon
and took very high resolution images of features in
regions never before studied.
The tantalizing new images and data indicate
Europa has a thin ice crust covering either liquid
water or slush. Scientists are intrigued by the
prospect that a slushy concoction of chemicals in this
region could nurture life. The briefing will include
outside experts raising the possibility that Europa's
oceans may contain thermal vents, sea ice and other
phenomena found on Earth (Sw Tellus/Jordan).
The estimated age of Europa's surface also will
be discussed, with controversial new information
leading some scientists to conclude the surface is
much younger than previously believed. As evidence of
that, images will be shown of relatively smooth,
crater-free areas.
NASA Television is available through GE-2,
Transponder 9C at 85 degrees West longitude, vertical
polarization, with a frequency of 3880 Mhz, and audio
of 6.8 Mhz. The new images of Europa will be released
on the Galileo Internet home page at the following URL:
JPL NASA Galileo
Europa-end-
Apparently
NEW IMAGES HINT AT WET AND WILD HISTORY FOR EUROPA
Wed Apr 9 12:22:58 1997
Chunky ice rafts and relatively smooth, crater-free patches
on the surface of Jupiter's frozen moon Europa suggest a younger,
thinner icy surface than previously believed, according to new
images from Galileo's spacecraft released today.
The images were captured during Galileo's closest flyby of
Europa on Feb. 20, 1997, when the spacecraft came within 363 miles
of the Jovian moon. These features, which lend credence to the
idea of hidden, subsurface oceans, also are stirring up
controversy among scientists who disagree about the age of
Europa's surface.
Dr. Ronald Greeley, an Arizona State University geologist and
Galileo imaging team member, said the ice rafts reveal that Europa
had, and may still have, a very thin ice crust covering either
liquid water or slush.
"We're intrigued by these blocks of ice, similar to those
seen on Earth's polar seas during springtime thaws," Dr. Greeley
said. "The size and geometry of these features lead us to believe
there was a thin icy layer covering water or slushy ice, and that
some motion caused these crustal plates to break up."
"These rafts appear to be floating and may, in fact, be
comparable to icebergs here on Earth," said another Galileo
imaging team member, Dr. Michael Carr, a geologist with the U.S.
Geological Survey. "The puzzle is what causes the rafts to
rotate. The implication is that they are being churned by
convection."
The new images of Europa's surface also have sparked a lively
debate among scientists. Galileo imaging team member Dr. Clark
Chapman is among those who believe the smoother regions with few
craters indicate Europa's surface is much younger than previously
believed. In essence, Chapman, a planetary scientist at Southwest
Research Institute, Boulder, CO, believes the fewer the craters,
the younger the region. Clark based his estimate on current
knowledge about cratering rates, or the rate at which astronomical
bodies are bombarded and scarred by hits from comets and asteroids.
"We're probably seeing areas a few million years old or less,
which is about as young as we can measure on any planetary surface
besides Earth," said Chapman. "Although we can't pinpoint exactly
how many impacts occurred in a given period of time, these areas
of Europa have so few craters that we have to think of its surface
as young."
Chapman added, "Europa's extraordinary surface geology
indicates an extreme youthfulness -- a very alive world in a state
of flux."
However, Carr sees things differently. He puts Europa's
surface age at closer to one billion years old.
"There are just too many unknowns," Carr said. "Europa's
relatively smooth regions are most likely caused by a different
cratering rate for Jupiter and Earth (Sw Tellus/Jordan). For example, we believe
that both Earth's moon and the Jovian moon, Ganymede, have huge
craters that are 3.8 billion years old. But when we compare the
number of smaller craters superimposed on these large ones,
Ganymede has far fewer than Earth's moon. This means the
cratering rate at Jupiter is less than the cratering rate in the
Earth-moon system."
Scientists hope to find answers to some of the questions
surrounding Europa and its possible oceans as the Galileo
spacecraft continues its journey through the Jovian system.
"We want to look for evidence of current activity on Europa,
possibly some erupting geysers," Greeley said. "We also want to
know whether Europa's surface has changed since the Voyager
spacecraft flyby in 1979, or even during the time of the Galileo
flybys."
The craft will return for another Europa flyby on Nov. 6,
1997, the final encounter of Galileo's primary mission. However,
eight more Europa flybys are planned as part of Galileo's two-year
extended mission, which also will include encounters with two
other Jovian moons, Callisto and Io.
The Jet Propulsion Laboratory manages the Galileo mission for
NASA's Office of Space Science, Washington, DC.
Images and other data received from Galileo are posted on the
Galileo mission home page on the World Wide Web at URL:
JPL NASA Galileo
Flooding fear after ice volcano erupts
By Roger Highfield, Science Editor
ICELAND remained on alert last night as a volcanic eruption under
Europe's largest glacier threatened to cause widespread flooding along
its south coast. The volcano sent plumes of steam and ash up to
33,000 feet while molten rock spewed from a five-mile fissure. But the
main concern was the melting ice, which sent water pouring into the
Grimsv=F6tn caldera, a crater-like basin underneath the glacier. The water
appeared to be close to filling the caldera lake yesterday and
glaciologists predicted an imminent glacier burst. Icelanders continued
to reinforce barriers along the banks of the Skeidara river and prepared
to dig channels through roads in the threatened region to give the
torrent of water a free path, limiting potential damage to bridges,
power stations and telephone lines. The glacier lies 120 miles east of
Reykjavik and about the same distance south of the Arctic Circle. It is
separated from the coast by a fringe of farmland. Scientists monitoring
the eruption said that enough water to cover a square mile 850 yards
deep had collected under the glacier, bringing the level in the lake to
its highest this century. "It is now at a critical level and should
start to flow out at any time," said a spokesman.
Glacier
James B. Pollack
, conceived that nearly lossless scattering by wavelength-sized particles of
water ice could explain the low microwave emissivity and high radar reflectivity of Saturn's (Sw Saturnus) rings.
Pollack
- Ganymede
- Components of Comets Components of Comets
- Violent Eruptions Violent Eruptions
- Mottled Nucleus Mottled Nucleus
- Hale Bopp Hale Bopp
- Hyakutake Hyakutake
- Halley's Comet Halley's Comet
- Stardust
- Tail
Apparently
Online Comet Page from Sky & Telescope Magazine.
Basics of Space Flight
working?
working?
The blue tail is composed of charged particles, while the broad whiter
is composed of dust particles lit up by the sun.
NASA's Infrared Telescope Facility (IRTF) on Mauna Kea,
HI, will dedicate several days of observing time to study
the release of dust and ice grains from the nucleus of the
[Interrupt Process]are composed primarily of water.
Spectral observations of the molecules vaporized from the
nucleus should provide samples of molecular abundances that
were present at the time of the formation of the Solar
System. The Extreme Ultraviolet Explorer spacecraft will
make observations of neon and helium for comparison with the
water production rates to be measured by the IRTF.
Comet
on the Comet's Surface
During the course of long-term observations, which began in
August 1995, astronomers unexpectedly caught the comet going
through a sudden brief outburst, where, in little more than an
hour, the amount of dust being spewed from the nucleus increased at
least eight-fold. "The surface of Hale-Bopp's nucleus must be an
incredibly dynamic place, with 'vents' being turned on and off as
new patches of icy material are rotated into sunlight for the first
time," Weaver said.
Comet
A Complex,
To their surprise, astronomers found that water ice
sublimates (turns directly from a frozen solid into a gas) at a
different rate than the trace ices, implying that those components
are not contained within the water on the comet. This conclusion
is further supported by Hubble data showing that the rate at which
dust left the nucleus was much different than the sublimation rate
of water. This result is contrary to previous models for a comet's
nucleus, which suggest that the trace components, such as carbon
disulfide ice, are contained inside of the most abundant ice on the
comet, frozen water. As water sublimates, the trace components and
dust should be released at similar rates, but this is not what
Hubble observed.
Comet
Apparently
Hale Bopp
LASCO Comet (from SOHO ) HOME PAGE
This is a large animated GIF file showing the comet's (Hyakutake) motion over six days, April 30 - May 5, 1996
Sol w/ Hyakutake Movie - B&W Gif 1533k.
Hyakutake and CME- Color Gif 477k bytes.
another movie - closeup - same source
Comet Movie (Blue filter) - Color Gif 765k bytes.
X-Ray s Hyakutake .
NASA TO OBSERVE AND PUBLISH IMAGES OF COMET HYAKUTAKE
the release of dust and ice grains from the nucleus of the
comet. These ices are composed primarily of water.
Spectral observations of the molecules vaporized from the
nucleus should provide samples of molecular abundances that
were present at the time of the formation of the Solar
System.
Images from IRTF and many other sources will be posted
here .
Comet
Apparently
This historic photograph shows a wide-angle view of Halley's Comet as it appeared over Flagstaff, Arizona on May 13, 1910.
The streaks at lower left are the city lights of Flagstaff, and the large bright object below the comet is the planet Venus (Sw Venus).
The best known of all comets, Halley orbits the Sun, and travels close enough to be seen from the Earth (Sw Tellus/Jordan) approximately once every 75 years. Its appearances have been recorded at least 30 times over the past 2000 years, and scientists have accurately predicted its return starting with its appearance in 1758.
Comet
Apparently
The fourth Discovery mission,
Stardust, originated from the same group of proposals and was
formally selected in November 1995. Following a February 1999
launch, Stardust is designed to gather first-time samples of
interstellar dust and dust spewed from the comet Wild-2 and
return them to Earth (Sw Tellus/Jordan) in 2006 for detailed analysis.
Comet
Apparently
RELEASE: 97-89
SPACECRAFT WATCH FOR COMET HALE-BOPP TAIL DISRUPTION
watching for a break in Comet Hale-Bopp's plasma ion tail.
ion tail likely would be disrupted when it enters a region
around the Sun known as the "current sheet."
complicated
interaction between the comet and the Sun's influence and magnetic
fields. As a comet comes closer to the Sun, ices from the nucleus
(a porous structure of dust and ice composed of frozen gases) are
continually vaporized, dislodging the dust, which is formed by the
comet's weak gravity into a cloud, called a co
