Norii de pe Saturn

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The New Horizons probe pictures a 290km-high (180 miles) plume from the volcano Tvashtar, which is situated near the north pole of the Jovian moon Io. The probe continues to return stored data from its recent flyby of Jupiter.

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Major space missions move ahead

The European and US space agencies are moving ahead on their next major missions to explore the Solar System.
Nasa has begun choosing a destination for a "flagship" robotic venture along the lines of Cassini-Huygens, which has been exploring Saturn and its moons.
It is considering four targets: the Jupiter system, Jupiter's moon Europa, and Saturn's moons Enceladus and Titan.
The European Space Agency has called for proposals for one flagship mission and another medium-sized mission.
Europa, Titan and Enceladus are also among the destinations expected to be proposed under the European Space Agency's (Esa) "Cosmic Visions" programme of exploration.
Other proposals likely to be submitted include a mission to return soil from a near-Earth asteroid.
Titan resembles a primordial Earth, and it can serve as a laboratory to show us how unusual and complex organic chemistry takes place

Curt Niebur, Nasa
"There are some ambitious projects being proposed," said John Zarnecki, director of the Centre for Earth, Planetary Space and Astronomical Research (Cepsar) at the Open University, UK.
"We've been talking about them for months or even years. Teams are together and proposals are being prepared."
And many of the issues are topics of discussion here in Texas this week at the 38th Lunar and Planetary Science Conference.


Life lessons

Professor Zarnecki is part of an international consortium behind a mission to Europa proposal being prepared for submission to the European Space Agency.

He is also involved with a team hoping to mount a European return to Titan. This time, a probe might survey the saturnian moon's surface by balloon.

The American and European agencies are developing their space exploration programmes separately, but both say co-operation further down the line is a distinct possibility.
Some scientists would like to go back to Titan
Nasa and Esa are looking at similar timescales for the launch of their respective missions. Nasa is planning for a launch date sometime after 2015; Esa plans its missions for the period between 2015 and 2018.
The US space agency (Nasa) has drawn together four science definition teams to investigate one target each. They will scope out how the missions might be performed.
Curt Niebur, discipline scientist at Nasa's headquarters in Washington DC, told the BBC News website: "All three of these worlds hold our interest because of their unusual similarities to Earth and the knowledge they can give us about how life does, or does not, start.
"Chemically, Titan resembles a primordial Earth, and it can serve as a laboratory to show us how unusual and complex organic chemistry takes place."


Under the ice

A probe to Europa has been on the wish lists of planetary scientists for a decade.
Thought to host an ocean of water under its icy shell, this Jupiter moon is considered to be one of the best places in the Solar System to search for extraterrestrial life.

"It has the three ingredients that life needs: liquid water, energy and nutrients," said Dr Niebur.
Europa may have oceans and micro-organisms under its ice
Professor Ron Greeley, a planetary scientist at Arizona State University, has been appointed to co-chair the Nasa science definition team for a Europa mission. He told BBC News: "We fly one flagship roughly every decade; it takes a lot of resources to do that category of mission.
"We will determine what the major science goals are and how to do them. These include what instruments could do the job, what orbits are required, how we could operate in the harsh radiation environment of Europa."
Scientists have long wanted to burrow through Europa's ice to the ocean beneath, but John Zarnecki says that, for now, this may be too ambitious.
He favours a two-stage approach, in which an orbiter is sent first, possibly with ground-penetrating radar, followed later by a lander capable of penetrating the ice.
"Others say we should go for a lander and a penetrator straight away, but I don't know how feasible that is, financially and technically. Landing on Europa is very demanding, you have to brake very hard on approach," he said.

Fast riser

Saturn's moon Enceladus has recently surged up the list of priority targets for exploration.
When the Cassini-Huygens probe arrived at the Saturn system in 2004, it observed water vapour erupting in huge geysers from an active volcanic region at Enceladus' south pole.
This combination of heat and liquid water close to the surface makes it interesting to astrobiologists, scientists who study the origin and evolution of life in the Universe.
Nasa's science definition teams will report back in August.

An independent evaluation will take place over the following few months with a view to choosing a target for the flagship mission.
Scientists have to submit their letters of intent to the European Space Agency by 30 March. They will then need to submit fuller mission proposals by the end of June.
A previous joint Esa-Nasa mission to Europa was dropped following budgetary changes at the US space agency in 2006.


sursa:   http://news.bbc.co.uk/2/hi/science/nature/default.stm

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Hot start explains moon's geysers

The plumes of water that erupt from Saturn's icy satellite Enceladus can be traced back to a radioactive "meltdown" shortly after the moon formed.
The discovery, in 2005, of water vapour spewing from geysers at Enceladus' south pole took scientists by surprise.
How this tiny, ice-covered moon generated the amounts of heat needed to fuel these eruptions was a puzzle.
Now scientists say a short-lived burst of radioactivity early in its history kicked off a slow cooking of its core.
The new model for Enceladus' evolution was presented at the Lunar and Planetary Sciences Conference here in Houston, Texas.


Pocket dynamo

When the Voyager 2 probe visited Saturn in the 1980s, it found that Enceladus was unlike many of the other moons in its neighbourhood, whose pockmarked surfaces bore testament to billions of years of heavy bombardment.
By contrast, Enceladus had a relatively smooth, young surface that must have been renewed by some recently active process.
In 2005, Nasa's Cassini orbiter discovered an active region near the moon's south pole marked by tiger stripe-like features. Geysers were seen at this location to hurl water vapour and ice crystals into space.
Since then, the challenge for researchers has been to figure out how this diminutive ball of ice and rock produced the heat necessary to power these eruptions.

The answer, say Dennis Matson and Julie Castillo-Rogez of Nasa's Jet Propulsion Laboratory in California, probably lies in a brief period of radioactive heating when the moon was a youngster.
The model supports the recent finding that Enceladus' plumes contain molecules that require searing temperatures in order to form.
Dr Castillo-Rogez said the "only way" to achieve such high temperatures was "through the rapid decay of some radioactive species".

Dr Matson said that temperatures in Enceladus' interior could have reached as high as 1,000 Kelvin (727C).
"I don't know if it is that hot today, but it certainly got up that high," he said.


Rapid decay

Enceladus started off 4.5 billion years ago as a jumbled-up ball of ice and rock containing the rapidly decaying radioactive isotopes aluminium-26 and iron-60.
The moon probably acquired these radioactive species from minerals called calcium-aluminium-rich inclusions (CAIs), which formed early in Solar System history and are found today in meteorites.
According to the new model, the decay of these isotopes over a period of about seven million years would have generated enormous amounts of heat.

This heat melted the moon's ice, causing the rocky material to sink to the moon's centre, where it consolidated to form a core.
Once this intense, but short-lived period of heating was over, other effects may have taken over the warming of the moon's interior.
More slowly decaying radioactivity in the core along with the tidal forces exerted on Enceladus by Saturn's gravity may be responsible for the heating which continues today.


Gas detection
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The researchers say their model neatly explains the detection of gaseous nitrogen in the plume expelled from geysers.
Nitrogen is not thought to have been part of Enceladus' original make-up. Instead, Dr Matson and Dr Castillo-Rogez believe it is formed via the breakdown of ammonia, where the warm core and the surrounding liquid water meet.
However, the decomposition of ammonia to form gaseous nitrogen requires temperatures of about 577C (1,070F).
Slowly decaying radioactivity and tidal forces cannot account for such high temperatures alone, but they can when combined with the "hot start" model.
Since the discovery of Enceladus' plume by Cassini, the moon has become a high priority target for future exploration.
With a brew of organic chemicals in the interior, a heat source and liquid water, the moon has all the key ingredients needed for life.



fig 1: The heat emission is associated with the tiger stripe features which mark the southern pole. The temperatures are in Kelvin (zero K equals -273C)

fig 2 :Cassini has seen plumes of material head into space

fig 3 :enceladus  "cold geyser" model

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Probe reveals seas on Saturn moon



Nasa's Cassini probe has found evidence for seas, probably filled with liquid hydrocarbons, at the high northern latitudes of Saturn's moon Titan.
The dark features, detected by Cassini's radar, are much bigger than any lakes already detected on Titan.
The largest is some 100,000 sq km (39,000 sq miles) - greater in extent than North America's Lake Superior.
It covers a greater fraction of Titan than the proportion of Earth covered by the Black Sea.
The Black Sea is the Earth's largest inland sea and covers about 0.085% of our planet's surface.

The newly observed body on Titan covers at least 0.12% of that world's surface. Cassini team members argue that this gives them reason to call it a sea.

Since Cassini's radar has caught only a portion of each of the new features, only their minimum size is known.



Methane and ethane

Titan is the second largest moon in the Solar System and has a diameter that is almost twice that of Earth's Moon.
While there is no definitive proof that these seas contain liquid, their shape, their dark appearance in radar that indicates smoothness, along with other properties, point to the presence of liquids.
The liquids are probably a combination of methane and ethane, given the conditions on Titan and the abundance of methane and ethane gases and clouds in Titan's atmosphere.
"Carl Sagan [the astronomer] said that Titan must be covered with oceans, and that these replenished the atmosphere with methane," explained Charles Wood, chair of space studies at the University of North Dakota, US.
But that vision of hydrocarbon oceans had to be scrapped when Cassini peered through Titan's organic haze and found a chaotic, geologically active surface, but no large bodies of liquid.

Recently, the orbiter started to spot lake-like features at Titan's northerly regions.

"They are limited to about 65 degrees latitude," said Charles Wood, although he added that river-like channels seemed to be everywhere on Titan.
The discovery of these even larger bodies might hold the solution to the problem of replenishment of the atmosphere with methane.
After making these findings, Cassini team members plan to re-point the orbiter's radar instrument during a May flyby so that it can pass directly over the large dark features imaged by the cameras.
The Cassini-Huygens mission is a cooperative project of the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency (Asi).

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Icy map to probe Europa's secrets


Scientists have produced a global geological map of Jupiter's moon Europa, which has been proposed as a destination for a future space mission.
Interest in Europa has been fuelled by indications that a liquid water ocean lurks beneath its outer shell of ice.
The mapping effort will help build a geological history of the enigmatic moon and target future explorations.

Galileo explored the Jupiter system from 1995 to 2003.
The work was presented here at the Lunar and Planetary Science Conference in Houston.
The maps have allowed the scientists to identify several distinct geological units on Europa. Understanding the distribution and age relationships of these units can assist the reconstruction of a geological history for the moon.
Europa's surface is young, active and smooth with few craters. But it is criss-crossed by a network of fractures, thought to be where the icy shell has been prised apart by the tidal forces of Jupiter.

We're trying to figure out what's what on the surface so we can go and explore further - Ron Greeley, Arizona State University

"When we make planetary maps, we're pretty limited by fieldwork, so 'ground truth-ing' is difficult - but not impossible, as we've found with the Mars Rovers," said Professor Ron Greeley, director of planetary geology at Arizona State University (ASU) in Tempe, US.

"We have to rely on remote sensing information. On Earth, this is conventionally done in exploration for oil or mineral deposits. The data is used to make maps to figure out the best places to go and explore.

"That's what we're doing with Europa. We're trying to figure out what's what on the surface so we can go and explore further."



Salty ocean

Voyager 2, launched in 1977, was the first spacecraft to fly past Europa, sending back snatched glimpses of the surface at a resolution of about 2km (1.2 miles) per pixel.
Galileo made multiple flybys of the moon, building up a collection of images at different resolutions, ranging from 12.6 to 0.23km (7.8-0.14 miles) per pixel.
Compiling these pictures into a global map has required painstaking work by Ron Greeley, Thomas Doggett and their colleagues at ASU.

"We do not have global coverage, even at the lowest resolution. It is very non-uniform. Also, the illumination of the surface differs widely from one dataset to another," explained Professor Greeley.

Europa, the fourth largest of Jupiter's satellites, is a high priority for future exploration. Study of its magnetic field by the Galileo probe provided strong evidence for a salty ocean beneath the ice.
The moon contains all the ingredients needed for the emergence of life: liquid water, an energy source (provided by the tidal pull exerted by Jupiter's gravity) and organic chemicals.

If life ever emerged on Europa, researchers believe it could exist in an environment similar to terrestrial deep ocean hydrothermal vents or Antarctica's Lake Vostok.



Mission proposals

Nasa has drawn up science definition teams to assess four potential targets for a "flagship" robotic mission to launch after 2015. These targets are the Jupiter system, Europa and Saturn's moons Enceladus and Titan.
The agency has appointed Ron Greeley and Robert Pappalardo from Nasa's Jet Propulsion Laboratory in California to co-chair a team of about a dozen experts who will set out the major science objectives for a Europa mission.

Europa's distinctive icy shell could be 20km thick

Their work will look at what instruments a spacecraft should take, what orbits would be required for the mission and how the probe might operate in the Jovian moon's harsh radiation environment.
After the four teams report back in the summer, officials at Nasa HQ in Washington DC will evaluate the case for a mission and decide which to carry forward.

In addition, an international consortium is preparing a Europa mission proposal to be submitted under the European Space Agency's (Esa) Cosmic Visions programme of space exploration. This consortium is exploring a potential link-up with Japanese partners.
A "dream" concept for the exploration of Europa would be a robotic probe, perhaps powered by radioactive decay, that could melt through the ice and explore the ocean beneath.

But this would pose formidable technical challenges: the ice shell could be about 20km (12 miles) thick, according to one model.
"Is the technology there to do that? Possibly. My own personal feeling is that it is fantastically ambitious," said Professor John Zarnecki, from the UK's Open University, who is a member of the consortium hoping to mount a European mission to the Jovian moon.
"I think there should be a two-stage approach, beginning with an orbiter, perhaps with ground-penetrating radar and perhaps a way of measuring the gravity field - which is another way to tell what's beneath the surface. Then we go for a lander and a penetrator."

Just getting to Europa is tough, a spacecraft would have to pick up lots of speed and then break hard to reach it. In addition, the harsh radiation environment gives a spacecraft orbiting the moon a lifetime of just 66 days, according to an Esa feasibility study.



fig 1 : On the map, blue represents different plains, green is for chaotic terrain. Also shown are impact craters (yellow), crater ejecta (brown), wide bands (pink), major ridges (blue lines), pits and domes (green dots). Areas with worse than 1.7km/px resolution or no coverage at all are shown in white.

fig 2: Geological features on the surface of Europa could be explained by the existence of a warm, convecting layer of ice several kilometres below a brittle ice crust (A). An alternative model (B) proposes an underlying layer of liquid water with a depth of more than 100km (60 miles).

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Big Auroras on Jupiter


So you thought Northern Lights were big in Alaska? "That's nothing," says Randy Gladstone of the Southwest Research Institute in San Antonio, Texas. "Jupiter has auroras bigger than our entire planet."

Last month, Gladstone and colleagues used NASA's Chandra X-ray Observatory to capture this picture:FIG 1 si FIG 2  ( in raze x)
The purple ring traces Jupiter's X-ray auroras. Gladstone calls them "Northern Lights on steroids. They're hundreds of times more energetic than auroras on Earth."
Chandra has observed Jupiter's auroras many times before, but this recent dataset is exceptional both in length and quality. Gladstone hopes it will help him solve some mysteries lingering for almost 30 years.

Jupiter's auroras were discovered by the Voyager 1 spacecraft in 1979. A thin ring of light on Jupiter's nightside looked like a stretched-out version of our own auroras on Earth. But those early photos merely hinted at the power involved. The real action, astronomers soon learned, was taking place at high-energy wavelengths invisible to the human eye. In the 1990s, ultraviolet cameras on the Hubble Space Telescope photographed raging lights thousands of times more intense than anything ever seen on Earth, while X-ray observatories saw auroral bands and curtains bigger than Earth itself.

Jupiter's hyper-auroras never stop. "We see them every time we look," says Gladstone. You don't see auroras in Alaska every time you look, yet on Jupiter the Northern Lights always seem to be "on."

Gladstone explains the difference: On Earth, the most intense auroras are caused by solar storms. An explosion on the sun hurls a billion-ton cloud of gas in our direction, and a few days later, it hits. Charged particles rain down on the upper atmosphere, causing the air to glow red, green and purple. On Jupiter, however, the sun is not required. "Jupiter is able to generate its own lights," says Gladstone.

The process begins with Jupiter's spin: The giant planet turns on it axis once every 10 hours and drags its planetary magnetic field around with it. As any science hobbyist knows, spinning a magnet is a great way to generate a few volts—it's the basic principle of DC motors. Jupiter's spin produces 10 million volts around its poles.

"Jupiter's polar regions are crackling with electricity," says Gladstone, "and this sets the stage for non-stop auroras."

The polar electric fields grab any charged particles they can find and slam them into the atmosphere. Particles for slamming can come from the sun, but Jupiter has another, more abundant source nearby: the volcanic moon Io, which spews oxygen and sulfur ions (O+ and S+) into Jupiter's spinning magnetic field. ( fig 3 )

Somehow, these ions make their way to Jupiter's poles where electric fields send them hurtling toward the planet below. Upon entering the atmosphere, "their electrons are first stripped away by molecules they run into, but as they slow down they start grabbing electrons back. The 'charge exchange reaction' produces intense X-ray auroras," he explains.

So Jupiter's Northern Lights are, in a sense, volcano powered. Mystery solved? Not quite.

No one knows exactly how volcanic exhaust meanders from Io out through Jupiter's magnetosphere and back to Jupiter's poles. "We're still trying to figure it out," says Gladstone.

But that is a minor detail compared to another, even bigger puzzle: There is an X-ray "pulsar" inside Jupiter's northern auroras. Sometimes Chandra sees it, sometimes not. When it's on, the pulsar emits gigawatt bursts of X-rays with a regular beat of 45 minutes.
Gladstone suspects the pulsar has nothing to do with Io's volcanoes, but instead is caused by the sun. "Maybe Jupiter's magnetic field, when it gets hit by a solar wind gust, rings like a bell with a 45-minute period," he speculates. "There are many other possibilities as well."

The February 2007 dataset may hold important clues. "Chandra observed the auroras for 15 hours, and we weren't the only ones watching," he says. The Hubble Space Telescope, the FUSE satellite, XMM-Newton (a European X-ray observatory), the New Horizons spacecraft and many ground-based observatories were all taking data at the same time. The campaign was timed to coincide with New Horizons flyby of Jupiter—a slingshot maneuver designed to increase its velocity en route to Pluto.

"Jupiter's auroras have never been observed by so many telescopes at once," says Gladstone. "I'm really excited by these data, and the analysis is just beginning."

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Cassini Views Titan from Bottom to Top

Cassini's science instruments studied Titan during the May 28, 2007, flyby. As seen from Earth, Cassini dipped behind Titan near the south pole and re-emerged near the north pole. From this unique vantage point, Cassini's radio science instrument used a radio signal to study the properties of Titan's atmosphere, and the infrared and visible-light cameras imaged a bright surface feature on Titan named Dilmun

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Neon Saturn

In this false-color image, the Cassini spacecraft captures Saturn's glow, represented in brilliant shades of electric blue, sapphire and mint green, while the planet's shadow casts a wide net on the rings.  The colors represent different wavelengths: red is thermal heat originating within the planet; in blue, icy ring particles shimmer in sunlight scattered through the rings; in green, a thick covering of high-altitude hazes strongly reflect sunlight.

This striking false-color mosaic was created from 25 images taken by Cassini's visual and infrared mapping spectrometer over a period of 13 hours, and captures Saturn in nighttime and daytime conditions. The visual and infrared mapping spectrometer acquires data simultaneously at 352 different wavelengths, or spectral channels. Data at wavelengths of 2.3, 3.0 and 5.1 microns were combined in the blue, green and red channels of a standard color image, respectively, to make this false-color mosaic.


On the night side (right side of image), with no sunlight, Saturn's own thermal radiation lights things up. This light at 5.1 microns wavelength (some seven times the longest wavelength visible to the human eye) is generated deep within Saturn, and works its way upward, eventually escaping into space. Thick clouds deep in the atmosphere block that light. An amazing array of dark streaks, spots, and globe-encircling bands is visible instead. Saturn's strong thermal glow at 5.1 microns even allows these deep clouds to be seen on portions of the dayside (left side), especially where overlying hazes are thin and the glint of the sun off of them is minimal. These deep clouds are likely made of ammonium hydrosulfide and cannot be seen in reflected light on the dayside, since the glint of the sun on overlying hazes and ammonia clouds blocks the view of this level.

A pronounced difference in the brightness between the northern and southern hemispheres is apparent. The northern hemisphere is about twice as bright as the southern hemisphere. This is because high-level, fine particles are about half as prevalent in the northern hemisphere as in the south. These particles block Saturn's glow more strongly, making Saturn look brighter in the north.

[lylyt_ice]

   Egal ce spun toti ,eu inclin sa pledez pentru "lampa Chinezeasca"

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Two more active moons around Saturn


Saturn's moons Tethys and Dione are flinging great streams of particles into space, according to data from the NASA/ESA/ASI Cassini mission to Saturn. The discovery suggests the possibility of some sort of geological activity, perhaps even volcanic, on these icy worlds.

The particles were traced to the two moons because of the dramatic movement of electrically charged gas in the magnetic environs of Saturn. Known as plasma, the gas is composed of negatively charged electrons and positively charged ions, which are atoms with one or more electrons missing. Because they are charged, the electrons and ions can get trapped inside a magnetic field.
Saturn rotates around itself in just 10 hours and 46 minutes. This sweeps the magnetic field and the trapped plasma through space. Just like a child on a fast-spinning merry-go-round, the trapped gas feels a force trying to throw it outwards, away from the centre of rotation. 

Soon after Cassini reached Saturn, in June 2004, it revealed that the planet's hurried rotation squashes the plasma into a disc and that great fingers of gas are indeed being thrown out into space from the disc's outer edges. Hotter, more tenuous plasma then rushes in to fill the gaps.
Now, Jim Burch of the Southwest Research Institute, USA, and colleagues have made a careful study of these events using the Cassini Plasma Spectrometer (CAPS). They have shown that the direction of the ejected electrons points back towards Tethys and Dione. "It establishes Tethys and Dione as important sources of plasma in Saturn's magnetosphere," says Burch.

UUntil this result, among Saturn's inner moons only Enceladus was known to be an active world, with huge geysers spraying gases hundreds of kilometres above the moon's surface. "This new result seems to be a strong indication that there is activity on Tethys and Dione as well," says Andrew Coates from the Mullard Space Science Laboratory, University College London, and a collaborator on this latest work.

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Hydrocarbons, Necessary For Life, Found On Saturn's Moon Hyperion



NASA's Cassini spacecraft has revealed for the first time surface details of Saturn's moon Hyperion, including cup-like craters filled with hydrocarbons that may indicate more widespread presence in our solar system of basic chemicals necessary for life.
Te up-close view of Hyperion shows a low-density body blasted by impacts over eons. Scientists believe that the spongy appearance of Hyperion is caused by a phenomenon called thermal erosion, in which dark materials accumulating on crater floors are warmed by sunlight and melt deeper into the surface, allowing surrounding ice to vaporize away. (Credit: NASA/JPL/Space Science Institute)Hyperion yielded some of its secrets to the battery of instruments aboard Cassini as the spacecraft flew close by in September 2005. Water and carbon dioxide ices were found, as well as dark material that fits the spectral profile of hydrocarbons.

A paper appearing in the July 5 issue of Nature reports details of Hyperion's surface craters and composition observed during this flyby, including keys to understanding the moon's origin and evolution over 4.5 billion years. This is the first time scientists were able to map the surface material on Hyperion.

"Of special interest is the presence on Hyperion of hydrocarbons – combinations of carbon and hydrogen atoms that are found in comets, meteorites, and the dust in our galaxy," said Dale Cruikshank, a planetary scientist at NASA's Ames Research Center, Moffett Field, Calif., and the paper's lead author. "These molecules, when embedded in ice and exposed to ultraviolet light, form new molecules of biological significance. This doesn't mean that we have found life, but it is a further indication that the basic chemistry needed for life is widespread in the universe."

Cassini's ultraviolet imaging spectrograph and visual and infrared mapping spectrometer captured compositional variations in Hyperion's surface. These instruments, capable of mapping mineral and chemical features of the moon, sent back data confirming the presence of frozen water found by earlier ground-based observations, but also discovered solid carbon dioxide (dry ice) mixed in unexpected ways with the ordinary ice.

Images of the brightest regions of Hyperion's surface show frozen water that is crystalline in form, like that found on Earth.

"Most of Hyperion's surface ice is a mix of frozen water and organic dust, but carbon dioxide ice is also prominent. The carbon dioxide is not pure, but is somehow chemically attached to other molecules," explained Cruikshank.

Prior spacecraft data from other moons of Saturn, as well as Jupiter's moons Ganymede and Callisto, suggest that the carbon dioxide molecule is "complexed," or attached with other surface material in multiple ways. "We think that ordinary carbon dioxide will evaporate from Saturn's moons over long periods of time," said Cruikshank, "but it appears to be much more stable when it is attached to other molecules."

"The Hyperion flyby was a fine example of Cassini's multi-wavelength capabilities. In this first-ever ultraviolet observation of Hyperion, the detection of water ice tells us about compositional differences of this bizarre body," said Amanda Hendrix, Cassini scientist on the ultraviolet imaging spectrograph at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Hyperion, Saturn's eighth largest moon, has a chaotic spin and orbits Saturn every 21 days. The July 5 issue of Nature also includes new findings from the imaging team about Hyperion's strange, spongy-looking appearance.

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Saturn's Old Moon Iapetus Retains Its Youthful Figure



Saturn's distinctive moon Iapetus (eye-APP-eh-tuss) is cryogenically frozen in the equivalent of its teenage years. The moon has retained the youthful figure and bulging waistline it sported more than three billion years ago, scientists report.



"Iapetus spun fast, froze young, and left behind a body with lasting curves," said Julie Castillo, Cassini scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Unlike any other moon in the solar system, Iapetus is the same shape today as it was when it was just a few hundred million years old; a well-preserved relic from the time when the solar system was young.

Cassini flew by Iapetus in early 2005 and discovered the moon had a walnut shape, bulging at its midsection. On top of that it has a chain of mountains located exactly along its equator.

Scientists now think the moon's bulging midriff and slow spin rate point to heating from long-extinct radioactive elements present when the solar system was born.

"We've modeled how Iapetus formed its big, spin-generated bulge and why its rotation slowed down to its present nearly 80-day period. As an unexpected bonus, Iapetus also told us how old it was," said Dennis Matson, Cassini project scientist at JPL. "You would expect a very fast-spinning moon to have this bulge, but not a slow-spinning moon, because the bulge would have been much flatter."

Scientists calculate Iapetus originally rotated much faster--at least five hours, but less than 16 hours per revolution. The fast spin gave the moon an oblate shape that increased the surface area (in the same way the surface area of a round balloon stretches when the balloon is pressed into an oblate shape). By the time the rotation slowed down to a period of 16 hours, the outer shell of the moon had frozen. Furthermore, the surface area of the cold moon was now smaller. The excess surface material was too rigid to go back smoothly into the moon. Instead, it piled up in a chain of mountains at the equator.

"Iapetus' development literally stopped in its tracks," said Castillo. "In order for tidal forces to slow Iapetus to its current spin rate, its interior had to be much warmer, close to the melting point for water ice." The challenge in developing a model of how Iapetus came to be "frozen in time" has been in deducing how it ever became warm enough to form a bulge in the first place, and figuring out what caused the heat source to turn off, leaving Iapetus to freeze.

The heat source had to have a limited life span, to allow the moon's crust to rapidly become cold and retain its immature shape. After looking at several models, scientists concluded that the heat came from its rocks, which contain short-lived radioactive isotopes aluminum-26 and iron-60 (which decay very rapidly on a geologic timescale). Since these elements decay at a known rate, this allowed scientists to "carbon date" Iapetus by using aluminum-26 instead of carbon. Scientists calculate the age of Iapetus to be roughly 4.564 billion years old.

Evidence for these same isotopes (aluminum-26 and iron-60) has been found in meteorites formed in the inner solar system. Therefore, there is a possibility of comparing the early chronology of the outer solar system with other objects in the inner solar system, such as Earth, Earth's moon and asteroids.

"This is the first direct evidence of the early spin history for a satellite in the outer solar system. It teaches us more about how the speed of a body's rotation influenced its evolution, and broadens our knowledge of the early history of outer planet satellites," said Matson.

Credit: NASA/JPL/Space Science Institute)

[Curiosul]

Intrucat vad ca degeaba scrie: "Sectiunea de limba romana" ca apar mesaje in engleza atunci pun si eu un articol interesant despre norii lui Saturn in limba straina pe care o stiu cel mai bine daca tot nu conteaza ca aici e sectiunea in limba romana:


Сатурн - шестая по удаленности от Солнца и вторая после Юпитера по размеру планета Солнечной системы. Известен больше всего опоясывающими его яркими кольцами. Легко различим невооруженным глазом; планета известна с доисторических времен.

Сатурн - самая дальняя планета, которую можно увидеть невооруженным глазом - Галилей в 1610 году впервые наблюдал ее с помощью подзорной трубы и обнаружил по обеим сторонам диска 2 меньших по размеру "тела". И только в 1656 году Христиан Гюйгенс объяснил истинную природу этих тел, выдвинув гипотезу о существовании вокруг планеты кольца.

В 1675 году Кассини удалось разглядеть внутри кольца разделительную полосу, получившую в честь итальянского астронома название; щель Кассини. Все тот же Кассини открыл, кроме того, пересекающие планету параллельные полосы, похожие на полосы Юпитера, только менее явные.

В конце XVIII века Уильям Гершель впервые вычислил период вращения Сатурна на основе изучения ряда характеристик этих полос - 10 ч 16 мин, что почти совпадает с истинным периодом - 10 ч 13 мин.

Вблизи Сатурна побывало три зонда. Первым был "Пионер-1", который после исследования Юпитера пролетел недалеко от Сатурна в сентябре 1979 года. Фотографии, сделанные зондом, позволили познакомиться с невидимыми с Земли кольцами и маленьким спутником.

Вторым прибывшим к планете зондом был "Вояджер-1", приблизившийся к ней в ноябре 1980 года на расстояние 64 000 км. Он передал данные об основных спутниках. "Вояджер-2" подлетел к Сатурну в августе 1981 года и должен был проследовать к Урану и Нептуну, имея совершенно иную орбиту, чем у его зонда-собрата.

Орбитальная и физическая характеристика. Сатурн - вторая от Солнца из четырех газообразных планет Солнечной системы. У него такая же структура, как и у Юпитера, и даже одинаковый элементный состав: водород и гелий.

По модели внутренней структуры у Сатурна имеется каменистое ядро, вокруг которого находится слой металлического водорода, а выше - слой молекулярных водорода и гелия, смыкающийся с нижними слоями атмосферы. Одна из особенностей планеты - очень низкая, наименьшая из всех планет Солнечной системы плотность - она ниже плотности воды. Одним из подтверждений этого факта является форма планеты, кажущейся приплюснутой на полюсах и очень сильно раздутой на экваторе. Полярный диаметр почти на 10% меньше экваториального.

Сатурну требуется 29,5 лет для полного оборота вокруг Солнца. Он находится на среднем расстоянии от нашей звезды в 9,5 АЕ, то есть в 9,5 раз дальше от Солнца, чем Земля. На такое расстояние доходит очень малое количество солнечного света - в 90 раз меньше, чем количество света, доходящего до нашей планеты.

[Arckadii]

Iata traducerea in engleza a textului expus de Curiosul in limba rusa:


"Saturn - sixth on the distance from the Sun and second in size after Jupiter planet solar system. Known most surrounding its bright rings. Easy to discern the naked eye; planet known since prehistoric times.

Saturn - the long-distance planet, which can be seen naked eye - Galileo in 1610 for the first time saw it through pipes and podzornoy found on both sides of the disc 2 smaller "body". I only Christian Huygens in 1656 explained the true nature of the bodies, making the hypothesis of the existence of rings around the planet.

In Cassini in 1675 managed to discern the dividing strip inside the ring, which has received the honour in the name of the Italian astronomer; crack Cassini. All the same Cassini opened, in addition, parallel bands crossing the planet similar to the bands of Jupiter, just less obvious.

At the end of the XVIII century William Herschel first rotation period of Saturn calculated on the basis of examination of a number of characteristics of these bands - 10 hours 16 minutes, almost the same as the genuine period - 10 h 13 min.

Near the three visited Saturn probe. The first was the Pioneer-1, which, after a study of Jupiter flew close to Saturn in September 1979. Photos made probe allowed to get acquainted with invisible from the Earth rings and small satellite.

The second arrived to the planet probe was Voyager-1, draws near to it in November 1980, at a distance of 64000 km. He conveyed the major satellites. Voyager-2 "flew to Saturn in August 1981 and had to go to Uranus and Neptune, with an entirely different orbit than that of his fellow-probe.

Orbital and physical characteristics. Saturn - the second of four from the Sun gaseous planets of the solar system. He has the same structure as that of Jupiter, and even the same elemental composition: hydrogen and helium.

According to the model of the internal structure of Saturn has a rocky nucleus around which is a layer of metallic hydrogen, and above - a layer of molecular hydrogen and helium, with the lower layers smykayuschiysya atmosphere. One of the features of the planet - is very low, the lowest of all the planets of the solar system density - less than the density of water. One of the confirmation of this fact is in the world, seemingly priplyusnutoy at the poles and is highly inflated at the equator. Polar diameter of almost 10% less than the equatorial.

Saturn is required 29.5 years for a full traffic around the Sun. He is on the average distance from the star in our AE 9.5, that is, 9.5 times further from the Sun than the Earth. At a distance comes a very small amount of sunlight - in 90 times less than the number of light before reaching the planet."


Intrucat engleza este o limba cu influente mult mai mari decat limba rusa, am sa va rog sa incercati sa o folositi.
Pentru texte scrise in alte limbi, va invit sa folositi cu incredere GOOGLE TRANSLATE http://www.google.com/translate_t .
Are 2 optiuni interesante: 1. traducerea integrala a unui text dintr-o alta limba in engleza
                                   2. traducerea completa a unui site dintr-o alta limba in engleza.

Ark

[pri3st3ss]

Saturn îºi ascunde inelele!


Saturn, ,,bijuteria sistemului solar", la a cãrui vedere pânã ºi astronomii veterani nu se pot opri sã nu suspine, pare sã-ºi piardã inelele, tendinþa fiind observatã de experþi din întreaga lume.

Ampla sa reþea de inele se concentreazã rapid într-o linie subþire. ,,Inelele s-au îngustat considerabil în cursul anului trecut", explicã Efrain Morales Rivera, un astronom amator din Aguadilla, Puerto Rico. ,,Diviziunea Cassini (o ,,pauzã" neagrã între inele) a devenit foarte greu de vãzut", a adãugat el. Acum aproximativ 400 de ani, acelaºi fenomen l-a uimit ºi pe Galileo.

Privind printr-o lunetã primitivã, el a descoperit inelele lui Saturn în 1610, anunþând imediat lumea despre existenþa unei ,,minuni foarte stranii". Un an mai târziu, el a observat cu o uimire ºi mai mare cã inelele tind sã disparã. În 1612 ele pãreau sã fi dispãrut cu totul, iar Galileo a renunþat sã mai priveascã spre Saturn. De fapt, spun specialiºtii NASA, inelele nu dispar, ci se aºazã într-un plan aproape perpendicular pe cel al observatorilor de pe Terra, fiind deci mai greu de vãzut.

Explicaþia stã în miºcarea de revoluþie a planetei Saturn în jurul Soarelui, fenomenul repetându-se la fiecare 14-15 ani. În clipa de faþã, inelele saturniene continuã sã se ,,subþieze", urmând ca pe 4 septembrie 2009 ele sã fie aproape invizibile. Momentul este ideal, spun astronomii, pentru mai buna observare a sateliþilor lui Saturn, precum ºi a inelelor exterioare mai subþiri, greu de distins în condiþii ,,normale".


sursa: evenimentul zilei