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Titan i zivot na njemu
Earth and Saturn's moon Titan show striking similarities because both occupy "sweet spots" in our Solar System, researchers have said.
Many processes that occur on Earth also take place on this moon, say scientists participating in the US-European Cassini-Huygens mission.
Wind, rain, volcanism and tectonic activity all seem to play a role in shaping Titan's surface.
One scientist even sees a way that life could survive on the freezing world.
"Titan is perhaps the most Earth-like place in the Solar System other than Earth, in terms of the balance of processes," says Jonathan Lunine, of the University of Arizona, US, who is an interdisciplinary scientist for Cassini-Huygens.
"Wind-driven processes, river channels, evidence of rain, possible lakes and geological features that may have to do with volcanism and tectonism."
Different chemistry
But the chemistry that drives these processes is radically different between the two worlds. For example, methane seems to perform many of the same roles on Titan that water plays on Earth.
Dr Lunine believes that Earth and Titan both have similar processes occurring because they occupy "sweet spots" in the Solar System. Being in one these spots requires striking a balance between size, or mass, and distance from the Sun.
To demonstrate the idea, Dr Lunine considered three planets in the inner Solar System: Venus, Earth and Mars.
The mass of a body corresponds to an ability to sustain heat flow from its interior, while distance from the Sun is correlated with the ability to retain liquid water, a driver of geological activity on Earth.
Venus is about the same size as Earth. But it is so close to the Sun that any water it had must have boiled off. As such, there is no hydrological cycle and no tectonic activity, says Lunine.
Mars is distant enough from the Sun to retain water. But its small size caused it to cool quickly, turning water to ice and ending large-scale geological activity. Earth occupies an intermediate position - the "sweet spot".
The researcher then turned to three bodies in the outer Solar System: Ganymede, Titan and Triton. The chemistry is different, but similar principles apply.
Jupiter's moon Ganymede, the closest of the three to the Sun, is similar in size to Titan, but lacks the methane and nitrogen that drive liquid processes on the Saturnian moon: "It's a kind of baked out version of Titan," said Lunine.
Neptune's moon Triton, much further from the Sun than both Ganymede and Titan, possesses methane and nitrogen. But its small size caused them to freeze, ending any prospect of geological activity.
Scientists have been revealing new details about Titan at the meeting in Cambridge. Ralph Lorenz of the University of Arizona, US, said that the river channels and flows on Titan were fashioned by "monsoon" events.
'Catastrophic rains'
It takes a relatively long time for methane to build up to a point where it can rain down on Titan's surface. Scientists, therefore, think rains are only occasional, but catastrophic, when they occur.
Evidence also suggests Titan is constantly being resurfaced by a fluid mixture of water and ammonia spewed out by volcanoes and hot springs, explaining why Titan is not littered with impact craters like its neighbours
A surface feature called Ganesa Macula may show just such a flow emanating from a volcanic crater.
The moon's icy surface is also covered with a film, or patina, of organic compounds, Cassini-Huygens data shows.
One researcher has even proposed a way for life to survive on the giant Saturnian satellite. It is too cold for organisms to survive on the surface of Titan, where temperatures are about -178C (-289F).
But David Grinspoon, of the Southwest Research Institute, US, says organisms could occupy specific niches, such as hot springs. They could use acetylene, in reaction with hydrogen gas, to release enough energy to power metabolism, and possibly to heat their environments.
The Cassini spacecraft entered orbit around Saturn on 1 July, 2004, on a mission to explore the ringed planet and its satellites.
In December, it released the piggybacked Huygens probe on a collision course with Titan. Two weeks later, Huygens tumbled through the moon's atmosphere and made a successful touchdown on the surface.
New results from the mission were presented at the American Astronomical Society Division of Planetary Sciences meeting in Cambridge, UK.
Ovde
Dopuna: 19 Sep 2005 11:14
Titanovo juzno more
The first sea discovered on any surface other than Earth's may have been found on Saturn’s moon Titan.
New radar images from the Cassini spacecraft, which made its eighth close approach to the moon on 7 September, have revealed what appears to be a very distinct shoreline, fed by meandering channels carved deeply in the surrounding terrain.
The dark, flat region next to the bright shoreline "is the area where liquid or a wet surface has most likely been present, now or in the recent past," says Steve Wall, Cassini radar team deputy leader from NASA-JPL.
And several long sinuous channels can be seen cutting through the bright region and ending at the shoreline, suggesting the existence of an Earth-like cycle of evaporation, rainfall and river systems to carry the liquid back to the sea. But instead of water, the liquid in this case is believed to be methane, kept liquid at Titan's -179°C. surface temperature.
Thick atmosphere
Seas of liquid methane, perhaps mixed with other hydrocarbons, had long been expected on Titan, the second-largest moon in the solar system. It is also the only moon with a thick atmosphere - thicker than Earth's.
Seas seemed necessary to explain the amount of methane seen in Titan's atmosphere. The fact that no clear evidence for such seas had been found was one of the big mysteries of the Cassini mission.
"We've been looking for evidence of oceans or seas on Titan for some time," Wall says. The quest was one of the main goals of the four-year Cassini mission. The discovery of the new features suggests Titan may indeed have periodic episodes of methane rainfall.
Ellen Stofan, another radar team scientist, says the network of bright channels indicate "that fluids, probably liquid hydrocarbons, have flowed across this region".
Some of the channels extend more than 100 km, says Larry Soderblom of the US Geological Survey in Flagstaff, Arizona. The channels appear to be of two different types, some long and deep with few tributaries, others forming denser networks. "Some of them may have been fed by springs, while others are more complicated networks that were likely filled by rainfall," Soderblom said.
Vise
Dopuna: 29 Sep 2005 11:52
Casssini proleteo pored Hyperion-a
Just two days after Cassini visited Saturn's moon Tethys, it has flown past Hyperion, one of the smaller and odder moons of the ringed planet.
Hyperion is potato-shaped: 360 kilometres long, but only about 250 kilometres across. Its rotation is chaotic, tumbling unpredictably under the influence of Saturn's and Titan's gravity. And it is exceptionally dark for a Saturnian moon, reflecting only 30% of the light that falls on it, with a distinctly red tint.
The biggest question for Cassini to answer is why Hyperion is so misshapen when other asteroids and moons of about this size are much more spherical. One theory is that it is merely a fragment of a larger moon that was shattered in a violent impact.
Cassini's pictures certainly show a tortured world, riven by craters and girdled by a giant cliff face tens of kilometres high.
The new images were gathered early on Monday morning, from as close as 500 kilometres to Hyperion's surface. During the flyby, Cassini's radar also measured slight changes in the speed of the spacecraft. This will give an idea of the strength of Hyperion's gravity, and therefore its mass. Mission scientists hope to discover whether the moon is solid rock or a loosely packed "rubble pile".
The Cassini team should also be able to map the chemical make-up of Hyperion's surface to discover whether it is dusted with dark material drifting in from Saturn’s sooty outer moon, Phoebe.
Ovde
Dopuna: 05 Okt 2005 12:44
Cassini snimio sundjerasti Hyperion
It may have the look of a giant sponge, but this is Saturn's moon Hyperion, as pictured by the Cassini spacecraft.
The US-European probe has just made a flyby of the satellite, crossing its surface at a distance of just 500km.
The surface is speckled with impact craters which scientists say have been modified by some process, not yet understood, to create the strange look.
Much of the interior of Hyperion is empty space, suggesting it is little more than a pile of space rubble.
Researchers say they are keen to learn the nature of the dark material which seems to cover the floor of some craters.
Also in Cassini's sights recently has been the moon Tethys. It is much bigger.
Vise
Dopuna: 12 Okt 2005 11:39
Titanova mrlja je povrsinska sminka
A 300-mile-wide patch that outshines everything else on Titan at long infrared wavelengths appears not to be a mountain, a cloud or a geologically active hot spot, University of Arizona scientists and Cassini team members say.
"We must be looking at a difference in surface composition," said Jason W. Barnes, a postdoctoral researcher at UA's Lunar and Planetary Lab. "That's exciting because this is the first evidence that says not all of the bright areas on Titan are the same. Now we have to figure out what those differences are, what might have caused them."
When NASA's Cassini spacecraft flew by Titan on March 31 and again on April 16, its visual and infrared mapping spectrometer saw a feature that was spectacularly bright at 5-micron wavelengths just southeast of the continent-sized region called Xanadu.
The bright spot occurs where Cassini's visible-wavelength imaging cameras photographed a bright arc-shaped feature approximately the same size in December 2004 and February 2005.
Vise
Dopuna: 19 Okt 2005 11:18
Ledeni Dion snimljen izbliza
The Cassini spacecraft has captured a stunning image of Saturn's moon Dione against the golden hue of the ringed planet.
Imaging scientists used the blue, green and infrared filters to approximate the colours as the eye would see them.
The spacecraft was nearly in the same plane as Saturn's rings when the view was obtained on 11 October.
Cassini arrived in orbit around Saturn on 1 July 2004 on a four-year mission to explore the planet and its moons.
The $3.2bn mission is a joint venture between the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency (Asi).
Dione orbits about 337,400km (about 234,500 miles) from Saturn. The moon has a diameter of 1,118km (695 miles).
The heavily cratered body is the second densest satellite of Saturn.
Ovde
Dopuna: 31 Okt 2005 22:21
Cassini snimio mesto sletanjana Titanu
The US Cassini spacecraft will return images of the landing zone on Saturn's moon Titan where Europe's Huygens probe touched down earlier this year.
Scientists hope Cassini's flyby will put in context the images returned by Huygens when it parachuted down through Titan's atmosphere on 14 January.
On Friday, the US spacecraft passed Titan from 1,353km (841 miles) up, using radar to peer at its surface.
Cassini released Huygens on 25 December 2004 for its rendezvous with Titan.
The US probe carried Huygens with it on the seven-year voyage from Earth to Saturn, which ended on 1 July 2004, when Cassini entered orbit around the ringed planet.
This is Cassini's ninth planned flyby of Saturn's large moon.
The spacecraft's radar imaged the dark terrain west of a continent-like feature on Titan called Xanadu, which includes the Huygens landing site.
The Cassini-Huygens mission is a co-operative project between the US space agency (Nasa), the European Space Agency (Esa) and the Italian space agency (Asi).
Ovde
Dopuna: 18 Nov 2005 22:41
Blizak susret
The Cassini spacecraft has captured a striking image of Saturn's moons Dione and Tethys passing each other across the planet's ring system.
The larger moon in the foreground is Dione, which measures 1,126km (700 miles) across, and the smaller moon is the 1,071km- (665-mile-) wide Tethys.
The image was taken in visible light with Cassini's narrow-angle camera on 22 September 2005.
Cassini is at a distance of about 860,000km from Dione in the photo.
The dark groove, or division, that can be seen in the rings shares its name with the orbiting spacecraft.
Italian astronomer Jean Dominique Cassini (1625 -1712) made many observations of Saturn and its moons, discovering the Cassini Division in 1675.
Since entering orbit around Saturn on 1 July 2004, the spacecraft has made two flybys of Dione and five of Tethys.
The pass of Dione revealed a surface covered by craters and fractures exposing bright material to the surface. It is thought to be largely composed of water-ice, with a rocky core.
Cassini's flyby of Tethys showed up a huge crater called Odysseus and a giant fissure called Ithaca Chasma which is roughly 65km (40 miles) wide, and covers three-fourths of Tethys' circumference.
Scientists think the enourmous trench could have been created by the moon's liquid crust hardening before its interior.
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).
Ovde
Dopuna: 29 Nov 2005 22:18
Cassini snimio Saturnov mesec
NASA's Cassini spacecraft has captured unique views of two of Saturn's moons. The probe’s first close encounter with the large moon Rhea was somewhat eclipsed by a sidelong snapshot of the moon Enceladus, revealing active volcanic plumes above its surface.
On a previous, much closer pass by Enceladus, Cassini detected that the south pole of Enceladus is spewing out a vast plume of water vapour that stretches hundreds of kilometres from the moon's surface and keeps Saturn's E-ring topped up – but it has now captured the first images of this activity. On Sunday, 27 November, Cassini was positioned so that the Sun was behind the moon, causing one side of Enceladus to be illuminated as a fine crescent, with its volcanic plumes backlit.
Enceladus is only the third body in the solar system to show signs of active volcanism, besides Earth and Io, Jupiter's moon. Even though this volcanism is relatively gentle, planetary scientists cannot yet work out what is driving it. The new pictures could help by revealing the muzzle velocity of the moon's plumes.
Vise
Dopuna: 01 Dec 2005 10:27
Titan
Saturn's planet-size moon Titan has dramatic weather, with turbulent high-altitude winds, periodic floods of liquid methane and possibly lightning, scientists said Wednesday in describing a world that may look like Earth before life developed.
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