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Old 01-12-2012, 11:05 PM   #76
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CICLOPS: Rev160: Jan 16 - Feb 9 '12:
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Cassini continues its exploration of the Saturn system with the 24-day Rev160, which begins on January 16 at its farthest distance from the planet. This point is also called the orbit's apoapse. At this point, Cassini will be 2.90 million kilometers (1.80 million miles) from Saturn's cloud tops. The spacecraft is in the middle of the first equatorial phase of the Cassini Solstice Mission, which lasts until May 2012. During this phase, the spacecraft's orbits lie within the equatorial plane of the planet, providing opportunities to encounter Saturn's numerous moons, image the rings edge-on, and look at Saturn's cloud tops without the rings obscuring the view. Sixty ISS observations are planned for Rev160, the vast majority dedicated to an encounter with Titan and Saturn storm monitoring.

ISS begins its observations for Rev160 a day after apoapse on January 17 with a quick observation of Saturn and its faded northern hemisphere storm. Three more such observations are planned that day. These "Storm Watch" observation sequences are designed to take advantage of short, two-minute segments when the spacecraft turns the optical remote sensing (ORS) instruments back to Saturn as a waypoint between other experiments' observations. These sequences include blue, clear, two methane band, and one full-frame, continuum band filter images. Twenty-two more are planned between January 18 and 25, while seven are planned between February 6 and 8. Between the first two storm watch observations on January 17, ISS will image Titan's Fensal-Aztlan region from a distance of 3.94 million kilometers (2.45 million miles) in an effort to look for clouds in the moon's atmosphere as part of the "Titan Monitoring Campaign". ISS will take a look at Titan again on January 18, this time from a distance of 2.23 million kilometers (1.39 million miles). After the Titan observation on January 17, ISS will acquire a pair of Saturn cloud tracking observations. Both last for two hours using sets of images taken 10 minutes apart in order to measure wind speeds in Saturn's atmosphere by tracking clouds. Four more of these will be taken on January 19 and 20, though each of these later Saturn wind observations will last five hours rather than two. Cassini takes another "Titan Monitoring Campaign" observation on January 20 from a distance of 2.87 million kilometers (1.78 million miles), looking for clouds across the moon's trailing hemisphere.

On January 21, ISS will observe different latitudes of Saturn's atmosphere at low, moderate, and high emission angles to study again Saturn's upper haze layers and their effects on our ability to observe lower-altitude cloud structures. A similar observation will be taken on January 26. On January 22, ISS will image Titan's Senkyo, Garotman Terra, Tollan Terra, and Yalaing Terra regions from a distance of 3.20 million kilometers (1.99 million miles) in an effort to look for clouds in the moon's atmosphere. This observation also will be useful to see if the remnant bright spot in Yalaing Terra from the late 2010 "Arrow Storm" remains. A similar observation taken from a distance of 3.06 million kilometers (1.90 million miles) will be taken on January 24 and will cover the sub-Saturn hemisphere. On January 23, the Composite Infrared Spectrometer (CIRS) will observe Saturn for 22 hours while ISS rides along, taking a set of images ever couple of hours. Afterward, ISS will observe Siarnaq for 12 hours in order to pin down the orientation of this small, outer satellite's north pole axis.

On January 28 at 18:30 UTC, Cassini will reach periapse, its closest point to Saturn, for Rev160 at an altitude of 206,310 kilometers (128,200 miles). The only ISS observation planned for this period is a ride along observation with the Visual and Infrared Mapping Spectrometer (VIMS). ISS will acquire a series of narrow-angle-camera images of Saturn's night side to look for lightning.

Two days after periapse, Cassini encounters Titan on January 30 at 13:40 UTC for the 82nd time. This is the second of nine Titan flybys planned for 2012 with the next encounter scheduled for February 19. T81 is a high-altitude flyby with a close-approach distance of 31,131 kilometers (19,343 miles). This flyby will allow for imaging of Adiri and the southern anti-Saturn hemisphere regions of Titan outbound from the encounter. Before the encounter, CIRS and the Ultraviolet Imaging Spectrometer (UVIS) will acquire spectral scans of Titan's night side. First, CIRS will scan across Titan using its far-infrared channel. Next, UVIS will acquire an extreme and far-ultraviolet scan followed by a stare at the bright limb of Titan.

At closest approach, control of spacecraft pointing will switch to ISS with the Visual and Infrared Mapping Spectrometer (VIMS) riding along. This flyby is one of only two flybys during the Solstice Mission where the camera is the "prime" instrument during closest approach of a Titan encounter. The other prime flyby for ISS was T80 earlier this month. The two optical remote sensing instruments will focus their attention on Ontario Lacus, a large hydrocarbon lake near Titan's south pole, during a five-hour observation. Scientists will be interested too see whether lake levels have dropped further since the last time the lake was observed during the T51 flyby in March 2009. This is the last opportunity for these instruments to view Ontario Lacus before the end of the mission because this area is moving into darkness as the seasons progress toward southern winter and northern summer. Afterward, CIRS and VIMS will repeat their observations from the inbound leg of the flyby, this time covering Titan's day side. ISS will ride along with the inbound and outbound CIRS observations. Between February 1 and 4, ISS will acquire three cloud monitoring sequences. Unlike the regular Titan Monitoring Campaign observations, these are much lengthier and are designed not only to monitor for the presence of clouds, but also to track them so their speeds can be measured. These observations will be centered over Belet, eastern Belet, and Hetpet Regio, respectively. A shorter, Titan Monitoring Campain sequence will be taken on February 6 from a distance of 3.58 million kilometers (2.22 million miles) centered on the Senkyo region on Titan.

After another Saturn storm watch sequence, ISS will acquire an astrometric observation of Saturn's small, inner moons, including Janus and Polydeuces. Astrometric observations are used to improve our understanding of the orbits of these small satellites, which can be influenced by Saturn's larger icy satellites. A second astrometric sequence will be taken on February 7, this time covering Epimetheus, Telesto, and Prometheus. Afterward, ISS will search for Trojan satellites near the L5 point on Titan's orbit. Similar co-orbital moons have been found for Tethys and Dione. Finally on February 7, ISS will image Titan once again for 11 hours, tracking clouds across Titan's sub-Saturn hemisphere.

On February 9, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev161. Rev161 includes a targeted flyby of Titan.

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Old 01-13-2012, 06:41 AM   #77
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NASA / NASA JPL:
Cassini Testing Part of Its Radio System

January 12, 2012

PASADENA, Calif. -- Engineers with NASA's Cassini mission are conducting diagnostic testing on a part of the spacecraft's radio system after its signal was not detected on Earth during a tracking pass in late December. The spacecraft has been communicating with Earth using a backup part.

The issue occurred with the ultra-stable oscillator, which is used for one type of radio science experiment and also as a means of sending data back to Earth. The spacecraft is currently using an auxiliary oscillator, whose frequency stability is adequate for transmitting data from the spacecraft to Earth. Tests later this month will help mission managers decide whether it will be possible to bring the ultra-stable oscillator back into service.

Some of the data collected for the radio science experiment using the auxiliary oscillator will be of lesser quality than that from the ultra-stable oscillator. Signals used for occultation experiments - where scientists analyze how radio signals are affected as they travel through Saturn's rings or the atmospheres of Saturn and its moons back to Earth - will be of lesser quality. A second kind of radio science investigation using gravity measurements to probe the internal structure of Saturn or its moons will not be affected. Cassini carries 12 science experiments.

The cause is still under investigation, but age may be a factor. The spacecraft launched in 1997 and has orbited Saturn since 2004. Cassini completed its prime mission in 2008 and has had two additional mission extensions. This is the first time its ultra-stable oscillator has had an issue.

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Old 01-24-2012, 12:58 PM   #78
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NASA / NASA JPL:
Cassini Sees the Two Faces of Titan's Dunes

January 23, 2012

A new analysis of radar data from NASA's Cassini mission, in partnership with the European Space Agency and the Italian Space Agency, has revealed regional variations among sand dunes on Saturn's moon Titan. The result gives new clues about the moon's climatic and geological history.

Dune fields are the second most dominant landform on Titan, after the seemingly uniform plains, so they offer a large-scale insight into the moon's peculiar environment. The dunes cover about 13 percent of the surface, stretching over an area of 4 million square miles (10 million square kilometers). For Earthly comparison, that's about the surface area of the United States.

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Data from NASA's Cassini spacecraft show that the sizes and patterns of dunes on Saturn's moon Titan vary as a function of altitude and latitude.
Image credit: NASA/JPL-Caltech, and NASA/GSFC/METI/ERSDAC/JAROS and U.S./Japan ASTER Science Team


Though similar in shape to the linear dunes found on Earth in Namibia or the Arabian Peninsula, Titan's dunes are gigantic by our standards. They are on average 0.6 to 1.2 miles (1 to 2 kilometers) wide, hundreds of miles (kilometers) long and around 300 feet (100 meters) high. However, their size and spacing vary across the surface, betraying the environment in which they have formed and evolved.

Using radar data from the Cassini spacecraft, Alice Le Gall, a former postdoctoral fellow at NASA's Jet Propulsion Laboratory, Pasadena, Calif., who is currently at the French research laboratory LATMOS, Paris, and collaborators have discovered that the size of Titan's dunes is controlled by at least two factors: altitude and latitude.

In terms of altitude, the more elevated dunes tend to be thinner and more widely separated. The gaps between the dunes seem to appear to Cassini's radar, indicating a thinner covering of sand. This suggests that the sand needed to build the dunes is mostly found in the lowlands of Titan.

Scientists think the sand on Titan is not made of silicates as on Earth, but of solid hydrocarbons, precipitated out of the atmosphere. These have then aggregated into grains 0.04 inch in size by a still unknown process.

In terms of latitude, the sand dunes on Titan are confined to its equatorial region, in a band between 30 degrees south latitude and 30 degrees north latitude. However, the dunes tend to be less voluminous toward the north. Le Gall and colleagues think that this may be due to Saturn's elliptical orbit.

Titan is in orbit around Saturn, and so the moon's seasons are controlled by Saturn's path around the sun. Because Saturn takes about 30 years to complete an orbit, each season on Titan lasts for about seven years. The slightly elliptical nature of Saturn's orbit means that the southern hemisphere of Titan has shorter but more intense summers. So the southern regions are probably drier, which implies they have less ground moisture. The drier the sand grains, the more easily they can be transported by the winds to make dunes. "As one goes to the north, we believe the soil moisture probably increases, making the sand particles less mobile and, as a consequence, the development of dunes more difficult." says Le Gall.

Backing this hypothesis is the fact that Titan's lakes and seas are not distributed symmetrically by latitude. These reserves of liquid ethane and methane are predominantly found in the northern hemisphere, suggesting again that the soil is moister toward the north and so, again, the sand grains are less easy to transport by the wind.

"Understanding how the dunes form as well as explaining their shape, size and distribution on Titan's surface is of great importance to understanding Titan's climate and geology because the dunes are a significant atmosphere-surface exchange interface", says Nicolas Altobelli, ESA's Cassini-Huygens project scientist. "In particular, as their material is made out of frozen atmospheric hydrocarbon, the dunes might provide us with important clues on the still puzzling methane/ethane cycle on Titan, comparable in many aspects with the water cycle on Earth."

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ESA: The two faces of Titan's dunes
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Old 02-06-2012, 09:54 PM   #79
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The Planetary Society Blog: Pretty picture: Enceladus, in lovely color

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Old 02-06-2012, 10:14 PM   #80
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Beautiful! Stunning!
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Old 02-09-2012, 12:07 PM   #81
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CICLOPS: Rev161: Feb 9 - Mar 1 '12:
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Cassini continues its exploration of the Saturn system with the 24-day Rev161, which begins on February 9 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 2.84 million kilometers (1.77 million miles) from Saturn's cloud tops. The spacecraft is in the middle of the first equatorial phase of the Cassini Solstice Mission, a phase which lasts until May 2012. During this phase, the spacecraft's orbits lie within the equatorial plane of the planet, providing opportunities to encounter Saturn's numerous moons, to image the rings edge-on, and to look at Saturn's cloud tops without the rings obscuring the view. Forty-two ISS observations are planned for Rev161, the vast majority dedicated to an encounter with Titan and Saturn storm monitoring.

ISS begins its observations for Rev161 two days after apoapse on February 11 with a quick observation of Saturn and its faded northern hemisphere storm with a second such observation planned later that day. These "Storm Watch" observation sequences are designed to take advantage of short, two-minute segments when the spacecraft turns the optical remote sensing (ORS) instruments back to Saturn as a waypoint between other experiments' observations. These sequences include blue, clear, two methane band, and one full-frame, continuum band filter images. Eleven more such sequences are planned between February 12 and 18, while four are planned for February 24 and 25. Between the first two storm watch observations on February 11, ISS will acquire an astrometric observation of Saturn's small, inner moons, including Epimetheus, Prometheus, Methone, and Polydeuces. Astrometric observations are used to improve our understanding of the orbits of these small satellites, which can be influenced by Saturn's larger icy satellites. After another Saturn Storm Watch observation, ISS will observe Titan for 11 hours as part of the "Titan Exploration at Apoapse" (TEA) campaign. These lengthy observations are designed to monitor clouds on the satellite as well as to track the clouds' motions. This TEA observation will cover the Fensal-Aztlan region of Titan from a distance of 3.82 million kilometers (2.38 million miles).

On February 14, ISS will take a look at Titan, this time covering eastern Xanadu and northwestern Fensal from a distance of 2.89 million kilometers (1.80 million miles). The observation is an effort to look for clouds in the moon's atmosphere as part of the "Titan Monitoring Campaign" (TMC). These TMC observations are shorter than TEA observations and are simply used to see if clouds are present rather than tracking the clouds' movements. After another Saturn storm watch observation, ISS will acquire an astrometric observation, looking at Janus, Anthe, Telesto, Polydeuces, and Prometheus. On February 16, ISS will observe a crescent Titan in order to examine the moon's upper haze layers, such as the north and south polar hoods. This observation will be taken from a distance of 1.59 million kilometers (0.99 million miles). The next day, the wide-angle camera will be used to examine the vertical structure of the E ring. Researchers will be examining the location of the ring with respect to the planet's equatorial plane to study the effects of solar radiation pressure and Saturn's magnetic field on the eccentricity of the fine particles in the E ring.

Two days before periapse, Cassini encounters Titan on February 19 at 08:43 UTC for the 83rd time. This is the third of nine Titan flybys planned for 2012, and is the last of the first equatorial phase of the mission. The next flyby is scheduled for May 22. T82 is a relatively high-altitude flyby with a close-approach distance of 3,803 kilometers (2,363 miles). This flyby will allow for imaging of Titan's Senkyo region outbound from the encounter and a crescent Titan inbound. For nearly the entire encounter, the Composite Infrared Spectrometer (CIRS) will be the primary pointing instrument, with ISS riding along. Before closest approach, CIRS will acquire a series of nadir and limb temperature and compositional mapping scans using both their far- and mid-infrared channels. ISS also will have a short observation ten hours before encountering Titan. The camera will run through a series of methane, continuum-band, and ultraviolet filters in order to study the moon's upper haze layers.

At closest approach, CIRS will acquire a pair of limb temperature scans using their far-infrared channel. These scans will focus primarily on atmosphere above Titan's mid-southern latitudes. CIRS also will look at the composition of aerosols in the moon's haze layers. For the rest of the encounter, CIRS will acquire another set of nadir and limb temperature and compositional mapping scans, this time covering Titan's sunlit side.

On February 21 at 05:23 UTC, Cassini will reach periapse for Rev161 at an altitude of 134,680 kilometers (83,690 miles) above Saturn's cloud tops. Both of ISS's periapse observations will be taken the day before. First, the narrow-angle camera will ride along with the Ultraviolet Imaging Spectrometer (UVIS) to monitor Saturn's aurora australis. Next, ISS will observe Enceladus' plume, monitoring activity at the south polar jets just five weeks before the next flyby of the moon.

On February 24, ISS will image Titan's sub-Saturn hemisphere from a distance of 2.88 million kilometers (1.79 million miles). ISS will take a look at Titan again on February 29, this time from a distance of 2.81 million kilometers (1.75 million miles) and covering eastern Xanadu and the region around Menrva.

On March 1, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev162. Rev162 includes a close, non-targeted flyby of Enceladus.

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Old 02-23-2012, 06:30 PM   #82
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NASA / NASA JPL:
The Many Moods of Titan

February 23, 2012

A set of recent papers, many of which draw on data from NASA's Cassini spacecraft, reveal new details in the emerging picture of how Saturn's moon Titan shifts with the seasons and even throughout the day. The papers, published in the journal Planetary and Space Science in a special issue titled "Titan through Time", show how this largest moon of Saturn is a cousin - though a very peculiar cousin - of Earth.

"As a whole, these papers give us some new pieces in the jigsaw puzzle that is Titan," said Conor Nixon, a Cassini team scientist at the NASA Goddard Space Flight Center, Greenbelt, Md., who co-edited the special issue with Ralph Lorenz, a Cassini team scientist based at the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. "They show us in detail how Titan's atmosphere and surface behave like Earth's - with clouds, rainfall, river valleys and lakes. They show us that the seasons change, too, on Titan, although in unexpected ways."

A paper led by Stephane Le Mouelic, a Cassini team associate at the French National Center for Scientific Research (CNRS) at the University of Nantes, highlights the kind of seasonal changes that occur at Titan with a set of the best looks yet at the vast north polar cloud.

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This series of false-color images obtained by NASA's Cassini spacecraft shows the dissolving cloud cover over the north pole of Saturn's moon Titan.
Image credit: NASA/JPL-Caltech/University of Arizona/CNRS/LPGNantes
This series of images obtained by NASA's Cassini spacecraft shows several views of the north polar cloud covering Saturn's moon Titan.
Image credit: NASA/JPL-Caltech/University of Arizona/CNRS/LPGNantes/SSI
This artist's concept shows a possible model of Titan's internal structure that incorporates data from NASA's Cassini spacecraft.
Image credit: A. D. Fortes/UCL/STFC


A newly published selection of images - made from data collected by Cassini's visual and infrared mapping spectrometer over five years - shows how the cloud thinned out and retreated as winter turned to spring in the northern hemisphere.

Cassini first detected the cloud, which scientists think is composed of ethane, shortly after its arrival in the Saturn system in 2004. The first really good opportunity for the spectrometer to observe the half-lit north pole occurred on December 2006. At that time, the cloud appeared to cover the north pole completely down to about 55 degrees north latitude. But in the 2009 images, the cloud cover had so many gaps it unveiled to Cassini's view the hydrocarbon sea known as Kraken Mare and surrounding lakes.

"Snapshot by snapshot, these images give Cassini scientists concrete evidence that Titan's atmosphere changes with the seasons," said Le Mouelic. "We can't wait to see more of the surface, in particular in the northern land of lakes and seas."

In data gathered by Cassini's composite infrared mapping spectrometer to analyze temperatures on Titan's surface, not only did scientists see seasonal change on Titan, but they also saw day-to-night surface temperature changes for the first time. The paper, led by Valeria Cottini, a Cassini associate based at Goddard, used data collected at a wavelength that penetrated through Titan's thick haze to see the moon's surface. Like Earth, the surface temperature of Titan, which is usually in the chilly mid-90 kelvins (around minus 288 degrees Fahrenheit), was significantly warmer in the late afternoon than around dawn.

"While the temperature difference - 1.5 kelvins - is smaller than what we're used to on Earth, the finding still shows that Titan's surface behaves in ways familiar to us earthlings," Cottini said. "We now see how the long Titan day (about 16 Earth days) reveals itself through the clouds."

A third paper by Dominic Fortes, an outside researcher based at University College London, England, addresses the long-standing mystery of the structure of Titan's interior and its relationship to the strikingly Earth-like range of geologic features seen on the surface. Fortes constructed an array of models of Titan's interior and compared these with newly acquired data from Cassini's radio science experiment.

The work shows the moon's interior is partly or possibly even fully differentiated. This means that the core is denser than outer parts of the moon, although less dense than expected. This may be because the core still contains a large amount of ice or because the rocks have reacted with water to form low-density minerals.

Earth and other terrestrial planets are fully differentiated and have a dense iron core. Fortes' model, however, rules out a metallic core inside Titan and agrees with Cassini magnetometer data that suggests a relatively cool and wet rocky interior. The new model also highlights the difficulty in explaining the presence of important gases in Titan's atmosphere, such as methane and argon-40, since they do not appear to be able to escape from the core.

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Old 02-29-2012, 08:44 AM   #83
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Universe Today: Moons Large and Small


Titan and Prometheus are dwarfed by giant Saturn (NASA/JPL/SSI)
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Old 03-01-2012, 01:05 PM   #84
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CICLOPS: Rev162: Mar 1 - Mar 18 '12:
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Cassini continues its exploration of the Saturn system with the 18-day Rev162, which begins on March 1 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 2.38 million kilometers (1.48 million miles) from Saturn's cloud tops. The spacecraft is nearing the end of the first equatorial phase of the Cassini Solstice Mission, a phase which lasts until May 2012. During this phase, the spacecraft's orbits lie within the equatorial plane of the planet, providing opportunities to encounter Saturn's numerous moons, image the rings edge-on, and look at Saturn's cloud tops without the rings obscuring the view. Thirty-eight ISS observations are planned for Rev162, the vast majority dedicated to Saturn storm monitoring and to the non-targeted encounters with Rhea and Enceladus.

ISS begins its observations for Rev162 the day after apoapse on March 2 with a look at Titan from a distance of 1.96 million kilometers (1.22 million miles). The observation is an effort to look for clouds in the moon's atmosphere as part of the "Titan Monitoring Campaign" (TMC). This observation, of a crescent Titan, is designed to study changes in Titan's upper haze layers. Later that day, ISS will acquire a lengthy, 18-hour observation of Thrymr, one of Saturn's distant, irregular moons. This observation will be taken from a distance of 9.48 million kilometers (5.89 million miles), and when combined with additional observations of this irregular satellite, is designed to measure Thrymr's rotational period. Similar observations will be taken of two more outer satellites, Jarnsaxa and Mundilfari, on March 8 and 9. On March 5, 6, and 7, ISS will ride along with the Ultraviolet Imaging Spectrometer (UVIS) to monitor Saturn's aurora australis. On March 9, ISS will perform a TMC observation of Titan, this time at much lower phase angles. This will allow for monitoring of cloud features across the sub-Saturn hemisphere of the moon from a distance of 881,000 kilometers (547,000 miles).

On March 10 at 02:13 UTC, Cassini will reach periapse for Rev162 at an altitude of 135,530 kilometers (84,210 miles). ISS observations will be taken during two non-targeted encounters of Saturn's icy satellites, first of Enceladus (albeit seven hours after closest approach) and later of Rhea. Cassini will fly by Enceladus at a distance of 9,176 kilometers (5,701 miles) on March 9. A few hours later, ISS will take a look at Enceladus's leading hemisphere from a distance of 175,000 kilometers (108,000 miles). The camera system will take two sets of color and polarized filter images of the satellite, with the sets separated by an hour. ISS will then image Titan from a distance of 1.54 million kilometers (0.96 million miles).

At 15:03 UTC, Cassini will fly by Saturn's second largest moon, Rhea, at a close-approach distance of 41,858 kilometers (26,009 miles). ISS will acquire three sets of observations during this flyby. First, ISS will ride along with a series of scans of a crescent Rhea by the Composite Infrared Spectrometer (CIRS) about three hours before closest approach. During closest approach, ISS will acquire a 30-frame mosaic of Rhea's leading hemisphere, including the Mamaldi and Tirawa impact basins. Afterward, ISS will search for particles within the Rhea's possible ring system. Particles as small as 5 to 10 meters (16 to 32 feet) could be detected in these images.

On March 11, ISS will acquire four, quick observations of Saturn and its faded northern hemisphere storm. These "Storm Watch" observation sequences are designed to take advantage of short, two-minute segments when the spacecraft turns the optical remote sensing (ORS) instruments back to Saturn as a waypoint between other experiments' observations. These sequences include blue, clear, two methane band, and one full-frame, continuum band filter images. Thirteen more such observations are planned between March 12 and 18. Also on March 11, ISS will perform a TMC observation of Titan from a distance of 2.45 million kilometers (1.52 million miles). This will allow for monitoring of cloud features across the sub-Saturn hemisphere of the moon. During this image set, portions of Titan will be obscured by Saturn's rings and Janus will transit the moon's north polar region. Immediately afterward, ISS will observe Enceladus as it passes in front of Titan. ISS will take another look at Titan on March 13, from a distance of 2.88 million kilometers (1.79 million miles), this time looking at the Fensal-Aztlan region.

On March 12, ISS will acquire an astrometric observation of Saturn's small, inner moons, including Epimetheus, Helene, Pandora, Telesto, Anthe, and Methone. Astrometric observations are used to improve our understanding of the orbits of these small satellites, which can be influenced by Saturn's larger icy satellites. Additional astrometric observations will be taken on March 13, 15, and 17. On March 14, ISS will observe another satellite mutual event as Tethys passes in front of Dione. Tethys will be 1.69 million kilometers (1.05 million miles) away, while Dione will be 2.20 million kilometers (1.37 million miles) away.

On March 18, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev163. Rev163 includes a targeted flyby of Enceladus and non-targeted encounters with Dione and Janus.

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Old 03-02-2012, 05:59 PM   #85
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Oxygen envelops Saturn's icy moon Dione.

http://www.bbc.co.uk/news/science-environment-17225127
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Old 03-03-2012, 01:39 AM   #86
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NASA / NASA JPL:
Cassini Detects Hint of Fresh Air at Dione

March 02, 2012

NASA's Cassini spacecraft has "sniffed" molecular oxygen ions around Saturn's icy moon Dione for the first time, confirming the presence of a very tenuous atmosphere. The oxygen ions are quite sparse - one for every 0.67 cubic inches of space (one for every 11 cubic centimeters of space) or about 2,550 per cubic foot (90,000 per cubic meter) - show that Dione has an extremely thin neutral atmosphere.

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This view highlights tectonic faults and craters on Dione, an icy world that has undoubtedly experienced geologic activity since its formation.
Image credit: NASA/JPL/Space Science Institute


At the Dione surface, this atmosphere would only be as dense as Earth's atmosphere 300 miles (480 kilometers) above the surface. The detection of this faint atmosphere, known as an exosphere, is described in a recent issue of the journal Geophysical Research Letters.

"We now know that Dione, in addition to Saturn's rings and the moon Rhea, is a source of oxygen molecules," said Robert Tokar, a Cassini team member based at Los Alamos National Laboratory, Los Alamos, N.M., and the lead author of the paper. "This shows that molecular oxygen is actually common in the Saturn system and reinforces that it can come from a process that doesn't involve life."

Dione's oxygen appears to derive from either solar photons or energetic particles from space bombarding the moon's water ice surface and liberating oxygen molecules, Tokar said. But scientists will be looking for other processes, including geological ones, that could also explain the oxygen.

"Scientists weren't even sure Dione would be big enough to hang on to an exosphere, but this new research shows that Dione is even more interesting than we previously thought," said Amanda Hendrix, Cassini deputy project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., who was not directly involved in the study. "Scientists are now digging through Cassini data on Dione to look at this moon in more detail."

Several solid solar system bodies - including Earth, Venus, Mars and Saturn's largest moon Titan - have atmospheres. But they tend to be typically much denser than what has been found around Dione. However, Cassini scientists did detect a thin exosphere around Saturn's moon Rhea in 2010, very similar to Dione. The density of oxygen at the surfaces of Dione and Rhea is around 5 trillion times less dense than that at Earth's surface.

Tokar said scientists suspected molecular oxygen would exist at Dione because NASA's Hubble Space Telescope detected ozone. But they didn't know for sure until Cassini was able to measure ionized molecular oxygen on its second flyby of Dione on April 7, 2010 with the Cassini plasma spectrometer. On that flyby, the spacecraft flew within about 313 miles (503 kilometers) of the moon's surface.

Cassini scientists are also analyzing data from Cassini's ion and neutral mass spectrometer from a very close flyby on Dec. 12, 2011. The ion and neutral mass spectrometer made the detection of Rhea's thin atmosphere, so scientists will be able to compare Cassini data from the two moons and see if there are other molecules in Dione's exosphere.

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SPACE.com: Saturn's Icy Moon Dione Has Oxygen Atmosphere

Universe Today: Saturn’s “Wispy” Moon Has An Oxygen Atmosphere
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Old 03-12-2012, 07:10 PM   #87
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NASA / NASA JPL:
Cassini Captures New Images of Icy Moon

March 12, 2012

These raw, unprocessed images of Saturn's second largest moon, Rhea, were taken on March 10, 2012, by NASA's Cassini spacecraft. This was a relatively distant flyby with a close-approach distance of 26,000 miles (42,000 kilometers), well suited for global geologic mapping.

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Portrait of Rhea
NASA's Cassini spacecraft took this raw, unprocessed image of Saturn's moon Rhea on March 10, 2012. The camera was pointing toward Rhea at approximately 26,019 miles (41,873 kilometers) away.
Image credit: NASA/JPL-Caltech/SSI
Rhea's Surface
NASA's Cassini spacecraft took this raw, unprocessed image of Saturn's moon Rhea on March 10, 2012. The camera was pointing toward Rhea at approximately 26,257 miles (42,258 kilometers) away.
Image credit: NASA/JPL-Caltech/SSI
Rhea Close-up
NASA's Cassini spacecraft took this raw, unprocessed image of Saturn's moon Rhea on March 10, 2012. The camera was pointing toward Rhea at approximately 26,157 miles (42,096 kilometers) away.
Image credit: NASA/JPL-Caltech/SSI
Shadowed Rhea
NASA's Cassini spacecraft took this raw, unprocessed image of Saturn's moon Rhea on March 10, 2012. The camera was pointing toward Rhea at approximately 71,495 miles (115,060 kilometers) away.
Image credit: NASA/JPL-Caltech/SSI


During the flyby, Cassini captured these distinctive views of the moon's cratered surface, creating a 30-frame mosaic of Rhea's leading hemisphere and the side of the moon that faces away from Saturn. The observations included the large Mamaldi (300 miles, or 480 kilometers, across) and Tirawa (220 miles, or 360 kilometers, across) impact basins and the 29-kilometer (47-kilometer) ray crater Inktomi, one of the youngest surface features on Rhea (about 950 miles, or 1,530 kilometers, across).

All of Cassini's raw images can be seen at http://saturn.jpl.nasa.gov/photos/raw/.

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Old 03-12-2012, 07:21 PM   #88
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Again, that probe is absolutely exemplary, the volume of scientific data transmitted to Earth over all those years is awesome !
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Old 03-13-2012, 08:12 PM   #89
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NASA / NASA JPL:
Cassini Spies Wave Rattling Jet Stream on Jupiter

March 12, 2012

PASADENA, Calif. -- New movies of Jupiter are the first to catch an invisible wave shaking up one of the giant planet's jet streams, an interaction that also takes place in Earth's atmosphere and influences the weather. The movies, made from images taken by NASA's Cassini spacecraft when it flew by Jupiter in 2000, are part of an in-depth study conducted by a team of scientists and amateur astronomers led by Amy Simon-Miller at NASA's Goddard Space Flight Center in Greenbelt, Md., and published in the April 2012 issue of Icarus.

"This is the first time anyone has actually seen direct wave motion in one of Jupiter's jet streams," says Simon-Miller, the paper's lead author. "And by comparing this type of interaction in Earth's atmosphere to what happens on a planet as radically different as Jupiter, we can learn a lot about both planets."

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Following the path of one of Jupiter's jet streams, a line of V-shaped chevrons travels west to east just above Jupiter's Great Red Spot. Most of the planet is unfolded here in a single, flat map made on December 11 and 12, 2000, when NASA's Cassini spacecraft flew past Jupiter. At the left, the chevrons run into another storm called the South Equatorial Disturbance (SED).
Credit: NASA/JPL/Space Science Institute


Like Earth, Jupiter has several fast-moving jet streams that circle the globe. Earth's strongest and best known jet streams are those near the north and south poles; as these winds blow west to east, they take the scenic route, wandering north and south. What sets these jet streams on their meandering paths-and sometimes makes them blast Florida and other warm places with frigid air-are their encounters with slow-moving waves in Earth's atmosphere, called Rossby waves.

In contrast, Jupiter's jet streams "have always appeared to be straight and narrow," says co-author John Rogers, who is the Jupiter Section Director of the British Astronomical Association, London, U.K., and one of the amateur astronomers involved in this study.

Rossby waves were identified on Jupiter about 20 years ago, in the northern hemisphere. Even so, the expected meandering winds could not be traced directly, and no evidence of them had been found in the southern hemisphere, which puzzled planetary scientists.

To get a more complete view, the team analyzed images taken by NASA's Voyager spacecraft, NASA's Hubble Space Telescope, and Cassini, as well as a decade's worth of observations made by amateur astronomers and compiled by the JUPOS project.

The movies zoom in on a single jet stream in Jupiter's southern hemisphere. A line of small, dark, v-shaped "chevrons" has formed along one edge of the jet stream and zips along west to east with the wind. Later, the well-ordered line starts to ripple, with each chevron moving up and down (north and south) in turn. And for the first time, it's clear that Jupiter's jet streams, like Earth's, wander off course.

"That's the signature of the Rossby wave," says David Choi, the postdoctoral fellow at NASA Goddard who strung together about a hundred Cassini images to make each time-lapse movie. "The chevrons in the fast-moving jet stream interact with the slower-moving Rossby wave, and that's when we see the chevrons oscillate."

The team's analysis also reveals that the chevrons are tied to a different type of wave in Jupiter's atmosphere, called a gravity inertia wave. Earth also has gravity inertia waves, and under proper conditions, these can be seen in repeating cloud patterns.

"A planet's atmosphere is a lot like the string of an instrument," says co-author Michael D. Allison of the NASA Goddard Institute for Space Studies in New York. "If you pluck the string, it can resonate at different frequencies, which we hear as different notes. In the same way, an atmosphere can resonate with different modes, which is why we find different kinds of waves."

Characterizing these waves should offer important clues to the layering of the deep atmosphere of Jupiter, which has so far been inaccessible to remote sensing, Allison adds.

Crucial to the study was the complementary information that the team was able to retrieve from the detailed spacecraft images and the more complete visual record provided by amateur astronomers. For example, the high resolution of the spacecraft images made it possible to establish the top speed of the jet stream's wind, and then the amateur astronomers involved in the study looked through the ground-based images to find variations in the wind speed.

The team also relied on images that amateur astronomers had been gathering of a large, transient storm called the South Equatorial Disturbance. This visual record dates back to 1999, when members of the community spotted the most recent recurrence of the storm just south of Jupiter's equator. Analysis of these images revealed the dynamics of this storm and its impact on the chevrons. The team now thinks this storm, together with the Great Red Spot, accounts for many of the differences noted between the jet streams and Rossby waves on the two sides of Jupiter's equator.

"We are just starting to investigate the long-term behavior of this alien atmosphere," says co-author Gianluigi Adamoli, an amateur astronomer in Italy. "Understanding the emerging analogies between Earth and Jupiter, as well as the obviously profound differences, helps us learn fundamentally what an atmosphere is and how it can behave."

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Universe Today: Jupiterís Jet Streams Get Thrown Off Course
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Old 03-14-2012, 07:39 PM   #90
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NASA / NASA JPL:
Cassini Garners Top Honor From Air and Space Museum

March 14, 2012

PASADENA, Calif. - NASA's Cassini mission to Saturn, managed by the Jet Propulsion Laboratory, Pasadena, Calif., has received the top group honor from the Smithsonian's National Air and Space Museum - the Trophy for Current Achievement. Representatives for Cassini will receive the trophy on March 21 at a black-tie dinner in Washington, D.C.

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With giant Saturn hanging in the blackness and sheltering Cassini from the sun's blinding glare, the spacecraft viewed the rings as never before, revealing previously unknown faint rings and even glimpsing its home world.
Image credit: NASA/JPL-Caltech


"Here we are some 15 years since Cassini launched and it's amazing how well the spacecraft has operated," said Charles Elachi, director of JPL. "Thanks to the superb work of both the development team and the operations team, Cassini has been able to show us the beauty and diversity of the Saturn system and, beyond that, to study what is really a miniature solar system in its own right."

The trophies for current and lifetime achievement are the National Air and Space Museum's most prestigious awards. They recognize outstanding achievements in the fields of aerospace science, technology and their history.

"The National Air and Space Museum Trophy is among the most prestigious awards given by the Smithsonian, it recognizes significant aerospace accomplishments," said National Air and Space Museum Director Jack Dailey. "We are pleased to present it to the Cassini-Huygens Flight Team in the Current Achievement category."

The Cassini-Huygens mission, a cooperative project of NASA, the European Space Agency and the Italian Space Agency, launched in 1997. It performed a dramatic burn in June 2004 to slide into orbit around Saturn and, in December of that year, the spacecraft successfully released ESA's Huygens probe to pass down through the atmosphere of Saturn's largest moon Titan.

Mission highlights include discovering a plume of water ice and organic particles spraying from the icy moon Enceladus and watching signs of seasonal change from northern winter into northern spring, such as the evolution of a monster storm in Saturn's northern hemisphere. Cassini and Huygens have also revealed just how Earth-like Titan is, as the only body in the solar system other than Earth that has stable liquid on the surface. The mission has discovered two new rings around Saturn and four new moons.

The Cassini spacecraft has also been navigating the Saturn system for nearly eight years with accuracies often better than half a mile (kilometer) while 700 to 800 million miles (1.2 to 1.3 billion kilometers) away from Earth. Cassini has also flown within 16 miles (25 kilometers) of the surface of Enceladus and many times through the upper atmosphere of Titan

The project completed its original prime mission in 2008 and has been extended twice. It is now in its solstice mission, which will enable scientists to observe seasonal change in the Saturn system through the northern summer solstice.

"We are very proud of what Cassini has accomplished," said Robert Mitchell, Cassini program manager based at JPL. "But our workhorse spacecraft still has much work left to do. We can't wait to see what Saturn, its rings and photogenic moons will reveal to us next."

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