"Кассини" !

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 14 мин. назад

Enceladus' polar jets, viewed from afar, backlit by sunlight while the moon itself glows in reflected Saturn-shine https://go.nasa.gov/2vukLYW 

https://saturn.jpl.nasa.gov/resources/7707/

Jets from a Distance

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Photojournal: PIA21338

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July 17, 2017

Enceladus' intriguing south-polar jets are viewed from afar, backlit by sunlight while the moon itself glows softly in reflected Saturn-shine.

Observations of the jets taken from various viewing geometries provide different insights into these remarkable features. Cassini has gathered a wealth of information in the hopes of unraveling the mysteries of the subsurface ocean that lurks beneath the moon's icy crust.

Спойлер

This view looks toward the Saturn-facing hemisphere of Enceladus (313 miles or 504 kilometers across). North is up. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 13, 2017.

The view was acquired at a distance of approximately 502,000 miles (808,000 kilometers) from Enceladus and at a sun-Enceladus-spacecraft, or phase, angle of 176 degrees. Image scale is 3 miles (5 kilometers) per pixel.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. The Cassini imaging team homepage is at http://ciclops.org.

Credit

NASA/JPL-Caltech/Space Science Institute


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http://blogs.esa.int/rocketscience/2017/07/15/ground-stations-go-dancing-with-cassini/

Posted on 15 July 2017 by Daniel

Ground stations go dancing with Cassini

A complex coordinated 'dance' between ESA and NASA tracking stations is following Cassini during its Grand Finale.

In Cassini's Grand Finale orbits – the final chapter of its nearly 20-year mission – the spacecraft travels in an elliptical path that sends it diving at tens of thousands of kilometers per hour through the 2400-km space between the rings and the planet where no spacecraft has ventured before.

May, June and July have been busy months for Cassini, as a series of complex ground-station tracking passes involving ESA's Deep Space Antennas (DSA) and NASA's Deep Space Network (DSN) captured a series Grand Finale radio science passes.

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Ring Crossing: In this still fr om the short film Cassini's Grand Finale, the spacecraft is shown diving between Saturn and the planet's innermost ring. Credit: NASA/JPL-Caltech

The Cassini mission has performed radio science observations many times during its time at Saturn. Previously, the mission relied solely on the antennas of NASA's Deep Space Network for these observations.

Now, the addition of new ESA tracking capabilities is helping provide the continuous signal reception needed during Cassini radio science activities. But it means the two agencies' networks must work closely together.

Hearing the distant shout

ESA deep space ground stations began working with Cassini last year, conducting a series of test 'passes' – a 'pass' occurs when a spacecraft arcs into line-of-sight visibility above a station and continues until it disappears below the station's horizon as Earth rotates – using their large, 35-meter-diameter, 630-tonne antennas pointed with exquisite accuracy at Cassini in the sky, listening for the craft's call fr om Saturn.


ESA DSA-1 New Norcia, Western Australia. Credit: ESA

In an initial test on 10 August 2016, ESA's tracking station at New Norcia, Western Australia, received signals transmitted by Cassini across 1.4 billion km of space – the most distant 'catch' ever for an ESA station.

Now, during the 22 'inside-the-rings' orbits of the Grand Finale, ESA stations are putting into practice the experience learned last year and are receiving Cassini's signals, focussing on radio science gravity and ring occultation measurements, and delivering the data received to scientists in the U.S. and Europe for scientific analysis.

Tugged by gravity & passing through particles

The gravity experiments aim at measuring Saturn's gravitational field with an unprecedented level of detail in order to gain insights into the planet's interior structure, and at constraining the scenario of formation of Saturn's rings by determining the rings' mass.

[/li]
• Variations in Cassini's orbit – even minute ones – fr om its expected trajectory can be detected by analysing the Doppler shift in the craft's transmitted signal[1], enabling the tugs due to gravity to be studied and measured.
  

The radio science occultations aim at analysing the fine-scale structure of the rings and the physical properties of its particles.

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• Radio science occultations occur when the signals that Cassini transmits to the ground stations pass through the rings – affecting the signals in certain ways that can be studied and analysed.
  

Dipping and diving

The 22 Grand Finale orbits are bringing Cassini between Saturn and its rings; the spacecraft's closest approach to Saturn, reached during each passage through the ring plane, ranges between approximately 1655 km and 3910 km with respect to Saturn's '1 bar level.' (This the place in the atmosphere wh ere air pressure is the same as at sea-level on Earth. It's also approximately the height of Saturn's tallest clouds.)

For six of these closest approach passages (the last one to occur on 19 July), the spacecraft had its High Gain Antenna pointed toward Earth to perform radio occultation measurements of the rings and the radio science gravity experiments.

These radio tracking passes run for very long periods – lasting up to 37 hours, meaning that no single ESA or NASA station has visibility of Saturn for the entire pass.

Visibility: why the ESA-NASA station activity is so complex As mentioned above, a pass starts when a spacecraft rises into line-of-sight view above one local horizon, seen from the station's location, and continues until it drops out of sight below another horizon, the movement being due to the station rotating with the planet (good example with pictures here from when an ESA station tracked NASA's Juno Earth flyby in 2013). Since the Earth is rotating, a routine tracking pass link from any single ground station to a planetary mission typically can last only a few hours – but Cassini radio science needs much longer. In comparison, for Earth missions (which typically orbit Earth 14 times per day), passes last just a few minutes!

Uninterrupted receipt of signals

For Cassini radio science, receipt of the craft's signal must be uninterrupted in order to obtain measurements of Saturn's gravitational effects on the spacecraft without gaps.

To achieve the extra-long passes that Cassini needs, and since we can't simply slow down Earth's rotation, a series of very technically challenging, real-time handovers of Cassini's received signal was planned between multiple ESA and NASA ground stations.

This effort involves antennas located in Argentina (ESA), California (NASA), Spain and Australia (ESA and NASA).

"We are now getting into a new mode of radio science, giving much more accurate measurements of gravitational effects compared to previous observations wh ere the effects of ring density on radio signal propagation were the main topic of study," Daniel Firre, ESA Service Manager for NASA cross support.

Complex 'station dance'

The handover plan between antennas to receive the spacecraft's signal has been organised to provide the necessary continuous coverage, and has necessitated very close technical and organisational cooperation between the two networks across multiple continents.

Incredibly, there can be up to seven stations involved in a single pass.

The graphic below illustrates how each ground station tracks Cassini's signal during these passes. Each station is represented by a different colour. Cassini's signal is tracked as Saturn (and hence Cassini) rises and sets in the sky above each station.


Typical multi-station, ESA-NASA tracking pass for Cassini Credit: NASA/JPL-Caltech
C – NASA Canberra DSN
NN – ESA New Norcia DSA
M – NASA Madrid DSN
ML – ESA Malargüe DSA
G – NASA Goldstone DSN

Note that the optimum angle for the ground station antennas is between 25 and 30 degrees above the horizon; below this "cut-off angle," there are too many things that could disturb the communication link with the spacecraft.

As a result, ESA's stations in the southern hemisphere are in the best position to receive the Cassini's signal due to Saturn's location in the sky right now. This can be clearly seen in the diagram, wh ere M(adrid) and G(oldstone) have visibilities of around 30 degrees, while Malargüe and New Norcia are at nearly 80 degrees.

Cassini is a sophisticated spacecraft; it can receive signals in X-band and transmit in S-band, X-band and Ka-band (details on these frequencies here).

For the radio science passes, Cassini is transmitting and the stations on Earth are receiving; every time one receiving station rotates out of view, the succeeding station picks up, and there is a five-second overlap to avoid losing contact (note that the coloured coverage arcs in the graphic above overlap).

Not all the stations can receive all three of Cassini's frequencies; nonetheless, the station-to-station handovers are so well coordinated that it is always possible to receive at least two of them.

Feeling the pull of a gas giant

Saturn's gravity field and the mass of the rings are detected by means of what are called "range rate" measurements – basically, measuring the rate at which the distance from the ground station to the spacecraft varies. These measurements are enabled by Cassini's on-board X-band radio system, along with the five DSN and two ESA stations working in tight coordination.


Beautiful sunset view of ESA's new 35m deep space station, Malargüe, Argentina, as seen by Salvador Marti, from our ESTRACK team, in 2012. Credits: ESA/S. Marti

Gravity field measurements are obtained by comparing the detected speed of the spacecraft (technically, its radial velocity, with accuracies of about 0.05 mm/s) to a model of the spacecraft's orbit that takes in consideration the effects of the Doppler shift.

Cassini radio science observations will provide crucial clues on how and when Saturn and its rings formed, as well as their relation to its moons: a large ring mass would allow the rings to be as old as the Saturnian system, formed 4.5 billion years ago, while a smaller ring mass suggests that the rings must be much younger, possibly formed by the breakup of a large comet or small moon.

Ring occultations

As described above, occultation observations happen when the rings partially block Cassini's radio signals enroute to Earth.

During the Grand Finale, these observations are taking advantage of the spacecraft's ultra-close perspective on the rings, which allows the radio signal to systematically sweep across the ring system from quite close.

The campaign tracked occultations during the six radio science gravity orbits (the so-called "RSS orbits" when Cassini's radio science subsystem was active) and two "Ring Segment" orbits (orbits 276 and 282 – see the Grand Finale orbit guide for details).


The Grand Finale orbits take Cassini between the planet and its rings. Credit: NASA JPL-Caltech

The radio occultations are short in duration (less than 26 minutes), starting almost immediately after Cassini dives through the ring plane, and they cover the entire main ring system. The technique can measure up to three frequencies, profiling the ring structure and constraining the structures' physical properties.


Credit: NASA/JPL-Caltech

The collective ring coverage of the RSS Grand Finale occultations is unprecedented in the Cassini mission. Never before has such a close occultation observation technique been attempted.

"By marshalling the two agencies' stations together, the overall science return from Cassini is being significantly enhanced, as their sensitive radio 'ears' can listen for signals from the craft as it is tugged by gravity or as the signals pass through the rings, providing additional, important information to help us understand this incredible system," says Nicolas Altobelli, ESA's Cassini-Huygens project scientist.

These powerful scientific insights are being made possible through intense coordination and cooperation between the ground stations of ESA and its NASA partners – truly a technical and expertise tour de force within a Grand Finale.

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ESA Operations‏Подлинная учетная запись @esaoperations 9 ч. назад

#ICYMI Ground stations go dancing w/@CassiniSaturn: ESA stations work w/@NASAJPL's #DSN network to 'catch' science http://blogs.esa.int/rocketscience/2017/07/15/ground-stations-go-dancing-with-cassini/ ...



9 ч. назад

ESA's 2nd last @CassiniSaturn radio-science tracking pass set for tmrrow 24:00CEST start - runs for 6hrs via Malargüe station #grandfinale

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ESA Operations‏Подлинная учетная запись @esaoperations 23 мин. назад

Our 2nd-last tracking pass for @CassiniSaturn starts 1sec after midnight CEST tonight & runs 6hrs #GrandFinale http://blogs.esa.int/rocketscience/2017/07/15/ground-stations-go-dancing-with-cassini/ ...

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ESA Operations‏Подлинная учетная запись @esaoperations 58 мин. назад

Seeing @CassiniSaturn's signal loud & clear at #ESOC today! OK, not so loud from 1.2bn km, but clear! Last ESA tracking in the #GrandFinale

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 3 мин. назад

We've successfully completed ring crossing number 14 of 22 in the #GrandFinale mission. https://go.nasa.gov/2qcf2Vx 

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ESA Operations‏Подлинная учетная запись @esaoperations 2 ч. назад

Last radio-science support for @CassiniSaturn by ESA ended at 22:00CEST. New Norcia station #Australia now ending tracking pass #GrandFinale



2 ч. назад

Best wishes to the entire @CassiniSaturn team for a smooth & successful #GrandFinale #BigDive We'll be following every day!

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 30 мин. назад

Just started #GrandFinale orbit 15. We'll be watching for clouds on Titan, listening for lightning on Saturn. More: https://go.nasa.gov/2uhIPi3 

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https://saturn.jpl.nasa.gov/mission/grand-finale/grand-finale-orbit-guide/#Orbit_15

IN PROGRESS: Orbit 285 - July 22 - July 29

[TH]Event[/TH][TH]Date[/TH][TH]Spacecraft Time (UTC)[/TH][TH]Local Time (PDT)[/TH][TH]Notes[/TH]

Apoapse	Jul 22	1:27 p.m.	6:27 a.m.
Ring Crossing #15	Jul 25	6:55 p.m.	11:55 a.m.
Downlink	Jul 26	6:10 a.m.	11:10 p.m. (July 25)	Estimated Earth Received Time (ERT) is 12:27 a.m. PDT on July 19.

[/li]
• During this orbit Cassini's imaging cameras, the Imaging Science Subsystem (ISS), takes priority to observe Saturn's moon Titan for two periods, each lasting several hours, to image the moon's atmosphere and surface, in particular to watch Titan's clouds form and change. The spacecraft's Composite Infrared Spectrometer (CIRS) and Visible and Infrared Mapping Spectrometer (VIMS) observe Titan as well.
• The Ultraviolet Imaging Spectrograph (UVIS) observes swaths of both Saturn's northern and southern auroral zones, with the north in sunlight while the south is in darkness.
• During this orbit, the spacecraft rolls to calibrate Cassini's magnetometer (MAG) for its high-intensity magnetic field observations to be performed when the spacecraft is nearest Saturn.
• Cassini's Radio and Plasma Wave Science (RPWS) instrument is active during the MAG rolls to capture "whistlers" produced by Saturn lightning.
• During this orbit, Cassini gets within 1,750 miles (2,810 kilometers) of Saturn's 1-bar level. Cassini also passes within 3,040 miles (4,890 kilometers) of the inner edge of Saturn's D ring.
  

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 11 мин. назад

Seen from #Saturn's cloud tops, the planet's rings would arc across the sky. Details: https://go.nasa.gov/2uPWoYV 

https://saturn.jpl.nasa.gov/resources/7711/

Ring-Bow

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Photojournal: PIA21339

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July 24, 2017

Although the rings lack the many colors of the rainbow, they arc across the sky of Saturn. From equatorial locations on the planet, they'd appear very thin since they would be seen edge-on. Closer to the poles, the rings would appear much wider; in some locations (for parts of the Saturn's year), they would even block the sun for part of each day.

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This view looks toward the sunlit side of the rings from about 19 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on April 10, 2017.

The view was obtained at a distance of approximately 680,000 miles (1.1 million kilometers) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 128 degrees. Image scale is 43 miles (69 kilometers) per pixel.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. The Cassini imaging team homepage is at http://ciclops.org.

Credit

NASA/JPL-Caltech/Space Science Institute

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 41 мин. назад

The latest observations fr om our #GrandFinale at #Saturn continue to "surprise and delight" scientists: https://go.nasa.gov/2eIhzpx 

https://saturn.jpl.nasa.gov/news/3083/saturn-surprises-as-cassini-continues-its-grand-finale/

July 24, 2017
Saturn Surprises As Cassini Continues its Grand Finale

Спойлер

This false-color view fr om NASA's Cassini spacecraft gazes toward the rings beyond Saturn's sunlit horizon, wh ere a thin haze can be seen along the limb. Image credit: NASA/JPL-Caltech/Space Science Institute

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As NASA's Cassini spacecraft makes its unprecedented series of weekly dives between Saturn and its rings, scientists are finding -- so far -- that the planet's magnetic field has no discernable tilt. This surprising observation, which means the true length of Saturn's day is still unknown, is just one of several early insights from the final phase of Cassini's mission, known as the Grand Finale.

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Other recent science highlights include promising hints about the structure and composition of the icy rings, along with high-resolution images of the rings and Saturn's atmosphere.

Cassini is performing beautifully in the final leg of its long journey. Its observations continue to surprise and delight as we squeeze out every last bit of science that we can get.

- Earl Maize, Cassini Project Manager

Cassini is now in the 15th of 22 weekly orbits that pass through the narrow gap between Saturn and its rings. The spacecraft began its finale on April 26 and will continue its dives until Sept. 15, when it will make a mission-ending plunge into Saturn's atmosphere.

"Cassini is performing beautifully in the final leg of its long journey," said Cassini Project Manager Earl Maize at NASA's Jet Propulsion Laboratory, Pasadena, California. "Its observations continue to surprise and delight as we squeeze out every last bit of science that we can get."

Cassini scientists are thrilled as well -- and surprised in some cases -- with the observations being made by the spacecraft in the finale. "The data we are seeing from Cassini's Grand Finale are every bit as exciting as we hoped, although we are still deep in the process of working out what they are telling us about Saturn and its rings," said Cassini Project Scientist Linda Spilker at JPL.

Early Magnetic Field Analysis

Based on data collected by Cassini's magnetometer instrument, Saturn's magnetic field appears to be surprisingly well-aligned with the planet's rotation axis. The tilt is much smaller than 0.06 degrees -- which is the lower lim it the spacecraft's magnetometer data placed on the value prior to the start of the Grand Finale.

This observation is at odds with scientists' theoretical understanding of how magnetic fields are generated. Planetary magnetic fields are understood to require some degree of tilt to sustain currents flowing through the liquid metal deep inside the planets (in Saturn's case, thought to be liquid metallic hydrogen). With no tilt, the currents would eventually subside and the field would disappear.

Any tilt to the magnetic field would make the daily wobble of the planet's deep interior observable, thus revealing the true length of Saturn's day, which has so far proven elusive.

"The tilt seems to be much smaller than we had previously estimated and quite challenging to explain," said Michele Dougherty, Cassini magnetometer investigation lead at Imperial College, London. "We have not been able to resolve the length of day at Saturn so far, but we're still working on it."

The lack of a tilt may eventually be rectified with further data. Dougherty and her team believe some aspect of the planet's deep atmosphere might be masking the true internal magnetic field. The team will continue to collect and analyze data for the remainder of the mission, including during the final plunge into Saturn.

The magnetometer data will also be evaluated in concert with Cassini's measurements of Saturn's gravity field collected during the Grand Finale. Early analysis of the gravity data collected so far shows discrepancies compared with parts of the leading models of Saturn's interior, suggesting something unexpected about the planet's structure is awaiting discovery.

Sampling Saturn

In addition to its investigation of the planet's interior, Cassini has now obtained the first-ever samples of the planet's atmosphere and main rings, which promise new insights about their composition and structure. The spacecraft's cosmic dust analyzer (CDA) instrument has collected many nanometer-size ring particles while flying through the planet-ring gap, while its ion and neutral mass spectrometer (INMS) has sniffed the outermost atmosphere, called the exosphere.

https://saturn.jpl.nasa.gov/system/video_items/241_PIA21620_moviewithaudio.m4v
This colorful spectrogram represents data collected by Cassini's Radio and Plasma Wave Science instrument as it crossed through Saturn's D ring on May 28, 2017. Image Credit: NASA/JPL-Caltech/University of Iowa

During Cassini's first dive through the gap on April 26, the spacecraft was oriented so its large, saucer-shaped antenna would act as a shield against oncoming ring particles that might cause damage. While at first it appeared that there were essentially no particles in the gap, scientists later determined the particles there are very small and could be detected using the CDA instrument.

The cosmic dust analyzer was later allowed to peek out from behind the antenna during Cassini's third of four passes through the innermost of Saturn's main rings, the D ring, on June 29. During Cassini's first two passes through the inner D ring, the particle environment there was found to be benign. This prompted mission controllers to relax the shielding requirement for one orbit, in hopes of capturing ring particles there using CDA. As the spacecraft passed through the ring, the CDA instrument successfully captured some of the tiniest particles there, which the team expects will provide significant information about their composition.

During the spacecraft's final five orbits, as well as it final plunge, the INMS instrument will obtain samples deeper down in the atmosphere. Cassini will skim through the outer atmosphere during these passes, and INMS is expected to send particularly important data on the composition of Saturn's atmosphere during the final plunge.

Amazing Images

Not to be outdone, Cassini's imaging cameras have been hard at work, returning some of the highest-resolution views of the rings and planet they have ever obtained. For example, close-up views of Saturn's C ring -- which features mysterious bright bands called plateaus -- reveal surprisingly different textures in neighboring sections of the ring. The plateaus appear to have a streaky texture, whereas adjacent regions appear clumpy or have no obvious structure at all. Ring scientists believe the new level of detail may shed light on why the plateaus are there, and what is different about the particles in them.

On two of Cassini's close passes over Saturn, on April 26 and June 29, the cameras captured ultra-close views of the cloudscape racing past, showing the planet from closer than ever before. Imaging scientists have combined images from these dives into two new image mosaics and a movie sequence. (Specifically, the previously released April 26 movie was updated to greatly enhance its contrast and sharpness.)

https://saturn.jpl.nasa.gov/system/video_items/240_PIA21617_videopan.m4v
This mosaic combines views captured by Cassini as it made the first dive of the mission's Grand Finale on April 26, 2017, and shows details in bands and swirls in the atmosphere. Image Credit: NASA/JPL-Caltech/SSI/Hampton University

Launched in 1997, Cassini has orbited Saturn since arriving in 2004 for an up-close study of the planet, its rings and moons, and its vast magnetosphere. Cassini has made numerous dramatic discoveries, including a global ocean with indications of hydrothermal activity within the moon Enceladus, and liquid methane seas on another moon, Titan.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the mission for NASA's Science Mission Directorate, Washington. JPL designed, developed and assembled the Cassini orbiter.

More information about the Cassini mission:

https://www.nasa.gov/cassini

https://saturn.jpl.nasa.gov

News media contact:

Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
 818-394-7013
 preston.dyches@jpl.nasa.gov

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Видеоматериалы из статьи:

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Видео 2

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 59 мин. назад

A vast swath of Saturn's atmosphere, as seen during the first #GrandFinale dive on April 26. Details: https://go.nasa.gov/2eIy1Ws
https://saturn.jpl.nasa.gov/system/video_items/240_PIA21617_videopan.m4v

https://saturn.jpl.nasa.gov/resources/7712/

Cassini Noodle Mosaic of Saturn

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https://saturn.jpl.nasa.gov/system/video_items/240_PIA21617_videopan.m4v
Photojournal: PIA21617

[свернуть]

July 24, 2017

This mosaic of images combines views captured by NASA's Cassini spacecraft as it made the first dive of the mission's Grand Finale on April 26, 2017. It shows a vast swath of Saturn's atmosphere, fr om the north polar vortex to the boundary of the hexagon-shaped jet stream, to details in bands and swirls at middle latitudes and beyond.

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The full image, nicknamed the "Noodle."

The mosaic is a composite of 137 images captured as Cassini made its first dive toward the gap between Saturn and its rings. It is an update to a previously released image product (see PIA21441). In the earlier version, the images were presented as individual movie frames, whereas here, they have been combined into a single, continuous mosaic. The mosaic is presented as a still image as well as a video that pans across its length. Imaging scientists referred to this long, narrow mosaic as a "noodle" in planning the image sequence.

The first frame of the mosaic is centered on Saturn's north pole, and the last frame is centered on a region at 18 degrees north latitude. During the dive, the spacecraft's altitude above the clouds changed from 45,000 to 3,200 miles (72,400 to 8374 kilometers), while the image scale changed from 5.4 miles (8.7 kilometers) per pixel to 0.6 mile (1 kilometer) per pixel.

The bottom of the mosaic (near the end of the movie) has a curved shape. This is wh ere the spacecraft rotated to point its high-gain antenna in the direction of motion as a protective measure before crossing Saturn's ring plane.

The images in this sequence were captured in visible light using the Cassini spacecraft wide-angle camera. The original versions of these images, as sent by the spacecraft, have a size of 512 by 512 pixels. The small image size was chosen in order to allow the camera to take images quickly as Cassini sped over Saturn.

These images of the planet's curved surface were projected onto a flat plane before being combined into a mosaic. Each image was mapped in stereographic projection centered at 55 degree north latitude.

In the movie version, the mosaic is magnified. It begins with a magnification factor of two and smoothly enlarges to a factor of four by the end.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. The Cassini imaging team homepage is at http://ciclops.org.
 
Credit

NASA/JPL-Caltech/Space Science Institute/Hampton University
 

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 1 ч. назад

New, detailed images of Saturn's C ring reveal a streaky texture that is very different from the surrounding regions https://go.nasa.gov/2eIhzpx 

https://saturn.jpl.nasa.gov/news/3083/saturn-surprises-as-cassini-continues-its-grand-finale/
или
см #2195

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 1 ч. назад

Sounds from a ring crossing: data collected by the Radio and Plasma Wave Science instrument on May 28. Details: https://go.nasa.gov/2eIrsmX
https://saturn.jpl.nasa.gov/system/video_items/241_PIA21620_moviewithaudio.m4v

https://saturn.jpl.nasa.gov/resources/7714/

Cassini's First D-Ring Crossing

Спойлер

https://saturn.jpl.nasa.gov/system/video_items/241_PIA21620_moviewithaudio.m4v

Photojournal: PIA21620

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July 24, 2017

The sounds and colorful spectrogram in this still image and video represent data collected by the Radio and Plasma Wave Science, or RPWS, instrument on NASA's Cassini spacecraft, as it crossed through Saturn's D ring on May 28, 2017.

Спойлер

This was the first of four passes through the inner edge of the D ring during the 22 orbits of Cassini's final mission phase, called the Grand Finale. During this ring plane crossing, the spacecraft was oriented so that its large high-gain antenna was used as a shield to protect more sensitive components from possible ring-particle impacts. The three 33-foot-long (10-meter-long) RPWS antennas were exposed to the particle environment during the pass.

As tiny, dust-sized particles strike Cassini and the RPWS antennas, the particles are vaporized into tiny clouds of plasma, or electrically excited gas. These tiny explosions make a small electrical signal (a voltage impulse) that RPWS can detect. Researchers on the RPWS team convert the data into visible and audio formats, some like those seen here, for analysis. Ring particle hits sound like pops and cracks in the audio.

Particle impacts are seen to increase in frequency in the spectrogram and in the audible pops around the time of ring crossing as indicated by the red/orange spike just before 14:23 on the x-axis. Labels on the x-axis indicate time (top line), distance from the planet's center in Saturn radii, or Rs (middle), and latitude on Saturn beneath the spacecraft (bottom).

These data can be compared to those recorded during Cassini's first dive through the gap between Saturn and the D ring, on April 26 (see PIA21446). While it appeared from those earlier data that there were essentially no particles in the gap, scientists later determined the particles there are merely too small to create a voltage detectable by RPWS, but could be detected using Cassini's dust analyzer instrument.

After ring plane crossing (about 14:23 onward) a series of high pitched whistles are heard. The RPWS instrument detects such tones during each of the Grand Finale orbits and the team is working to understand their source.

The D ring proved to contain larger ring particles, as expected and recorded here, although the environment was determined to be relatively benign – with less dust than other faint Saturnian rings Cassini has flown through.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, Calif. manages the mission for NASA's Science Mission Directorate, Washington, D.C. The radio and plasma wave science team is based at the University of Iowa, Iowa City.
 
Credit

NASA/JPL-Caltech/University of Iowa

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 9 мин. назад

No slowing down! Yesterday, latest pictures & findings: http://go.nasa.gov/2eIhzpx  Right now, ring crossing #15: https://go.nasa.gov/2aNCy6t 

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 9 мин. назад

During this pass, the spacecraft rolls to calibrate the magnetometer for magnetic field observations https://go.nasa.gov/2uUyKKH 
Video

Magnetometer (MAG)

CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 10 мин. назад

These scenes are simulated here using the @NASA_Eyes app, which you can download for free at: http://eyes.nasa.gov 

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 20 мин назад

We've successfully completed ring crossing 15 of 22. Learn more about our #GrandFinale at #Saturn: https://go.nasa.gov/1Up1oba 

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CassiniSaturn‏Подлинная учетная запись @CassiniSaturn 31 мин. назад

#Saturn in a different light. This view comes from our visual and infrared mapping spectrometer. Learn more: https://go.nasa.gov/2uZLvDy 

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https://saturn.jpl.nasa.gov/news/3093/new-insights-into-titans-complex-chemistry/

July 26, 2017

New Insights into Titan's Complex Chemistry


Caption: Titan's complex atmosphere. Image credit: NASA/JPL-Caltech/SSI › Full image and caption

Cassini has made a surprising detection of a molecule that is instrumental in producing complex organics within the hazy atmosphere of Saturn's moon Titan. In a new study published in The Astrophysical Journal Letters, scientists identified what are known as "carbon chain anions." These linear molecules are understood to be building blocks of more complex molecules, and might even have acted as the basis for the earliest forms of life on Earth.
 
> Read the full story from ESA (the European Space Agency)

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http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Has_Cassini_found_a_universal_driver_for_prebiotic_chemistry_at_Titan

Has Cassini found a universal driver for prebiotic chemistry at Titan?

26 July 2017
The international Cassini-Huygens mission has made a surprising detection of a molecule that is instrumental in the production of complex organics within the hazy atmosphere of Saturn's moon Titan.

Titan boasts a thick nitrogen and methane atmosphere with some of the most complex chemistry seen in the Solar System. It is even thought to mimic the atmosphere of early Earth, before the build-up of oxygen. As such, Titan can be seen as a planet-scale laboratory that can be studied to understand the chemical reactions that may have led to life on Earth, and that could be occurring on planets around other stars.

Спойлер

In Titan's upper atmosphere, nitrogen and methane are exposed to energy fr om sunlight and energetic particles in Saturn's magnetosphere. These energy sources drive reactions involving nitrogen, hydrogen and carbon, which lead to more complicated prebiotic compounds.

These large molecules drift down towards the lower atmosphere, forming a thick haze of organic aerosols, and are thought to eventually reach the surface. But the process by which simple molecules in the upper atmosphere are transformed into the complex organic haze at lower altitudes is complicated and difficult to determine.

Chemistry in Titan's atmosphere

One surprising outcome of the Cassini mission was the discovery of a particular type of negatively charged molecule at Titan. Negatively charged species – or 'anions' – were not something scientists expected to find, because they are highly reactive and should not last long in Titan's atmosphere before combining with other materials. Their detection is completely reshaping current understanding of the hazy moon's atmosphere.

In a new study published in Astrophysical Journal Letters, scientists identified some of the negatively charged species as what are known as 'carbon chain anions'. These linear molecules are understood to be building blocks towards more complex molecules, and may have acted as the basis for the earliest forms of life on Earth.

The detections were made using Cassini's plasma spectrometer, called CAPS, as Cassini flew through Titan's upper atmosphere, 950–1300 km above the surface. Interestingly, the data showed that the carbon chains became depleted closer to the moon, while precursors to larger aerosol molecules underwent rapid growth, suggesting a close relationship between the two, with the chains 'seeding' the larger molecules.

"We have made the first unambiguous identification of carbon chain anions in a planet-like atmosphere, which we believe are a vital stepping-stone in the production line of growing bigger, and more complex organic molecules, such as the moon's large haze particles," says Ravi Desai of University College London and lead author of the study.

"This is a known process in the interstellar medium, but now we've seen it in a completely different environment, meaning it could represent a universal process for producing complex organic molecules.

"The question is, could it also be happening within other nitrogen-methane atmospheres like at Pluto or Triton, or at exoplanets with similar properties?"

"The prospect of a universal pathway towards the ingredients for life has implications for what we should look for in the search for life in the Universe," says co-author Andrew Coates, also from UCL, and co-investigator of CAPS.

"Titan presents a local example of exciting and exotic chemistry, from which we have much to learn."

Cassini's 13-year odyssey in the Saturnian system will soon draw to a close, but future missions, such as the international James Webb Space Telescope and ESA's Plato exoplanet mission are being equipped to look for this process not only in our own Solar System but elsewh ere. Advanced ground-based facilities such as ALMA could also enable follow-up observations of this process at work in Titan's atmosphere, from Earth.

"These inspiring results from Cassini show the importance of tracing the journey from small to large chemical species in order to understand how complex organic molecules are produced in an early Earth-like atmosphere," adds Nicolas Altobelli, ESA's Cassini–Huygens project scientist.

"While we haven't detected life itself, finding complex organics not just at Titan, but also in comets and throughout the interstellar medium, we are certainly coming close to finding its precursors."

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