July 8, 2005

Saturn's Icy Realm

Three of Saturn's icy moons are seen here, along with the magnificent water-ice rings and the cold gaseous envelope of the planet's atmosphere. Saturn's dark shadow stretches completely across the rings.

At nine and a half times farther from the Sun than Earth, Saturn inhabits the deep cold of the outer solar system. The Sun appears only 1 percent as bright there as it appears at Earth, creating an environment where ice dominates over rock.

The icy Moons visible here, from left to right are: Janus (181 kilometers, or 113 miles, across), Enceladus (505 kilometers, or 314 miles, across), and Epimetheus (116 kilometers, or 72 miles, across).

The image was taken in visible green light with the Cassini spacecraft wide-angle camera on June 1, 2005, at a distance of approximately 2.4 million kilometers (1.5 million miles) from Saturn. The image scale is 139 kilometers (86 miles) per pixel.

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July 12, 1005

Solar Eclipses . . . Daily
Saturn's moon Prometheus is seen here emerging from the darkness of Saturn's shadow. Prometheus is 102 kilometers (63 miles) across. This shepherd moon, like most of Saturn's moons, always keeps the same face pointing toward the planet. An observer on the moon's Saturn-facing side would never see the Sun directly overhead at noon, for the planet would always be in the way (creating an eclipse). Instead, the Sun would rise in the east, but as noon approached the eclipse would begin, bringing darkness a second time. Night comes twice on Prometheus. This image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 3, 2005, at a distance of approximately 2.1 million kilometers (1.3 million miles) from Saturn. The image scale is 13 kilometers (8 miles) per pixel.

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July 13, 2005

Cassini Photo Contest Results
The votes have been counted, and the most popular photo is...

July 15, 2005

Rings At Opposition

When Cassini gazes down at Saturn's rings with the Sun directly behind the spacecraft, an unusual phenomenon called the "opposition effect" can be seen. The effect is visible here as a bright region, near right, toward the inner edge of the A ring.

The precise nature of the effect at Saturn is still under scrutiny by imaging scientists. However the effect in Saturn's rings can be witnessed from Earth, when the viewing conditions are right. It can also be seen in photographs of the lunar surface taken by the Apollo astronauts.

To understand the effect, imagine an observer standing on a dry, sandy beach. When the Sun is directly behind the observer, the shadows cast by the grains in the field of view in front of the observer will fall directly behind the grains and will not be visible. When the Sun is at any other angle relative to the observer, the shadows cast by the grains will be visible to the observer. These shadows in the field of view make the scene a bit darker. This effect would cause a centrally bright spot to appear on the sandy surface in the first case, but not in the second.

For Cassini, the opposition effect is seen when the angle between the Sun, the rings and the spacecraft is extremely close to zero. For the sequence of images during which this view was obtained, Cassini maintained this viewing angle and the bright spot appeared to move across the rings with the spacecraft's motion.

The moon Janus (181 kilometers, or 113 miles, across) is seen here at lower left.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on June 7, 2005, at a distance of approximately 738,000 kilometers (458,000 miles) from Saturn. The image scale is 40 kilometers (25 miles) per pixel.

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July 18, 2005

F Ring Shepherds

Saturn's moons Prometheus and Pandora are captured here in a single image taken from less than a degree above the dark side of Saturn's rings. Pandora is on the right, and Prometheus is on the left. Prometheus is 102 kilometers (63 miles) across. Pandora is 84 kilometers (52 miles) across.

The two moons are separated by about 69,000 kilometers (43,000 miles) in this view.

The F ring, extending farthest to the right, contains a great deal of fine, icy material that is more the size of dust than the boulders thought to comprise the dense B ring. These tiny particles are particularly bright from this viewing geometry, especially at right near the ansa, or edge.

At left of center, a couple of ringlets within the Encke gap (325 kilometers, or 200 miles wide) can also be easily seen due to their fine dust-sized material. The other dark features in the rings are density waves and bending waves.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 20, 2005, when Cassini was a mean distance of 1.85 million kilometers (1.15 million miles) from the moons. The image scale is about 11 kilometers (7 miles) per pixel on both moons.

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July 19, 2005

Cassini-Huygens Top 10 Science Highlights

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July 20, 2005

Fantasy Made Real
The majesty of Saturn overwhelms in this image from Cassini. Saturn's moon Tethys glides past in its orbit, and the icy rings mask the frigid northern latitudes with their shadows. Tethys is 1,071 kilometers (665 miles) across. The image was taken in visible green light with the Cassini spacecraft wide-angle camera on June 10, 2005, at a distance of approximately 1.4 million kilometers (900,000 miles) from Saturn. The image scale is 80 kilometers (50 miles) per pixel.

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July 22, 2005

Prometheus On the Edge

Cassini peers through the icy particles that comprise Saturn's rings as Prometheus sits perched on the planet's limb (edge). The rings cast shadows on the planet, with darker regions corresponding to places where the ring material is denser. The narrow dense regions are created by gravitational resonances with moons, like Prometheus, that orbit near the rings. Prometheus is 102 kilometers (63 miles) across.

The thin, bright core of the F ring can be seen against the planet and above Prometheus.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 3, 2005, at a distance of approximately 2.1 million kilometers (1.3 million miles) from Saturn. The image scale is 13 kilometers (8 miles) per pixel.

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July 22, 2005

SOHO Watches Saturn and Cassini Pass Behind the Sun

In this SOHO image taken July 21, 2005, the Sun is represented by the white circle in the center. Saturn is the bright object to the left of the Sun. Interestingly, the streak accompanying Saturn is not the rings but a distortion caused by Saturn's brightness.

Saturn is approaching "superior conjunction," that is, it will be almost directly behind the Sun from Earth -- thus the Cassini spacecraft, in orbit around Saturn, will not be able to send or receive transmissions normally. Regular science data collection has been temporarily suspended.

As Cassini passes closest by the limb (edge) of the Sun on July 24 PDT, communications will be impossible because of the Sun's radio noise. The spacecraft will regain full communication with Earth on July 27, once again returning Saturn science data. In the meantime, controllers are sending approximately 100 commands per day to test communication status. Cassini radio scientists are taking advantage of this opportunity to study the Sun's corona from its effects on the radio signals that reach Earth.

SOHO (Solar and Heliospheric Observatory Satellite) orbits the Sun parked in one of the five gravitational-neutral spots, called Lagrange Points. This specific spot, called L1, stays in the same place relative to the Sun and the Earth, offering a continuously uninterrupted view of the Sun.

Saturn is not in sight again until the evening of July 24. After that date, it will be to the RIGHT of the sun.

For more information on "superior conjunction," visit:
http://www.jpl.nasa.gov/basics/bsf1-2.html#conj

For more information on the Lagrange Points, visit:
http://map.gsfc.nasa.gov/m_mm/ob_techorbit1.html

For more information on SOHO, visit:
http://sohowww.nascom.nasa.gov/

Finally, the latest SOHO images are available at:
http://sohowww.nascom.nasa.gov/data/realtime/c3/1024/latest.gif

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me@rescam.org

July 25, 2005

Bizarre Sounds of Saturn's Radio Emissions

Click here to play sounds of Saturn's radio emissions, which have changes in frequency (127Kb Wave Sound).

Saturn is a source of intense radio emissions, which have been monitored by the Cassini spacecraft. The radio waves are closely related to the auroras near the poles of the planet. These auroras are similar to Earth's northern and southern lights. This is an audio file of Saturn's radio emissions.

The Cassini spacecraft began detecting these radio emissions in April 2002, when Cassini was 374 million kilometers (234 million miles) from the planet, using the Cassini radio and plasma wave science instrument. The instrument has now provided the first high resolution observations of these emissions, showing that show an amazing array of variations in frequency and time. In this example, it appears as though the three rising tones are launched from the more slowly varying narrowband emission near the bottom of this display. If this is the case, it represents a very complicated interaction between waves in Saturn's radio source region, but one which has also been observed at Earth.

Time on this recording has been compressed such that 13 seconds corresponds to 27 seconds. Since the frequencies of these emissions are well above the audio frequency range, we have shifted them downward by a factor of 260.

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me@rescam.org

July 25, 2005

Eerie Sounds of Saturn's Radio Emissions

Click here to play sounds of Saturn's radio emissions, which have changes in frequency (718 Kb Wave Sound).

Saturn is a source of intense radio emissions, which have been monitored by the Cassini spacecraft. The radio waves are closely related to the auroras near the poles of the planet. These auroras are similar to Earth's northern and southern lights. This is an audio file of radio emissions from Saturn.

The Cassini spacecraft began detecting these radio emissions in April 2002, when Cassini was 374 million kilometers (234 million miles) from the planet, using the Cassini radio and plasma wave science instrument.

The radio and plasma wave instrument has now provided the first high resolution observations of these emissions, showing an amazing array of variations in frequency and time. The complex radio spectrum with rising and falling tones, is very similar to Earth's auroral radio emissions. These structures indicate that there are numerous small radio sources moving along magnetic field lines threading the auroral region.

Time on this recording has been compressed, so that 73 seconds corresponds to 27 minutes. Since the frequencies of these emissions are well above the audio frequency range, we have shifted them downward by a factor of 44.

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me@rescam.org

July 26, 2005

Zooming in on Enceladus

As it swooped past the south pole of Saturn's moon Enceladus on July 14, 2005, Cassini acquired high resolution views of this puzzling ice world. From afar, Enceladus exhibits a bizarre mixture of softened craters and complex, fractured terrains.

This large mosaic of 21 narrow-angle camera images have been arranged to provide a full-disk view of the anti-Saturn hemisphere on Enceladus. This mosaic is a false-color view that includes images taken at wavelengths from the ultraviolet to the infrared portion of the spectrum, and is similar to another, lower resolution false-color view obtained during the flyby. In false-color, many long fractures on Enceladus exhibit a pronounced difference in color (represented here in blue) from the surrounding terrain.

A leading explanation for the difference in color is that the walls of the fractures expose outcrops of coarse-grained ice that are free of the powdery surface materials that mantle flat-lying surfaces.

The original images in the false-color mosaic range in resolution from 350 to 67 meters (1,148 to 220 feet) per pixel and were taken at distances ranging from 61,300 to 11,100 kilometers (38,090 to 6,897 miles) from Enceladus. The mosaic is also part of a movie sequence of images from this flyby.

Watch movie of Enceladus from global view to close-up of surface (7.9MB)

As it swooped past the south pole of Saturn's moon Enceladus on July 14, 2005, Cassini acquired increasingly high-resolution views of this puzzling ice world. These views have been combined into this exciting movie sequence. The movie provides a stunning, up-close look at what is surely one of the youngest surfaces in the Saturn system.

From afar, Enceladus exhibits a bizarre mixture of softened craters and complex, fractured terrains. The movie zooms in on the southern polar terrains and closes in on one of the tectonic stripes that characterize this region which is essentially free of sizeable impact scars.

The bright oblong area seen during the zoom is an intermediate resolution image from near the time of closest approach that has been melded into the lower resolution mosaic, and artificially brightened.

The movie ends on the highest resolution image acquired by Cassini which reveals a surface dominated by ice blocks between 10 and 100 meters (33 and 330 feet) across, lying in a region that is unusual in its lack of the very fine-grained frost that seems to cover the rest of Enceladus.

The lack of frost and the absence of craters are indicators of a youthful surface.

The initial image in the movie is a large mosaic of 21 narrow-angle camera images that have been arranged to provide a full-disk view of the anti-Saturn hemisphere on Enceladus. This mosaic is a false-color view that includes images taken at wavelengths from the ultraviolet to the infrared portion of the spectrum, and is similar to another, lower resolution false-color view obtained during the flyby. In false-color, many long fractures on Enceladus exhibit a pronounced difference in color (represented here in blue) from the surrounding terrain.

A leading explanation for the difference in color is that the walls of the fractures expose outcrops of coarse-grained ice that are free of the powdery surface materials that mantle flat-lying surfaces.

The original images in the false-color mosaic range in resolution from 350 to 67 meters (1,148 to 220 feet) per pixel and were taken from distances ranging from 61,300 to 11,100 kilometers (38,090 to 6,897 miles) from Enceladus. The mosaic is also available separately.

Image scale is about 37 meters (121 feet) per pixel in the wide-angle camera image and about 4 meters (13 feet) per pixel in the narrow-angle image. Both of these ultra-high resolution views were acquired from an altitude of approximately 208 kilometers (129 miles) above Enceladus as the spacecraft near the time of closest approach during the flyby.

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July 29, 2005

Wind World
Far above the howling winds of Saturn, its icy moons circle the planet in silence. Mimas is seen near the upper right, while Tethys hovers at the bottom. Dark shadows cast by the see-through rings slice across the northern hemisphere. Mimas is 397 kilometers (247 miles) across. Tethys is 1,071 kilometers (665 miles) across. The dark, doughnut-shaped storm near the south pole is at least 1,600 kilometers (1,000 miles) across and could easily swallow any of Saturn's moons except giant Titan (5,150 kilometers, 3,200 miles across). The image was taken with the Cassini spacecraft wide-angle camera on June 21, 2005, through a filter sensitive to wavelengths of infrared light centered at 752 nanometers at a distance of approximately 2.2 million kilometers (1.3 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 53 degrees. The image scale is 125 kilometers (78 miles) per pixel.

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August 1, 2005

Rhea's Bright Blemish
This view of Saturn's moon Rhea shows the tremendous bright splat that coats much of the moon's leading hemisphere. The bright feature may be impact-related and is visible in other Cassini images of Rhea. Rhea is 1,528 kilometers (949 miles) across. North on Rhea is up in this view. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on June 25, 2005, at a distance of approximately 1.1 million kilometers (700,000 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of less than one degree. Resolution in the original image was 7 kilometers (4 miles) per pixel. The image has been contrast-enhanced and magnified by a factor of two to aid visibility.

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August 3, 2005

Opposition View
The "opposition effect" can be seen in this image of Saturn's B ring. The bright spot occurs where the angle between the spacecraft, the Sun and the rings is near zero. Studies of the opposition effect on Saturn's rings may help scientists constrain some of the properties of ring particles, such as their sizes and spatial distribution. Another recently released image from Cassini also shows this interesting effect of viewing geometry (see Rings At Opposition). The image was taken in visible light with the Cassini spacecraft wide-angle camera on June 26, 2005, at a distance of approximately 478,000 kilometers (297,000 miles) from Saturn. The image scale is 3 kilometers (2 miles) per pixel.

Cassini's Flies by "Death Star" Moon
The great eye of Saturn's moon Mimas (MY-muss), a 130-kilometer-wide (80-mile) impact crater called Herschel, stares out from the battered moon in this raw image taken by the Cassini spacecraft during a flyby on August 2. The Herschel crater is the moon's most prominent feature, and the impact that formed it probably nearly destroyed Mimas. Cassini flew by Mimas at 62,700 kilometers (38,800 miles) above the moon's surface, bringing it closer to the little moon than ever before.

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August 4, 2005

Saturn's Auroras

The Cassini spacecraft has obtained new images of Saturn's auroral emissions, which are similar to Earth's Northern Lights. Images taken on June 21, 2005, with Cassini's ultraviolet imaging spectrograph are the first from the mission to capture the entire "oval" of the auroral emissions at Saturn's south pole.

In the side-by-side, false-color images, blue represents aurora emissions from hydrogen gas excited by electron bombardment, while red-orange represents reflected sunlight. The images show that the aurora lights at the polar regions respond rapidly to changes in the solar wind.

Previous images have been taken closer to the equator, making it difficult to see the polar regions. Changes in the emissions inside the Saturn south-pole aurora are visible by comparing the two images, taken about one hour apart. The brightest spot in the left aurora fades, and a bright spot appears in the middle of the aurora in the second image.

Made by slowly scanning the ultraviolet imaging spectrograph instrument across the planet, the images contain more than 2,000 wavelengths of spectral information within each picture, which helps researchers study Saturn's auroras, gases, hazes and their changing distributions.

Like Earth's aurora, those on Saturn form in an oval at high latitudes around each pole, along with associated spots and streaks. The ultraviolet imaging spectrograph data shows that the Saturn aurora lasts at least one hour, but small changes are visible in that time between the two images.

The same process produces auroras on both planets: variations in the plasma environment release trapped electrons, which stream along the magnetic field lines into the upper atmosphere. There, they collide with atoms and molecules, exciting them to higher energies. The atoms and molecules release this added energy by radiating light at particular characteristic colors and wavelengths. On Earth, this light is mostly from oxygen atoms and nitrogen molecules. On Saturn, it is from emissions of molecular and atomic hydrogen.

The Cassini-Huygens mission is a cooperative project of NASA, 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 Cassini- Huygens mission for NASA's Space Science Mission Directorate in Washington D.C. The Cassini orbiter was designed, developed and assembled at JPL. The ultraviolet imaging spectrograph was built at, and the team is based at the University of Colorado, Boulder.

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August 5, 2005

Mimas Showing False Colors
This false color image of Saturn's moon Mimas reveals variation in either the composition or texture across its surface.

During its approach to Mimas on Aug. 2, 2005, the Cassini spacecraft narrow-angle camera obtained multi-spectral views of the moon from a range of 228,000 kilometers (142,500 miles).

This image is a color composite of narrow-angle ultraviolet, green, infrared and clear filter images, which have been specially processed to accentuate subtle changes in the spectral properties of Mimas' surface materials. To create this view, three color images (ultraviolet, green and infrared) were combined with a single black and white picture that isolates and maps regional color differences to create the final product.

Shades of blue and violet in the image at the right are used to identify surface materials that are bluer in color and have a weaker infrared brightness than average Mimas materials, which are represented by green.

Herschel crater, a 140-kilometer-wide (88-mile) impact feature with a prominent central peak, is visible in the upper right of the image. The unusual bluer materials are seen to broadly surround Herschel crater. However, the bluer material is not uniformly distributed in and around the crater. Instead, it appears to be concentrated on the outside of the crater and more to the west than to the north or south. The origin of the color differences is not yet understood. It may represent ejecta material that was excavated from inside Mimas when the Herschel impact occurred. The bluer color of these materials may be caused by subtle differences in the surface composition or the sizes of grains making up the icy soil.

This image was obtained when the Cassini spacecraft was above 25 degrees south, 134 degrees west latitude and longitude. The Sun-Mimas-spacecraft angle was 45 degrees and north is at the top.

Flying Over Mimas
This movie was made of narrow-angle images taken over a period of seven hours during Cassini's close encounter with Saturn's moon Mimas on Aug. 2, 2005. In the movie the moon appears to rotate through about 115 degrees and the range varies from 253,000 to 64,000 kilometers (158,000 to 40,000 miles). The image scale in the final pan across the surface is about 760 meters (about 2,500 feet) per pixel.

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August 18, 2005

Rhea: Polar View

Like the rest of Rhea's surface, the southern polar region of this Saturn moon has been extensively re-worked by cratering over the eons. This close-up shows that most sizeable craters have smaller, younger impact sites within them. Near the left lies an intriguing gash.

The largest well-defined crater visible here is an oval-shaped impact toward the upper right. The crater is 115 by 91 kilometers (71 by 57 miles) in size.

Cassini acquired this view during a distant flyby of Rhea (1,528 kilometers, or 949 miles across) on July 14, 2005.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera at a distance of approximately 239,000 kilometers (149,000 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 56 degrees. The image was obtained using a filter sensitive to wavelengths of infrared light centered at 930 nanometers. The image scale is about 1 kilometer (0.6 miles) per pixel.

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August 19, 2005

Looking Down on Epimetheus

From 34 degrees above Saturn's equatorial plane, Cassini gazed down at Saturn's moon Epimetheus. The region seen here includes territory farther north and east than that imaged in March 2005 (see Up-Close and Colorful).

The two largest craters visible here are the only officially named features on Epimetheus. The crater at the left (at about the 9 o'clock position) is named Pollux; the crater at lower left (containing a string of several smaller craters) is called Hilairea. Epimetheus is 116 kilometers (72 miles) across.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 14, 2005, at a distance of approximately 87,000 kilometers (54,000 miles) from Epimetheus and at a Sun-Epimetheus-spacecraft, or phase, angle of 95 degrees. The image scale is 520 meters (1,710 feet) per pixel.

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August 22, 2005

Supreme Beauty
Swirling cloud bands, delicate ring shadows and icy moons make the Saturn system a place of supreme natural beauty. Even Cassini's remarkable images can only provide the slightest sense of the experience of actually being there. Tethys (at the right, 1,071 kilometers, or 665 miles across) and Mimas (near the center, 397 kilometers, or 247 miles across) are captured here against the planet's turbulent atmosphere. Although the rings are only a thin strip from this angle, one can see the structure of the entire main ring system in its shadow on the planet - from the C ring at the bottom to the faint specter of the F ring at the top. The image was taken in visible violet light with the Cassini spacecraft wide-angle camera on July 16, 2005, at a distance of approximately 1.2 million kilometers (700,000 miles) from Saturn. The image scale is 66 kilometers (41 miles) per pixel.

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