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Seasons of Ice and Shadow
Cassini at Saturn - 2007 Wall Calendar

Since I couldn't find a decent Cassini wall calendar, I decided to make my own.

Click on the thumbnail at left, or the picture for any of the months below for a larger view. The actual calendar is printed in full color at 200dpi (2200 x 1700 pixels).

Notes:

  • CafePress.com doesn't let you put custom text outside the photo area. I did my best to identify each photo and source without intruding too much into the picture area; more detailed info is below.
     
  • CafePress.com prints on-demand using an automated process. If there is any problem with the print quality, contact their help desk for immediate replacement.
 
Cover: The Greatest Saturn Portrait ...Yet
The Greatest Saturn Portrait ...Yet (PIA06193)PIA06193: While cruising around Saturn in early October 2004, Cassini captured a series of images that have been composed into the largest, most detailed, global natural color view of Saturn and its rings ever made.

This grand mosaic consists of 126 images acquired in a tile-like fashion, covering one end of Saturn's rings to the other and the entire planet in between. The images were taken over the course of two hours on Oct. 6, 2004, while Cassini was approximately 6.3 million kilometers (3.9 million miles) from Saturn. Since the view seen by Cassini during this time changed very little, no re-projection or alteration of any of the images was necessary.

Three images (red, green and blue) were taken of each of 42 locations, or "footprints," across the planet. The full color footprints were put together to produce a mosaic that is 8,888 pixels across and 4,544 pixels tall. The smallest features visible in the mosaic are 38 kilometers (24 miles) across.

Many of Saturn's splendid features noted previously in single frames taken by Cassini are visible in this one detailed, all-encompassing view: subtle color variations across the rings, the thread-like F ring, ring shadows cast against the blue northern hemisphere, the planet's shadow making its way across the rings to the left, and blue-grey storms in Saturn's southern hemisphere to the right. Tiny Mimas and even smaller Janus are both faintly visible at the lower left.

The Sun-Saturn-Cassini, or phase, angle at the time was 72 degrees; hence, the partial illumination of Saturn in this portrait. Later in the mission, when the spacecraft's trajectory takes it far from Saturn and also into the direction of the Sun, Cassini will be able to look back and view Saturn and its rings in a more fully-illuminated geometry.

Image and Text Credit: NASA/JPL/Space Science Institute
 

January: The Face of Phoebe
The Face of Phoebe (PIA06064)PIA06064: Phoebe's true nature is revealed in startling clarity in this mosaic of two images taken during Cassini's flyby on June 11, 2004. The image shows evidence for the emerging view that Phoebe may be an ice-rich body coated with a thin layer of dark material. Small bright craters in the image are probably fairly young features. This phenomenon has been observed on other icy satellites, such as Ganymede at Jupiter. When impactors slammed into the surface of Phoebe, the collisions excavated fresh, bright material -- probably ice -- underlying the surface layer. Further evidence for this can be seen on some crater walls where the darker material appears to have slid downwards, exposing more light-colored material. Some areas of the image that are particularly bright - especially near lower right - are over-exposed.

An accurate determination of Phoebe's density -- a forthcoming result from the flyby -- will help Cassini mission scientists understand how much of the little moon is comprised of ices.

This spectacular view was obtained at a phase, or Sun-Phoebe-spacecraft, angle of 84 degrees, and from a distance of approximately 32,500 kilometers (20,200 miles). The image scale is approximately 190 meters (624 feet) per pixel. No enhancement was performed on this image.

Image and Text Credit: NASA/JPL/Space Science Institute
 

February: Encountering Iapetus

Encountering Iapetus (PIA06166)PIA06166: On New Year's Eve 2004, Cassini flew past Saturn's intriguing moon Iapetus, capturing the four visible light images that were put together to form this global view.

Note: The original image is black and white. The color seen here is from PIA07766: Iapetus Spins and Tilts, and is close to natural color.

The scene is dominated by a dark, heavily-cratered region, called Cassini Regio, that covers nearly an entire hemisphere of Iapetus. Iapetus is 1,436 kilometers (892 miles) across. The view is centered on the moon’s equator and on roughly 90 degrees west longitude -- a location that always faces the direction of Iapetus's orbital motion around Saturn.

Within Cassini Regio, and especially near the equator, dark deposits with a visual reflectivity of only about 4 percent coat nearly everything with remarkable uniformity. However, at latitudes of about 40 degrees, the surface transitions to a much brighter, icy terrain near the pole where the brightest icy materials have reflectivity over 60 percent. However, this region is not uniform: Close inspection reveals that the surface is stained by crudely north-south trending wispy streaks of darker material, typically a few kilometers wide and sometimes tens of kilometers long.

An ancient, 400-kilometer wide (250 miles) impact basin appears just above the center of the disc. The basin is heavily overprinted by more recent, smaller impact craters. The basin rim is delineated by steep scarps that descend to the basin floor. Many of these scarps, as well as walls of nearby craters, appear bright, probably due to exposed outcrops of relatively clean ice. Particularly at mid-latitudes, the brightest scarp exposures appear to face away from the equator (i.e. toward the pole). Often, the opposite south-facing scarps are stained with the lower-brightness material.

The most unique, and perhaps most remarkable feature discovered on Iapetus in Cassini images is a topographic ridge that coincides almost exactly with the geographic equator. The ridge is conspicuous in the picture as an approximately 20-kilometer wide (12 miles) band that extends from the western (left) side of the disc almost to the day/night boundary on the right. On the left horizon, the peak of the ridge reaches at least 13 kilometers (8 miles) above the surrounding terrain. Along the roughly 1,300 kilometer (800 mile) length over which it can be traced in this picture, it remains almost exactly parallel to the equator within a couple of degrees. The physical origin of the ridge has yet to be explained. It is not yet clear whether the ridge is a mountain belt that has folded upward, or an extensional crack in the surface through which material from inside Iapetus erupted onto the surface and accumulated locally, forming the ridge.

The origin of Cassini Regio is a long-standing debate among scientists. One theory proposes that its dark material may have erupted onto Iapetus's icy surface from the interior. Another theory holds that the dark material represented accumulated debris ejected by impact events on dark, outer satellites of Saturn. Details of this Cassini image mosaic do not definitively rule out either of the theories. However, they do provide important new insights and constraints.

The uniform appearance of the dark materials at the equator, the apparent thinning and spottiness of the dark materials at progressively higher latitudes and dark wispy streaks near the distal margin of Cassini Regio strongly suggest that dark material was emplaced as a coating. One of the important new results is that no clear evidence can be found that erupted fluids have resurfaced Cassini Regio. The high density of impact craters argues that the terrain underlying the dark coating is relatively ancient and has not been eradicated by its emplacement. Thus, Cassini Regio may have had its origin in plume-style eruptions in which dark particulate materials accumulated on the surface as fallout, perhaps in conjunction with the creation of the equatorial ridge. On the other hand, the dark deposits in Cassini Regio may be a surface coating consistent with, and perhaps more simply explained by, the fall of dark materials from outside.

The view has been oriented so that the north pole is toward the top of the picture. Cassini acquired the images in this mosaic with its narrow angle camera on Dec. 31, 2004, at a distance of about 172,400 kilometers (107,124 miles) from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 50 degrees. The image scale is 1 kilometer (0.6 miles) per pixel. The image has been contrast enhanced to aid visibility of surface features.

Image and Text Credit: NASA/JPL/Space Science Institute
 

March: Nature's Canvas
Nature's Canvas (PIA06142)PIA06142: In a splendid portrait created by light and gravity, Saturn's lonely moon Mimas is seen against the cool, blue-streaked backdrop of Saturn's northern hemisphere. Delicate shadows cast by the rings arc gracefully across the planet, fading into darkness on Saturn's night side.

The part of the atmosphere seen here appears darker and more bluish than the warm brown and gold hues seen in Cassini images of the southern hemisphere, due to preferential scattering of blue wavelengths by the cloud-free upper atmosphere.

The bright blue swath near Mimas (398 kilometers, or 247 miles across) is created by sunlight passing through the Cassini division (4,800 kilometers, or 2,980 miles wide). The rightmost part of this distinctive feature is slightly overexposed and therefore bright white in this image. Shadows of several thin ringlets within the division can be seen here as well. The dark band that stretches across the center of the image is the shadow of Saturn's B ring, the densest of the main rings. Part of the actual Cassini division appears at the bottom, along with the A ring and the narrow, outer F ring. The A ring is transparent enough that, from this viewing angle, the atmosphere and threadlike shadows cast by the inner C ring are visible through it.

Images taken with red, green and blue filters were combined to create this color view. The images were obtained with the Cassini spacecraft narrow angle camera on Nov. 7, 2004, at a distance of 3.7 million kilometers (2.3 million miles) from Saturn. The image scale is 22 kilometers (14 miles) per pixel.

Image and Text Credit: NASA/JPL/Space Science Institute
 

April: Bright Ice, Dirty Ice
Bright Ice, Dirty Ice (PIA06653)PIA06653: Saturn's icy moon Enceladus hovers above Saturn's exquisite rings in this color view from Cassini. The rings, made of nearly pure water ice, have also become somewhat contaminated by meteoritic dust during their history, which may span several hundred million years. Enceladus shares the rings' nearly pure water ice composition, but appears to have eluded dust contamination through resurfacing processes that scientists are still trying to understand. Enceladus is 505 kilometers (314 miles) across.

Dust affects the rings' color, while differences in brightness are attributable to varying particle sizes and concentrations.

The images for this natural color view were taken with the Cassini spacecraft narrow-angle camera on April 5, 2005, at a distance of approximately 2.2 million kilometers (1.4 million miles) from Saturn through red, green and blue spectral filters. The image scale is 13 kilometers (8 miles) per pixel.

Image and Text Credit: NASA/JPL/Space Science Institute
 

May: Zooming In On Enceladus (Mosaic)
Zooming In On Enceladus (PIA06254)PIA06254: 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 (see PIA06249). 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 (see PIA06253).

Image and Text Credit: NASA/JPL/Space Science Institute
 

June: Dazzling Color
Dazzling Color (PIA07771)PIA07771: Cool and icy Dione floats in front of giant Saturn bedecked in a dazzling array of colors.

The surface of Dione, which exhibits contrasting bright and dark areas when viewed up close, appears pale in this image. It is Saturn's multi-hued cloud bands that boldly steal the show. Discrete clouds and eddies in Saturn's northern hemisphere can be seen within the faint shadows of the rings on the planet. Dione is 1,118 kilometers (695 miles) across.

Cassini is in a phase of its mission in which its orbit will be nearly equatorial for some time. This view was obtained from about one-third of a degree out of the ring plane.

Images taken with red, green and blue filters were used to create this natural-color view. The images were obtained with the wide-angle camera on Sept. 22, 2005, from a distance of approximately 803,000 kilometers (499,000 miles) from Dione and at a sun-Dione-spacecraft, or phase, angle of about 43 degrees. The image scale is about 48 kilometers (30 miles) per pixel.

Image and Text Credit: NASA/JPL/Space Science Institute
 

July: When Moons Align
When Moons Align (PIA07644)PIA07644: In a rare moment, the Cassini spacecraft captured this enduring portrait of a near-alignment of four of Saturn's restless moons.

Note: The original image is black and white. Titan's color was obtained from: PIA07729: Looking on the Brightside of Titan, and the rings' color from PIA06653: Bright Ice, Dirty Ice

Seen here are Titan (5,150 kilometers, or 3,200 miles across) and Dione (1,126 kilometers, or 700 miles across) at bottom; Prometheus (102 kilometers, or 63 miles across) hugs the rings at center; Telesto (24 kilometers, or 15 miles across) is a mere speck in the darkness above center.

Timing is critical when trying to capture a view of multiple bodies, like this one. All four of the moons seen here were on the far side of the rings from the spacecraft when this image was taken; and about an hour later, all four had disappeared behind Saturn.

This image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 17, 2005, at a distance of approximately 3.4 million kilometers (2.1 million miles) from Titan and 2.5 million kilometers (1.6 million miles) from Dione. The image scale is 16 kilometers (10 miles) per pixel on Dione and 21 kilometers (13 miles) per pixel on Titan.

Image and Text Credit: NASA/JPL/Space Science Institute
 

August: Dione and Saturn
Dione and Saturn (PIA06155)PIA06155: Cassini captured Dione against the globe of Saturn as it approached the icy moon for its close rendezvous on Dec. 14, 2004. This natural color view shows the moon has strong variations in brightness across its surface, but a remarkable lack of color, compared to the warm hues of Saturn's atmosphere. Several oval-shaped storms are present in the planet's atmosphere, along with ripples and waves in the cloud bands.

The images used to create this view were obtained with the Cassini spacecraft wide-angle camera at a distance of approximately 603,000 kilometers (375,000 miles) from Dione through a filter sensitive to wavelengths of ultraviolet light centered at 338 nanometers. The Sun-Dione-spacecraft, or phase, angle is 34 degrees. The image scale is about 32 kilometers (20 miles) per pixel.

Image and Text Credit: NASA/JPL/Space Science Institute
 

September: The Face of Beauty
The Face of Beauty (PIA07772)PIA07772: Few sights in the solar system are more strikingly beautiful than softly hued Saturn embraced by the shadows of its stately rings.

The gas planet's subtle northward gradation from gold to azure is a striking visual effect that scientists don't fully understand. Current thinking says that it may be related to seasonal influences, tied to the cold temperatures in the northern (winter) hemisphere. Despite Cassini's revelations, Saturn remains a world of mystery.

Currently, the rings' shadows shield the mid-northern latitudes from the harshest of the sun's rays. As Saturn travels around the sun in its 29-year orbit, the shadows will narrow and head southward, eventually blanketing the opposite hemisphere.

Images taken with blue, green and red spectral filters were used to create this color view, which approximates the scene as it would appear to the human eye. The view was brightened to enhance detail visible in the rings and within their shadows.

The images were obtained with the Cassini wide-angle camera from a distance of approximately 999,000 kilometers (621,000 miles) from Saturn on May 4, 2005, as the spacecraft cruised a few degrees above the ring plane. The image scale is about 60 kilometers (37 miles) per pixel on Saturn.

Image and Text Credit: NASA/JPL/Space Science Institute
 

October: Odd World
Odd World (PIA07740)PIA07740: This stunning false-color view of Saturn's moon Hyperion reveals crisp details across the strange, tumbling moon's surface. Differences in color could represent differences in the composition of surface materials. The view was obtained during Cassini's close flyby on Sept. 26, 2005.

Hyperion has a notably reddish tint when viewed in natural color. The red color was toned down in this false-color view, and the other hues were enhanced, in order to make more subtle color variations across Hyperion's surface more apparent.

Images taken using infrared, green and ultraviolet spectral filters were combined to create this view. The images were taken with the Cassini spacecraft's narrow-angle camera at a distance of approximately 62,000 kilometers (38,500 miles) from Hyperion and at a Sun-Hyperion-spacecraft, or phase, angle of 52 degrees. The image scale is 362 meters (1,200 feet) per pixel.

Image and Text Credit: NASA/JPL/Space Science Institute
 

November: Panoramic Rings
Panoramic Rings (PIA06175)PIA06175: Saturn's most prominent feature, its dazzling ring system, takes center stage in this stunning natural color mosaic which reveals the color and diversity present in this wonder of the solar system. Gaps, gravitational resonances and wave patterns are all present, and the delicate color variations across the system are clearly visible.

This image shows a quarter of the full mosaic (PIA06175), which covers a distance of approximately 62,000 kilometers along the ring plane, from a radius of 74,565 kilometers to 136,780 kilometers (46,333 to 84,991 miles) from the planet's center.

This view is from Cassini's vantage point beneath the ring plane. The rings are tilted away from Cassini at an angle of about 4 degrees.

Images taken using red, green and blue spectral filters were used to create this natural color mosaic. The images were acquired using the Cassini spacecraft narrow angle camera on Dec. 12, 2004, at a distance of approximately 1.8 million kilometers (1.1 million miles). The image scale is 10.5 kilometers (6.5 miles) per pixel.

Image and Text Credit: NASA/JPL/Space Science Institute
 

December: Ringside with Dione
Ringside with Dione (PIA07744)PIA07744: Speeding toward pale, icy Dione, Cassini's view is enriched by the tranquil gold and blue hues of Saturn in the distance. The horizontal stripes near the bottom of the image are Saturn's rings. The spacecraft was nearly in the plane of the rings when the images were taken, thinning them by perspective and masking their awesome scale. The thin, curving shadows of the C ring and part of the B ring adorn the northern latitudes visible here, a reminder of the rings' grandeur.

It is notable that Dione, like most of the other icy Saturnian satellites, looks no different in natural color than in monochrome images.

Images taken on Oct. 11, 2005, with blue, green and infrared (centered at 752 nanometers) spectral filters were used to create this color view, which approximates the scene as it would appear to the human eye. The images were obtained with the Cassini spacecraft wide-angle camera at a distance of approximately 39,000 kilometers (24,200 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 22 degrees. The image scale is about 2 kilometers (1 mile) per pixel.

Image and Text Credit: NASA/JPL/Space Science Institute
 

About Cassini
Artists's Conception of Cassini Saturn Orbit Insertion (PIA03883)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 mission for NASA's Science Mission Directorate, Washington, D.C.

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.

PIA03883: Cassini's Saturn Orbit Insertion. This is an artists concept of Cassini during the Saturn Orbit Insertion (SOI) maneuver on July 1, 2004, just after the main engine began firing. The spacecraft is moving out of the plane of the page and to the right (firing to reduce its spacecraft velocity with respect to Saturn) and has just crossed the ring plane.

The SOI maneuver, which was approximately 90 minutes long, allowed Cassini to be captured by Saturn's gravity into a five-month orbit. Cassini's close proximity to the planet after the maneuver offered a unique opportunity to observe Saturn and its rings at extremely high resolution.

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

Image and Text Credit: NASA/JPL/Space Science Institute
 

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