Wednesday, November 30, 2011

Kraken Mare


The Cassini spacecraft looks toward Saturn's largest moon, Titan, and spies the huge Kraken Mare in the moon's north.

Kraken Mare, a large sea of liquid hydrocarbons, is visible as a dark area near the top of the image. See PIA12811 and PIA11626 to learn more.

This view looks toward the Saturn-facing side of Titan (3,200 miles across, or 5,150 kilometers,). North on Titan is up and rotated 29 degrees to the left.

The image was taken with the Cassini spacecraft narrow-angle camera on September 14, 2011 using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers. The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 26 degrees. Image scale is 7 miles (12 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Tuesday, November 22, 2011

Hyperion


The Cassini spacecraft looks at Saturn's highly irregular moon Hyperion in this view from the spacecraft's flyby of the moon on August 25, 2011.

Hyperion (168 miles, or 270 kilometers across) has an irregular shape, and it tumbles through its orbit: that is, it does not spin at a constant rate or in a constant orientation. (A standard reference latitude-longitude system has not yet been devised for this moon.) Images such as this one extend previous coverage and allow a better inventory of the surface features, the satellite's shape and changes in its spin.

See PIA06243 and PIA07761 to learn more and to watch a movie.

The image was taken with the Cassini spacecraft narrow-angle camera using a combination of spectral filters sensitive to wavelengths of polarized green light centered at 617 and 568 nanometers. The view was obtained at a distance of approximately 36,000 miles (58,000 kilometers) from Hyperion and at a Sun-Hyperion-spacecraft, or phase, angle of 43 degrees. Image scale is 1,145 feet (349 meters) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Monday, November 21, 2011

Close-Up of Saturn's Northern Hemisphere Storm


The biggest, most long-lasting Saturnian storm seen by either NASA's Cassini or Voyager spacecraft roils the atmosphere of the gas giant in this nearly true-color mosaic of Cassini images.

See PIA14903 and PIA14905 to learn more about the size and development of this storm. This mosaic shows the storm's effects encircling the planet and was created using 126 images taken in succession as different parts of Saturn's northern hemisphere rotated into Cassini's view.

Images taken using red, green and blue spectral filters are usually combined to create a natural color view. Because visible red light images were not available, images taken using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers were used in place of red. So the color is close to natural color, but is not exact.

A second version of this mosaic is also included here (Figure 1). This view uses these same nearly true color filters, but the images were contrast enhanced. The result is a view that increases the visibility of features.

The head of the storm is near the center of the mosaic, and a train of vortices appears as blue spots just to the south of the head. These blue spots are parts of the storm's tail that have already encircled the planet and are approaching from the west (left in the image). The blue color indicates they have some high, semi-transparent haze but no thick clouds underneath because there are no white- or yellow-colored clouds shown here.

This mosaic covers an area ranging from about 18 degrees north latitude to 47 degrees north latitude. The views stretch the whole longitude range, passing through 360/0 degrees west longitude near the far right of the mosaics.

The images were obtained with the Cassini spacecraft narrow-angle camera on March 6, 2011, over about 11 hours (about a Saturnian day) at a distance of approximately 2 million miles (3.3 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 83 degrees. These mosaics are simple cylindrical map projections, defined such that a square pixel subtends equal intervals of latitude and longitude. At higher latitudes, the pixel size in the north-south direction remains the same, but the pixel size (in terms of physical extent on the planet) in the east-west direction becomes smaller. The pixel size is set at the equator, where the distances along the sides are equal. This map has a pixel size of 28 miles (45 kilometers) at the equator.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Sunday, November 20, 2011

Chronicling Saturn's Northern Storm


This series of images from NASA's Cassini spacecraft shows the development of the largest storm seen on the planet since 1990. These true-color and composite near-true-color views chronicle the storm from its start in late 2010 through mid-2011, showing how the distinct head of the storm quickly grew large but eventually became engulfed by the storm's tail.

The earliest image of the storm, taken December 5, 2010, is in the top left of the panel. The storm appears only as a small, white cloud on the terminator between the day side and night side of the planet. See PIA14905 for a magnified view of the storm at this time.

The next view, in the top middle of the panel and taken January 2, 2011, shows that the head quickly grew much larger and a tail began to trail a great distance eastward. Some of the clouds moved south and got caught up in a current that flows to the east (to the right) relative to the storm head. In the top right of the panel, this tail, which appears as slightly blue clouds south and now west (left) of the storm head, can be seen encountering the storm in the February 25 image.

The April 22 image, in the bottom left of the panel, is one of Cassini's last views of the storm when it still had a recognizable head. In this view, the tail is south of the head and is well established by this time.

The May 18 view, in the bottom middle, shows only the storm's tail. The head still existed at this time, but it is beyond the horizon and out of the field of view here.

Between the time of the May 18 image and the next image shown here (from August 12), the head of the storm was engulfed by the part of the storm's tail that spread eastward at the same latitude as the head. The August 12 image, in the bottom right, shows that the head has lost its distinct identity and is now just part of the jumble of the storm.

Also visible in these images are several of Saturn's moons and the shadows cast onto the planet by moons. For example, the planet's second largest moon, Rhea, can be seen in the February 25 view.

The February 25 and August 12 views are true color. Images taken using red, green and blue spectral filters were combined to create these natural-color views.

The December 5, January 2, April 22 and May 18 views are nearly true color. Because a visible red light image was not available, an image taken using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers was used in place of red. So the color is close to natural color, but it is not exact.

These views were acquired at distances ranges from approximately 1.4 million miles (2.2 million kilometers) to 1.9 million miles (3.0 million kilometers) from Saturn and at Sun-Saturn-spacecraft, or phase, angles of 41 degrees to 99 degrees. All the views are set to a scale of 101 miles (162 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Note: For other pictures in this series, see PIA14901: Eleven Hours Later and PIA14902: Birth of a Behemoth Storm.

Saturday, November 19, 2011

Saturn's Northern Hemisphere Storm


Saturn's northern storm marches through the planet's atmosphere in the top right of this false-color mosaic from NASA's Cassini spacecraft.

See PIA14905 to learn more about this storm and watch its development over several months. Earlier in the Cassini mission, the spacecraft chronicled a smaller storm in the southern hemisphere, called the "Dragon Storm." See PIA06197 to learn more about that storm and to see a similar, false-color view.

Saturn's atmosphere and its rings are shown here in a false-color composite made from 12 images taken in near-infrared light through filters that are sensitive to varying degrees of methane absorption. Red and orange colors in this view indicate clouds that are deep in the atmosphere. Yellow and green colors, most noticeable along the top edge of the view, indicate intermediate clouds. White and blue indicate high clouds and haze. The rings appear as a thin horizontal line of bright blue because they are outside of the atmosphere and not affected by methane absorption.

This view looks toward the northern, sunlit side of the rings from just above the ring plane.

The images were taken with the Cassini spacecraft wide-angle camera using a combination of spectral filters sensitive to wavelengths of near-infrared light. The images filtered at 890 nanometers are projected as blue. The images filtered at 728 nanometers are projected as green, and images filtered at 752 nanometers are projected as red.

The images were taken on January 11, 2011, over about 50 minutes, at a distance of approximately 569,000 miles (915,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 45 degrees. The images were re-projected to the same viewing geometry, so that scale in this final mosaic is 63 miles (102 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Note: For similar images, see PIA12828: Storm Head in False Color and PIA12829: Storm Tail in False Color.

Tuesday, November 15, 2011

Enceladus and Epimetheus


During a flyby of Saturn's moon Enceladus on October 1, 2011, the Cassini spacecraft snapped this portrait of the moon joined by its sibling Epimetheus and the planet's rings.

Enceladus (313 miles, or 504 kilometers across) takes up the center of the image, and its famous south polar jets can faintly be seen at the bottom of the image. See PIA11688 to learn more about those jets.

Epimetheus (70 miles, or 113 kilometers across) peeps into view from beyond the northern reaches of Enceladus. Lit terrain seen on Enceladus is in the area between the leading hemisphere and anti-Saturn side of the moon. North is up. This view looks toward the northern, sunlit side of the rings from just above the ringplane.

Enceladus and Epimetheus have been contrast enhanced and brightened by a factor 1.8 relative to the rings. Enceladus is closest to the spacecraft here.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera. The view was obtained at a distance of approximately 175,000 kilometers (109,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 151 degrees. Image scale is about 3,280 feet (1 kilometer) per pixel on Enceladus.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Tuesday, November 8, 2011

Tethys


Saturn's moon Tethys shows off its tortured surface in this Cassini spacecraft image.

On the top left of the image there is huge Odysseus Crater. See PIA07693 for a closer view. On the bottom right there is Ithaca Chasma, a series of scarps that runs north-south across the moon for more than 620 miles (1,000 kilometers). North on Tethys is up and rotated 25 degrees to the right. See PIA07734 and PIA10460 to learn more.

This view looks toward the area between the leading hemisphere and Saturn-facing side of Tethys (660 miles, or 1,062 kilometers across).

The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on September 14, 2011. The view was acquired at a distance of approximately 178,000 miles kilometers (287,000) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 11 degrees. Image scale is about 1 mile (2 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Tuesday, November 1, 2011

Hyperion


The sponge-like surface of Saturn's moon Hyperion is highlighted in this Cassini portrait, captured during the spacecraft's September 16, 2011, flyby.

Hyperion (168 miles, or 270 kilometers across) has an irregular shape, and it tumbles through its orbit: that is, it does not spin at a constant rate or in a constant orientation. (A standard reference latitude-longitude system has not yet been devised for this moon.) Images such as this one extend previous coverage and allow a better inventory of the surface features, the satellite's shape and changes in its spin. See PIA06243 and PIA07761 to learn more and to watch a movie.

The image was taken in visible blue light with the Cassini spacecraft narrow-angle camera. The view was obtained at a distance of approximately 55,000 miles (88,000 kilometers) from Hyperion and at a Sun-Hyperion-spacecraft, or phase, angle of 37 degrees. Image scale is 1,720 feet (524 meters) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute