Category Archives: Cassini

Saturn’s Moon Dione

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More about Dione from TNP.

From Cassini:
Dione appears cut in two by Saturn’s razor-thin rings, seen nearly edge-on in a view from NASA’s Cassini spacecraft. This scene was captured from just 0.02 degrees above the ring plane.

The bright streaks of Dione’s wispy terrain (see PIA12553) are seen near the moon’s limb at right. The medium-sized crater Turnus (63 miles, 101 kilometers, wide) is visible along Dione’s terminator.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 25, 2015. The view was acquired at a distance of approximately 1.4 million miles (2.3 million kilometers) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 115 degrees. Image scale is 8.6 miles (13.8 kilometers) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

Tethys

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A new look at Tethys from Cassini. We get a nice look at the 400 km / 249 mile wide crater called Odysseus.

Saturn’s moon Tethys appears to float between two sets of rings in this view from NASA’s Cassini spacecraft, but it’s just a trick of geometry. The rings, which are seen nearly edge-on, are the dark bands above Tethys, while their curving shadows paint the planet at the bottom of the image.

Tethys (660 miles or 1,062 kilometers across) has a surface composed mostly of water ice, much like Saturn’s rings. Water ice dominates the icy surfaces in the the far reaches of our solar system, but ammonia and methane ices also can be found.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on Nov. 23, 2015. North on Tethys is up. The view was obtained at a distance of approximately 40,000 miles (65,000 kilometers) from Tethys. Image scale is 2.4 miles (4 kilometers) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

Saturn in Methane

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When viewed through a methane filter the banding on Saturn really stands out.

The Cassini caption:
The soft, bright-and-dark bands displayed by Saturn in this view from NASA’s Cassini spacecraft are the signature of methane in the planet’s atmosphere.

This image was taken in wavelengths of light that are absorbed by methane on Saturn. Dark areas are regions where light travels deeper into the atmosphere (passing through more methane) before reflecting and scattering off of clouds and then heading back out of the atmosphere. In such images, the deeper the light goes, the more of it gets absorbed by methane, and the darker that part of Saturn appears.

The moon Dione (698 miles or 1,123 kilometers across) hangs below the rings at right. Shadows of the rings are also visible here, cast onto the planet’s southern hemisphere, in an inverse view compared to early in Cassini’s mission at Saturn (see PIA08168).

This view looks toward the unilluminated side of the rings from about 0.3 degrees below the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on Sept. 6, 2015, using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 728 nanometers.

The view was acquired at a distance of approximately 819,000 miles (1.32 million kilometers) from Saturn. Image scale is 49 miles (79 kilometers) per pixel. Dione has been brightened by a factor of two to enhance its visibility.

Rings!

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This is a raw image from Cassini.  The bright white specks you see are artifact that can be eliminated with processing.

This reminds me of a record album. A what? If you don’t know what that is ask your Grand Parents. 🙂

Image Credit: NASA/JPL-Caltech/Space Science Institute

Enceladus Surface

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One of the things that always strikes me about Enceladus is the differences in terrain.  Look at the terrain in the lower right side of the picture and how the crater is cut cleanly in half as is the whole side of the moon.

Here’s the Cassini description:

This half-lit view of Enceladus bears a passing resemblance to similar views of Earth’s own natural satellite, but the similarities end there. Earth’s rocky moon is covered in dark, volcanic basins and brighter, mountainous highlands — both exceedingly ancient. The surface of icy Enceladus is uniformly bright, far brighter than Earth’s moon. Large areas of Enceladus’ surface are characterized by youthful (on geologic timescales), wrinkled terrains.

Although the north pole of Enceladus (313 miles or 504 kilometers across) was dark when Cassini arrived at Saturn, the march of the seasons at Saturn have brought sunlight to the north and taken it from the south.

This view looks toward the leading hemisphere of Enceladus. North on Enceladus is up. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 8, 2015.

The view was acquired at a distance of approximately 80,000 miles (129,000 kilometers) from Enceladus. Image scale is 2,530 feet (772 meters) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

Tethys and Janus

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Click the image for a much larger version.

From Cassini:
Janus and Tethys demonstrate the main difference between small moons and large ones. It’s all about the moon’s shape.

Moons like Tethys (660 miles or 1,062 kilometers across) are large enough that their own gravity is sufficient to overcome the material strength of the substances they are made of (mostly ice in the case of Tethys) and mold them into spherical shapes. But small moons like Janus (111 miles or 179 kilometers across) are not massive enough for their gravity to form them into a sphere. Janus and its like are left as irregularly shaped bodies.

Saturn’s narrow F ring and the outer edge of its A ring slice across the scene.

This view looks toward the unilluminated side of the rings from about 0.23 degrees below the ring plane. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Oct. 27, 2015.

The view was obtained at a distance of approximately 593,000 miles (955,000 kilometers) from Janus. Image scale at Janus is 3.7 miles (6 kilometers) per pixel. Tethys was at a distance of 810,000 miles (1.3 million kilometers) for an image scale of 5 miles (8 kilometers) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

Saturn

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Here’s a new image from Cassini, before we get to the caption you can see a nice planet grouping while you are looking for comet Catalina:
Venus, Saturn, and Mars are nicely aligned in the morning sky in the coming days.  Go outside before sunrise and look roughly south east and you will see them.  Easy to see with nothing special required other than the effort to look.

Finders chart here – due east is off the left side of the chart.

Now for the Cassini caption:
It is easy to forget just how large Saturn is, at around 10 times the diameter of Earth. And with a diameter of about 72,400 miles (116,500 kilometers), the planet simply dwarfs its retinue of moons. One of those satellites, Tethys (660 miles or 1,062 kilometers across), is seen here at lower right.

This view looks toward the sunlit side of the rings from about 8 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera on March 7, 2015 using a spectral filter that preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

Tethys has been brightened by a factor of 2 to increase its visibility.

The view was acquired at a distance of approximately 1.6 million miles (2.6 million kilometers) from Saturn. Image scale is 10 miles (16 kilometers) per pixel. Tethys is slightly closer at 1.5 million miles (2.4 million kilometers) away, for an image scale of 9 miles (14 kilometers) per pixel.

NASA/JPL-Caltech/Space Science Institute

Three Moons

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The moons Enceladus and Rhea are easy to spot, the third moon, the tiny Atlas is only a little more difficult to find.

Have a look and see if you can find it before reading the Cassini caption below.

From Cassini:
What looks like a pair of Saturnian satellites is actually a trio upon close inspection.

Here, Cassini has captured Enceladus (313 miles or 504 kilometers across) above the rings and Rhea (949 miles or 1,527 kilometers across) below. The comparatively tiny speck of Atlas (19 miles or 30 kilometers across) can also be seen just above and to the left of Rhea, and just above the thin line of Saturn’s F ring.

This view looks toward the unilluminated side of the rings from about 0.34 degrees below the ring plane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 24, 2015.

The view was obtained at a distance of approximately 1.8 million miles (2.8 million kilometers) from Rhea. Image scale on Rhea is 10 miles (16 kilometers) per pixel. The distance to Enceladus was 1.3 million miles (2.1 million kilometers) for a scale of 5 miles (8 kilometers) per pixel. The distance to Atlas was 1.5 million miles (2.4 million) kilometers) for an image scale at Atlas of 9 miles (14 kilometers) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

Beautiful Dione

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The original caption:

Dione’s beautiful wispy terrain is brightly lit alongside Saturn’s elegant rings.

The “wisps” are relatively young fractures on the trailing hemisphere of Dione’s (698 miles or 1123 kilometers across) icy surface. See PIA06162 and PIA06163 for higher resolution views of Dione’s wispy terrain.

This view looks toward the anti-Saturn side of Dione. North on Dione is up. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 15, 2015.

The view was obtained at a distance of approximately 1.1 million miles (1.7 million kilometers) from Dione. Image scale is 7 miles (11 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.

Image Credit:NASA/JPL-Caltech/Space Science Institute

 

A Tale of Two Hemipheres

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The images from Cassini’s flyby of the Saturn moon Enceladus are starting to come in.

From Cassini:

Enceladus dramatically displays the contrast between its older and newer terrain.

Newer surfaces (on the left in the image) will not have had time to accumulate craters. But as material sits exposed on the surface, impact scars build up, as in the more heavily cratered area on the top and right. Scientists can use this, along with estimates of how frequently impacts happen, to determine ages of surfaces of solid planets and of moons like Enceladus (313 miles or 504 kilometers across).

This view looks toward the anti-Saturn side of Enceladus. North on Enceladus is up and rotated 36 degrees to the right. The image was taken in green light with the Cassini spacecraft narrow-angle camera on Aug. 18, 2015.

The view was acquired at a distance of approximately 85,000 miles (137,000 kilometers) from Enceladus. Image scale is 2,680 feet (818 meters) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute