Category Archives: Cassini

A Crescent Tethys

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Ring-shine reflecting off Tethys makes for a crescent Tethys.

Cassini caption:

Tethys, dwarfed by the scale of Saturn and its rings, appears as an elegant crescent in this image taken by NASA’s Cassini Spacecraft. Views like this are impossible from Earth, where we only see Saturn’s moons as (more or less) fully illuminated disks.

The region of Saturn seen at left is on the planet’s night side. Reflected light from the rings dimly illuminates the planet’s northern hemisphere.

This view looks toward the anti-Saturn side of Tethys. North on Tethys is up and rotated 24 degrees to the left. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Aug. 18, 2015.

The view was acquired at a distance of approximately 184,000 miles (296,000 kilometers) from Tethys. Image scale is 11 miles (18 kilometers) per pixel.

Image and caption: NASA/JPL-Caltech/Space Science Institute

Titan

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A mosaic of the Saturn moon Titan with its lakes of liquid hydrocarbons.

Cassini caption:
This composite image shows an infrared view of Saturn’s moon Titan from NASA’s Cassini spacecraft, acquired during the mission’s “T-114” flyby on Nov. 13, 2015. The spacecraft’s visual and infrared mapping spectrometer (VIMS) instrument made these observations, in which blue represents wavelengths centered at 1.3 microns, green represents 2.0 microns, and red represents 5.0 microns. A view at visible wavelengths (centered around 0.5 microns) would show only Titan’s hazy atmosphere (as in PIA14909). The near-infrared wavelengths in this image allow Cassini’s vision to penetrate the haze and reveal the moon’s surface.

During this Titan flyby, the spacecraft’s closest-approach altitude was 6,200 miles (10,000 kilometers), which is considerably higher than those of typical flybys, which are around 750 miles (1,200 kilometers). The high flyby allowed VIMS to gather moderate-resolution views over wide areas (typically at a few kilometers per pixel).

The view looks toward terrain that is mostly on the Saturn-facing hemisphere of Titan. The scene features the parallel, dark, dune-filled regions named Fensal (to the north) and Aztlan (to the south), which form the shape of a sideways letter “H.”

Several places on the image show the surface at higher resolution than elsewhere. These areas, called subframes, show more detail because they were acquired near closest approach. They have finer resolution, but cover smaller areas than data obtained when Cassini was farther away from Titan.

Near the limb at left, above center, is the best VIMS view so far of Titan’s largest confirmed impact crater, Menrva (first seen by the RADAR instrument in PIA07365). Similarly detailed subframes show eastern Xanadu, the basin Hotei Regio, and channels within bright terrains east of Xanadu. (For Titan maps with named features see http://planetarynames.wr.usgs.gov/Page/TITAN/target.)

Due to the changing Saturnian seasons, in this late northern spring view, the illumination is significantly changed from that seen by VIMS during the “T-9” flyby on December 26, 2005 (PIA02145). The sun has moved higher in the sky in Titan’s northern hemisphere, and lower in the sky in the south, as northern summer approaches. This change in the sun’s angle with respect to Titan’s surface has made high southern latitudes appear darker, while northern latitudes appear brighter.

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 visual and infrared mapping spectrometer team is based at the University of Arizona.

Image and caption: NASA/JPL/University of Arizona/University of Idaho

Tethys Against the Rings

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Another raw image, this one from the Cassini spacecraft orbiting Saturn.  We can see the moon Tethys with the Saturn ring system in the background.

Tethys is a most interesting moon with a number of features of note — see more detail here.   The huge 445 km crater Odyssesus is the very bright spot.

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

Dione and Enceladus

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Nice job Cassini and team!

The original caption from Cassini site:

Although Dione (near) and Enceladus (far) are composed of nearly the same materials, Enceladus has a considerably higher reflectivity than Dione. As a result, it appears brighter against the dark night sky.

The surface of Enceladus (313 miles or 504 kilometers across) endures a constant rain of ice grains from its south polar jets. As a result, its surface is more like fresh, bright, snow than Dione’s (698 miles or 1123 kilometers across) older, weathered surface. As clean, fresh surfaces are left exposed in space, they slowly gather dust and radiation damage and darken in a process known as “space weathering.”

This view looks toward the leading hemisphere of Enceladus. North on Enceladus is up and rotated 1 degree to the right. 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 52,000 miles (83,000 kilometers) from Dione. Image scale is 1,600 feet (500 meters) per pixel. The distance from Enceladus was 228,000 miles (364,000 kilometers) for an image scale of 1.4 miles (2.2 kilometers) per pixel.

Polar Vortex

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The Cassini spacecraft took this image of the polar vortex on Saturn’s moon Titan in 2012.

Now scientists have detected a monstrous new cloud of frozen compounds in the moon’s low- to mid-stratosphere – a stable atmospheric region above the troposphere, or active weather layer.

Read on for the Cassini press release:

Continue reading

Enceladus Flyby

On 28 October the Cassini did a flyby of the Saturn moon Enceladus. It was the deepest flyby into the plume of the moon since it was discovered. Cassini was to fly as close as 48 km / 30 miles from the surface.

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A view of Enceladus prior to the flyby.  There looks to be a small moon near the rings.

The flyby had three things in mind:
1. Confirm presence of molecular hydrogen (H2)
2. Better understand the chemistry of material in the plume
3. Determine the nature of the plume sources

Cassini was not designed to sample cryovolcanism, however it does have very powerful suite of scientific instruments making such a maneuver possible.

Below we have a view of the surface from just 124 km / 77 miles with a resolution of 15 meters / 49 ft per pixel:

enceladus124km

Original caption:
During its closest ever dive past the active south polar region of Saturn’s moon Enceladus, NASA’s Cassini spacecraft quickly shuttered its imaging cameras to capture glimpses of the fast moving terrain below. This view has been processed to remove slight smearing present in the original, unprocessed image that was caused by the spacecraft’s fast motion.

This view is centered on terrain at 57 degrees south latitude, 324 degrees west longitude. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Oct. 28, 2015.

Images: NASA/JPL-Caltech/Space Science Institute

Enceladus Moonscape

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Enceladus is a world divided. To the north, the terrain is covered in impact craters, much like other icy moons. But to the south, the record of impact cratering is much more sparse, and instead the land is covered in fractures, ropy or hummocky terrain and long, linear features.

Lit terrain seen here is on the trailing side of Enceladus. North on Enceladus is up. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on July 27, 2015.

The view was obtained at a distance of approximately 70,000 miles (112,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 25 degrees. Image scale is 0.4 miles (0.7 kilometers) per pixel.  – Cassini website

Click the image above to see a version I darkened to bring out the terrain for easier viewing.

Image: NASA/JPL-Caltech/Space Science Institute

The Complex F-ring of Saturn

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Saturn’s “F” ring is was discovered in 1979 by the Pioneer 11 spacecraft and is the last named ring found.  It is not the outermost ring.  The ring names  are alphabetical in order of discovery, starting at “A”.  The actual location of the rings are shown here going from inner to outer rings: D, C, B, A, F, G and E.

The Cassini site caption for the image:
Saturn’s dynamic F ring contains many different types of features to keep scientists perplexed. In this image we see features ring scientists call “gores,” to the right of the bright clump, and a “jet,” to the left of the bright spot.

Thanks to the ring’s interaction with the moons Prometheus and Pandora, and perhaps a host of smaller moonlets hidden in its core, the F ring is a constantly changing structure, with features that form, fade and re-appear on timescales of hours to days.

This view looks toward the unilluminated side of the rings from about 7 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 15, 2015.

The view was acquired at a distance of approximately 295,000 miles (475,000 kilometers) from Saturn and at a Sun-ring-spacecraft, or phase, angle of 117 degrees. Image scale is 1.8 miles (2.9 kilometers) per pixel.

 

Image: NASA/JPL-Caltech/Space Science Institute

The Northern Canyons of Enceladus

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The image above shows what I call canyons (NASA calls them “cracks/fractures”) in the northern polar region of Enceladus.

I didn’t find any data describing the size of the “canyons”  in the press release so I went to the Enceladus section of JPL’s  Saturn Moons Explorer and sure enough did not find these canyons.   I did find other similar features to have a width of 100 to 400 meters.

Image caption from NASA / JPL:
NASA’s Cassini spacecraft zoomed by Saturn’s icy moon Enceladus on Oct. 14, 2015, capturing this stunning image of the moon’s north pole. A companion view from the wide-angle camera (PIA20010) shows a zoomed out view of the same region for context.

Scientists expected the north polar region of Enceladus to be heavily cratered, based on low-resolution images from the Voyager mission, but high-resolution Cassini images show a landscape of stark contrasts. Thin cracks cross over the pole — the northernmost extent of a global system of such fractures. Before this Cassini flyby, scientists did not know if the fractures extended so far north on Enceladus.

North on Enceladus is up. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera.

The view was acquired at a distance of approximately 4,000 miles (6,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 9 degrees. Image scale is 115 feet (35 meters) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute