Category Archives: Cassini

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

Pandora

Perhaps someday Pandora will accumulate enough matter to become spherical  – see the press release from the Cassini site to explain.

Won’t be anytime soon, it has a ways to go.

Although Mimas and Pandora, shown here, both orbit Saturn, they are very different moons. Pandora, “small” by moon standards (50 miles or 81 kilometers across) is elongated and irregular in shape. Mimas (246 miles or 396 kilometers across), a “medium-sized” moon, formed into a sphere due to self-gravity imposed by its higher mass.

The shapes of moons can teach us much about their history. For example, one explanation for Pandora’s elongated shape and low density is that it may have formed by gathering ring particles onto a dense core.

This view looks toward the unilluminated side of the rings from 0.26 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 26, 2015.

The view was obtained at a distance of approximately 485,000 miles (781,000 kilometers) from Pandora. Image scale is 3 miles (5 kilometers) per pixel. Mimas is 904,000 miles (1.4 million kilometers) from the spacecraft in this image. The scale on Mimas is 5.4 miles (8.4 kilometers) per pixel.

Image and press release: NASA/JPL-Caltech/Space Science Institute

Edge On

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The Cassini spacecraft captures two of Saturn’s moons as it looks across the ring plane from below almost edge on – less than a degree below the ring plane.

Both moons show up nicely in the larger version (click the image above)

Prometheus and Pandora are almost hidden in Saturn’s rings in this image.

Prometheus (53 miles or 86 kilometers across) and Pandora (50 miles or 81 kilometers across) orbit along side Saturn’s narrow F ring, which is shaped, in part, by their gravitational influences help to shape that ring. Their proximity to the rings also means that they often lie on the same line of sight as the rings, sometimes making them difficult to spot.

In this image, Prometheus is the left most moon in the ring plane, roughly in the center of the image. Pandora is towards the right. — 

Enceladus Global Ocean

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The scientists on Cassini’s mission have determined that the Saturn moon Enceladus has a slight wobble and that wobble cannot be caused by a body that is solid from surface to core.

The wobble is known as libration and it reveals that the crust of Enceladus is disconnected from its rocky interior.

The artists concept shows what it might look like inside.

Image credit: NASA/JPL-Caltech

 

From the Dark Side

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Cassini was on the dark side of Saturn looking toward the lit side when it took this picture.  The polar hexagon of  Saturn shows up nicely in this image.  Click the image above to get a larger version.

We can also see the moon Tethys in this image as a speck of light below the ring plane on  the left side. Tethys is 1062 km / 660 miles in diameter and looks so small because the image was taken at at distance of 2.4 million km / 1.5 million miles from Saturn – Saturn is huge!

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

 

 

 

Saturn and Dione

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This Cassini image shows Saturn and the moon Dione.  Notice how Dione looks crisp and Saturn a little on the dark side?  It’s because of the methane filter the image was taken with.

The sunlight seen in the infrared at a wavelength that is absorbed by methane.  The dark regions indicate areas where sunlight has to travel through more methane and therefore is filtered.   Dione has no atmosphere so there is no methane to absorb the light so the light is bright and unaltered as it reflects off.

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

Transit of Dione

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This is the moon Dione seen against a background of Saturn, what is known as a transit.  The image gives a good perspective of just how large Saturn is. The view is from 2.4 million km / 1.4 million miles from Cassini to Saturn and Dione is 1123 km / 698 miles across.

Transits are very important in astronomy and are used to precisely determine orbital parameters of planets and their atmospheres. We also see planetary transits from Earth of Venus and Mercury against the Sun.

We will have a transit of Mercury next year: 16 May 2016 but will have to wait until 11 December 2117 for the next transit of Venus.

NASA has a couple of fun transit sites, the first for Mercury and the second for Venus.

Click the image for a large version and check out the far rings, almost can make out perturbations.

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

Dione

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Here are a couple more images from Cassini’s final flyby of the Saturn moon Dione.

dionelandscapeThe image above was taken as Cassini was heading towards the moon. The impact basin on the lower right is called Evander and is about 350 km / 220 miles wide.

On the left you can see the bright Padua Chasma, reaching into the left side of the moon.

To the right we have a very nice close up of Dione from just 750 km / 470 miles giving a resolution of 45 meters per pixel. Click the thumbnail to see the bigger version, the picture gives a great sense of the icy make-up of the moon. North is down in this view.

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