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.
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.
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:
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.
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.
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.
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.
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
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. —