Come on now. That’s just a mind-blowing photo. We’re looking at Saturn’s moon, Daphnis, taken by NASA’s Cassini spacecraft as it made one of its ring-grazing passes over the outer edges of Saturn’s rings on Jan. 16, 2017. This is the closest view of the moon ever!
The little guy is just 5 miles (8 km) across and orbits within the 26-mile-wide (42 km) Keeler Gap in Saturn’s outer A-ring. We’ve only known about Daphnis since 2005, the year Cassini discovered it from orbit. Not only does the moon clear material within the A-ring to create the gap, its gravity raises waves along its edges in both horizontal and vertical directions. Cassini observed the vertical structures in 2009 around the time of Saturn’s equinox, when sunlight struck the rings at such a low angle, it dramatically enhanced detail and shadows in the scene (see below).
Like a couple of Saturn’s other small ring moons, Atlas and Pan, Daphnis appears to have a narrow ridge around its equator and a fairly smooth mantle of material on its surface — likely an accumulation of fine particles from the rings. A few craters are obvious at this resolution. An additional ridge can be seen further north that runs parallel to the equatorial band.
You can pick out remarkably small details in the rings in the new image. They have a subtle pebbly texture especially noticeable in the bands directly above the moon that hint at structures where particles are clumping together. In comparison to the otherwise sharp edges of the Keeler Gap, the wave peak in the gap’s edge at left has a softened appearance. This may be to fine ring particles spreading out into the gap following Daphnis’ last close approach to that edge on a previous orbit.
A faint, narrow tendril of ring material follows just behind Daphnis (to its left). This may have resulted from a moment when Daphnis drew a packet of material out of the ring, and now that packet is spreading itself out. Gods, it feels like we’re this close to seeing individual ring particles! I used to think Saturn’s rings were made of millions of small ice chunks. Looking at these images, it must surely be closer to trillions.
The photo was made from about 17,000 miles (28,000 km) from Daphnis with an image scale of 551 feet (168 meters) per pixel. In Greek mythology, Daphnis was a Sicilian shepherd who invented pastoral poetry. True to character, the moon Daphnis makes poetry for the eyes a billion miles from home at Saturn.