![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.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.](https://api.time.com/wp-content/uploads/2015/12/nasa-saturn-photos-cassini-spacecraft-04.jpg?quality=85&w=2400)
By TIME Photo and Jeffrey Kluger
![NASA's Cassini spacecraft spied details on the pockmarked surface of Saturn's moon Prometheus (86 kilometers, or 53 miles across) during a moderately close flyby on Dec. 6, 2015. This is one of Cassini's highest resolution views of Prometheus, along with PIA18186 and PIA12593.](https://api.time.com/wp-content/uploads/2015/12/nasa-saturn-photos-cassini-spacecraft-01.jpg?quality=75&w=2400)
![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.](https://api.time.com/wp-content/uploads/2015/12/nasa-saturn-photos-cassini-spacecraft-02.jpg?quality=75&w=2400)
![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.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.](https://api.time.com/wp-content/uploads/2015/12/nasa-saturn-photos-cassini-spacecraft-04.jpg?quality=75&w=2400)
![NASA's Cassini spacecraft captured this view of Saturn's moon Epimetheus (116 kilometers, or 72 miles across) during a moderately close flyby on Dec. 6, 2015. This is one of Cassini's highest resolution views of the small moon, along with PIA09813.](https://api.time.com/wp-content/uploads/2015/12/nasa-saturn-photos-cassini-spacecraft-03.jpg?quality=75&w=2400)
![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.](https://api.time.com/wp-content/uploads/2015/12/nasa-saturn-photos-cassini-spacecraft-05.jpg?quality=75&w=2400)
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Write to Jeffrey Kluger at jeffrey.kluger@time.com