Stunning. Incredible. Alright, I’ll shut up. But it’s not easy when the photos are this inspiring. NASA’s Cassini spacecraft has just returned some of the closest images of Saturn’s rings ever taken. Photos that need to be shared widely.
The view at top shows the outer edge of the B ring, the brightest of Saturn’s rings and easily visible in the smallest of telescopes. The edge appears sharp because the region next to the ring is cleared of ring particles by the moon Mimas. For every single orbit of Mimas, the ring particles — mostly made of water ice — are tugged on by the little moon. The repeated pulls force them into new orbits outside the gap. This all happens because the ring particles at this location orbit twice for every one orbit of Mimas. Astronomers call it a resonance, and it’s much like finding the sweet spot when giving someone a push on swing to provide the maximum boost.
A lot of structure is visible in the zone near the edge on the left. This is either due to some combination of the gravity of embedded objects too small to see, or temporary clumping triggered somehow by the resonance with Mimas. Either way, it has a cool name: scientists informally call it “straw.” The straw appears very drawn out because to capture the photo a fairly long exposure was needed, causing the embedded clumps of ring material to smear into thin streaks as they moved in their orbits about the planet.
By the way, the crud sprinkled across the image are zips and zaps caused by cosmic rays and high speed particles in Saturn’s dangerous radiation environment striking the camera sensor.
The second photo is perhaps even more amazing and features a density wave in Saturn’s A ring, the next ring out from the B ring. The multiple ripples across this section of the ring are created by the gravity of the moons Janus and Epimetheus, which share the same orbit around Saturn. Although the processes are different, the wave pattern resembles the one we see when a rock is dropped into a pond. Both are disturbances in a medium, one caused by gravity, the other by a rock striking a liquid. The dark stripes at left are “wakes” from a recent pass of the ring moon Pan, which unlike Mimas, is actually embedded within the ring.
Cassini will dive closer and closer to Saturn’s rings during the remaining 7½ months of its mission before it finally plunges into Saturn’s atmosphere and gets crushed by that planet’s enormous gravity. For the moment, Cassini’s cameras can resolve ring features as small as 0.3 miles (550 meters) across, similar to the height of the One World Trade Center in New York City. Expect closer and even more amazing photos to come as the mission winds to an end in September.