Saturn’s rings are made of billions of discrete particles of ice and dust, marshalled by the mathematics of gravity and momentum into thousands of concentric bands. Most of them look neat, regular, and ordered.
Then there’s the F Ring.
Circling Saturn outside the main group of rings, it too consists of many icy particles. But in the F Ring, those particles share their orbit with a pair of moonlets called Prometheus and Pandora. These tiny worlds (Prometheus is about 148 kilometers across) are famously known as “shepherd moons” because they orbit on either side of the F Ring and set its bounds, between 30 and 500 kilometers wide. But instead of merely constraining the ring, their slight gravity is enough to perturb the tiny particles as they pass, stretching and pulling the ring into twisting filaments.
In the very recent sequence above, dramatic back lighting from the sun gives the ring a neon glow against the blackness of space and makes it easier to discern the ring’s ever-changing structure.
These observations of the F Ring are an example of what Cassini does best: discovering the dynamic, complex, weird and beautiful worlds of Saturn, places you’d never even imagine when watching the planet from a distance.
This post originally appeared as a guest blog entry on The Planetary Society web site.
With all the attention on Mars and Mercury the past few days, here’s a previously unpublished view of Venus. I constructed this sequence from raw images taken in ultraviolet light by the Venus Monitoring Camera on board the Venus Express orbiter.
Among the mission’s discoveries during its six years at the second planet, Venus Express has recently seen evidence that active volcanoes may be hiding under these seemingly serene clouds.
The twin GRAIL probes are circling low over the moon, studying its internal structure by measuring slight distortions in its gravitational field.
The spacecraft also carry cameras as part of the MoonKAM (Moon Knowledge Acquired by Middle school students) project, an education program led by Sally Ride Science, the science education company founded by Dr. Sally Ride. Students from around the world choose places on the moon for the probes to image. Students then use the images to study lunar features while also learning about potential future landing sites.
Maria Zuber, GRAIL’s lead scientist, tells more about the mission and about the kids taking part in MoonKAM (this is the only thing I can imagine that would make me want to go back to middle school):