Arc of Ice and Light

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.

animation of Saturn's F Ring
Saturn’s F Ring: billions of icy particles strung into ropy filaments by the gravity of small shepherd moons, and set aglow by sunlight. This sequence of images was captured by Cassini on February 14, 2013. I’ve removed some of the visual noise caused by cosmic rays hitting the imaging sensor. Credit: NASA/JPL/SSI/Dunford

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.

Venus Approach

Venus
The swirling clouds of Venus. Image: ESA/ W. Markiewicz (MPAe, Lindau)/Bill Dunford

With all the attention on Mars and Mercury the past few days, here’s a previously unpublished view of Venus.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.

Moon Flight

animation of frames from GRAIL showing the lunar surface
animation of moon images from GRAIL
A series of frames from one of the twin GRAIL orbiters, taken earlier this month, showing the lunar surface. These shots were chosen by middle school students as part of the MoonKAM project. Credit: NASA/JPL/Sally Ride Science/Bill Dunford

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):

The Saturn System: Up Close and in Motion

Credit: NASA/JPL/Space Science Institute

Some views of the ever-shifting Saturn system by Cassini during the past few days. Credit: NASA/JPL/SSI

Some views of the ever-shifting Saturn system, all sent by Cassini during the past few days.
Credit: NASA/JPL/SSI Animation by Bill Dunford

We have a treasure trove of spectacular vistas this week from Cassini at Saturn. All of these raw images from Titan, Tethys and other tourist stops in the Saturn system arrived on Earth in just the past few days. Continue reading “The Saturn System: Up Close and in Motion”