NASA’s Cassini spacecraft took these stunning photos of Saturn’s rings on December 18, 2016, while it was performing one of its ‘ring-grazing’ orbits.
This Cassini image features a density wave in Saturn’s A ring (at left) that lies around 83,575 miles (134,500 km) from Saturn. Density waves are accumulations of particles at certain distances from the planet. This feature is filled with clumpy perturbations, which researchers informally refer to as ‘straw.’ The wave itself is created by the gravity of Saturn’s moons Janus and Epimetheus, which share the same orbit around the gas giant. Elsewhere, the scene is dominated by ‘wakes’ from a recent pass of the ring moon Pan. The image was taken in visible light with Cassini’s wide-angle camera on December 18, 2016. The view was obtained at a distance of approximately 34,000 miles (56,000 km) from the rings and looks toward the unilluminated side of the rings. Image credit: NASA / JPL-Caltech / Space Science Institute.
The views are some of the closest-ever images of the outer parts of Saturn’s main rings, giving planetary researchers an opportunity to observe features with names like ‘straw’ and ‘propellers.’
“These close views represent the opening of an entirely new window onto Saturn’s rings, and over the next few months we look forward to even more exciting data as we train our cameras on other parts of the rings closer to the planet,” said Cassini scientist Dr. Matthew Tiscareno, from the SETI Institute.
This image shows a region in Saturn’s outer B ring. Cassini viewed this area at a level of detail twice as high as it had ever been observed before. The view here is of the outer edge of the B ring, at left, which is perturbed by the most powerful gravitational resonance in the rings: the ‘2:1 resonance’ with Saturn’s icy moon Mimas. This means that, for every single orbit of Mimas, the ring particles at this specific distance from Saturn orbit the planet twice. This results in a regular tugging force that perturbs the particles in this location. A lot of structure is visible in the zone near the edge on the left. This is likely due to some combination of the gravity of embedded objects too small to see, or temporary clumping triggered by the action of the resonance itself. Scientists informally refer to this type of structure as ‘straw.’ This image was taken using a fairly long exposure, causing the embedded clumps to smear into streaks as they moved in their orbits. Later Cassini orbits will bring shorter exposures of the same region, which will give researchers a better idea of what these clumps look like. But in this case, the smearing does help provide a clearer idea of how the clumps are moving. The image was taken in visible light with Cassini’s wide-angle camera on December 18, 2016. The view was obtained at a distance of approximately 32,000 miles (52,000 km) from the rings and looks toward the unilluminated side of the rings. Image credit: NASA / JPL-Caltech / Space Science Institute.
Cassini is now about halfway through its ‘ring-grazing’ phase — 20 orbits that dive past the outer edge of the main ring system.
The ring-grazing orbits (or F-ring orbits) began on November 30, 2016, and will continue until late April 2017, when Cassini begins its grand finale.
During the 22 finale orbits, Cassini will repeatedly plunge through the gap between the rings and Saturn. The first finale plunge is scheduled for April 26.
For now, the orbiter is shooting past the outer edges of the rings every week, gathering some of its best images of the rings and moons.
Already Cassini has sent back the closest-ever views of Saturn’s tiny moons Daphnis and Pandora.
This image shows a region in Saturn’s outer B ring. Cassini viewed this area at a level of detail twice as high as it had ever been observed before. And from this view, it is clear that there are still finer details to uncover. Researchers have yet to determine what generated the rich structure seen in this view, but they hope detailed images like this will help them unravel the mystery. In order to preserve the finest details, this image has not been processed to remove the many small bright blemishes, which are created by cosmic rays and charged particle radiation near the planet. The image was taken in visible light with Cassini’s wide-angle camera on December 18, 2016. The view was obtained at a distance of approximately 32,000 miles (51,000 km) from the rings, and looks toward the unilluminated side of the rings. Image credit: NASA / JPL-Caltech / Space Science Institute.
Some of the structures seen in the latest images have not been visible at this level of detail since the spacecraft arrived at Saturn in mid-2004.
At that time, fine details like straw and propellers — which are caused by clumping ring particles and small, embedded moonlets, respectively — had never been seen before.
Cassini came a bit closer to the rings during its arrival at Saturn, but the quality of those arrival images was not as high as in the new views.
Those precious few observations only looked out on the backlit side of the rings, and the team chose short exposure times to minimize smearing due to Cassini’s fast motion as it vaulted over the ring plane. This resulted in images that were scientifically stunning, but somewhat dark and noisy.
This image shows a region in Saturn’s A ring. The level of detail is twice as high as this part of the rings has ever been seen before. The view shows a section of the A ring known to researchers for hosting belts of propellers — bright, narrow, propeller-shaped disturbances in the ring produced by the gravity of unseen embedded moonlets. Several small propellers are visible in this view. These are on the order of 10 times smaller than the large, bright propellers whose orbits scientists have routinely tracked. The prominent feature at left is a density wave created by the ring’s gravitational interaction with Saturn’s moon Prometheus (the 12:11 resonance). The image was taken in visible light with Cassini’s wide-angle camera on December 18, 2016. The view was obtained at a distance of approximately 33,000 miles (54,000 km) from the rings and looks toward the unilluminated side of the rings. Image credit: NASA / JPL-Caltech / Space Science Institute.
In contrast, the close views Cassini has begun capturing in its ring-grazing phase are taking in both the backlit and sunlit side of the rings.
Instead of just one brief pass lasting a few hours, the orbiter is making several dozen passes during these final months.
“As the person who planned those initial orbit-insertion ring images — which remained our most detailed views of the rings for the past 13 years – I’m taken aback by how vastly improved are the details in this new collection,” said Cassini imaging team leader Dr. Carolyn Porco, from the Space Science Institute.
“How fitting it is that we should go out with the best views of Saturn’s rings we’ve ever collected.”
This article is based on a press-release from NASA.