Cassini Dives Through Saturn’s Rings, Sends Stunning Closeups


This raw image shows Saturn’s north polar region (left half) and part of its north polar hexagon. At right, we see the rings stacked up in the distance. The photo was taken captured by NASA’s Cassini spacecraft during its first Grand Finale dive past the planet on April 26, 2017. The hexagon is a persistent cloud pattern shaped by jet streams and the “eye” a large spinning vortex. I left the image as Cassini sent it; if the perspective is confusing, give it a quarter-turn to the left in your mind’s eye.
Credits: NASA/JPL-Caltech/Space Science Institute

NASA’s Cassini spacecraft made its successful first-ever dive through the narrow gap between the planet Saturn and its rings on April 26 and sent back images that might just turn your eyes into saucers. As it dove through the gap, the probe came within about 1,900 miles (3,000 km) of Saturn’s cloud tops and within about 200 miles (300 km) of the innermost visible edge of the rings. While mission managers were confident Cassini would pass through the gap successfully, they took extra precautions with this first dive, as the region had never been explored.

This animation shows the changing perspective on Saturn as Cassini dove through the ring plane on April 26. Credit: NASA/JPL-Caltech/SSI/Jason Major

“No spacecraft has ever been this close to Saturn before. We could only rely on predictions, based on our experience with Saturn’s other rings, of what we thought this gap between the rings and Saturn would be like,” said Cassini Project Manager Earl Maize of NASA’s Jet Propulsion Laboratory in Pasadena, California. “I am delighted to report that Cassini shot through the gap just as we planned and has come out the other side in excellent shape.”

The gap between the innermost D ring and the top of Saturn’s atmosphere is about 1,500 miles (2,000 km) wide. Based on the best models, scientists expected Cassini to encounter only the tiniest pieces of ring dust, about the size of smoke particles. The spacecraft zipped through the region at around 77,000 mph (124,000 kph) relative to the planet, so small particles hitting a sensitive area could potentially have disabled the spacecraft.

A raw image showing a view across Saturn’s rings taken by Cassini during its first crossing. Credit: NASA/JPL-Caltech/SSI

To protect itself against possible impacts, the spacecraft put its arms in front of its face so to speak, using its 13-foot (4 meter)-wide dish-shaped antenna as a shield, orienting it in the direction of oncoming ring particles. This meant that the spacecraft was out of contact with Earth during the ring-plane crossing. Contact was re-established about 20 hours after the crossing to the relief of mission control.

The polar votex is seen up close in this raw image on April 26 during Cassini’s first Grand Finale orbit. The feature is 1,240 miles (2,000 km) across with cloud speeds as fast as 330 mph. Credit: NASA/JPL-Caltech/SSI

The images, the closest ever taken of Saturn’s atmosphere and especially the magnificent north polar hexagon, a six-sided atmospheric feature with sides 8,600 miles (13, 800 km) long (slightly greater than the diameter of Earth) and a spinning storm at its center that looks for all the world like water swirling around a bathtub drain. I sorted through the raw images and selected a few of my favorites. Click the link and you may find others you like.

High clouds in Saturn’s atmosphere forms white whorls in this Cassini photo. Credit: NASA/JPL-Caltech/SSI

It’s one down and 21 to go. That’s how many ring plane crossings remain before NASA directs the probe to burn up in Saturn’s atmosphere. Cassini’s next dive through the gap is scheduled in just a couple days on May 2.

Cassini will thread the needle between the planet and Saturn’s innermost D-ring 21 more times before ending its mission. The blue arcs represent ring plane crossings; the orange curve shows its final impact with Saturn’s atmosphere come September 15. Click the image to see a video of the excitement at mission control during the first crossing on April 26. Credit: NASA