After more than twelve years in orbit around Saturn, NASA’s Cassini spacecraft is now in its final year of operation…and newly-positioned in an orbit that will send it soaring high over the planet’s north pole as well as close by the outer edge of its glorious shining rings.
Over the course of 20 week-long “ring-grazing orbits” — the first of which was completed on Dec. 4 — Cassini will obtain close-up images and data on the composition and structure of Saturn’s rings and nearby shepherd moons.
It’s the mission’s penultimate phase, heralding the end of Cassini in September 2017.
“This is it, the beginning of the end of our historic exploration of Saturn,” said Cassini imaging team leader Carolyn Porco. “Let these images — and those to come — remind you that we’ve lived a bold and daring adventure around the solar system’s most magnificent planet.”
Round and round they go… the animation above, made from 14 raw images taken by NASA’s Cassini spacecraft on August 23, 2016, shows the moons Prometheus and Atlas orbiting Saturn within the Roche Division gap between its A (top right) and F (center) rings. The gravitational tug of Prometheus (92 miles / 148 km long) is strong enough to pull on the fine, smoke-like icy particles of the F ring, creating streamer and “clump” features that follow it along.
The much smaller Atlas (23 miles / 37 km wide) follows a path around Saturn just past the outer edge of the A ring. It was once thought to be a “shepherd moon” of the A ring, but it’s now known that the pull of the more distant Janus and Epimetheus are responsible for that.
Atlas does have its very own ring, though—a very faint (i.e., not visible above) band of material that runs along its orbit named R/2004 S 1, discovered by the Cassini mission in July 2004.
Image credit: NASA/JPL-Caltech/SSI. Animation by Jason Major.
The lines of Saturn’s rings appear to get sharply bent as their reflected light passes through the upper atmosphere of the planet before being captured by Cassini’s camera in this raw image, acquired on June 9, 2016.
Enormous Saturn of course is, by volume, nearly all atmosphere with a solid core only about the size of Earth. The bands of tans, blues, purples and pale greens we see in Cassini images are just the tops of clouds, and even more transparent layers of atmosphere exist above those, gradually fading out into space. Like what astronauts see from orbit when the Moon passes behind these upper layers, getting squished in the process, Saturn’s rings appear to be distorted by the same refractive process for Cassini. It’s literally an optical illusion, as obviously the rings aren’t changing shape at all!
The image above has been cropped and rotated for artistic effect; see the original raw image here.
A crowning achievement of the Cassini mission to Saturn is the discovery of water vapor jets spraying out from Enceladus‘ southern pole. First witnessed by the spacecraft in 2005, these icy geysers propelled the little 320-mile-wide moon into the scientific spotlight. After 22 flybys of Enceladus during its nearly twelve years in orbit around Saturn, Cassini has gathered enough data to determine that there is a global subsurface ocean of salty liquid water beneath Enceladus’ frozen crust—an ocean that gets literally sprayed into space. Now, new findings from Cassini and researchers at the Planetary Science Institute—with a little help from a star called Epsilon Orionis—has shown that at least some of the vapor jets get a boost in activity when Enceladus is farther from Saturn.
Drumroll please… the little moon Telesto! (You like it, you really like it!) This image, captured by Cassini on Jan. 14, 2016, shows Saturn’s moon Telesto – a “leading trojan” of the much larger satellite Tethys.
A trojan moon is one that orbits a parent body within the same path as a more massive satellite, positioned at the Lagrangian points L4 and L5… usually at 60º ahead and behind within the orbit relative to the overall center (which, in the case of Tethys, is Saturn.)
The irregularly-shaped, 15-mile (24-km) -wide Telesto rides around Saturn ahead of Tethys, making it the moon’s “leading” trojan. Its slightly larger sister Calypso follows behind Tethys as the trailing trojan. All three orbit the ringed planet at a distance of over 183,000 miles (294,000 km).
After nearly eleven and a half years in orbit around Saturn the Cassini spacecraft has made its last-ever targeted flyby of Enceladus, the 320-mile-wide moon of Saturn that has intrigued scientists and the public alike with its active water ice geysers for more than a decade since their discovery. On Saturday Dec. 19, 2015, Cassini performed its E-22 flyby of Enceladus, coming within 3,106 miles (5,000 km) of the moon’s fractured and frozen surface as it sped by at over 21,000 mph. It captured some incredible images along the way, including the one above showing a crescent-lit Enceladus from its night side silhouetted against the hazy upper atmosphere of Saturn, 150,000 miles beyond.
Take a look through some more raw images from the E-22 flyby below.