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.”
The distant ice giant Uranus may not have been visited by a spacecraft since Voyager 2’s “Grand Tour” flyby in 1986 but the data gathered then is still being used today to make new discoveries. Most recently, researchers think they have found evidence of two previously unknown moons around Uranus, potentially bringing the planet’s count up to 29.
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.
If you’ve been a faithful reader of Lights in the Dark over the past five years you know that I just love Cassini (and you probably do too!) In orbit around Saturn since 2004, Cassini has taken us on an intimate tour of the Saturnian system for a decade now, revealing the incredible beauty of the ringed planet and its family of moons like no spacecraft ever has before. Thanks to Cassini and the Huygens probe, we have seen the surface of Titan for the first time, witnessed the jets of Enceladus, discovered many previously-unknown moons (and moonlets) and basically learned more about Saturn over the past ten years than since Galileo first pointed his telescope at it.
Although nearing the end of its life span, Cassini still has a few good years left and scientists are taking full advantage of its remaining time around Saturn to learn as much as they can before the spacecraft makes its final dive into the planet’s atmosphere in 2017.* The video above shows what awaits Cassini in the years ahead — some of its best discoveries may be yet to come. Check it out!
*The exact plan for the end of Cassini’s mission has not yet been finalized.
You don’t typically see Saturn’s rings looking like this, but then you can’t see in ultraviolet like Cassini (or many insects) can! The image above was acquired by the UVIS (UltraViolet Imaging Spectrograph) instrument aboard the Cassini-Huygens spacecraft on June 30, 2004, just as it was entering orbit around Saturn.
The area shown here is about 10,000 km (6,200 miles) across. It’s a small section of ring segments… just a portion of Saturn’s magnificent expanse of rings. Part of the C ring, toward Saturn, is along the left, and the inner edge of the B ring begins just right of the center. The colors are related to the composition of the ring particles; blue and green colors are from bright water ice, reds are rings with darker, “dirtier” particles.
While the colors aren’t “real” per se — our eyes simply can’t see UV light — the association of colors we can see to specific UV wavelengths allows scientists to accurately observe relative differences in the ring segments.
“It is cool that we can pick our own colors in the pictures we produce,” said Dr. Larry W. Esposito, a professor of Astrophysical and Planetary Sciences at the University of Colorado and UVIS Principal Investigator. “No person has ever seen ultraviolet light, although some butterflies can. Our pictures may thus represent a ‘butterfly’s-eye view’ of the Saturn system.”
Click the image to access a higher-resolution image on ESA’s Flickr page, and read more about the Cassini mission here.