Shepherd moon Prometheus hovers just inside the reflective F ring
Lit by eerie, reflected light from Saturn’s F ring (and a casting a faint shadow through a haze of icy “mist”) Saturn’s moon Prometheus can be seen in the raw image above, captured by Cassini’s narrow-angle camera on Feb. 5 from a distance of 667,596 miles (1,074,392 km). It’s also receiving some light reflected off Saturn, which is off frame at the top (where the outermost edge of the A ring and the Keeler gap can be seen.)
As the potato-shaped Prometheus approaches the ring it yanks fine, icy material in towards itself, temporarily stretching the bright particles into long streamers and gaps and even kicking up bright clumps in the ring. It’s a visual demonstration of gravity at work! Watch an animation of this below, made from images acquired just before and after the one above:
Streamers and clumps created by the passing Prometheus on Feb. 5, 2014. (NASA/JPL/SSI. Animation by Jason Major.)
At its longest Prometheus is about 92 miles (148 km) across, but only 42 miles (68 km) in width. It circles Saturn in a wave-shaped, scalloping orbit once every 14.7 hours.
Cassini narrow-angle camera image of Janus from Sept. 10, 2013 (NASA/JPL-Caltech/SSI)
One of 62 moons discovered thus far orbiting giant Saturn, Janus is a 111-mile (179-km) -wide pockmarked potato composed of rock and ice rubble. The image above shows Janus as seen with Cassini’s narrow-angle camera on September 10, 2013, from a distance of 621,000 miles (1 million km), floating against the blackness of space.
Despite its apparent isolation in the image above, though, Janus isn’t alone. It shares its orbit around Saturn with its slightly smaller sister moon Epimetheus, and they regularly catch up to each other — and even switch places.
Janus and Epimetheus: Saturn’s “dancing moons” (NASA/JPL/SSI)
Janus and Epimetheus travel in nearly the same track, about 94,100 miles (151,500 km) out from Saturn. They occasionally pass each other, their gravity causing them to switch speeds and positions as they do; Janus goes faster and higher one time, slower and lower the next – but the two never come within more than about 6,200 miles of each other.
The two moons switch positions roughly every four years.
This scenario is referred to in astrophysics as a 1:1 resonance. Astronomers were initially confused when the moons were discovered in 1966 as it wasn’t known at the time that there were actually two separate moons in a single orbit. (This wasn’t confirmed until Voyager 1’s visit to Saturn in 1980.) It’s been suggested that Janus and Epimetheus will eventually come to orbit a single Lagrangian point around Saturn instead of trading places… in about another 20 million years.
The view above looks toward the Saturn-facing side of Janus. Covered in both dark and light colored material, Janus’ surface is thought to be coated with a layer of fine dust that slides down its steeper slopes, revealing the brighter ice beneath.
Cassini image of Janus from April 2010 (NASA/JPL-Caltech/SSI)
We recently interviewed Dr. Kevin Grazier, on of the scientist who has worked extensively on the Cassini mission. Here’s what he had to tell us about that mission’s discoveries.
“My name is Kevin Grazier. I am a planetary scientist, and for my research I do long-term integrations or simulations of early solar system evolution. I’m a former scientist on the Cassini mission and a consultant to several TV series such as Defiance, Falling Skies, the movie Gravity, and formerly, Battlestar Galactica.”
What are Cassini’s most amazing discoveries?
“Cassini has essentially rewritten the book on the Saturn system. I was on the spacecraft team for 15 years. I worked as a science planner and as the Investigation Scientist on the ISS instrument. (That’s Imaging Science Subsystem, not International Space Station.) And of the discoveries we found, I’m trying to think of what I’d call or classify as the most exciting.”
“One was predicted – the fact that it was believed that there could be ice volcanoes on Enceladus. And as a matter of fact, there are volcanoes on Enceladus, or active venting, however you want to look at that. Those vents create the “E” ring, so we have a ring created by material vented off Enceladus. That’s pretty exciting, because we see an active object venting material, and there aren’t a lot of active objects in the solar system.”
This mosaic of Titan was created from the first flyby of the moon by Cassini in 2004. Credit: NASA/JPL/SS
“The surface of Titan is really fantastic. We have open oceans or seas of hydrcarbons on Titan. We have the possibility of an open ocean underneath the crust, just like we believe is under the surface of Europa. We have one image which seems to capture what might be a volcanic eruption. That’s important, because in the outer solar system, planetary science considers ice a rock. What a rock is defined as depends on where you are in the solar system. So in the outer solar system, ice is a rock. All of the moons in the outer solar system except Io have icy crusts. Now, if you have a volcanic eruption on Titan, we have an eruption of magma, and if ice is a rock, that eruption is water. So we have evidence of magma chambers which could be cauldrons of life-giving water.”
“How cool is that? How counter-intuitive is that? How science-fiction-y is that? That one of the most interesting places to look for is a lava chamber or magma chamber that could be suitable for sustaining life. I think that’s really exciting.”
Saturn makes a beautifully striped ornament in this natural-color image, showing its north polar hexagon and central vortex (Credit: NASA/JPL-Caltech/Space Science Institute)
Cassini couldn’t make it to the mall this year to do any Christmas shopping but that’s ok: we’re all getting something even better in our stockings than anything store-bought! To celebrate the holiday season the Cassini team has shared some truly incredible images of Saturn and some of its many moons for the world to “ooh” and “ahh” over. So stoke the fire, pour yourself a glass of egg nog, sit back and marvel at some sights from a wintry wonderland 900 million miles away…
Thanks, Cassini… these are just what I’ve always wanted! (How’d you know?)
Saturn’s southern hemisphere is growing more and more blue as winter approaches there — a coloration similar to what was once seen in the north when Cassini first arrived in 2004:
Saturn’s southern hemisphere images from a million miles away (Credit: NASA/JPL-Caltech/Space Science Institute)
(The small dark spot near the center right of the image above is the shadow of the shepherd moon Prometheus.)
Titan and Rhea, Saturn’s two largest moons, pose for Cassini:
Rhea (front) and Titan, images by Cassini in June 2011 (Credit: NASA/JPL-Caltech/Space Science Institute)
The two moons may look like they’re almost touching but in reality they were nearly half a million miles apart!
Titan’s northern “land of lakes” is visible in this image, captured by Cassini with a special spectral filter able to pierce through the moon’s thick haze:
Titan images by Cassini on Oct. 7, 2013 (Credit: NASA/JPL-Caltech/Space Science Institute)
The frozen, snowball-like surface of the 313-mile-wide moon Enceladus:
Enceladus: a highly-reflective and icy “snowball in space” (Credit: NASA/JPL-Caltech/Space Science Institute)
(Even though Enceladus is most famous for its icy geysers, first observed by Cassini in 2005, in these images they are not visible due to the lighting situations.)
Seen in a different illumination angle and in filters sensitive to UV, visible, and infrared light the many fractures and folds of Enceladus’ frozen surface become apparent:
View of the trailing face of Enceladus (Credit: NASA/JPL-Caltech/Space Science Institute)
Because of Cassini’s long-duration, multi-season stay in orbit around Saturn, researchers have been able to learn more about the ringed planet and its fascinating family of moons than ever before possible. Cassini is now going into its tenth year at Saturn and with much more research planned, we can only imagine what discoveries (and images!) are yet to come in the new year(s) ahead.
“Until Cassini arrived at Saturn, we didn’t know about the hydrocarbon lakes of Titan, the active drama of Enceladus’ jets, and the intricate patterns at Saturn’s poles,” said Linda Spilker, the Cassini project scientist at NASA’s Jet Propulsion Laboratory. “Spectacular images like these highlight that Cassini has given us the gift of knowledge, which we have been so excited to share with everyone.”
The full mosaic from the Cassini imaging team of Saturn on July 19, 2013... the "Day the Earth Smiled"
Just to demonstrate how far-reaching that Saturn snapshot of Earth this year was, the Skopje Astronomical Society (from Macedonia) made a video celebrating “The Day The Earth Smiled”, when the Cassini spacecraft looked at Earth on July 19 and thousands of people made pictures and video showing what they were doing at that time.
Watch the video, then look at some stunning pictures of Saturn below the jump.
Saturn and its rings, as seen from above the planet by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute. Assembled by Gordan Ugarkovic.
Mosaic of Saturn seen in eclipse in September 2006. Earth is the bright dot just inside the F ring at upper left. (CICLOPS/NASA/JPL-Caltech/SSI)A false-color view of Saturn’s storm, as seen through Cassini’s wide-angle camera. The blue bands at the edge are Saturn’s rings. Credit: NASA/JPL-Caltech/SSISaturn, its rings and three moons are visible in this image from Cassini. Credit: NASA/ESA
A white storm in Saturn’s northern hemisphere, as seen on Dec. 14, 2010. Credit: Anthony Wesley
While 2014 budget negotiations are not finalized yet, there’s already some noise of concern in different space communities that depend on NASA. Here’s a brief roundup of some of the news lately:
Could the Cassini Saturn mission get the axe? Wired’s Adam Mann warns that NASA may not be able to fund all of its planetary science missions in the coming year. Based on a statement that Jim Green, NASA’s planetary science director, made to an agency advisory council earlier this month, Mann narrows in on the Curiosity and Cassini missions as the big flagship missions that are requiring the most in terms of resources. Cassini is functioning perfectly and providing reams of data from Saturn and its moons, causing concern from planetary scientists about losing it early.
Only one commercial crew partner? NASA issued a cautious news release this week saying it is prepared to launch Americans from their own soil in 2017, “subject to the availability of adequate funding.” The agency is now moving into a new phase of its commercial crew program called Commercial Crew Transportation Capability (CCtCap), saying it is prepared to “award one or more CCtCap contracts no later than September 2014.” That means that the three companies currently funded — Boeing Co., Sierra Nevada Corp. and SpaceX — may face stiff competition for more money.
New report suggesting stopping NASA’s human spaceflight program: Before reading any further, do not jump to conclusions — making recommendations like this is a common practice by the Congressional Budget Office, which looks at all possibilities as it presents options for spending. Still, Space Politics’ Jeff Foust presents the report and generates some interesting comments after his story about the value of human spaceflight. For context, NASA and its international agency partners will need to make a decision fairly soon about continuing space station operations past 2020, so it’s possible the human spaceflight program could change.
What do you think of these proposals? Let us know in the comments.
The "pale blue dot" of Earth as seen from Cassini on July 19, 2013.
This summer, for the first time ever, the world was informed that its picture was going to be taken from nearly a billion miles away as the Cassini spacecraft captured images of Saturn in eclipse on July 19. On that day we were asked to take a moment and smile and wave at Saturn, from wherever we were, because the faint light from our planet would be captured by Cassini’s camera, shielded by Saturn from the harsh glare of the Sun.
A few preliminary images were released just a few days later showing the “pale blue dot” of Earth nestled within the glowing bands of Saturn’s rings. It was an amazing perspective of our planet, and we were promised that the full mosaic of Cassini images was being worked on and would be revealed in the fall.
Well, it’s fall, and here it is:
The full mosaic from the Cassini imaging team of Saturn on July 19, 2013… the “Day the Earth Smiled”
“After much work, the mosaic that marks that moment the inhabitants of Earth looked up and smiled at the sheer joy of being alive is finally here. In its combination of beauty and meaning, it is perhaps the most unusual image ever taken in the history of the space program.”
In this panorama of the Saturnian system, a view spanning 404,880 miles (651,591 km), we see the planet silhouetted against the light from the Sun. It’s a unique perspective that highlights the icy, reflective particles that make up its majestic rings and also allows our own planet to be seen, over 900 million miles distant. And it’s not just Earth that was captured, but the Moon, Venus, and Mars were caught in the shot too.
According to the description on the CICLOPS page, “Earth’s twin, Venus, appears as a bright white dot in the upper left quadrant of the mosaic… between the G and E rings. Mars also appears as a faint red dot embedded in the outer edge of the E ring, above and to the left of Venus.”
This was no simple point-and-click. Over 320 images were captured by Cassini on July 19 over a period of four hours, and this mosaic was assembled from 141 of those images. Because the spacecraft, Saturn, and its moons were all in constant motion during that time, affecting not only positions but also levels of illumination, imaging specialists had to adjust for that to create the single image you see above. So while all elements may not be precisely where they were at the same moment in time, the final result is no less stunning.
“This version was processed for balance and beauty,” it says in the description. (And I’ve no argument with that.)
See below for an annotated version showing the position of all visible objects, and read the full article on the CICLOPS page for an in-depth description of this gorgeous and historic image.
2013 Saturn mosaic, annotated version.
“I hope long into the future, when people look again at this image, they will recall the moment when, as crazy as it might have seemed, they were there, they were aware, and they smiled.”
All images credit NASA/JPL-Caltech/Space Science Institute
UPDATE 11/13: CICLOPS Director Carolyn Porco describes how this image was acquired and assembled in this interview video from the World Science Festival:
Titan's north pole is home to many methane lakes. Credit: NASA
A combination of exceptionally clear weather, the steady approach of northern summer, and a poleward orbital path has given Cassini — and Cassini scientists — unprecedented views of countless lakes scattered across Titan’s north polar region. In the near-infrared mosaic above they can be seen as dark splotches and speckles scattered around the moon’s north pole. Previously observed mainly via radar, these are the best visual and infrared wavelength images ever obtained of Titan’s northern “land o’ lakes!”
Titan is currently the only other world besides Earth known to have stable bodies of liquid on its surface, but unlike Earth, Titan’s lakes aren’t filled with water — instead they’re full of liquid methane and ethane, organic compounds which are gases on Earth but liquids in Titan’s incredibly chilly -290º F (-180º C) environment.
While one large lake and a few smaller ones have been previously identified at Titan’s south pole, curiously almost all of Titan’s lakes appear near the moon’s north pole.
Infrared observations of Titan’s northern lakes. The cross marks Titan’s geographic north pole. (NASA/JPL-Caltech/SSI)
For an idea of scale, the large lake at the upper right above (and the largest lake on Titan) Kraken Mare is comparative in size to the Caspian Sea and Lake Superior combined. Kraken Mare is so large that sunlight was seen reflecting off its surface in 2009. Punga Mare, nearest Titan’s pole, is 240 miles (386 km) across.
Besides revealing the (uncannily) smooth surfaces of lakes — which appear dark in near-infrared wavelengths but would also be darker than the surrounding landscape in visible light — these Cassini images also show an unusually bright terrain surrounding them. Since the majority of Titan’s lakes are found within this bright region it’s thought that there could be a geologic correlation; is this Titan’s version of karst terrain, like what’s found in the southeastern U.S. and New Mexico? Could these lakes be merely the visible surfaces of a vast underground hydrocarbon aquifer? Or are they shallow pools filling depressions in an ancient lava flow?
Annotated infrared mosaic of Titan’s north pole (NASA/JPL-Caltech/SSI)
Or, are they the remains of once-larger lakes and seas which have since evaporated? The orange-hued regions in the false-color mosaic may be evaporite — the Titan equivalent of salt flats on Earth. The evaporated material is thought to be organic chemicals originally from Titan’s haze particles that were once dissolved in liquid methane.
“Is this an indication that with increased warmth, the seas and lakes are starting to evaporate, leaving behind a deposit of organic material,” wrote Carolyn Porco, Cassini Imaging Team Leader, in an email earlier today. “…in other words, the Titan equivalent of a salt-flat?”
The largest lake at Titan’s south pole, Ontario Lacus, has been previously compared to such an ephemeral lake in Namibia called the Etosha Pan. (Read more here.)
These observations are only possible because of the extended and long-term study of Saturn and its family of moons by the Cassini spacecraft, which began with its establishing orbit in 2004 and has since continued across multiple seasons over a third of the ringed planet’s year. The existence of methane lakes on Titan is undoubtedly fascinating, but how deep the lakes are, where they came from and how they behave in Titan’s environment have yet to be discovered. Luckily, the changing season is on our side.
“Titan’s northern lakes region is one of the most Earth-like and intriguing in the solar system,” said Linda Spilker, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We know lakes here change with the seasons, and Cassini’s long mission at Saturn gives us the opportunity to watch the seasons change at Titan, too. Now that the sun is shining in the north and we have these wonderful views, we can begin to compare the different data sets and tease out what Titan’s lakes are doing near the north pole.”
The images shown above were obtained by Cassini’s visual and infrared mapping spectrometer (VIMS) during a close flyby of Titan on Sept. 12, 2013.
Read more on the Cassini Imaging Central Laboratory for Operations (CICLOPS) site here and on the NASA site here.
“But how thrilling it is to still be uncovering new territory on this fascinating moon… a place that, until Cassini’s arrival at Saturn nearly 10 years ago, was the largest single expanse of unseen terrain we had remaining in our solar system. Our adventures here have been the very essence of exploration. And it’s not over yet!”
Saturn and its rings, as seen from above the planet by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute/Gordan Ugarkovic
So what did NASA do during the US government shutdown? You can’t just turn off spacecraft that are operating millions of miles away, so missions like the Mars rovers and the Cassini spacecraft at Saturn continued to send back images to Earth during the 16 days that most of NASA wasn’t up and running like usual. On October 10, 2013, as Cassini flew high above the planet’s equatorial plane, the spacecraft’s camera took 36 images of Saturn, a dozen each using the various red, green, and blue filters used to create color images. The images were transferred back to Earth and put on the Cassini raw images page. Gordan Ugarkovic from Croatia, and a member of the image editing wizards at UnmannedSpaceflight.com, grabbed the raw files, processed them, then assembled the images into this jaw-dropping mosaic.
This is a view from Saturn that we could never get from Earth; only a spacecraft orbiting the planet could take it. You can see the north pole and the swirling maelstrom of clouds that creates the hexagonal polar vortex, the thin bands in Saturn’s atmosphere, and — of course — what really stands out is the incredible view of Saturn’s rings. To see the original 3 MB version, see this page on UMSF.
“You shouldn’t be surprised to see processing artifacts here and there,” cautioned Ugarkovic via email to Universe Today. “It is, after all, based on raw JPEG images only.”
But in the words of UMSF’s Astro0, “That’s the sort of view I’ve dreamed I would only ever see in a science fiction movie or if we had some kind of amazing futuristic spacecraft orbiting around that distant ringed planet….WAIT! We do!”
For more of what NASA did during the shutdown, Bill Dunford at Riding With Robots put together a great summary, quoting the @SarcasticRover that “You can’t shut down awesome.” Bill started the #ThingsNASAMightTweet hashtag that reminded everyone of all the things NASA does, but they couldn’t tweet about during the shutdown. People from around the world chimed in, adding what was important to them about NASA, and as of today, tweets with that hashtag have passed 27 million impressions.
