Saturn's moon Prometheus creates streamer channels in the planet's rings. Credit: NASA/JPL/Space Science Institute
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I’ve frequently said the Cassini spacecraft is an artist, so when Carolyn Porco, the mission’s imaging team lead, mentioned on Twitter that Saturn’s moon Prometheus is akin to Michelangelo, I had to take a look. Wow, this gorgeous image is suitable for framing! Visible in the perturbed, thin F ring, is the potato-shaped Prometheus, and having performed the perturbing, it continues in its orbit. Click the image for the super-huge version.
Prometheus (148 kilometers, 92 miles across) periodically creates streamer-channels in the F ring, and the moon’s handiwork can be seen as the dark channels. Here’s a movie made from Cassini images showing this process:
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 1, 2010. A star is also visible through the rings near the center right of the image.
There are also some additional features in the F ring, courtesy of Prometheus.
This Cassini image shows icy particles in Saturn’s F ring clumping into giant snowballs as the moon Prometheus makes multiple swings by the ring. Scientists say that the gravitational pull of the moon sloshes ring material around, creating wake channels that trigger the formation of objects as large as 20 kilometers (12 miles) in diameter.
“Scientists have never seen objects actually form before,” said Carl Murray, a Cassini imaging team member based at Queen Mary, University of London. “We now have direct evidence of that process and the rowdy dance between the moons and bits of space debris.”
Using images obtained by NASA's Cassini mission, astronomers followed several of what are likely to be dozens of small moons orbiting within the outer edge of Saturn's A ring -- the outermost of the planet's large, dense rings -- from 2005 to 2009.
Scientists for NASA’s Cassini mission noticed some weird-looking propeller-like shapes in the outer edge of Saturn’s A ring. What could be creating these unusual contours? A closer look revealed they were being formed by dozens of moving moonlets. Normally, these kilometer-sized moons would have been almost impossible to see, since they are embedded within the rings. “However, their presence is betrayed by the large tell-tale ‘propeller’ structures they generate in the ring material on either side of them,” said Carolyn Porco, leader of the Cassini imaging team, and co-author on a new paper on these propeller moons. In an email, Porco said similar features had been seen earlier in other locations in Saturn’s rings, but were “much smaller, harder to see, and so numerous that there was no hope of following any one of them. The new propellers, and the moonlets that create them, are some ten times larger and much easier to identify and follow from image to image and year to year.”
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The team said the ability to watch as the embedded moons’ orbits evolve over time could give scientists valuable new clues about how planets form and grow around stars in young solar systems.
“What is outstanding about these new findings is the insight they ultimately will provide into the early stages of solar system formation,” said Porco, “when growing planets become large enough to open gaps in the ring material around them and ultimately truncate their own growth.”
The scientists have tracked eleven of these moons since 2006. Most are between one and several kilometers in diameter, too small to be imaged directly by Cassini’s cameras, but are only distinguishable by the unique double-armed propeller features.
The area in the middle of Saturn’s outermost dense A ring is now known as the “propeller belts,” and the new moonlets have been given appropriate names.
“You may find it amusing that these large propellers have unofficially been named after famous aviators,” Porco said. “Those flight enthusiasts among you will recognize Bleriot, Earhart, Santos-Dumont, and others.”
“You would expect any object that’s just orbiting Saturn on its own should stay in a constant path,” said lead author Matthew Tiscareno from Cornell University. “What we actually see is that the orbits are changing.”
The most likely explanation, he said, is that the moons are actually interacting with the disk: exchanging angular momentum with the ring particles around them either through gravity or by direct collisions.
Still, other explanations, like resonant interactions with more distant moons, have not been ruled out as causes.
Scientists will be keeping an eye on these wandering little moons in order to figure out if the disk itself is driving the changes, similar to the interactions that occur in young solar systems. If it is, Tiscareno said, this would be the first time such a measurement has been made directly.
A Cassini image of the moon Daphnis making waves in Saturn's rings. Credit: NASA/JPL/Space Science Institute
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Saturn’s moon Daphnis is only 8 kilometers wide, but it has a fairly substantial effect on the A ring, making waves on the ring’s edge. According to Carolyn Porco on Twitter, this is the closest look yet at this mini, moving moon. Daphnis resides in the Keeler Gap, which is about 42 km wide, but the moon’s eccentric orbit causes its distance from Saturn to vary by almost 9 km, and its inclination causes it to move up and down by about 17 km. That may not sound like much, but within a small gap, this variability causes the waves seen in the edges of the gap. We’ve only known about Daphnis’ existence since 2005, one of the many discoveries made by the Cassini spacecraft, and this is the first image where Daphnis is more than just a little dot. Click on the image to get a closer look.
This image is hot off the presses, as it was taken on July 5, 2010, and sent to Earth just yesterday (July 6). See below for a great new look at Saturn’s ring.
New raw image of Saturn's rings. Credit: NASA/JPL/Space Science Institute
Click the image for a larger version, and prepare to be wowed!
This is Saturn’s moon Dione, in crisp detail, against a hazy, ghostly Titan. Simply stunning.
The “wispy” terrain on Dione is visible, and on Titan are hints of atmospheric banding around Titan’s north pole. This view looks toward the Saturn-facing hemisphere of Dione (1123 kilometers, 698 miles across) and Titan (5150 kilometers, 3200 miles across), and was taken on April 10, 2010.
No images available yet from Cassini’s extremely close flyby of Titan over the weekend where it buzzed the hazy moon at an altitude of just 880 kilometers (547 miles) above the surface.
That is 70 kilometers (43 miles) lower than it has ever been at Titan before. The reason for attempting such a close pass is to try and establish if Titan has a magnetic field of its own. But the Cassini team went through hours and hours of calculations for this close flyby, as Titan’s atmosphere applies torque to objects flying through it, much the same way the flow of air would wiggle your hand around if you stuck it outside a moving car window. According to the Cassini website, when engineers calculated the most stable and safe angle for the spacecraft to fly, they found it was almost the same as the angle that would enable Cassini to point its high-gain antenna to Earth. So they cocked the spacecraft a fraction of a degree, enabling them to track the spacecraft in real-time during its closest approach. They set up the trajectory with thrusters firing throughout the flyby to maintain pointing automatically.
The images and data gathered should be amazing, as if everything went as planned, the flyby ended with the ultra violet imaging spectrograph (UVIS) instrument capturing a stellar occultation outbound from Titan. We’ll keep you posted!
Rhea poses with Saturn's rings; Janus and Prometheus are off in the distance. Credit: NASA/JPL/Space Science Institute. Click for larger version
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Oh, wow — what a gorgeous image! Just the latest from our resident artist in space, the Cassini spacecraft. Rhea, saturn’s second largest moon sits in front of the rings, joined by two smaller moons in the background. Rhea (1528 kilometers, 949 miles across) is in the center foreground. Janus (179 kilometers, 111 miles across) can be seen beyond the rings on the right of the image. Prometheus (86 kilometers, 53 miles across) is visible orbiting between the main rings and the thin F ring on the left of the image. Lit terrain seen on Rhea is on the area between that moon’s trailing hemisphere and anti-Saturn side. This view looks toward the northern, sunlit side of the rings from just above the ringplane.
If you like contrast images, there’s a great one below.
Saturn's rings contrast with the blackness of space. Credit: NASA/JPL/Space Science Institute
This image is a beautiful contrast between dark and light. Atlas can be seen just above the center of this Cassini spacecraft image as the moon orbits in the Roche Division between Saturn’s A ring and thin F ring.
Titan, Saturn's rings and Enceladus. Credit: NASA/JPL/SSI
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Wow. Cassini the artist has struck again, this time with amazing images from the close flyby of Enceladus that we wrote a preview about earlier this week. Cassini flew by Enceladus during the early hours of May 18 UTC, coming within about 435 kilometers (270 miles) of the moon’s surface. The raw images came in late last night, and in my inbox this morning was an email from Stuart Atkinson, (no relation, but great name) alerting me to the treasures. Stu himself has called this image “the new iconic image of the space age,” and Emily Lakdawalla of the Planetary Blog has called these images “some of the most amazing Cassini has captured yet.”
What you’re seeing here is hazy Titan, backlit by the Sun, with Saturn’s rings in the foreground– plus, at the way bottom is the limb of the night side of Enceladus’ south pole. Emily has created a flipped, annotated image (plus there’s more Enceladus jaw-droppers below:
nceladus, Titan, and the rings of Saturn (explained) Credit: NASA/JPL/SSI/annotated by Emily Lakdawa. Click for larger version.
The 'fountains' of Enceladus. Credit: NASA/JPL/SSI
Three huge “fountains” of Enceladus geysers are visible in this raw image taken by Cassini on May 18, 2010. The camera was pointing toward Enceladus at approximately 14,972 kilometers away, and the image was taken using the CL1 and CL2 filters. Emily, with her photo editing prowess, has created a movie from four different images as Cassini cruised closer to the moon.
Plus there’s this very interesting raw image from Cassini:
Raw image from Cassini on May 18. Credit: NASA/JPL/SSI
Explanations anyone?
Cassini will be flying by Titan in the early hours of May 20 UTC, coming within 1,400 kilometers (750 miles) of the surface. Although Cassini will primarily be doing radio science during this pass to detect subtle variations in the gravitational tug on the spacecraft by Titan, hopefully we’ll see some new visible light images of Titan, as well.
Saturn's rings, made dark in part as the planet casts its shadow across them, cut a striking figure before Saturn's largest moon, Titan. Credit: NASA/JPL/Space Science Institute
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There’s nothing up the sleeves of the Cassini imaging team in this image; it is real! Is the moon Titan being cut in half by Saturn’s rings? What is actually happening here is that the middle part of the rings are made dark as Saturn casts its shadow across them. Cassini was just in the right place at the right time, making it appear as though Titan is being sliced in half! The night side of the planet is to the left, out of the frame of the image. Illuminated Titan can be seen above, below and through gaps in the rings. Click the image for a larger version.
As an added benefit in this shot, Mimas (396 kilometers, 246 miles across) is near the bottom of the image, and Atlas (30 kilometers, 19 miles across) can barely be detected near the thin F ring just above the center right of the image. Lit terrain seen here is the area between the leading hemisphere and Saturn-facing side of Titan (5,150 kilometers, 3,200 miles across). This view looks toward the northern, sunlit side of the rings from just above the ringplane.
Below are a few more magical images from Cassini:
Here the moon Enceladus appears strung along a wispy ring of Saturn, likely the G ring. Look close and Enceladus’ plumes are visible, too.
Enceladus and a wispy ring. Credit: NASA/JPL/Space Science Institute Pandora and Epimetheus sit on Saturn's rings. Credit: NASA/JPL/Space Science Institute
Two of Saturn’s small moons appear to be sitting on Satun’s thin F ring in this image.
From the CICLOPS website:
Pandora (81 kilometers, 50 miles across) is on the left, and Epimetheus (113 kilometers, 70 miles across) is on the right. This view looks toward the northern, sunlit side of the rings from just above the ringplane. Both moons are closer to Cassini than the rings are. Pandora is slightly closer to Cassini than Epimetheus here.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 23, 2009. The view was acquired at a distance of approximately 1.3 million kilometers (808,000 miles) from Pandora and Epimetheus. Image scale is 8 kilometers (5 miles) per pixel.
Artist's impression of the Cassini spacecraft making a close pass by Saturn's inner moon Enceladus to study plumes from geysers that erupt from giant fissures in the moon's southern polar region. Copyright 2008 Karl Kofoed/NASA. Click for full size version.
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Observations from two instruments on the Cassini spacecraft shows the moon Enceladus leaves a complex pattern of ripples and bubbles in its wake as it orbit Saturn. The ringed planet’s magnetosphere is filled with electrically charged particles (plasma) originating from both the planet and its moons, and as Enceladus plows through the plasma “spiky” features form that represent bubbles of low energy particles, said Sheila Kanani who led a team of scientists from University College, London who discovered the phenomenon.
Cassini has made nine flybys of the icy, geyser-filled moon Enceladus (Saturn’s sixth-largest moon) since 2005. The closest of these have taken the spacecraft’s suite of instruments just 25 km from Enceladus’s surface, which scientists believe conceals a saline ocean. Heated vents at the south pole of the moon release a plume of material, consisting mainly of icy grains and water vapour, into space.
Measurements from the Cassini Plasma Spectrometer (CAPS) and the Magnetospheric IMaging Instrument (MIMI) show that both the moon and its plume are continuously soaking up the plasma, which rushes past at around 30 kilometers per second, leaving a cavity downstream. In addition, the most energetic particles which zoom up and down Saturn’s magnetic field lines are swept up, leaving a much larger void in the high energy plasma. Material from Enceladus, both dust and gas, is also being charged and forming new plasma.
The mysterious spiky features in the CAPS data shows a complex picture of readjustment downstream from Enceladus.
“Eventually the plasma closes the gap downstream from Enceladus but our observations show that this isn’t happening in a smooth, orderly fashion. We are seeing spiky features in the plasma that last between a few tens of seconds and a minute or two. We think that these might represent bubbles of low energy particles formed as the plasma fills the gap from different directions,” said Kanani. Since Cassini arrived at Saturn, it has been building up a picture of the vital and unexpected role that Enceladus plays in Saturn’s magnetosphere.
“Enceladus is the source of most of the plasma in Saturn’s magnetosphere, with ionised water and oxygen originating from the vents forming a big torus of plasma that surrounds Saturn. We may see these spiky features in the wake of Saturn’s other moons as they interact with the plasma but, to date, we have only studied Enceladus in sufficient detail,” said Kanani.
She presented her results at the Royal Astronomical Society’s National Astronomy Meeting in Glasgow, Scotland this week.
NASA’s Cassini spacecraft has captured images of lightning on Saturn, allowing the scientists to create the first movie showing lightning flashing on another planet. “Ever since the beginning of the Cassini mission, a major goal of the Imaging Team has been the detection of Saturnian lightning,” said team leader Carolyn Porco in an email. Porco said the ability to capture the lightning was a direct result of the dimming of the ringshine on the night side of the planet during last year’s Saturn equinox. “And these flashes have been shown to be coincident in time with the emission of powerful electrostatic discharges intercepted by the Cassini Radio and Plasma Wave experiment,” Porco added.
This figure illustrates the unexpected and bizarre pattern of daytime temperatures found on Saturn's small inner moon Mimas (396 kilometers, or 246 miles, in diameter). Credit: NASA/JPL/GSFC/SWRI/SSI
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Mimas has drawn a fair amount of attention with its “Death Star”-like appearance, but with new images from the Cassini spacecraft, this icy moon of Saturn has just gotten a lot more interesting. The highest-resolution-yet temperature map and images of Mimas reveal surprising patterns on the surface of the small moon, including unexpected hot regions that resemble “Pac-Man” eating the Death Star crater (officially known as Herschel Crater), as well as striking bands of light and dark in crater walls. “After much deliberation, we have concluded: Mimas is NOT boring,” said Carolyn Porco, Cassini imaging team leader, in an e-mail about the new images. “Who knew?!” And best of all, Porco added, “be sure you have a pair of red/green glasses handy ’cause you won’t want to miss peering into gigantic Herschel crater in 3D!”
Cassini collected the data on Feb. 13, and Porco said the team has spent some quality time poring over the images. She said the details in the moon’s craters that reminded the imaging team of features seen on Phoebe and Hyperion, plus the thermal signature is very peculiar and the team can’t yet explain it. Herschel Crater in 3-D. Credit: NASA/JPL/Space Science Institute. Click for larger version.
“Other moons usually grab the spotlight, but it turns out Mimas is more bizarre than we thought it was,” said Linda Spilker, Cassini project scientist at JPL. “It has certainly given us some new puzzles.”
Scientists were expecting smoothly varying temperatures peaking in the early afternoon near the equator. Instead, the warmest region was in the morning, along one edge of the moon’s disk, making a sharply defined Pac-Man shape, with temperatures around 92 Kelvin (minus 294 degrees Fahrenheit). The rest of the moon was much colder, around 77 Kelvin (minus 320 degrees Fahrenheit). A smaller warm spot – the dot in Pac-Man’s mouth – showed up around Herschel, with a temperature around 84 Kelvin (minus 310 degrees Fahrenheit).
The warm spot around Herschel makes sense because tall crater walls (about 5 kilometers, or 3 miles, high) can trap heat inside the crater. But scientists were completely baffled by the sharp, V-shaped pattern.
“We suspect the temperatures are revealing differences in texture on the surface,” said John Spencer, who works with Cassini’s composite infrared spectrometer. “It’s maybe something like the difference between old, dense snow and freshly fallen powder.”
Denser ice quickly conducts the heat of the sun away from the surface, keeping it cold during the day. Powdery ice is more insulating and traps the sun’s heat at the surface, so the surface warms up.
Even if surface texture variations are to blame, scientists are still trying to figure out why there are such sharp boundaries between the regions, Spencer said. It is possible that the impact that created Herschel Crater melted surface ice and spread water across the moon. That liquid may have flash-frozen into a hard surface. But it is hard to understand why this dense top layer would remain intact when meteorites and other space debris should have pulverized it by now, Spencer said. Dark regions below bright crater walls and streaks on some of the walls are seen in this mosaic of Saturn's moon Mimas. Credit: NASA/JPL/Space Science Institute. Click for larger version.
Icy spray from the E ring, one of Saturn’s outer rings, should also keep Mimas relatively light-colored, but the new visible-light images from the flyby paint a picture of surprising contrasts. Cassini imaging team scientists didn’t expect to see dark streaks trailing down the bright crater walls or a continuous, narrow pile of concentrated dark debris tracing the foot of each wall.
The pattern may appear because of the way the surface of Mimas ages, said Paul Helfenstein, a Cassini imaging team associate based at Cornell University, Ithaca, N.Y. Over time, the moon’s surface appears to accumulate a thin veil of silicate minerals or carbon-rich particles, possibly because of meteor dust falling onto the moon, or impurities already embedded in surface ice.
As the sun’s warming rays and the vacuum of space evaporate the brighter ice, the darker material is concentrated and left behind. Gravity pulls the dark material down the crater walls, exposing fresh ice underneath. Although similar effects are seen on other moons of Saturn, the visibility of these contrasts on a moon continually re-paved with small particles from the E ring helps scientists estimate rates of change on other satellites.
“These processes are not unique to Mimas, but the new high-definition images are like Rosetta stones for interpreting them,” Helfenstein said.
