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The Cassini team posted this image today, sending “bats wishes” for a happy, healthy and fun Halloween. And this give all of us here at Universe Today a chance to wish everyone a fun, safe, almost-full-Moon-lit, eat-your-favorite-treats, happy Hallow’s Eve. Click the image for a larger version.
Also, as a heads up, Cassini will be flying by the moon Enceladus next week, on Nov. 2, approaching within about 100 kilometers (62 miles) of the surface. The spacecraft has gone closer during a previous flyby (25 kilometers or 15 miles), but this time it will be going deep into the heart of the plume from the geysers on the tiger-striped moon. The objective is to analyze the particles in the plume with instruments that can detect the size, mass, charge, speed and composition. This will happen at about 7:40 a.m. UTC and the spacecraft will spend only about a minute in the plume.
Wow! This is really neat! We’ve long known that Saturn has aurorae, and the Cassini team recently took a series of images to see if they could catch an aurora in action near Saturn’s north pole. As always, the folks at UnmannedSpaceflight.com are always on the lookout for the latest images being beamed back to Earth, and one of the UMSFer’s, Astro0, saw this image series, realized what the Cassini team was trying to do, and used the images to put together this movie. You’ll see Saturn’s limb, moving stars, streaks that are likely cosmic ray hits, and flaring aurorae, or “curtains of light” that can sometimes rise 1,200 miles (2,000 km) above the cloud tops near Saturn’s poles. Astronomers say that while aurorae on Earth shine for a few hours at most, on Saturn they can last for days. Additionally, if you were on Saturn, the aurora would look like a faint red glow. Most of the energy in Saturn’s aurora is not in the form of visible light, though and instead they mostly glow in ultraviolet (UV) or infrared wavelengths. Read our previous article about the infrared aurorae at Saturn.
Artist concept of the new Saturnian Ring. Image courtesy Anne Verbiscer
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The Spitzer Space Telescope has spied an enormous ring around Saturn, the largest and farthest distant band around this ringed world. Just how big is this ring? “If you had infrared eyes like Spitzer,” said Anne Verbiscer, research astronomer at the University of Virginia, Charlottesville, “from Earth, it would look like one full moon on either side of Saturn.” That’s incredibly huge! The bulk of its material starts about six million kilometers (3.7 million miles) away from the planet and extends outward roughly another 12 million kilometers (7.4 million miles). A billion Earths could fit in the volume of space this ring occupies.
So, why hasn’t this gigantic structure been detected previously?
“It is very, very faint; extremely tenuous,” Verbiscer told Universe Today. “If you were standing inside the ring you wouldn’t even know it. In a cubic kilometer of space there are only 10-20 particles. The particles are about the same size as fog particles, but they are very spread out. We’re just looking at the thermal emissions these little particles are giving off; we’re not looking at reflected sunlight at all in the observations we did with Spitzer. That’s what makes Spitzer the perfect instrument to use to try and find such a dust structure. This ring is completely analogous to debris disks around other stars that Spitzer has observed.”
The research team didn’t just stumble upon this ring; they were searching for it. The team includes Verbiscer, Douglas Hamilton of the University of Maryland, College Park, and Michael Skrutskie, of the University of Virginia, Charlottesville. They used the longer-wavelength infrared camera on Spitzer, called the multiband imaging photometer, and did their observations in February 2009 before Spitzer ran out of coolant in May and began its “warm” mission. The dark and light side of Iapetus. Credit: NASA/JPL/Space Science Institute
“For more than 300 years, people have been trying to explain the appearance of Saturn’s moon Iapetus, (which was discovered by Giovanni Cassini in 1671) and why one side of the moon is light and the other very dark,” said Verbiscer. “For the past 35 years, another moon, Phoebe has come up as a possible explanation, , as there is a connection between those two moons. Phoebe itself is very, very dark, and it matches the albedo or brightness of the dark material of Iapetus’ leading hemisphere. Phoebe has a retrograde orbit and Iapetus is in a pro-grade orbit. So if particles are launched off of Phoebe and spiral inward toward Saturn they would be smacking Iapetus right on that leading hemisphere.”
Verbiscer said that dynamically, this explanation for Iapetus’ dark side has been talked about and tried to be modeled. But no one had thought of using Spitzer to look for any dust in that area. “So, that was our idea,” she said. “The title of our proposal was ‘A New Saturnian Ring.’ We were definitely looking for a dust structure associated with Phoebe and in the same orbit, and that is precisely what we see.”
Verbiscer said it would be very difficult even for the Cassini spacecraft, and especially the imaging cameras to see this ring, since it shows up only in infrared. Plus Cassini is inside of this ring, and would have to look out past Saturn’s other rings. “This ring is so big but yet so faint, it would be difficult to know when you were looking at it and when you weren’t.”
The vertical height and orbital inclination of this ring matches perfectly with Phoebe’s orbit on the sky. “If you were to plot where Phoebe appears over time as it goes around Saturn, the ring matches exactly, Verbiscer said. “Think of a quarter spinning on a table; the ring has the same vertical tip to it, and Phoebe’s orbit does the same type of thing.”
As to whether the dust particles from Phoebe itself or if Phoebe “shepherding” some particles into that configuration, the scientists don’t have definite proof, but most likely the dust particles are from Phoebe. “We don’t have firm confirmation of that, but it is strongly suggestive that it comes from Phoebe,” Verbiscer said. “The materials all together amounts to what you would get from excavating a crater about a kilometer in diameter on Phoebe.” Cassini image of Phoebe. Credit: NASA/JPL
Phoebe is 200 km across and heavily cratered, so a 1 km crater is not an overly huge crater. “So, we can’t look at a certain crater on Phoebe and say that one created the ring,” Verbiscer explained. “It’s likely it’s from several different smaller impacts, and ring keeps getting supplied from subsequent impacts and micrometeorites hitting Phoebe, launching material into this ring, putting dust and material from Phoebe’s surface into a Phoebe-like orbit.”
But there still is a bit of a mystery about the color of Iapetus’ leading hemisphere.
The two moons have frequently been compared in composition, and in near infrared, they share absorption features. In the ultraviolet, however, the spectra don’t match as well. “In terms of color, on Iapetus, the dark color looks a little more red compared to Phoebe, so there is a little color mismatch,” Verbiscer said. “It could be the particles launched from Phoebe mix with whatever is on Iapetus, which might account for the color difference. That might be something interesting to explore, to do some spectral mixing models to come up with some primordial Iapetus material and mix with Phoebe’s material see if they get reddened somehow.”
The ring itself is too faint to take a spectra to try and determine what materials make up the ring, but the assumptions are the materials come from the top surface of Pheobe’s cratered surface, which also might include some ice. Cassini close-ups of the moon from 2004 show bright craters, hinting that ice is close to the surface.
Spitzer was able to sense the glow of the cool dust, which is only about 80 Kelvin (minus 316 degrees Fahrenheit). Cool objects shine with infrared, or thermal radiation; for example, even a cup of ice cream is blazing with infrared light. “By focusing on the glow of the ring’s cool dust, Spitzer made it easy to find,” said Verbiscer.
Lead image caption: Artist concept of the new Saturnian Ring. Credit: NASA/JPL-Caltech/R. Hurt (SSC) The inset credit (Saturn, Phoebe, and Iapetus) is NASA/JPL/SSI. Image courtesy Anne Verbiscer
Ripples in Saturn's F ring. Credit: NASA/JPL/Space Science Institute
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Two shepherding moons continue to affect Saturn’s F ring in this amazing image captured by Cassini. Pandora on the outside of the ring and Prometheus on the inside, periodically create what are called “streamer-channels,” seen here in the F ring. The potato-shaped Prometheus pulls a streamer of material from the ring and leaves behind a dark channel. During its 14.7-hour orbit of Saturn, Prometheus (102 kilometers, or 63 miles across) reaches the point in its elliptical path, called apoapse, where it is farthest away from Saturn and closest to the F ring, and the moon’s gravity is just strong enough to draw a “streamer” of material out of the core region of the F ring.
The creation of such streamers and channels occurs in a cycle that repeats each Prometheus orbit: when Prometheus again reaches apoapse, it draws another streamer of material from the F ring. But since Prometheus orbits faster than the material in the ring, this new streamer is pulled from a different location in the ring about 3.2 degrees (in longitude) ahead of the previous one.
In this way, a whole series of streamer-channels is created along the F ring. In some observations, 10 to 15 streamer-channels can easily be seen in the F ring at one time.
This view looks toward the northern, sunlit side of the rings from about 10 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 20, 2009. The view was obtained at a distance of approximately 2.3 million kilometers (1.4 million miles) from Saturn. Image scale is 13 kilometers (8 miles) per pixel.
Crescent Rhea and Saturn's rings. Credit: NASA/JPL/Space Science Institute
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The Cassini team released some incredible images earlier this week of the Saturn system during equinox, and followed up with this beauty of a crescent moon Rhea beneath the rings of Saturn. NASA has also put together a multimedia presentation of recent pictures of Saturn, set to music, and it is stunning. Run, don’t walk and click here to watch. (Flash required)
With these great images, it is no wonder that the leader of the Cassini imaging team, Carolyn Porco has been presented with an award for her work, the Lennart Nilsson Award for photography for capturing “worlds that are otherwise hidden from human sight.” The award committee’s citation reads:
“Carolyn Porco combines the finest techniques of planetary exploration and scientific research with aesthetic finesse and educational talent. While her images, which depict the heavenly bodies of the Saturn system with unique precision, serve as tools for the world’s leading experts, they also reveal the beauty of the universe in a manner that is an inspiration to one and all.”
Congratulations Dr. Porco!
Here’s some info about the image above:
Rhea (1528 kilometers, 949 miles across) is near the middle of the bottom of the image. This view looks toward the northern, sunlit side of the rings from about 4 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft wide-angle camera on Aug. 24, 2009. The view was obtained at a distance of approximately 1.6 million kilometers (994,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 137 degrees. Image scale is 95 kilometers (59 miles) per pixel.
Saturn at Equinox. credit: NASA/JPL/Space Science Institute
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Every 14.8 Earth years, equinox occurs at Saturn. But this is the first time there has been a spacecraft in situ to watch what happens when the sun is directly overhead at the equator, illuminating the rings directly edge-on. New images compiled from the Cassini spacecraft show a rare and breathtaking display of nature: the setting of the sun on Saturn’s rings. The image above — a mosaic of 75 different images — shows the beauty of this ringed world, but the most surprising revelation from these new images are that newly discovered lumps and bumps in the rings are as high as the Rocky Mountains.
Saturn's rings reaching new heights. Credit: NASA/Space Science Institute
The shadows in this image have lengths as long as 500 kilometers (310 miles), meaning the structures casting the shadows reach heights of almost 4 kilometers (2.5 miles) above the ringplane. These heights are much greater than those previously observed for the Daphnis edge waves, and are very likely caused by the distance between Daphnis and the inner edge of its gap getting unusually small at certain times
“We thought the plane of the rings was no taller than two stories of a modern-day building and instead we’ve come across walls more than 2 miles [3 kilometers] high,” said Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colo. “Isn’t that the most outrageous thing you could imagine? It truly is like something out of science fiction.”
“The biggest surprise was to see so many places of vertical relief above and below the otherwise paper-thin rings,” said Linda Spilker, deputy project scientist at JPL. “To understand what we are seeing will take more time, but the images and data will help develop a more complete understanding of how old the rings might be and how they are evolving.”
Propeller feature in the rings. Credit: NASA/Space Science Institute
An unusually large propeller feature has been detected just beyond the Encke Gap in this Cassini image of Saturn’s outer A ring, taken a couple days after the planet’s August 2009 equinox. Propeller-like features, a few kilometers long, centered on and created by the action of small embedded moonlets only about 330 feet (100 meters) across, were discovered early in the mission. These findings constituted the first recognition that bodies smaller than the 8-kilometer-wide ring moon, Daphnis, in the outer A ring and bigger than the largest ring particles (about 30 feet, or 10 meters, across) were present in Saturn’s rings. New insights into the nature of Saturn's rings are revealed in this panoramic mosaic of 15 images taken during the planet's August 2009 equinox.
Waves in the inner B ring, first seen in Saturn orbit insertion images, are now more obvious and distinct. This mosaic combines 15 separate images. Also visible are bright spokes, consisting of tiny particles elevated above the ring plane and surrounded by the dark outer B ring, can also be seen near the middle of the mosaic.
These two Cassini images, taken four years before Saturn’s August 2009 equinox, have taken on a new significance as data gathered at equinox indicate the streaks in these images are likely evidence of impacts into the planet’s rings.
In one unexpected equinox discovery, imaging scientists have uncovered evidence for present-day impacts onto the rings. Bright, and hence elevated, clouds of tiny particles, sheared out by orbital motion into streaks, up to 3,000 miles (5,000 kilometers) long, have been sighted in the A and C rings. These clouds — very likely thrown up by impacts — rising above the dark ring plane are more directly catching the sun’s rays during equinox, and are hence well lit and easily visible by contrast.
By the brightness and dimensions of the streaks, scientists estimate the impactor sizes at roughly one meter, and the time since impact at one to two days. These equinox data now lend more confidence to the impact interpretation of earlier Cassini images, taken in 2005, showing similar streaks in the C ring. In the 2005 images, the impactors are likely much smaller than one meter, and yet have left a visible ejecta cloud. All together, these observations are heralded as the first visual confirmation of a long-held belief that bits of interplanetary debris continually rain down on Saturn’s rings and contribute to their erosion and evolution.
Summing up the past several months of Cassini’s exploration of Saturn during this unusual celestial event, imaging team leader Carolyn Porco in Boulder, Colo., said, “This has been a moving spectacle to behold, and one that has left us with far greater insight into the workings of Saturn’s rings than any of us could have imagined. We always knew it would be good. Instead, it’s been extraordinary.”
Star Trek fan? Like Cassini and Saturn? The very busy planetary scientist Carolyn Porco also has a visual graphics company, Diamond Sky Productions and they have created some new wallpapers featuring scenes from the latest Star Trek motion picture. The images are copyrighted, so we can’t post them here, but no doubt you’ll want to take a look at these spectacular images over at Diamond Sky’s website. Enjoy!
Saturn lightning storm. Credit: RPWS Team/NASA/JPL/Space Science Institute
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The Cassini spacecraft has been in orbit around Saturn since 2004 and during its mission, has watched nine different lightning storms rage on the planet. But this latest one is the longest lasting and most powerful storm yet: it has been going on since mid-January 2009 with no end in sight. It broke the storm duration record of 7.5 months set by another thunderstorm observed by Cassin between November 2007 and July 2008. Lightning discharges in Saturn’s atmosphere emit very powerful radio waves which are about 10,000 times stronger than their terrestrial counterparts and the huge thunderstorms in Saturn’s atmosphere have diameters of about 3,000 km.
The storm is coursing through “Storm Alley,” a region which lies 35 degrees south of Saturn’s equator where these mammoth storms occur. On board Cassini measuring these storms are the antennas and receivers of the Cassini Radio and Plasma Wave Science (RPWS) instrument.
“These lightning storms are not only astonishing for their power and longevity,” Dr. Georg Fischer of the Austrian Academy of Sciences, “the radio waves that they emit are also useful for studying Saturn’s ionosphere, the charged layer that surrounds the planet a few thousand kilometers above the cloud tops. The radio waves have to cross the ionosphere to get to Cassini and thereby act as a natural tool to probe the structure of the layer and the levels of ionization in different regions.” Image of a lightning storm on Saturn: Credit: NASA/JPL/Space Science Institute
The observations of Saturn lightning using the Cassini RPWS instrument are being carried out by an international team of scientists from Austria, the US and France. Results have confirmed previous studies of the Voyager spacecraft indicating that levels of ionization are approximately 100 times higher on the day-side than the night side of Saturn’s ionosphere.
“The reason why we see lightning in this peculiar location is not completely clear,” said Fischer. “It could be that this latitude is one of the few places in Saturn’s atmosphere that allow large-scale vertical convection of water clouds, which is necessary for thunderstorms to develop. However, it may be a seasonal effect. Voyager observed lightning storms near the equator, so now that Saturn has passed its equinox on 11 August, we may see the storms move back to equatorial latitudes.”
Saturn’s role as the source of lightning was given added confirmation during Cassini’s last close flyby of Titan on August 25. During the half hour that Cassini’s view of Saturn was obscured by Titan, no lightning was observed. “Although we know from Cassini images where Saturn lightning comes from, this unique event was another nice proof for their origin.” said Fischer.
Fischer presented his findings at the European Planetary Science Congress in Potsdam, Germany.
Radiation belt map of the ions with energies between 25-60 MeV, in Saturn's magnetosphere, based on several years of Cassini MIMI/LEMMS data. The structure of this radiation belt is almost perfectly stable for more than 5 years of Cassini observations, despite the intense variability of the radiation belts, outside the location of Tethys.
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A new, temporary radiation belt has been detected at Saturn, located about 377,000 km from the center of the planet, near the orbit of the moon Dione. The temporary radiation belt was short-lived and formed three times in 2005. It was observed as sudden increases in the intensity of high energy charged particles in the inner part of Saturn’s magnetosphere, in the vicinity of the moons Dione and Tethys, and likely was caused by a change in the intensities of cosmic rays at Saturn.
“These intensifications, which could create temporary satellite atmospheres around these moons,” said Dr. Elias Roussos, “occurred three times in 2005 as a response to an equal number of solar storms that hit Saturn’s magnetosphere and formed a new, temporary component to Saturn’s radiation belts.”
The discovery was made possible by Cassini’s five-plus year mission, allowing scientists to observe and assess changes in Saturn’s radiation belts. An international team of astronomers made the discovery analyzing data from the Magnetospheric Imaging instrument (MIMI) on Cassini MIMI’s LEMMS sensor, which measures the energy and angular distribution of charged particles in the magnetic bubble that surrounds Saturn.
Saturn's moon Dione. Credit: NASA
The new belt, which has been named “the Dione belt”, was only detected by MIMI/LEMMS for a few weeks after each of its three appearances. The team believe that newly formed charged particles in the Dione belt were gradually absorbed by Dione itself and another nearby moon, named Tethys, which lies slightly closer to Saturn at an orbit of 295 000km.
Unlike the Van Allen belts around the Earth, Saturn’s radiation belts inside the orbit of Tethys are very stable, showing negligible response to solar storm occurrences and no variability over the five years that they have been monitored by Cassini.
Interestingly, it was found that the transient Dione belt was only detected outside the orbit of Tethys. It appeared to be clearly separated from the inner belts by a permanent radiation gap all along the orbit of Tethys.
“Our observations suggest that Tethys acts as a barrier against inward transport of energetic particles and is shielding the planet’s inner radiation belts from solar wind influences. That makes the inner, ionic radiation belts of Saturn the most isolated magnetospheric structure in our solar system“, said Dr Roussos.
The radiation belts within Tethys’s orbit probably arise from the interaction of the planet’s main rings and atmosphere and galactic cosmic ray particles that, unlike the solar wind, have the very high energies needed to penetrate the innermost Saturnian magnetosphere. This means that the inner radiation belts will only vary if the cosmic ray intensities at the distance of Saturn change significantly.
However, Roussos emphasized that outside the orbit of Tethys, the variability of Saturn’s radiation belt might be enhanced in the coming years as solar maximum approaches. “If solar storms occur frequently in the new solar cycle, the Dione belt might become a permanent, although highly variable, component of Saturn’s magnetosphere, which could affect significantly Saturn’s global magnetospheric dynamics,” he said.
The new findings were presented at the European Planetary Science Congress in Potsdam, Germany.
Saturn on August 12, 2009 just after equinox. Credit: NASA
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Here’s one of the first raw images of Saturn taken by the Cassini spacecraft just after equinox, on August 12, 2009. The planet sure looks naked without its rings! But not to fear, the rings are still there; we just can’t see them very well — only a thin line. That’s because the sun was shining directly straight-on at the rings at Saturn’s equinox, and the spacecraft was in the right place, too. Equinox occurs every half-Saturn-year which is equivalent to about 15 Earth years. The illumination geometry that accompanies equinox lowers the sun’s angle to the ringplane and causes out-of-plane structures and some moons to cast long shadows across the rings. The ring shadows themselves have become a rapidly narrowing band cast onto the planet. Below, see another image with the rings visible as the spacecraft changed its angle.
