Saturn is divided by its rings and the moons Tethys and Epimetheus. Credit: NASA/JPL/Space Science Institute
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Two moons and Saturn’s rings create a lopsided “divided by” symbol on the giant planet in one of the latest images released by the Cassini science team. The rings also cast shadows and darken the southern hemisphere of the planet. The moon Tethys (1,062 kilometers, or 660 miles across) sits above the rings, while the smaller moon Epimetheus (113 kilometers, or 70 miles across) hovers below. This image was taken by Cassini’s narrow-angle camera on March 8, 2011. See below for a few more recent looks at Saturn.
The moon Prometheus sits amid Saturn's rings. Credit: NASA/JPL/Space Science InstituteA dark Saturn with rings and shadows. Credit: NASA/JPL/Space Science Institute
Check out more images on the Cassini website. There are some brand new images in the “raw image” section, including some great looks at Titan. And look for more great images of Titan soon, as Cassini’s next close flyby of Saturn’s largest moon will be on May 8.
NASA's Cassini spacecraft has spotted a glowing patch of ultraviolet light near Saturn's north pole that marks the presence of an electrical circuit that connects Saturn with its moon Enceladus. Two images obtained by Cassini's ultraviolet imaging spectrograph on Aug. 26, 2008, separated by 80 minutes, showing how the ‘footprint’ moved according to changes in the position of Enceladus. Credit: NASA/JPL/University of Colorado/Central Arizona College
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The geysers and jets of Enceladus have just become more intriguing. A glowing patch of ultraviolet light near Saturn’s north pole appears to be evidence of a magnetic connection between the planet and the icy, geyser-spewing moon. Data from the Cassini spacecraft have revealed that the jets of gas and icy grains that emanate from the south pole of Enceladus become electrically charged and form an ionosphere, and the motion of Enceladus and its ionosphere through a magnetic bubble that surrounds Saturn acts like a dynamo, setting up a newly-discovered electrical current system that links the moon to the planet.
This video demonstrates the hiss-like radio noise generated by electrons moving along magnetic field lines from Enceladus to a glowing patch of ultraviolet light on Saturn.
Cassini’s Plasma Spectrometer’s electron spectrometer, (CAPS-ELS) has detected the beams of electrons that flow back and forth between Saturn and Enceladus. Magnetic field lines, invisible to the human eye but detectable by the fields and particles instruments on the spacecraft, arc from Saturn’s north polar region to south polar region. Enceladus resides in the arc of a set of the field lines and feeds charged particles into the Saturn atmosphere. The finding is part of a paper published in Nature.
From data Cassini collected in 2008, scientists saw a glowing patch of ultraviolet light emissions near Saturn’s north pole that marked the presence of a circuit between the two bodies, even though the moon is 240,000 kilometers (150,000 miles) away from the planet.
The patch occurs at the end of a magnetic field line connecting Saturn and its moon Enceladus. The area, known as an auroral footprint, is the spot where energetic electrons dive into the planet’s atmosphere, following magnetic field lines that arc between the planet’s north and south polar regions.
“The footprint discovery at Saturn is one of the most important fields and particle revelations from Cassini and ultimately may help us understand Saturn’s strange magnetic field,” said Marcia Burton, a Cassini fields and particles scientist at NASA’s Jet Propulsion Laboratory. “It gives us the first visual connection between Saturn and one of its moons.”
The auroral footprint measures approximately 1,200 kilometers (750 miles) by less than 400 kilometers (250 miles), covering an area comparable to California or Sweden. At its brightest, the footprint shone with an ultraviolet light intensity far less than Saturn’s polar auroral rings, but comparable to the faintest aurora visible at Earth without a telescope in the visible light spectrum. Scientists have not found a matching footprint at the southern end of the magnetic field line.
Scientists already knew that the giant planet Jupiter is linked to three of its moons by charged current systems set up by the satellites orbiting inside its giant magnetic bubble, the magnetosphere, and that these current systems form glowing spots in the planet’s upper atmosphere. The latest discovery at Enceladus shows that similar processes take place at the Saturnian system too.
“This now looks like a universal process — Jupiter’s moon Io is the most volcanic object in the solar system, and produces a bright spot in Jupiter’s aurora, “ said Dr. Andrew Coates from the University College in London, a co-author of the new paper. “Now, we see the same thing at Saturn — the variable and majestic water-rich Enceladus plumes, probably driven by cryovolcanism, cause electron beams which create a significant spot in Saturn’s aurora too.”
Titan holds yet more secrets, far beneath its haze...
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Saturn’s moon Titan just keeps throwing surprises at us. A multi-layered atmosphere thicker than our own? Check. A hydrologic cycle that relies on methane as the operating liquid? Check. Rivers, streams and lakes filled with this same liquid? Check, check and check. And now, scientists are suspecting that Titan may have yet another surprise: a subsurface ocean.
Observations of Titan’s rotation and orbit, carried out by researchers at the Royal Observatory of Belgium using Cassini data, point at an unusual rotational inertia; that is, its resistance to changes in its motion, also known as moment of inertia or angular mass. Basically Titan moves in a way that is not indicative of a solid body of its previously assumed density and mass. Rather, its motion – both around its own axis and in its tidally-locked orbit around Saturn – are more in line with an object that isn’t uniformly solid.
Titan's thick clouds hide its surface well. NASA / JPL / SSI / J.Major
According to the math, Titan may very well be filled with liquid!
Or, at least, have a liquid layer of considerable depth beneath its surface. How far below the surface, how deep and exactly what kind of liquid are all speculative at this point…it’s suggested that it may be a subsurface ocean of yet more methane. This would help answer the question of where Titan gets all of its methane in the first place; methane, – a.k.a. natural gas – is a compound that breaks down quickly in sunlight. In fact, the high-level haze that surrounds the moon like a wispy blue shell is made up of this broken-down methane. So if this stuff is raining down onto the surface in giant, frigid drops and filling streams and lakes, but is still being broken down by ultraviolet light from the Sun to enshroud the entire moon (Titan is BIG, remember…at 5,150 km – 3,200 miles – wide, it’s over a third the size of Earth!) then there has to be somewhere that this methane is coming from.
If these calculations are right, it may be coming from underground.
We propose a new Cassini state model for Titan in which we assume the presence of a liquid water ocean beneath an ice shell… with the new model, we find a closer agreement between the moment of inertia and the rotation state than for the solid case, strengthening the possibility that Titan has a subsurface ocean.
– Rose-Marie Baland et al.
Of course in order for this hypothesis to be proven many more numbers are going to have to be crunched and more data reviewed. And more possibilities considered, too; Titan’s orbital irregularities may in fact be the result of external forces, such as a close pass by a comet or other large body. Still, there’s something to be investigated here and you can bet there’ll be no shortage of attention on a problem as intriguing as this!
Titan may soon be joining the short list of moons speculated to possess subsurface oceans, alongside Jupiter’s Europa and Ganymede and sister Saturnian satellite Enceladus…and who knows how many others?
Dramatic plumes, both large and small, spray water ice out from many locations along the famed "tiger stripes" near the south pole of Saturn's moon Enceladus. Credit: NASA/JPL/Space Science Institute
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The south polar region of Enceladus is turning out to be a veritable heat pump. The fissure- and geyser-laden region on this moon of Saturn is churning out internal heat-generated power of about 15.8 gigawatts, which is approximately 2.6 times the power output of all the hot springs in the Yellowstone region, or comparable to 20 coal-fueled power stations. This is more than an order of magnitude higher than scientists had predicted, according to Carly Howett, the lead author of a study published in the Journal of Geophysical Research on March 4. Just how that much power is being generated, however, is unknown.
“The mechanism capable of producing the much higher observed internal power remains a mystery and challenges the currently proposed models of long-term heat production,” said Howett.
2008 data from Cassini’s composite infrared spectrometer indicates a surprisingly high output of temperature from the south polar terrain on Enceladus, which makes it even more likely that liquid water exists below Enceladus’ surface, Howett said.
A 2007 study predicted the internal heat of Enceladus, if principally generated by tidal forces arising from the orbital resonance between Enceladus and another moon, Dione, could be no greater than 1.1 gigawatts averaged over the long term. Heating from natural radioactivity inside Enceladus would add another 0.3 gigawatts.
So these new readings come as a surprise.
This graphic, using data from NASA's Cassini spacecraft, shows how the south polar terrain of Saturn's moon Enceladus emits much more power than scientists had originally predicted. Images credit: NASA/JPL/SWRI/SSI
Recently, scientists studying ice particles ejected from the plumes discovered that some of the particles are salt-rich, and are probably frozen droplets from a saltwater ocean in contact with Enceladus’ mineral-rich rocky core. The presence of a subsurface ocean, or perhaps a south polar sea between the moon’s outer ice shell and its rocky interior would increase the efficiency of the tidal heating by allowing greater tidal distortions of the ice shell.
“The possibility of liquid water, a tidal energy source and the observation of organic (carbon-rich) chemicals in the plume of Enceladus make the satellite a site of strong astrobiological interest,” said Howett, who is a postdoctoral researcher at Southwest Research Institute in Boulder, Colorado.
The activity is centered on four roughly parallel linear trenches, 130 kilometers (80 miles) long and about 2 kilometers (1 mile) wide, informally known as the “tiger stripes.” These fissures eject great plumes of ice particles and water vapor continually into space, and have elevated temperatures due to heat leaking out of Enceladus’ interior.
Along one fissure, called Baghdad Sulcus, temperatures exceed 180 Kelvin ( – 92 C, -135 F), and may be higher than 200 Kelvin (- 73 C, -100 F). While chilly by Earth standards, peak temperatures, the temperatures are a cozy oasis compared to the numbing 50 Kelvin (-223 C, -370 F) of their surroundings.
Ever imagine creating your own IMAX movie? Cinematographer Stephen Van Vuuren is working to do just that, and has created flythough sequences from thousands of images from the Cassini spacecraft’s tour of the Saturn system. The video above is just a sampling of this non-profit, giant-screen art film effort “that takes audiences on a journey of the mind, heart and spirit from the big bang to the near future via the Cassini-Huygens Mission at Saturn,” according to the “Outside In” website.
Saturn, its rings and moons small to large in this Cassini image. Credit: NASA/JPL/Space Science Institute
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This latest offering from the Cassini spacecraft shows a wide-angle view of Saturn, its rings, and a sampling of the planet’s moons in varying sizes. Saturn’s largest moon, Titan, is in the center of the image, with the smaller moon Enceladus on the far right, while appearing just below the rings on the far left beyond the thin F ring is teeny-tiny Pandora. Oh, to have this view out your spacecraft window as you approach the ringed-world for a flyby!
How do the moons shown here vary in size? Titan is 5,150 kilometers, or 3,200 miles, across. Enceladus is 504 kilometers, or 313 miles across, while Pandora is 81 kilometers, or 50 miles across. This view looks toward anti-Saturn side of Titan and toward the northern, sunlit side of the rings from just above the ringplane.
The image was taken with the Cassini spacecraft wide-angle camera on Jan. 15, 2011, from a distance of about 844,000 kilometers (524,000 miles) from Titan. Image scale is 50 kilometers (31 miles) per pixel.
Titan peeks from behind two of Saturn's rings. Another small moon Epimetheus, appears just above the rings. Credit: NASA/JPL/Space Science Institute
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It seems Titan is getting more Earth-like all the time. There are lakes, rainfall (never mind that any liquids on Titan are frigid hydrocarbons), dust storms, lightning and all sorts of other activity going on it the atmosphere, along with clouds. And now, not just any clouds but cirrus clouds, very similar to what we have on Earth: thin, wispy clouds of ice particles high in the atmosphere. A team of researchers at NASA’s Goddard Space Flight Center say that unlike Titan’s brownish haze, the ice clouds are pearly white.
“This is the first time we have been able to get details about these clouds,” said Robert Samuelson, an emeritus scientist at Goddard and the co-author of a new paper published in the journal Icarus. “Previously, we had a lot of information about the gases in Titan’s atmosphere but not much about the [high-altitude] clouds.”
Using the Composite Infrared Spectrometer (CIRS) on NASA’s Cassini spacecraft scientists can get a “weather report” of sorts. Previously, scientists have found that Titan’s intriguing atmosphere has a one-way cycle that delivers hydrocarbons and other organic compounds to the ground as precipitation.
Those compounds don’t evaporate to replenish the atmosphere, but somehow the supply has not run out.
Additionally, puffy methane and ethane clouds had been found before by ground-based observers and in images taken by Cassini. But these new clouds are much thinner and located higher in the atmosphere.
“They are very tenuous and very easy to miss,” said Carrie Anderson, the paper’s lead author. “The only earlier hints that they existed were faint glimpses that NASA’s Voyager 1 spacecraft caught as it flew by Titan in 1980.”
So what are these cirrus clouds made of?
This mosaic of Titan was created from the first flyby of the moon by Cassini in 2004. Credit: NASA/JPL/SS
More than a half-dozen hydrocarbons have been identified in gas form in Titan’s atmosphere, but many scientists feel there are probably many more that haven’t yet been identified.
The clouds on Titan can’t be made from water because of the planet’s extreme cold. “If Titan has any water on the surface, it would be solid as a rock,” said Goddard’s Michael Flasar, the Principal Investigator for CIRS.
Instead, the key ingredient is likely methane. High in the atmosphere, some of the methane breaks up and reforms into ethane and other hydrocarbons, or combines with nitrogen to make materials called nitriles. Any of these compounds can probably form clouds if enough accumulates in a sufficiently cold area.
To find these cloud, the team focuses on the observations made when CIRS is positioned to peer into the atmosphere at an angle, grazing the edge of Titan. This path through the atmosphere is longer than the one when the spacecraft looks straight down at the surface. Planetary scientists call this “viewing on the limb,” and it raises the odds of encountering enough molecules of interest to yield a strong signal.
So, when the researchers look at the data, they can separate the telltale signatures of ice clouds from the other aerosols in the atmosphere. “These beautiful, beautiful ice clouds are optically thin, and they’re diffuse,” said Anderson. “But we were able to pick up on them because of the long path lengths of the observations.”
Saturn's moon Helene. Credit: NASA//JPL/SSI, image enhanced by Stu Atkinson
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The Cassini spacecraft recently had a mini ‘grand tour’ of several of Saturn’s moons and just sent back some great images of Helene, Mimas, Enceladus and Dione. Above is an amazing view of the Trojan moon Helene, which is only 32 kilometers (20 miles across) and shares an orbit with Dione. Cassini came withing 28,000 km (17,398 miles) of Helene. Thanks to Stu Atkinson for an enhanced version of this raw Cassini image. See one of the original raw images of Helene here.
This image of Saturn's moon Enceladus was obtained by NASA's Cassini spacecraft on Jan. 31, 2011. It shows the famous jets erupting from the south polar terrain of Enceladus. Image credit: NASA/JPL/SSI
Cassini captured several images of the plumes spewing from Enceladus, and other closeup views of the moon’s terrain.
Closeup of Enceladus from approximately 78,015 kilometers away. Credit: NASA/JPL/SSIThis view shows the bright, icy Mimas in front of Saturn's delicate rings. Image credit: NASA/JPL/SSI
Enceladus and Dione, as seen by Cassini. Credit: NASA/JPL/Space Science Institute
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We’ve all experienced the Moon Illusion, where our own full Moon looks bigger when seen on the Earth’s horizon. But how about this illusion where you can’t really tell which of these two moons of Saturn is actually bigger, or which is closer, as seen by the Cassini spacecraft? Here, Dione, top right, appears closer to the spacecraft because it is larger than the moon Enceladus, lower left. However, Enceladus was actually closer to Cassini when its visible light, narrow-angle camera took this image.
Dione (1,123 kilometers, or 698 miles, across) is more than twice the size of Enceladus (504 kilometers, or 313 miles, across). The two moons are contrasted with Enceladus’ bright, reflective trailing hemisphere, and Dione’s darker, micrometeor-dusted side, decorated with wispy lighter materials.
Cassini took this image on Dec. 1, 2010 from about 510,000 kilometers (317,000 miles) from Enceladus and approximately 830,000 kilometers (516,000 miles) from Dione. Image scale is 3 kilometers (2 miles) per pixel on Enceladus and 5 kilometers (3 miles) per pixel on Dione.
Rhea, Saturn's rings and some sister moons. Credit: NASA/JPL/Space Science Institute
Jia-Rui C. Cook from the Cassini team sent out an alert that raw images from Cassini’s closest flyby of Saturn’s moon Rhea have begun streaming to Cassini’s raw image page, and they are well worth a look. At closest approach, Cassini came within about 69 kilometers (43 miles) of Rhea’s surface on Jan. 11. But there’s also some interesting group photos from within the Saturn System. One of the best is this image, above. How many moons can you find? I probably wouldn’t have seen them all but Emily Lakdawalla at the Planetary Blog spied five moons and the rings in this one wide-angle shot. The large moon is Rhea; above Rhea and just below the rings, is Dione; above and to the left of Rhea is Tethys. Then there are two tiny moons: squint hard to see Prometheus as tiny lump on the rings to the left of Dione, and Epimetheus is hovering between Tethys and Rhea. See some more, including closeups of Rhea and Saturn’s storm, below.
