Cassini/Huygens Mission Update Thread Pt. 2

[centsworth_II]

Isn't the ring system, including shepard moons, doomed to fall into Saturn? <div class="Discussion_UserSignature"> </div>

 

[vogon13]

Resonances from moons act like 'curbs' to keep materials in place. Differential shear motion does tend to lower low edge of rings and lift high edge, but can be counteracted by resonances. Makes it tough to predict outcome of process.<br /><br />Should Iapetan ring become accepted, most likely differential shear motion depleted that system very rapidly, there being nothing to arrest it. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[white_noise]

Complicated in deed! headache.......<br /><br />a thought: Asume we have two objects, one at high orbit, the other at low orbit and they have gravitational pull between them (not neglegable). Every time the two objects approach each other (since they have different period), the low orbit guy pull at the high orbit guy, so high orbit guy loss a little energy and low orbit gain a little. As Time - /> infinity, the two objects will migrate to the same orbit?<br /><br />If generalize this to the saturn's ring, then the ring should have shrunk into one thick ring instead of a spread out thin ring? Why hasn't it? Or will it?

 

[white_noise]

Oh, resonance. Got to think about it.

 

[vogon13]

Differential shear motion works as follows:<br /><br />A particle in a lower, faster orbit makes physical contact with a particle in a very slightly higher, slower orbit. As a result of their contact, the particle in the lower faster orbit goes a little lower and a little faster. The contacted particle moves the other way, higher and slower.<br /><br />Bazillions of these teeny tiny thwaps all across a ring system make the low side steady go lower yet, and conversely, the high side goes higher. Process slows/ stops when particles spread out enough to quit tapping. Looks like the thin inner ring of Saturn has reached this state. The book 'The New Solar System' has a chapter about this. There is even a formula to calculate how fast the spreading occurs. I don't like math so haven't pushed numbers for Saturn or Iapetus. <br /><br />Something else that may modify rings is 'chipping' . This would increase number of particles while decreasing size of particles. Seems like this would affect spread rate too.<br /><br />A motivated 'orbit dynamacist' could put pages and pages in this thread about what is known about resonances. I'll resist the urge.<br /><br />The hypothetical rings of Iapetus are so much easier to think about (compared to Saturns') because of the simplicity of that system. It also means any rings around Iapetus are going to be very short lived. (and this doesn't even address the effects of a possible very tenuous Iapetan atmosphere interacting with a ring system). <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[white_noise]

You explained it pretty clear, thx!<br /><br />Still puzzled over one spot though: In the wave we observed , the particles are attracted by the moon's gravity, but then fall back and vibrate back and forth and eventually damp out, what is the restoring force that is causing this? I mean, if gravity accelerate them towards the moon, their velocity is changed and should have a different orbit hence forward (fall to the moon/ orbit the moon/ go to higher orbit/ go to lower orbit.......etc)? but there is a force to pull them back to their places.

 

[vogon13]

My take on that is the effect builds and then falls off as the particles approach and recede from the little moon. Particles closer to Saturn overtake the moon and particles further are overtaken by the moon. Recall, these close orbits differ in speed from the little moon only slightly, so all these things (from a particles' point of view) take quite a while to occur.<br /><br />In a dissipative system, the energy needs to be 'made up' somewhwere, and I suspect a micro contraction in the orbit of which ever larger satellite has a strong resonance closest to where this interesting interaction is occuring.<br /><br />This is all grossly simplified, I'm sure computer sims of all this are being done, and I'm sure they are hideously complex.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[white_noise]

You mean that the particles can't catch up with the moon so they fall back, right? But what I don't get is that when the particles approach the moon in the first place, their velocity has already been changed, they should take on a new orbit if no external force is applied? But something pull them back as if there is a spring attached to them.

 

[vogon13]

Particles all attract each other, too. This is an extraordinarily difficult math problem.<br /><br />Also, as particles clump into the 'waves' that changes how they all react to each other and the little moon. Remember, all this stuff acts on all the other stuff and vice versa.<br /><br />Positions of all the other moons important too. I really don't have feel or math lobes to go further with this.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[Leovinus]

<i>Saturn's brightly sunlit moon Rhea commands the foreground in this image from Cassini. The planet's splendid rings are discernible in the background. Rhea is 1,528 kilometers (949 miles) across.<br /><br />The spacecraft was just above the ringplane when it acquired this image, and thus captured the darkened appearance of the dense B ring when viewed with sunlight filtered through the rings. From this perspective, bright areas in the rings are regions of low density, containing very small particles that effectively scatter light toward Cassini.<br /><br />North on Rhea is up and rotated about 25 degrees to the left. This view shows principally the anti-Saturn hemisphere on Rhea. The right side of Rhea is overexposed.<br /><br />The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 18, 2005, at a distance of approximately 540,000 kilometers (340,000 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 110 degrees. The image scale is 3 kilometers (2 miles) per pixel. </i> <div class="Discussion_UserSignature"> </div>

 

[zavvy]

<b>'Ice Volcano' Found On Titan</b><br /><br />LINK<br /><br />The Cassini spacecraft has identified a possible ice volcano on Saturn's moon Titan, according to Nature magazine. <br /><br />The supposed cryovolcano shows up in images as a bright, circular, domed region about 30km in diameter with two possible flows extending westwards. <br /><br />It may be formed by an upwelling of hot ice from the interior, scientists say. <br /><br />The analysis of Titan's surface by the Vims instrument on Cassini also appears to show there are no methane oceans on the moon, as some had suggested. <br /><br />In Nature, Christophe Sotin and colleagues argue that the dome probably formed as plumes of icy material rose to the moon's surface before releasing methane gas into the atmosphere. <br /><br />The spectral data from the Vims images, which give scientists information on what the object is made of, suggest the dome and its "flows" are not composed predominantly of water-ice. <br /><br />The researchers claim that other explanations for the circular feature, such as it being a cloud, or the accumulation of particles similar to a sand dune, are unlikely. <br /><br />But Louise Prokter of Johns Hopkins University in Maryland, US, said the images were not of sufficient resolution to provide details below a few hundred metres, and suggested the dome might be an impact crater. <br /><br />She suggested that, if the feature was indeed an icy volcanic dome, it could be formed by nitrogen ice breaking through the surface. <br /><br />The Visual and Infrared Mapping Spectrometer (Vims) can discern wavelengths of light in the visible and infrared range of the spectrum in order to penetrate the thick organic haze which obscures Titan's surface. <br />

 

[Leovinus]

<i>Three very different worlds crowd the frame in this unique view from the Cassini spacecraft, which although partly overexposed, provides a splendid look at several major targets of interest for the mission.<br /><br />Titan (at the top) has a thick, hazy atmosphere. Cassini has observed it to be a world where complex geological and atmospheric processes are occurring. At 5,150 kilometers (3,200 miles) across, it is Saturn's largest moon, and is the second largest moon in the solar system, after Jupiter's moon Ganymede (5,262 kilometers, or 3,270 miles across).<br /><br />Tethys (at the bottom) has been battered by impacts over the eons, and some of its many craters are visible in this image. Tethys (1,071 kilometers, or 665 miles across) is one of Saturn's major icy moons, having a density close to that of water. This moon shows evidence that icy tectonic processes have occurred on its frozen surface, such as the immense canyon system called Ithaca Chasma.<br /><br />Epimetheus (center) is one of Saturn's "ring moons": small, porous bodies that orbit within or just beyond the rings. Cassini acquired the closest-ever view of cratered Epimetheus (116 kilometers, or 72 miles across) in March, 2005.<br /><br />Also near center are Saturn's F ring and the outer edge of the A ring to the left. In addition to the F ring's usually bright core, several other ringlets are resolved here, giving the ring a soft, wispy character that shows contrast with the more sharply defined A ring.<br /><br />Appearances can be deceiving in two dimensional images like this one where it is difficult to tell which objects are in the foreground and which are farther away. In this scene, Tethys is the closest object to Cassini, at 1.2 million kilometers (700,000 miles) away. Epimetheus is on the near side of the rings and is 1.4 million kilometers (900,000 miles) distant. The giant moon Titan is 2.7 million kilometers (1.7 million miles) away, more than twice as far from Cassini as Tethys.<br /><br />Thi</i> <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

<i>Cassini's climb to progressively higher elevations reveals the "negative" side of Saturn's rings. As the Sun shines through the rings, they take on the appearance of a photonegative: the dense B ring (at the center) blocks much of the incoming light, while the less dense regions scatter and transmit light.<br /><br />Close inspection reveals not one, but two moons in this scene. Mimas (397 kilometers, or 247 miles across) is easily visible near the upper right, but the shepherd moon Prometheus (102 kilometers, or 63 miles across) can also be seen. Prometheus is a dark spot against the far side of the thin, bright F ring. Most of Prometheus' sunlit side is turned away from Cassini in this view.<br /><br />The image was taken in visible light with the Cassini spacecraft wide-angle camera on April 15, 2005, at a distance of approximately 570,000 kilometers (350,000 miles) from Saturn. The image scale is 30 kilometers (19 miles) per pixel. </i> <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

<i>Saturn's atmosphere is essentially transparent at wavelengths visible to the human eye, but when the view through the atmosphere is oblique, as it is along the planet's limb (edge), it will distort anything seen through it. The refracted image of the rings in this image taken by Cassini of Saturn's night side abruptly terminates where Saturn's high-altitude haze becomes opaque.<br /><br />Saturn's F ring shepherd moon Prometheus (102 kilometers, or 63 miles across) hovers below the center. Had an image like this been taken a few minutes earlier, the appearance of Prometheus would also have been warped.<br /><br />Near the left edge of the image, the appearance of the Encke Gap in Saturn's rings is being refracted. As the gap emerges from behind the planet, its image is bent less and less, following the decreasing density profile of the atmosphere with altitude. The appearance of the Cassini Division is warped as well, near the top of this scene. The refraction effect is slightly different in this visible light image than in a previously released infrared view (see PIA06656).<br /><br />The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 28, 2005, at a distance of approximately 2 million kilometers (1.2 million miles) from Saturn. The image scale is 12 kilometers (7 miles) per pixel. </i> <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

<i>The shepherd moon, Pandora, is seen here alongside the narrow F ring that it helps maintain. Pandora is 84 kilometers (52 miles) across.<br /><br />Cassini obtained this view from about four degrees above the ringplane. Captured here are several faint, dusty ringlets in the vicinity of the F ring core. The ringlets do not appear to be perturbed to the degree seen in the core.<br /><br />The appearance of Pandora here is exciting, as the moon's complete shape can be seen, thanks to reflected light from Saturn, which illuminates Pandora's dark side. The hint of a crater is visible on the dark side of the moon.<br /><br />The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 4, 2005, at a distance of approximately 967,000 kilometers (601,000 miles) from Pandora and at a Sun-Pandora-spacecraft, or phase, angle of 117 degrees. The image scale is 6 kilometers (4 miles) per pixel. </i> <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

<i>Cassini looks toward Saturn's night side in this view, capturing a glimpse of Dione's tortured surface in the foreground and a far-off view of Epimetheus beyond Saturn. The spacecraft was just a 10th of a degree above the ringplane when this image was taken.<br /><br />Parts of Dione's surface have been stretched and ripped apart by tectonic forces. Some of these faults are visible here, as is a large impact basin (not seen in NASA Voyager spacecraft images) near the moon's south pole. Although this crater's diameter has not yet been measured by imaging scientists, it appears to be wider than 250 kilometers (155 miles), which would make it the largest impact structure yet identified on this moon. Dione is 1,118 kilometers (695 miles) across.<br /><br />Epimetheus (116 kilometers, or 72 miles across) presents a similar face here to that revealed in a spectacular false-color view from March, 2005 (see Epimetheus: Up-Close and Colorful ).<br /><br />The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 5, 2005, at a distance of approximately 910,000 kilometers (570,000 miles) from Dione, 1.28 million kilometers (800,000 miles) from Epimetheus and 1.42 million kilometers (880,000 miles) from Saturn. The image scale is 5 kilometers (3 miles) per pixel on Dione and 9 kilometers (6 miles) per pixel on Epimetheus. </i> <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

Here's the full-res shot <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

<i>Saturn's moon Pan is seen here orbiting within the Encke Gap in Saturn's A ring in two differently processed versions of the same Cassini image. The little moon is responsible for clearing and maintaining this gap, named for Johann Franz Encke, who discovered it in 1837. Pan is 20 kilometers (12 miles) across.<br /><br />The top image reveals two of the faint, dusty ringlets that occupy the gap along with Pan. One of the ringlets occupies nearly the same orbit as Pan, while the other is closer to the gap's inner edge. Not only do the ringlets vary in brightness, but they also appear to move in and out along their length, resulting in notable "kinks," which are similar in appearance to those observed in the F ring (see PIA06585). One possible explanation for the complex structure of the ringlets is that Pan may not be the only moonlet in this gap.<br /><br />Pan is responsible for creating stripes, called 'wakes,' in the ring material on either side of it. Since ring particles closer to Saturn than Pan move faster in their orbits, these particles pass the moon and receive a gravitational "kick" from Pan as they do. This kick causes waves to develop in the gap where the particles have recently interacted with Pan (see PIA06099), and also throughout the ring, extending hundreds of kilometers into the rings. These waves intersect downstream to create the wakes, places where ring material has bunched up in an orderly manner thanks to Pan's gravitational kick.<br /><br />In the bottom image, the bright stripes or wakes moving diagonally away from the gap's edges can be easily seen. The particles near the inner gap edge have most recently interacted with Pan and have just passed the moon. Because of this, the disturbances caused by Pan on the inner gap edge are ahead of the moon. The reverse is true at the outer edge: the particles have just been overtaken by Pan, leaving the wakes behind it.<br /><br />This image was taken in visible light with the Cassini spacecraft narrow-an</i> <div class="Discussion_UserSignature"> </div>

 

[bobvanx]

In the latest raw images on the Cassini site, is that the sun's reflection on the rings!?

 

[Leovinus]

It sure looks like it. Either that, or it is the sun on the other side of the rings. I wonder if they would dare risk pointing the camera right at the sun? <div class="Discussion_UserSignature"> </div>

 

[Leovinus]

A typical "reflection" shot from the raw image page: <div class="Discussion_UserSignature"> </div>

 

[bobvanx]

I don't think it's the sun viewed <i>through</i> the rings. In the full sequence of images at the Cassini website, we can see this bright spot marching across the rings, and then it disappears when we get to the gap. If it were the sun itself, I'd expect it to get so bright it overwhelmed the CCD.

 

[bobvanx]

A lake on Titan!!!<br /><br />http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1577<br /><br />...maybe

 

[Leovinus]

The picture: <div class="Discussion_UserSignature"> </div>

 

[bobvanx]

Thanks, Leo. Is this easier than using the image approval thread?<br /><br />The dark spot looks like it has an apron. It looks very much like a lake-filled caldera. Crater Lake on Titan?