Printable Version of Topic

Posted by: Floyd Sep 2 2011, 03:14 PM

From Looking Ahead: http://www.ciclops.org/view/6866/Rev153A lot going on this revolution:

Sixty-one ISS observations are planned for Rev153, the majority designed to monitor cloud systems in Saturn's atmosphere. The spacecraft also will encounter a number of Saturn's moons, including Titan, Pallene, Tethys, Enceladus, and Hyperion, for which ISS will acquiring imaging.

ISS will image the L5 Lagrange point (60 degrees behind satellite) regions of the moons Iapetus, Rhea and Dione to see if they have Trojan’s like Dione/Polydeuces and Tethys/Calypso.

Titan encounter Sept 12. CIRS, VIMS, UVIS, INMS, CAPS, ISS
Imaging Enceladus polar plume from night side at 42,224 km and two mosaics of sub-Saturn hemisphere. Sept 13
Imaging Tethys from 300,00 km Sept 13
Image Pallene from 25,960 km (38x26 pixels at that distance as only 3.6 x 2.5 miles) Sept 13
Image Hyperion from 58,015 km—a little further than last month. Sept 16.
Color image of Tethys passing in front of Titan's south polar hazes. Sep 16.
Mutual events Enceladus in front of Titan with Rings and Pandora in background Sept 17.

Posted by: Juramike Sep 7 2011, 02:42 AM

Saw these images come down of a starfield as taken from Saturn orbit, and well, started treating it as "the ultimate puzzle", and put together this 12-frame mosaic:

Posted by: Toma B Sep 7 2011, 07:58 AM

My God, it's full of stars!

Posted by: Decepticon Sep 7 2011, 08:46 AM

Very funny!

Posted by: JTN Sep 7 2011, 11:51 AM

http://nova.astrometry.net/user_images/2108#annotated (I won't quote details so as not to spoil it for puzzle fans )
(NB the service is advertised as experimental, so this link may rot.)

Posted by: Floyd Sep 7 2011, 12:27 PM

From Looking Ahead Rev 153:
ISS begins its observations for Rev153 two days after apoapse with a satellite search observation. ISS will image the L5 Lagrange point region of the moon Iapetus, about 60 degrees behind of the icy satellite in its orbit. This type of Lagrange point has been found to host Trojan moons before in the Saturn system. Cassini discovered the L5 Trojan moon of Dione now named Polydeuces in 2004. Another, Calypso, shares the same orbit as Tethys but lies 60 degrees behind it. This satellite search observation could detect objects as small as 90 meters near Iapetus' L5 point. Similar observations will be acquired of the L5 regions for Rhea and Dione on September 21 and 22, respectively.

What would be great is if someone made the images into a slow movie to see if any faint slowly moving object can be seen

Lots of good things to see in Rev153 (from thread I started a few days back)
Sixty-one ISS observations are planned for Rev153, the majority designed to monitor cloud systems in Saturn's atmosphere. The spacecraft also will encounter a number of Saturn's moons, including Titan, Pallene, Tethys, Enceladus, and Hyperion, for which ISS will acquiring imaging.

ISS will image the L5 Lagrange point (60 degrees behind satellite) regions of the moons Iapetus, Rhea and Dione to see if they have Trojan’s like Dione/Polydeuces and Tethys/Calypso.

Titan encounter Sept 12. CIRS, VIMS, UVIS, INMS, CAPS, ISS

Imaging Enceladus polar plume from night side at 42,224 km and two mosaics of sub-Saturn hemisphere. Sept 13
Imaging Tethys from 300,00 km Sept 13
Image Pallene from 25,960 km (38x26 pixels at that distance as only 3.6 x 2.5 miles) Sept 13
Image Hyperion from 58,015 km—a little further than last month. Sept 16.
Color image of Tethys passing in front of Titan's south polar hazes. Sep 16.
Mutual events Enceladus in front of Titan with Rings and Pandora in background Sept 17.

Posted by: Juramike Sep 7 2011, 01:46 PM

Ah! Thanks for that! I submitted it and a cropped version to the astronomy.net flickr bot but didn't get a response.

Posted by: Juramike Sep 10 2011, 01:59 PM

Paaliaq the Pixel! Four frame animation crated from an image sequence taken on September 8:

Posted by: titanicrivers Sep 11 2011, 05:08 AM

Nice montage Mike and impressive ID by Astrometry. I was wondering where the apparent orbit of Iapetus might be projected on the star field imaged especially the portion 60 degrees behind the position of Iapetus in its orbit. A rough estimate using the Solar System Simulator is given below. The starfield montage is rotated 180 degrees in this depiction. The second image is an approximate orbit projected on a higher resolution version of the starfield ... perhaps a region to concentrate on in blink compare or video constructs to see a moving body

Posted by: ugordan Sep 11 2011, 12:34 PM

Titan on September 9, CB3/GRN/UV3 plus some "artistic freedom" in processing:

Posted by: ugordan Sep 13 2011, 04:25 PM

Some lovely shots of Titan's south pole are available. NAC RGB view from 116 000 km:

I wonder if the star visible is Chi Aquarii mentioned in the Looking Ahead article.

Posted by: Stu Sep 13 2011, 07:27 PM

Absolutely beautiful...

Posted by: remcook Sep 13 2011, 09:43 PM

Wow, that detached haze layer is doing some funky stuff near the pole. There are some more close ups as well.
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS70/W00070005.jpg

Posted by: ugordan Sep 13 2011, 10:09 PM

Here's the WAC companion to that NAC shot, south is up:

I don't know. It used to look like a shadow of the optically thick haze on the detached layer before. Now it kind of depends on which filter you look at. It still looks like an ordinary shadow to me in the above color composite. Overall, it looks like the haze is thicker at the pole compared to other spots at the limb so maybe it pronounces this effect.

One reason I think it's a shadow is there's a slight hue shift toward orange in that haze "crack" as seen in the NAC view as sunlight passes through the orange haze layers before it sets.

Posted by: ngunn Sep 13 2011, 10:09 PM

I think there could be diurnal changes in the upper haze layer. Of course we only see the illuminated part, but suppose the haze gets more opaque when night's shadow falls. We might see the denser night haze briefly when early morning sunlight first reaches it. This would be most evident at the polar limb.

Posted by: Bjorn Jonsson Sep 14 2011, 12:43 AM

Seems partially due to Titan's own shadow but the strange thing is that the haze gets brighter just outside the shadow (which might be consistent with ngunn's suggestion above).

Beautiful images/color composites by the way - some of the best ones I've seen.

Posted by: remcook Sep 14 2011, 07:12 AM

Of course there's some shadows/darkness behind the bright bit, but the fact that the bright 'line' seems to go up in altitude significantly looks quite strange to me. There seems to be either a big pile-up of haze at the pole (polar cap?) + shadow, or a local increase in haze scattering, like the detached haze layer.
Very nice images by the way (yet again!)

Posted by: ugordan Sep 14 2011, 07:39 AM

I was thinking the increase in brightness could come from some funky forward-scattering properties of the orange haze ahead. To my eye it only appears to be pronounced in longer wavelengths. I can't think of a mechanism that would do that, though.

Also, did anyone actually try measuring pixel values to verify it really is brighter and not some optical illusion? I was too lazy to do that myself yesterday.

Posted by: remcook Sep 14 2011, 08:10 AM

As far as I can tell from stretching etc. it's actually brighter, especially at these very high altitudes.
Since the upper haze looks blue (although the line looks perhaps less blue than the rest), it seems to me the light there is mostly scattered only once by the haze, which would mean in this case that the scattering angle is about 100 degrees or so.
There is a very interesting paper by Lavvas et al. ( http://adsabs.harvard.edu/abs/2009Icar..201..626L ) which argues that the detached haze is indeed some sort of 'optical illusion' (not really) and is caused by the formation of these fractal paricles by clumping together of small particles. Because many small particles scatter more light than less bigger particles, the detached haze layer looks brighter, although there is not in fact more material there. I think that's a pretty cool idea. But there still needs to be some dymanics to explain some of the changes with time (see http://www.sp.ph.ic.ac.uk/~ingomw/Titan_Meeting/Titan_Science_Meeting/Program_files/West.pdf , last slide)

Posted by: Juramike Sep 14 2011, 02:13 PM

There actually IS more material at the inner boundary of the detached haze layer. Monomers (small particles) are bopping around in the uppermost atmosphere >500 km or so, increasing in density as you get lower. But at around 500 km (inner boundary of the detached haze layer) they start to clump together, get much bigger, and drop out of the layer, leaving a gap until you get to the lower haze deck. The haze layer at the critical monomer density. Any more dense, and the stuff sticks and drops out.

There was a very recent paper also by Lavvas et al. (2011) [I think it is this http://iopscience.iop.org/0004-637X/728/2/80 (pay for article)] that describes the agglomeration and does a good job of modeling the profile of Titan's layers and the location of the detached haze layers.

Posted by: remcook Sep 14 2011, 07:05 PM

Very cool paper. It's amazing how much Cassini has increased the knowledge about Titan.

But about the region below 500 km it says: "In this altitude region, the high atmospheric density and pressure decreases even further the particle settling velocity. ... This leads to a pile-up of the particles, demonstrated by the local increase of the particle density right below 500 km. The particle density decreases again at lower altitudes because of the enhanced coagulation rate, which enhances the particle growth" And: "We should note though that because of the small sedimentation velocity of the particles, the effects of atmospheric mixing and advection are expected to have a larger impact in the aerosol evolution for this region and this is not included in our model." The particles are still tiny there of course. So, I'm not sure that 'dropping out' actually takes place. In any case, the optical effect would be there.

Posted by: Bjorn Jonsson Sep 14 2011, 08:15 PM

Yes, I did - this is not an illusion.

Posted by: ngunn Sep 15 2011, 07:36 PM

That sounds very plausible to me, and is a more economical hypothesis than my earlier suggestion as it does not invoke diurnal changes. We know that the orange haze scatters photons predominantly into a narrow forward cone. Near the limb the uppermost part of that cone would miss the surface and escape tangentially into the upper haze layers. An observer inside the bright streak looking back toward the rising or setting sun would be doubly dazzled - by the sun itself and also by an exceptionally bright patch in the orange haze just below it, looking almost like a specular reflection.

It works for me (in a purely handwaving way!) until the experts come up with a better explanation.

That said, the possibility of diurnal changes in the haze layers cannot be altogether discounted as far as I'm aware.

Gordan - a direct question/request: You say the streak looks brighter at longer wavelengths. Can you construct an image, maybe in stretched colours, that shows this? The spectrum of the streak would be a clincher, I think.

Posted by: ugordan Sep 15 2011, 09:07 PM

Yeah, I don't think that impression holds up to closer scrutiny. Here's a CB3 (940 nm narrowband), 570 nm green and 440 nm violet filter combination and magnified 2x.


I don't see any obvious color shift in the haze color, as much as can be inferred from a raw image with scattered light effects. This composite does give a hint of the "normal" detached layer continuing normally behing "sunset" as seen by a faint reddish band and the brightening sort of splits off upwards.

Note also one lower density "crack" at higher altitude seems to pass through uninterrupted. I would expect it to be bent up as well if this was a major updraft.

Posted by: Ian R Sep 16 2011, 11:39 PM

This shot of Tethys has it all: a giant crater, a gaping chasm, and a tantalizing blue streak:

Posted by: PDP8E Sep 17 2011, 02:02 AM

Fabulous image Ian!
It is so tempting to say that the giant crater (Odysseus) is related to the chasmata on the other side of this frozen ice ball (boom ..stretch!)
But those pesky crater counters insist that chasm system is older! Who is right?
Great image!

Posted by: Juramike Sep 17 2011, 03:29 AM

Another version of Tethys RGB[IR1,GRN,UV3]:

Posted by: Juramike Sep 17 2011, 03:34 PM

5-frame mosaic of images taken along Enceladus' terminator through clear filters:

(note crater that got cut in half)

Posted by: Floyd Sep 17 2011, 04:11 PM

Thanks Mike. I was hoping someone would do something with the Enceladus images too.

Posted by: Gladstoner Sep 17 2011, 08:42 PM

.

Posted by: elakdawalla Sep 17 2011, 09:17 PM

Go read Paul "DrShank" Schenk's blog (or his most recent papers on colors of Saturn's satellites) for the answer to this question!

Posted by: Gladstoner Sep 18 2011, 10:57 AM

.

Posted by: scalbers Sep 18 2011, 07:53 PM

Very nice mosaic Juramike - looks like it could add some detail around the half-crater in this map:

http://laps.noaa.gov/albers/sos/sos.html#ENCELADUS

The crater in question is right near the left edge, just below the center. Reminds me of another half (cup shaped) crater near the bottom - and right edge.

Steve

Posted by: Adam Hurcewicz Sep 19 2011, 11:51 AM

My colour version of Hyperion (~93 000 km from Cassini)

ir1 N00175777
grn N00175776
uv3 N00175775

Posted by: Phil Stooke Sep 19 2011, 08:32 PM

Very nice!

Phil

Posted by: Gladstoner Sep 19 2011, 10:12 PM

.

Posted by: ngunn Sep 20 2011, 07:50 PM

It's hard to pick a favourite from this sequence, but here goes: http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS70/N00175978.jpg

Posted by: Astro0 Sep 20 2011, 11:10 PM

After downloading that lastest sequence of mutual moon events, I'm now seeing spots before my eyes

Posted by: elakdawalla Sep 21 2011, 03:47 AM

Pretty awesome, isn't it? I badly want to color-compose even a still from the last sequence with Titan, Dione, Pandora, and Pan (did you notice Pan zipping around the corner?) but I'm afraid it's beyond my skill.

Posted by: Adam Hurcewicz Sep 21 2011, 07:11 AM

Yesterday I upload to youtube animation of occult Titan by Dione

http://www.youtube.com/watch?v=LEJO2C3L9O

Posted by: ugordan Sep 21 2011, 07:58 AM

Is that what those two are? I just noticed there is a 4th moon visible to the right and up of Titan: http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS70/N00175978.jpg

One of the trojans?

Posted by: elakdawalla Sep 21 2011, 02:37 PM

I didn't notice that one! And it doesn't seem to show up in the Saturn Viewer either, at least not at the same scale:

But if I widen the view to the WAC FOV, you can see Methone. I wonder if it could be Methone, not quite showing up in the spot it was predicted to? Jason??

Posted by: pat Sep 21 2011, 06:56 PM

Sorry, its a 6th magnitude star, TYC 333-1215-1/HD 131476

Posted by: elakdawalla Sep 21 2011, 07:00 PM

Thanks, pat!

Posted by: Ian R Sep 24 2011, 12:28 PM

A random interjection: here's a nice little shot from the Hyperion encounter:

Posted by: kyokugaisha Sep 24 2011, 03:07 PM

Here's my rough attempt at a RGB composite of the Titan, Dione event.

Posted by: Ian R Sep 24 2011, 04:29 PM

*APPLAUDS*

Posted by: elakdawalla Sep 24 2011, 04:58 PM

THAT's the one I was waiting to see, thanks

Posted by: ngunn Sep 24 2011, 07:41 PM

Excellent!

Posted by: Juramike Sep 25 2011, 08:56 PM

Methanovision RGB[MT3,MT2,CB2] composite from September 21, 2011 almost 1 year after the Serpent Storm kicked off with a big upwelling and turbulence spreading. Detail enhanced with CB2 data. MT3 and MT2 look pretty typical, no local upwellings in the Serpent Storm wake region.

It's over. Nothin' but turbulence left....just a spindown and equilibration to back blandness.

<sniff>

Posted by: jasedm Sep 28 2011, 06:00 PM

Pallene raw image from 13th September, cleaned up a bit, enlarged and with some Saturnshine illumination
For a tiny moon, Pallene does seem remarkably 'smooth' in profile - almost a perfect peanut shape

Posted by: Phil Stooke Sep 29 2011, 07:50 PM

My version. This will be really nice when we get the raw data. The later images in the sequence are more distant but show more sunlit surface.

Phil

Posted by: jasedm Sep 30 2011, 12:50 PM

Nice.
I'm sure I can see a crater on the saturnshine terminator there.....