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'rock' satellite flybys, The next ten weeks
jasedm
post May 16 2008, 06:37 PM
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Cassini's orbits are now averaging 8-9 days apiece as the end of the prime mission approaches, and according to information posted on this forum, Cassini approaches within 75,000km of various 'rock' satellites EIGHTEEN times in the next ten weeks.
These flybys include the closest remaining encounters with Daphnis, Prometheus, Pandora, Epimetheus, Janus, and Pallene (all of these sub-30,000km).
Many close moon-encounters fall during Saturn eclipse, and there are many competing experiments around periapse, but hopefully there will be some planned ISS observations of these small moons at or around closest-approach...
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volcanopele
post May 16 2008, 06:52 PM
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Just a quick scan: Janus (Jun 30; 59000 km; high phase angle), Pallene (August 19; 43000 km)


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DrShank
post May 16 2008, 07:11 PM
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QUOTE (volcanopele @ May 16 2008, 12:52 PM) *
Just a quick scan: Janus (Jun 30; 59000 km; high phase angle), Pallene (August 19; 43000 km)



there is a sub-5000 km flyby of helene during extended mission, but i ve not yet found when!

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paul


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volcanopele
post May 16 2008, 07:57 PM
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It is on March 3, 2010 at 13:40:41UTC. Distance to Helene's surface is 1803.1 km.


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jasedm
post May 18 2008, 02:18 PM
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Some long range images (around 350,000km ) of Janus have just been posted example here
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jasedm
post Jul 15 2008, 03:43 PM
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Some more far-out janus shots have just been posted (seems like Janus is getting quite some attention at the moment)
This one from 255,000km, enlarged x2.5 and enhanced
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jasedm
post Jul 23 2008, 12:14 PM
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A couple of new images of Prometheus/F-ring have been posted, this one taken from a distance of around 450,000km.
I can't think of a single image which demonstrates gravity better than this - Newton (the old curmudgeon) would have loved it.
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centsworth_II
post Jul 23 2008, 02:18 PM
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QUOTE (jasedm @ Jul 23 2008, 08:14 AM) *
...I can't think of a single image which demonstrates gravity better than this...

Are you sure that's not the result of Prometheus' wake in the aether? laugh.gif
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Juramike
post Jul 23 2008, 02:22 PM
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QUOTE (jasedm @ Jul 23 2008, 07:14 AM) *
I can't think of a single image which demonstrates gravity better than this


Forgive my really naive question: How do we know it's not due to electrostatics?


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jasedm
post Jul 23 2008, 03:37 PM
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QUOTE (Juramike @ Jul 23 2008, 03:22 PM) *
Forgive my really naive question: How do we know it's not due to electrostatics?

Perhaps both processes are visible here. I've read that the outer elements of the F-ring appear to be smoke-sized particles, in which case I wouldn't be surprised if the passing 'wake' of the moon stirred up some of the 'smoke' creating visible ripples, but the 'core' of the ring (the two brighter threads in the image) are made up of much larger constituents, and the obvious kink is surely gravitationally-produced...

Just for context, this image was taken from below the ring plane, with Prometheus further from Cassini (by 800km or so) than the core of the ring.
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3488
post Jul 23 2008, 07:40 PM
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Hi everyone,

Think you may like this one. I'm surprised by the very high calibre of the membership here, this has been missed.

Janus in eclipse in Saturn's shadow, lit by the other moons from 33,000 KM. I have cropped, slightly enlarged it & brightened / contrast enhanced the image, as the original was very dark.

I'm afraid that I could do nothing about the cosmic ray / noise speckling.
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Andrew Brown.


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jasedm
post Jul 23 2008, 08:35 PM
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Hi Andrew, this is a view of Janus I've been looking forward to. I agree about the calibre of contributors here. Some of the very best image-smiths showcase their work on this site for all to enjoy.
This image though is Janus in sunlight just prior to eclipse - any image obtained by light due to Saturnshine would have been significantly degraded in terms of quality, and I don't think that there is enough light bouncing off adjacent moons to register in Cassini's optics during eclipse. (see versions of Helene posted in this section)
My own attempts to clean up this image owe more to artistic interpretation than anything else, and fall well short of standards here, so i've avoided posting them - I need some practice....

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volcanopele
post Jul 23 2008, 08:47 PM
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It wasn't missed, just covered in a different thread: http://www.unmannedspaceflight.com/index.p...st&p=119744

the increased noise is due to an increase in radiation levels in the region between Mimas and Janus/Epimetheus, not due to low light conditions.


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3488
post Jul 23 2008, 09:22 PM
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Thanks VP for setting me straight. I was aware of the Janus eclipse, & thought as the original image was so dark, that was taken during said eclipse, not just before.

I see your enhancement, considerably better than mine. I assume the G Ring is responsible for the trapped radiation? I'm not as familiar with the Saturn system as I am of the Jupiter system.

Once again, thanks VP & its great talking to you again.

Hi jasedm, I'm aware of the Enceladus eclipse imagery a while back, faintly lit by Rhea, Dione & Tethys, with Cassini taking a longer exposure, but being further away with a much larger target, it seems to work. Janus is small & close in to Saturn, so yes that would probably not work thinking about it more logically.

Andrew Brown.


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"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.
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ugordan
post Jul 23 2008, 09:26 PM
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QUOTE (3488 @ Jul 23 2008, 11:22 PM) *
I was aware of the Janus eclipse, & thought as the inmage was so dark, that was taken during said eclipse, not just before.

The image is dark because all the heavy radiation hits confused the automatic contrast stretch algorithm applied on the raws. It saw those high brightness pixels and thought it didn't need to brighten the image any more. In other words, this is closer to the actual 'raw' image downloaded from the spacecraft.


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