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Rev 227, Nov 30th - Dec 13th
jasedm
post Nov 26 2015, 07:28 PM
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Details for this revolution are available here

This is the orbit I've been looking forward to for some time as it affords us a closer glimpse at Atlas, Prometheus and Epimetheus.

In fact, Cassini approaches the latter two at a closer range than it will for the remainder of the mission, and observations are planned for both, as well as Atlas.
This, despite having to turn the spacecraft and use the high-gain antenna as a shield during ring-plane crossing to avoid any possible collisions with debris in the ring-plane.

This must have been an extra-specially complicated sequence of observations to plan, as it all happens at or around periapse.

I'm really looking forward to another view of Atlas particularly - can't wait!!!

Jase

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jccwrt
post Dec 7 2015, 08:15 PM
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Here's an RGB composite of astrometric observations of Mimas, Enceladus, and Tethys from December 3.


Moon Trio - Rev 227 by Justin Cowart, on Flickr
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peter59
post Dec 7 2015, 08:36 PM
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Flying saucer ?
http://saturn.jpl.nasa.gov/multimedia/imag...2/N00251477.jpg
Is it just the play of light and shadow, or really Atlas is extremely flat ?


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Free software for planetary science (including Cassini Image Viewer).
http://members.tripod.com/petermasek/marinerall.html
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jasedm
post Dec 7 2015, 08:39 PM
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Very nice Justin, thanks for that!

Cassini-Huygens has to be in the top five UMSF missions ever in terms of scientific return, ingenuity, and sheer beauty.
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jasedm
post Dec 7 2015, 09:16 PM
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QUOTE (peter59 @ Dec 7 2015, 08:36 PM) *
Flying saucer ?
http://saturn.jpl.nasa.gov/multimedia/imag...2/N00251477.jpg
Is it just the play of light and shadow, or really Atlas is extremely flat ?


I think Atlas really is that shape- a kernel of fairly solid spherical material with accretions of candy-floss icy-stuff around the equator.
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jasedm
post Dec 7 2015, 09:21 PM
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Prometheus close-ups now available:


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jasedm
post Dec 7 2015, 09:32 PM
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And Epimetheus....
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jasedm
post Dec 7 2015, 09:48 PM
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And the rings too... Just marvellous!


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jasedm
post Dec 7 2015, 10:08 PM
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Feel so privileged to have this ringside seat - sat on my backside at home, not having contributed anything meaningful to this mission yet able to access in almost real-time these stunning images from half-way across the solar-system.

Fantastic!

Jase
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Explorer1
post Dec 7 2015, 11:38 PM
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Gosh, and I thought that Methone was bizarre. Even though it should not be a surprise that orbiting in such a dusty environment blankets a satellite in dust, but to such an extent and depth...
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jccwrt
post Dec 8 2015, 01:03 AM
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QUOTE (peter59 @ Dec 7 2015, 02:36 PM) *
Flying saucer ?
http://saturn.jpl.nasa.gov/multimedia/imag...2/N00251477.jpg
Is it just the play of light and shadow, or really Atlas is extremely flat ?


It's a combination of both. Atlas has a small, roughly spheroidal body at the center, but it's accumulated a thick pancake of ring material along its equator extending out to around the moon's Roche limit. It reaches out far enough that it's blocking light from falling on the moon's southern hemisphere since it's getting close to the southern winter solstice.



A couple pictures of Epimetheus, IIRC these will be the best of the mission. It's suprisingly Phobos-like - smooth, old terrain peppered by a lot of smaller fresh craters. It's even got a few grooves here and there! It's also interesting to see some of the darker patches in the bottom of craters on the left side. Sort of looks like layering, although other image sets of the moon make it look more like loose dust that's moved around the moon.






And one of Prometheus around closest approach. I'm not sure if it's just a lighting effect, but it looks like many of the craters are surrounded by dark rings.


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Lewis007
post Dec 8 2015, 11:34 AM
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Two gif's of the mutual events of Mimas and Enceladus on December 3.
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Astro0
post Dec 8 2015, 12:17 PM
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A sequence of images from Cassini's close view of Epimetheus.
Surface flickering due to differences in filters for each frame. Noise and cosmic ray hits painted out.



Medium version: 1.87mb | Largest version: 5mb
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eliBonora
post Dec 8 2015, 05:23 PM
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My (small) moons' collection! smile.gif









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jasedm
post Dec 8 2015, 08:08 PM
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Very nice renderings everyone!

Incidentally, it looks as though the pointing for the Atlas sequence was fractionally off as it falls right on the edge of the FoV in the images.

Understandable though as its orbit is somewhat unpredictable. From Wikipedia:

"Atlas is significantly perturbed by Prometheus and to a lesser degree by Pandora, leading to excursions in longitude of up to 600 km (~0.25) away from the precessing Keplerian orbit with a rough period of about 3 years. Since the orbits of Prometheus and Pandora are chaotic, it is suspected that Atlas's may be as well.[1]"

Doubtless Aegaeon's imaging sequence on the next orbit has been designed to take account of that moon's orbital uncertainty. Add to that it's a very close, fairly fast flyby, of a moon that has a low albedo, and is tiny even compared to Atlas...

This shows the wisdom of the dozens (hundreds?) of astrometric observations of the small moons the Cassini team has written into the sequences on almost every revolution in recent years, refining their orbits to the finest degree possible.
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