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Posted by: jasedm Nov 26 2015, 07:28 PM

Details for this revolution are available http://www.ciclops.org/view/8268/Rev227

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

Posted by: jccwrt Dec 7 2015, 08:15 PM

Here's an RGB composite of astrometric observations of Mimas, Enceladus, and Tethys from December 3.

https://flic.kr/p/BUs8tQ
https://flic.kr/p/BUs8tQ by https://www.flickr.com/photos/132160802@N06/, on Flickr

Posted by: peter59 Dec 7 2015, 08:36 PM

Flying saucer ?
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS92/N00251477.jpg
Is it just the play of light and shadow, or really Atlas is extremely flat ?

Posted by: jasedm Dec 7 2015, 08:39 PM

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.

Posted by: jasedm Dec 7 2015, 09:16 PM

I think Atlas really is that shape- a kernel of fairly solid spherical material with accretions of candy-floss icy-stuff around the equator.

Posted by: jasedm Dec 7 2015, 09:21 PM

Prometheus close-ups now available:

Posted by: jasedm Dec 7 2015, 09:32 PM

And Epimetheus....

Posted by: jasedm Dec 7 2015, 09:48 PM

And the rings too... Just marvellous!

Posted by: jasedm Dec 7 2015, 10:08 PM

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

Posted by: Explorer1 Dec 7 2015, 11:38 PM

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...

Posted by: jccwrt Dec 8 2015, 01:03 AM

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.

https://flic.kr/p/AZG2xD

https://flic.kr/p/AZG2BX


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.

https://flic.kr/p/BUNqSY

Posted by: Lewis007 Dec 8 2015, 11:34 AM

Two gif's of the mutual events of Mimas and Enceladus on December 3.

Posted by: Astro0 Dec 8 2015, 12:17 PM

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: https://astro0.files.wordpress.com/2015/12/sequence21.gif | Largest version: https://astro0.files.wordpress.com/2015/12/sequence.gif

Posted by: eliBonora Dec 8 2015, 05:23 PM

My (small) moons' collection!

https://flic.kr/p/BNEP6U

https://flic.kr/p/B1Ronv

https://flic.kr/p/BNEN3b

https://flic.kr/p/B1KDhy

Posted by: jasedm Dec 8 2015, 08:08 PM

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.

Posted by: volcanopele Dec 8 2015, 08:28 PM

Yep, the observation is basically a series of two-frame mosaics. Should help to ensure that Aegaeon is in the FOV.

Posted by: Phil Stooke Dec 9 2015, 10:20 PM

A contrast stretch shows even more grooves on Epimetheus than show up at first glance.

Phil

Posted by: Ian R Dec 10 2015, 12:30 PM

I've added artificial color to the WAC clear-filtered frame of Epimetheus, approximating the view a human might have from the same vantage point.

Posted by: elakdawalla Dec 10 2015, 09:33 PM

Has anybody else tried their hand at the Atlas images? Here are my quick-and-dirty versions, but I know others can do better.

Posted by: Ian R Dec 11 2015, 03:20 AM

Eli's had a crack at Atlas already, Emily:

http://www.unmannedspaceflight.com/index.php?showtopic=8124&view=findpost&p=228437

This is my attempt at the Prometheus obs with a semi-automated method of removing the digital smuts:

Posted by: Ian R Dec 11 2015, 04:15 AM

Three-frame, clear-filtered stack of Atlas, enlarged by 250%. North is up.

Posted by: jasedm Dec 11 2015, 10:36 AM

Up late working on that one Ian!

Very nice.

Posted by: Ian R Dec 12 2015, 06:41 AM

Thanks Jase! Yeah, I work best after the Moon rises it seems ....

Posted by: Ian R Mar 14 2017, 06:04 PM

Looking at the PDS data for this medium-range flyby of Atlas, I realized a number of frames at the start of the sequence were taken against the backdrop of Saturn's night-side. Thanks to the faint illumination of the cloud decks with ring-shine, an extreme contrast stretch of the images reveals the moon's equatorial bulge and southern hemisphere in profile.

Posted by: Sean Mar 14 2017, 06:42 PM

Great catch!

Posted by: jasedm Mar 14 2017, 09:15 PM

Nice work!

Posted by: Steve5304 Mar 14 2017, 09:45 PM

At first I was really taken aback...Looks like Phobos 2 image from VSK in 1988