Holy moly are these back-to-back flybys of Rhea and Helene going to ROCK!!!! Jason's Rev 127 looking ahead article has all the details. Wispy terrain high-res mosaic -- close look at putative impact sites of former ring particles -- MIMI attempt to confirm presence of Rhea ring -- Imaging of pretty much all of Helene using Saturnshine to illuminate sub-Saturn hemisphere on approach, sunshine on anti-Saturn hemisphere on departure -- departure shots will be against Saturn as a backdrop -- C/A shots will use skeet shoot technique derived for Encelauds -- etc. etc. --

I can't wait!! Thanks Jason for the preview!!!

The CICLOPS Looking Ahead article for Rev127 (February 22-March 12) is now online, detailing the upcoming targeted flybys of Rhea and the trojan moon, Helene. In the case of Rhea, Cassini will fly within 100 km of the surface in order to confirm the presence of a set of narrow rings at that satellite. Images will be acquired of portions of the trailing hemisphere wispy terrain and the equator.

However, the flyby I am looking forward to the most is that of Helene on March 3 @ 13:41 UTC, with an altitude of 1,817 km. In preparation of this encounter, I have created an animation in Celestia showing the views of Helene from the ISS narrow-angle camera (missing some on the third trigger, since there were 48...and I'm tired):

Click to view attachment

To give you an idea of what Cassini has seen of Helene before:

Rev094 (November 25, 2008): http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=174939
Rev048 (July 20, 2007): http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=116643
Rev027 (August 17, 2006): http://saturn.jpl.nasa.gov/photos/raw/rawi...m?imageID=80845
Rev027 (August 17, 2006): http://saturn.jpl.nasa.gov/photos/raw/rawi...m?imageID=80858
Rev021 (February 25, 2006): http://saturn.jpl.nasa.gov/photos/raw/rawi...m?imageID=64363

I'm loving the ring-plane orbits with all these icy moon/rock encounters - lots more to come in the next few months. Thanks VP for the detail included in the looking ahead articles - always very informative, and appetite-whetting.
I must admit I'm a little surprised that that the the 'skeet-shoot' technique is being employed at Helene, but delighted nonetheless - it'll be very intriguing to see how 'smooth' the moon is at a few tens of metres resolution.

Hi,

just to mentioned:

As there won't be any more close encounters of this outer large saturnian satellite, these far imagings are the only opportunities to get some further informations, e.g. the north/south pole and hopefully the region around the 'Snowman'.
Any information of other - probably closer - encounters until 2017 available ?

Thanks & Bye.

I think not. A search of the SM-7_all.doc (posted here on UMSF somewhere) did not have the word Iapetus. If I recall correctly, it would have taken too much fuel to get into that orbit. If you go to the Cassini site, click Mission Overview, then Saturn Tour Dates. About 10 lines down on that page is a link Click here for a more complete list of the planned tour dates in 2010. From there you can get to activities for each remaining year of the mission.

Looking forward to this one as well.

If Helene is like Calypso, be great to get high resolution of 'striated' terrain. Plus the Rhea "ring" impactors.

Glorious!!!

Craig

Do we get some close ups of the intriguing equatorial stains ??

I am greatly interested in the 'stuff' orbiting Rhea too. Is it organized more like the asteroid belt (variety of inclinations and eccentricities), or more like the Saturnian rings (more planar and circular orbits)? And perhaps we can pin down the periods of the orbiting 'stuff' and see if there is a correlation to the Rhean period about Saturn.

Also, is more material within or outside the Rhean Roche limit . . . .

here are some nice perspective views of Rhea, target of the 100km pass next week.
they are based on stereo imaging of these regions acquired back in 2008. The first shows the western half
of the 6 km deep and 370 km wide Tirawa impact basin. The second shows the now
infamous blue equatorial streaks attributed to impact of Rhea's ring on to the surface. The frames
are from two Rhea flyover videos (too large to upload here) now on youtube (www.youtube.com/galsat400).
The Blue Streak movie shows one of these streaks lying across the top of a battered topographic ridge,
a common occurrence for these features consistent with a ring origin. The paper describing these
and the other Saturn ice moon color features has now been submitted for publication!

more details at http://stereomoons.blogspot.com
and http://www.youtube.com/galsat400

So,
about 75 images are online.

Here a quickout:
Click to view attachment
Distance: 1470377 km
Date: 2010-02-21

Nice but distant view of the snowman.

Btw., I thought about some unlisted encounters like this one, when Cassini is near apoapse, roughly 2.4 million kilometers away from Saturn.
From time to time the spacecraft gets in the vicinity of this outer large saturnian satellite.
May be one of the members is able to calculate the closest encounters until 2017 ?

Bye.

Try, use JPL HORIZONS Web-Interface to calculate distance Cassini - Iapetus
http://ssd.jpl.nasa.gov/horizons.cgi

Hi Adam,
Tried your link, but I can't get it to leave earth for an observer point. What am I doing wrong?

Try write:
@Iapetus
or
@608

I am not sure if MIMI data can confirm the disk/rings scenario. What MIMI data may tell us is whether the structures that will be observed during the flyby in electrons and ions, under a much different geometry compared to the two previous flybys, are consistent with that exciting scenario (or not). Consistent observations under much different geometries, may strengthen the initial interpretation, but definitely not prove it.

I think proof can only come from imaging observations (or maybe other, more direct methods than those based primarily on charged particle data).

if it cant be seen from orbit, the best case for corraborative proof then comes from the equatorial features i and others have shown above and elsewhere that are very difficult to attribute to anything but debris orbiting Rhea in a very thin and low density disk. but the motivation for the flyby is these "rings" so here's hoping they find something

But the equatorial features may simply indicate that there was a ring sometime in the past, and its collapse has formed them. Is that right? Its not necessary that the ring system/disk still exists (although in the context of the MIMI observations, one may assume that).

yes that is true, we cant determine the date of the equatorial features. they could be very recent or not forming today.
one thing is fairly clear is they are not ancient or they would have been erased by now!
paul

I.e. they wouldn't be as UV-bright as they are.

This may be pertinent:

From the latest Cassini significant events report:

"ULO has received an absolute timed real-time command file from the Cosmic Dust Analyzer instrument team. Starting on DOY-061T16:00, the commands will customize the instrument's visibility to bigger particles during the upcoming Rhea flyby on Mar. 2 and the following periapse passage. The command approval meeting for this file is scheduled for Thursday, Feb. 25.'

Quick, dirty gif of a mutual event with Dione and ... Rhea?
(That guess is based off what I found in Celestia I suspect it's Cassini trajectory is out of date.)

From the Rev127 Looking Ahead article: "Also on February 24, Cassini will observe Dione partially occult Enceladus and its south polar plume. During this observation, Dione will be 2.04 million kilometers (1.27 million miles) away from Cassini and Enceladus 2.27 million kilometers (1.41 million miles) away."

Thanks for the clarification. How can such structures be erased in a inactive moon? Charged particles or interplanetary dust impacts for instance? The E-ring dust can only modify the trailing hemisphere, I assume.

I am not sure if this would be compression artifacts or just maybe a quirk of the pixel geometry due to the differing colors, but some of the ridges and crater rims in the lower portion of the RH image in post 6 seem to have very fine crenelation (for lack of a better word).

Interesting JPL blog with a fantastic movie made by Cassini navigator Brent Buffington that shows each of the activities performed during Rhea flyby.
http://saturn.jpl.nasa.gov/video/videodetails/?videoID=207

Enceladus, plume and rings, RGB:
Click to view attachment

Animation of Helene flyby just uploaded to youtube (may take 30-60 minutes to finish processing, so be patient):

http://www.youtube.com/watch?v=0aVbvAojQlw

Only 4 hours and 4 minutes until Helene closest approach!

Rhea images have started coming down:
http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=214324
http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=214340
http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=214348
http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=214356
http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=214378

Handstitched mosaic of Rhea. Image sequence N00152147,51,55,59,67,75,83,91 taken on March 02, 2010 and received on Earth March 03, 2010.
Click to view attachment

Here's a global colour view of Rhea (IR-GR-VIO):

Click to view attachment

Is that vertical stripe in your first image some kind of image artefact?

No, it's a real crack.

Really neat images!

First Helene images arriving:

Saturnshine

Looks like the pointing is off

Well, Helene's surface certainly appears smooth as expected:

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=214400

It will be interesting to see the closeups...

Yes, but... we got a better shot of Saturn's cloudtops in return!

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=214425

Helene in Saturn-shine:

Click to view attachment

Yes, it is a bit disappointing, but have no fear! We get another flyby of this gal next year!

I guess this will be the highest resolution view of Helene for a while, then...

http://saturn.jpl.nasa.gov/multimedia/imag...8/N00152244.jpg

Nope this beats it:

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=214417

I imagine that some careful compositing, a la Tempel 1, might make for some beautiful mosaics with patches of high resolution. The varied perpectives of the lower-resolution global frames are very nice too.

Looks to me there's too much rotation to pull off a Deep Impact impactor-camera-type mosaic.

Cripes - now we've got gullies on Helene...

Phil

Phil, that sent a chuckle among the HiRISE people here

It just shows the standard we've come to expect from this mission that we're a tad disappointed with the images at closest approach. I'm sure the pointing commands for the follow-up flyby will be tweaked based on the results from this one, with even more spectacular results. Kudos to the Cassini team for the double-header flyby.

Incidentally, I wonder how difficult in comparison it will be to image Methone in a couple of years time. The flyby is a similar range, but Cassini will be travelling faster, and Methone is a tenth the size of Helene....

Have we had all the Rhea images now, and if so has anybody found signs of the possibly ring related equatorial marks?

Well, the issue might have been not so much the pointing, but our understanding of the position of Helene... mean, we were pointed where we planned it, but Helene was not where we expected it to be. High resolution images such as these presumably will also be used to help refine our knowledge of the orbit of Helene.

One of the better global raws, rotated so the large crater is at the top, and with a bit of shadow/highlight enhancement:

When was Newton taken off the wheel?

(Just kidding)

Andy

North is to the lower right in your image there.

Ah yes, you're right, I overlooked the rim of that (relatively) huge crater.