Rev 183 - Fourth and final Rhea flyby, Goodbye Rhea Options

[Holder of the Tw...]

This orbit of Cassini has already begun on March 4th, 2013. The major activity is a targeted flyby of Rhea starting on the 9th. Cassini will approach from the south, and this will be the last time it will get good direct (mostly centered) imaging of the south pole (thermal) and north pole (cameras). What little of Rhea remains unmapped will mostly be picked up on the north pole photos, although some of it at very low sun angles. During closest approach they will be gravity mapping the interior from radio doppler tracking.

"Finals" like this one are reminders that although the mission is not winding down yet, still the number of days ahead for Cassini are not as many as the days already behind. There will be three more close non-targeted flybys of Rhea in 2015 when Cassini will get within waving distance, but they will never again get up close and personal.

Looking ahead article

The other major activities are high latitude observations of Saturn and the rings, including more propeller searches. Only distant cloud monitoring observations of Titan are planned for this orbit.

[jasedm]

I was wondering if there was any slim chance of indirectly detecting putative ring material at Rhea during this last close flyby.
The cameras have turned up nothing on previous close flybys, or through long-exposures whilst Rhea is backlit.

Is there a tiny chance that during the doppler tracking at Rhea, the RSS signal will perceptibly dip, or drop-out as Cassini passes through Rhea's equatorial plane due to possible ring particles blocking the signal?

A bit of a one-in-a-million chance I suppose, as the time Cassini spends in ring plane is a matter of seconds on this flyby, but it would bolster the magnetospheric readings that hinted at rings for Rhea back in 2005.

[Holder of the Tw...]

Here is a paper that describes radio occultation of rings:

Stanford paper on radio occultation

Actually the paper concentrates on scattering, but there is quite a bit of discussion of occultation in it, too.

Based on a quick browse of that paper, and the fact that the Voyagers did not have detectable radio ring occultations at Jupiter or Neptune, and I can't locate anything on Cassini picking up the D or E rings at Saturn (could be wrong about those last two, though), I don't think there will be any possibility of a detectable radio occultation or scattering at Rhea. Sorry.

[jasedm]

Here is a paper that describes radio occultation of rings:

Interesting read - The equations went a bit over my head (must have been smoking behind the bike sheds instead of hunkering down during Maths classes at school) but nevertheless the paper clarifies for me the dynamical geometries, and densities of material necessary to detect planetary rings by occultation.

Thanks Holder

[kemcab2012]

Here's a short video comprised of the raw imagery from the ring studies during 183.

[ngunn]

Great Rhea images - here's one: http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=282184

[wildespace]

Great images from this last flyby! I've made a true-colour composite from the most recent images (10 March 2013).




Here's also a composite from IR, green, and UV filters:

[Phil Stooke]

Very nice! Playing some games with saturation, it looks like we pick up some regional variations.

Phil

[phase4]

Great images indeed, it's a beautiful landscape.

[dilo]

Is there any explanation for such strange sharp feature (fracture?):
http://www.ciclops.org/view/7583/Rhea_Rev_183_Raw_Preview_2

[wildespace]

Is there any explanation for such strange sharp feature (fracture?):
http://www.ciclops.org/view/7583/Rhea_Rev_183_Raw_Preview_2

This may be one of the ice cliffs caused by tectonic fracturing.

[Phil Stooke]

I'd say a small low-angle thrust fault like a (mini-)scarp on Mercury, now seen on the Moon too. Global compression from a small amount of 'shrinkage'.

Phil

[wildespace]

Titan, March 13 and 14, 2013. Images were taken approx 2.6 million km from the target. Impressive!

March 13, R/G/B true-colour


March 14, R/G/B true-colour You can clearly see Titan's blue atmosphere, made mostly of Nitrogen.


March 13 IR/G/UV false-colour


I created the above images from raw b&w images at http://saturn.jpl.nasa.gov/photos/raw/

There are also images taken through Methane band 1 and 3 filters. Can anyone please tell me what wavelengths those represent, and how could those 2 images be used for a colour composite like I did above.

[remcook]

The methane filters are narrow-band filters that probe wavelengths where methane absorbs strongly. This allows one to look higher into the atmosphere.
see here for a list of the filters:
http://www.unmannedspaceflight.com/index.php?showtopic=300

Of course you can use them to make colour composites. I think Juramike used them for some of his pretty images.

I don't think the raw images allows the creation of real "true colour"images, since they are stretched differently.

The blue is from the haze, not the molecular nitrogen. The haze acts somewhat like Rayleigh scattering, preferrably scattering blue wavelengths.

[wildespace]

I don't think the raw images allows the creation of real "true colour"images, since they are stretched differently.

The blue is from the haze, not the molecular nitrogen. The haze acts somewhat like Rayleigh scattering, preferrably scattering blue wavelengths.

Thanks, that explains why my rgb image of Titan is white instead of yellow.