2007-09-10 Iapetus (rev 49): Pre-flyby discussion, Closest approach of this odd moon Options

[TritonAntares]

Hi,

here a nice animation Tilmann Denk posted lately:


It shows the area (yellow line) visible from Cassini 20 min before until 20 min after closest approach. C/A at 2007-09-10, 14:15:40 UTC (16:15:40 MESZ).
As the field of view of both cameras (NAC & WAC) is much smaller than the theoretical observable area we'll only get images of some parts inside - exact footprints can hopefully be added soon.
The blue line marks the terminator - images in saturnshine are planned as mentioned above, but in a later stage of the encounter.

SSP -> sub-solar point
S/C -> sub-spacecraft point

Bye.

[tasp]

{Sorry if this has already been asked and answered}

Have we pinned down whether or not Cassini can take a picture faster than once a minute ??

[ugordan]

Have we pinned down whether or not Cassini can take a picture faster than once a minute ??

The short answer would be: yes.
The long answer would be: depends.

There are a number of factors determining the timeout for the next picture, for an explanation of the specifics refer to Porco et. al., section 3.7 (page 457). Depending on whether NAC and WAC are used simultaneously, image compression type, telemetry pickup rates and other instrument (VIMS, CIRS... ) simultaneous operation, a typical 1x1 binned ISS frame will take somewhere from 30 to 60 seconds before the next one can be taken. 45-ish seconds is a good rule of thumb IIRC.

I think it's reasonable to expect no more than 50 frames from WAC and NAC (so 100-ish total) in the 40 minute timeframe of the above animation.

[TritonAntares]

Hi,

I think I should put this here:

Really deep hit there - but also the height of the equatorial mountain range above the 'Snow Man' is striking!

Bye.

[Exploitcorporati...]

Thought you might enjoy that one. If anyone is an advocate for snowmen, it's you.

[ugordan]

Whoa. What's the source for that image?

EDIT: Ah, nevermind, found it.

[TritonAntares]

Hi,

lately arrived - these two 'footprint maps' of the fly-by:

(1) Inbound before C/A:

...

[TritonAntares]

...
(2) Outbound after C/A:


I'll add some infos about resolution (different footprint colors) and camera types (NAC/WAC) later...

Bye.

[Phil Stooke]

Comparing the DEM and the global maps, we see another segment of the equatorial mountain ridge. It really is global, as TritonAntares said above. Truly bizarre. I'm not happy with any of the suggestions for its formation, but I draw a complete blank when I try to figure it out.

Phil

[Rob Pinnegar]

Could someone put up a link to the source of that topographic map? I've looked in several of the usual places for it, and can't find it for some reason. Is there more where that came from?

Edit: Never mind, here's the link; and there *isn't* more where that came from:

http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2305.pdf

[TritonAntares]

...
I'll add some infos about resolution (different footprint colors) and camera types (NAC/WAC) later...

(1) Inbound:
|-> equatorial ridge under high phase (~120° ) / ~30 m/pxl (NAC)
|-> Voyager mountains under 90° phase at the horizon in WAC
|-> observations around C/A: phase 83° to 29° in 18,25 minutes / 10 m/pxl (NAC)
yellow lines-> change of limb from CASSINI
blue lines-> terminator

(2) Outbound:
|-> observations around C/A: phase 83° to 29° in 18,25 minutes / 10 m/pxl (NAC)
|-> dark-bright transition zone at medium latitudes, ~250 m/pxl (WAC)/ ~50 m/pxl (NAC)
|-> Voyager mountains, NAC ~45 m/pxl (NAC) + 1 WAC
|-> 2 small boxes more left, 25 minutes for VIMS-spectrometer
|-> mosaic of equatorial transition zone, ~1h / ~100 m/pxl (NAC) + 1 WAC
|-> terminator left / ~140 m/pxl (NAC) + Snowman in saturnshine (low phase)
|-> 15 pics mosaic, ~440 m/pxl (NAC)
Borders for last series:
yellow lines-> limb from CASSINI
blue lines-> terminator

We'll see a variety of surface structures, only one image (orange box) is sadly missing in the light green and blue mosaics:

The great southern Roncevaux Terra Basin will show up under lower resolution in pic 3, 4, 5 and 6.

Finally let me thank Tilmann Denk for sharing these 2 illustrations!

Bye.

[mchan]

And thanks, Trtion Antares, for sharing them in UMSF. I have looked forward to this encounter from before SOI, and the excitement continues to build.

[ugordan]

There's a new Iapetus color image on Cassini's home page: http://saturn.jpl.nasa.gov/multimedia/imag...fm?imageID=2621
It hasn't appeared on CICLOPS yet, probably within an hour of two.

As far as I know, this is the first actually "natural" color image of Iapetus released by the imaging team where they used RGB filters instead of infrared/ultraviolet filters. While the image itself is magnified and Cassini Regio is barely visible, it shows what I've been pointing out for a while, the color of the dark stuff is much subtler than the "cool" chocolate appearance portrayed in all previous CICLOPS composites.

This latest color image is more consistent with approx. natural color composites such as this one and this sequence. See this animation for a typical example of previous false color views for comparison.

[CAP-Team]

Wow, almost a black and white image!

[ugordan]

That particular image looks b/w because the bright ice is so much brighter than Cassini Regio the latter turns out very dark and color is practically lost. It does have color (even a bit of detectable color variation in approx. natural colored images), but it's best seen on views centered on the leading side (basically all earlier Cassini views) so image brightness can be optimized for low albedo material without overexposing the brighter (some 10x brighter) ice. If the color were as pronounced as in those enhanced color views, there still would be color visible even in this low resolution view.

Had that image been scaled up to brightnesses of this composite, the "clean" ice visible would be severely overexposed. Iapetus is all about contrast.