[X] My Assistant

[Decepticon]

Here's what extrapolating the current SPICE kernels yields:

IAPETUS 2005 NOV 12 14:34:49 185078153 415,451 km arcmin=12.1
IAPETUS 2006 JAN 25 21:13:08 191495653 873,345 km arcmin=5.7

IAPETUS 2006 APR 11 17:16:28 198047853 602,419 km arcmin=8.3
IAPETUS 2007 SEP 10 12:31:28 242699553 1,259 km arcmin=2186.8

Posted by jmknapp

This time a little further out.

Jan. 2006 - 879,000 km - 5.3 km/pixel - eastern Cassini Region and transition zone, part ofthe "moat" posted by VP


If anyone has made a animation of the encounter please post it!

[Decepticon]

Very Nice!

[Michael Capobian...]

Yes, this map shows the dotted line north of the moat much better than the official one. I'd be interested in seeing an exogenous explanation for it.

Michael

Very Nice!

[JRehling]

Yes, this map shows the dotted line north of the moat much better than the official one. I'd be interested in seeing an exogenous explanation for it.

Michael

I agree. In fact, I'd be interested in seeing a purely endogenous explanation, too!

(I'll interject here, high in my message: continued great work by Steve Albers!)

A purely endogenous explanation (eg, the ridge is a Europa/Enceladus style rift that sprayed the dark stuff out over hundreds of km, painting the surface) is going to have a very hard time explaining the patchy irregularities in eastern CR. One possibility (but a reach) is that the terrain is so extremely rugged that at the furthest reaches of the spray, when the material is coming in almost tangential to the geoid, that pronounced and bizarre topography could allow almost arbitrary complexity in the boundary. Really, any "geyser"ish explanation demands that. And sure enough, we know that Iapetus has, in general, appreciably nonspheroidal topography. But we won't be able to characterize the topography of eastern CR within the primary mission -- that would have to remain an ad hoc explanation. Even that seems to strain credulity at the Snowman craters, where the topography can only be so irregular (is a crater still vaguely bowl-shaped or not)? We can similarly (almost!) reject the exogenous explanations that have Iapetus having passed (in one event or many) through a cloud of material. The bizarre boundary of eastern CR is implausible in that case.

An endogenous explanation holding that the dark stuff flooded upwards can already be rejected. The northern boundary clearly shows that the dark stuff was emplaced by ballistic delivery from the south.

I think we're going to be left to conclude that the material sprayed outward from the surface of Iapetus, within what is now CR, in a fashion much more energetic and irregular than geysers could plausibly explain, and that some sort of impact event led to the staining of Iapetus.

The remaining flybys are going to show us western CR at very high resolution, and the southern boundary at decent resolution. We will not see the eastern/Snowman region in very high resolution (and sunlight rather than saturnshine) at all during the primary mission -- excepting decent coverage as Cassini departs the Sept. 2007 flyby and eventually the Snowman will rotate in.

For the sake of discussing whether or not Iaptus merits more flybys in the extended mission, I think not. The remaining flybys are going to show so much of the hardly-seen boundaries of CR at higher resolution that I can't see dedicating another flyby to finish the almost-complete map. ALTHOUGH, the one portion of the border that will not be mapped may be the single most intriguing! The big Snowman crater will be seen at about 1.3 million km distance in Sept 2007. A flyby to see that same region at higher resolution seems like a big cost for a small gain. In the absence of other reasons to have apoapsis be so far out, I would expect the extended mission to pull the apoapsis way in, so Titan encounters happen much more frequently, and the RADAR mapping can add a swath or two per month instead of a swath every few months.

[scalbers]

Even that seems to strain credulity at the Snowman craters, where the topography can only be so irregular (is a crater still vaguely bowl-shaped or not)? We can similarly (almost!) reject the exogenous explanations that have Iapetus having passed (in one event or many) through a cloud of material. The bizarre boundary of eastern CR is implausible in that case.

It looks like two of the Saturn-shine images looking from different angles at the Snowman crater could be reprojected in such a way to provide an interesting stereo pair. In the course of looking at experimental map images, I had switched between the two and a surprisingly deep Snowman crater popped out at me. Perhaps at some point I can try to provide two such images unless someone else beats me to it. The large angles involved may actually exaggerate the stereo effect.

[TritonAntares]

It looks like two of the Saturn-shine images looking from different angles at the Snowman crater could be reprojected in such a way to provide an interesting stereo pair. In the course of looking at experimental map images, I had switched between the two and a surprisingly deep Snowman crater popped out at me. Perhaps at some point I can try to provide two such images unless someone else beats me to it. The large angles involved may actually exaggerate the stereo effect.

Stereo images sounds quite interesting ...

I always wondered about the 'missing' central peak in the Saturn-shine images of the Snowman ...

...there should be something very huge...


Low contrast does explain this disappearance, but it also shows how misleading these Saturn-shine images can be.
Thinking about the equatorial ridge, I wouldn't be surprised if it is hidden in this low contrast pic.
A white (and following dark) linear structure beginning southwest of the largest Snowman crater could be a hint.

I'm very keen on seeing these stereo-images....