[X] My Assistant

[Rob Pinnegar]

According to the schedule on the main website, Cassini is gearing up for the "petal rotation" part of its tour. Consequently, it will be crossing the orbit of Iapetus several times between now and next spring.

Sadly, there are no close fly-bys (or should that be flys-by?) of Iapetus during this period, or in the subsequent parts of the tour between now and the close flyby scheduled for September 2007. However, just looking at some animations of the Cassini tour, it looks as if Cassini might get within a million kilometres of Iapetus once or twice during that period. Of course, Iapetus' orbital inclination to Saturn's equator complicates this, so it's hard to tell.

For those of you who have the software to do the calculations: What are the closest distant flybys of Iapetus between now and September 2007? Will any parts of Iapetus be seen at higher resolution than previously?

Also, what are the odds of a second Iapetus close flyby during the extended mission? I guess it's a bit problematical due to orbital-mechanical considerations and the fact that it would take up a lot of Cassini's time. However, I vaguely remember someone saying, a couple of months back, that it was under consideration.

[Rob Pinnegar]

Yup, you've got Ian's mystery basin nailed Phil, the one outlined with arrows above. That's the one I was looking at, too. It seems to show up really well in some images and not so well in others.

Just to reiterate something from earlier in this thread for clarification of some more recent posts: Jason mentioned a while back that the biggest basin on Iapetus is 850 km across, and is located in north-central Cassini Regio. (I also found a reference to this giant basin in a conference abstract somewhere.) However, the biggest easily discernable basin is the 550-km basin that is on the terminator in the images from the New Year's distant flyby. Unless I'm very wrong, this is the same one that (barely) shows up in the Voyager images.

Some of us have been trying to identify the 850-km basin's boundaries, but it's not easy to do. The only other thing that's been mentioned is that the 350-km basin in north-central Cassini Regio (which _is_ easy to spot) lies completely within the 850-km basin.

I wonder if the giant basin is along the lines of the Backside Basin on the Moon, i.e. really old and beat up and only easy to see in elevation maps?