[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.

[antoniseb]

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.

Iapetus is very interesting, and I hope they can arrange to get some good imagery of it. I am curious to know if the orbital mechanics would permit eventually being able to see more of the other side of the this moon close up... plus I'd love to know more about the equitorial ridge.

[JRehling]

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.

Sans calculations, I can say that the longitudes corresponding to the places where Cassini Regio *isn't* (it covers about 2/3 of the equator -- the other 1/3 of the equator and the region south of that is what I'm talking about) have never been seen at very good resolution, and it seems almost inevitable that long-range imagery will eventually improve on that when the apoapsis walks around the planet. Even a view from 2 million km would give us a better view of the CR border than anything we have yet, and 1 million km would be gravy. A single snap would define the CR border, and a sequence showing those longitudes rotating through the terminator would show us details of Roncevaux Terra in relief.

A second close flyby during the extended mission comes down to whether or not it wins out as a priority. That will simply come down to priorities and the length of the extended mission(s). I'm optimistic that Cassini will last long enough that we'll have more than one extended mission. But until the 2007 flyby has concluded, who can say how high the Iapetus priority will be? (It could go up or down, depending upon what we see.) Of course, Enceladus and Titan are guaranteed to be high priorities for an extended mission -- if an Iapetus flyby doesn't somehow serendipitously set up a desired Enceladus/Titan scenario, it's going to have a tough time competing with those two.

Iapetus is probably one of the #10-#15 intriguing worlds in the solar system, but Titan is clearly top five and Enceladus is vying for that. I don't think Cassini's done at Titan until it's radar mapped at *least* 2/3 of it, and we could benefit from all the coverage of Enceladus's southern region we can get. Note that Enceladus's southern region will pass into darkness at equinox ~2010, but possible plumes shooting upward could be observable (eg, with occultation studies) all "winter". Meanwhile, Titan's northern latitudes will only be coming into view after that, and since VIMS offers the highest possible IR resolution but has a narrow field of view, it could take many, many Titan passes to finish mapping that world, especially since VIMS and RADAR compete for time.

Let's hope Cassini lasts for decades and sates all of these needs.

[volcanopele]

Nov. 2005 - 416,000 km - 2.5 km/pixel - eastern and central Cassini Region, northern bright terrain
Jan. 2006 - 879,000 km - 5.3 km/pixel - eastern Cassini Region and transition zone, part ofthe "moat"
Apr. 2006 - 603,000 km - 3.6 km/pixel - leading side, South polar region

[Decepticon]

Nov. 2005 - 416,000 km - 2.5 km/pixel

http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1



Jan. 2006 - 879,000 km - 5.3 km/pixel


http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1

[Decepticon]

As a comparison...

Note that these where taken over a Million KM out, and look what great detail we saw.

Theses images were taken with the narrow angle camera between October 15-20, 2004, from distances of 1.2, 1.1 and 1.3 million kilometers (746,000, 684,000 and 808,000 miles) from Iapetus, respectively. The Sun-Iapetus-spacecraft, or phase, angle changes from 88 to 144 degrees across the three images. The image scale is approximately 7 kilometers (4.5 miles) per pixel.

Source http://ciclops.org/view.php?id=624&flash=1

[tedstryk]

It will be interesting to see what we can do with the raws from those.

This image, which I posted before, was taken from 2.5 million km, produced using the raw data from July 13, 2004.

[Rob Pinnegar]

That's one of the images of the side of Iapetus that faces away from Saturn, right? Nice processing job.

Is this just an optical illusion, or does that large impact basin have a faint "phantom twin" just to its lower left? It could be that some craters are just lining up to look like an arc, I suppose.

It's too bad that Iapetus isn't more "full" in this image. From what I remember, there's a huge honkin' impact basin (in Roncevaux Terra) that would be around the upper left edge of Iapetus, as seen from the angle of this shot. It might be the biggest one on Iapetus, and there haven't been any good images of it yet, just fuzzy ones from a distance. We won't get a good look at it for two more years (but when we do it will be from really close).

[volcanopele]

That's one of the images of the side of Iapetus that faces away from Saturn, right? Nice processing job.

Is this just an optical illusion, or does that large impact basin have a faint "phantom twin" just to its lower left? It could be that some craters are just lining up to look like an arc, I suppose.

It's too bad that Iapetus isn't more "full" in this image. From what I remember, there's a huge honkin' impact basin (in Roncevaux Terra) that would be around the upper left edge of Iapetus, as seen from the angle of this shot. It might be the biggest one on Iapetus, and there haven't been any good images of it yet, just fuzzy ones from a distance. We won't get a good look at it for two more years (but when we do it will be from really close).

There are many large impact basins on Iapetus. The largest is a 850-km wide basin in north central Cassini Region that has a 350-km wide basin superimposed on it

[Rob Pinnegar]

There are many large impact basins on Iapetus.  The largest is a 850-km wide basin in north central Cassini Region that has a 350-km wide basin superimposed on it 

I have to admit to not being able to see this 850-km basin, although the 350-km basin is easy enough to see.

[Decepticon]

April 12,2006


http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1

[jmknapp]

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

[jmknapp]

Here's an animation of the Sep. 10, 2007 flyby. Looks like Cassini is approaching from the dark side:



Iapetus flyby (10MB MPG)

[tedstryk]

Super resolution processing will really help with some of these images. Due to Iapetus being so far out, the flybys are at relatively low speed and so there is little shifting between images. There is also time to take a lot of them. I imagine some nice shots will be pulled from the data.

[JRehling]

Super resolution processing will really help with some of these images.  Due to Iapetus being so far out, the flybys are at relatively low speed and so there is little shifting between images.  There is also time to take a lot of them.  I imagine some nice shots will be pulled from the data.

I'll add a glum note -- all of these largely re-flyby areas seen earlier by Cassini! At least, at closest approach. As with Titan, there are major portions of the surface not seen closely, or only in saturnshine. I might expect more from the saturnshine images from these upcoming passes than from the "regular" views.