Iapetus looms

[mmcirvin]

Crescent Iapetus from about 200,000 km away, as Cassini heads into today's long flyby. This overexposed picture shows more topography and some faint Saturnshine details. The height of the equatorial ridge is still startling. The raw image archive also has the elements of a big mosaic taken yesterday of Saturn and its inner moons as seen from the neighborhood of Iapetus.

Emily Lakdawalla has color composites of earlier images, and a few details on what's happening now. Here's her in-depth article on the encounter, with timeline.

It sounds as if these (or more like them) are the last pictures we'll get until sometime Tuesday, after the flyby is done. Cassini is going to be very busy in the meantime.

Update: I guess there were more from that downlink! Nice pictures here from a little under 70,000 km off. Notice how all those craters cover the equatorial ridge--it must be relatively old.

Comments

[acw.livejournal.com]

In that spate of pictures from 60-70 Mm, I'm seeing something peculiar: an almost-linear double row of craters below the equatorial ridge and parallel to it. This is probably just the human eye seeing patterns where there are none, but to me it was striking.

[mmcirvin.livejournal.com]

Emily Lakdawalla mentioned the same thing, with the same warning that this could be a perceptual illusion. I didn't notice the chains until they were pointed out to me.

[mmcirvin.livejournal.com]

...in this post (http://www.planetary.org/blog/article/00001125/), which also has a large color composite of the crescent, and a lengthy description of how she made it (which is pretty close to what I do when I make Cassini composites).

[acw.livejournal.com]

Oh, duh. I guess I didn't read Emily's latest post carefully enough.

They look like portholes to me. Ancient starship.

It also occurs to me that the settling event that formed the ridge might also have produced parallel features nearby. I'm sure we'll have better data soon; the most likely explanation is "coincidence".

Hey, it just occurred to me that this could be a ring scar! Is Iapetus geometrically in the ring plane? How thick are the rings compared to the diameter of the moon?

[mmcirvin.livejournal.com]

Iapetus is the only major moon of Saturn whose orbit is *not* essentially in the ring plane; it's got a significant inclination. But it's entirely possible that that was not always true.

The rings of Saturn are very, very thin. The tiny moon Atlas, which orbits in the outer part of the ring system, has an equatorial bulge that may well be from accumulated ring material--it looks a little like an elongated flying saucer.