Thursday, August 6, 2009

Topography at outer edge of Saturn's B ring?

This very interesting Cassini image shows a close-up of the outer edge of Saturn's B ring. Saturn is far to the left, so the ring's orbital motion here is either up or down (and my best guess says down). The Cassini Division is to the right, just beyond the B ring. The Huygen's ringlet is the prominent gray band that orbits 300km beyond the B ring's edge.

Recall that Saturn is almost at equinox (Tuesday August 11!), so the Sun is just above Saturn's equator. Consequently, sunlight is streaming almost parallel to the ring plane, which allows even very modest vertical structures in the ring to cast long shadows across the ring plane. Evidently, the B ring's outer edge has topography, since it cast shadows that are hundreds of kilometers long! Judging by how ragged the shadows are, this ring-edge seems to resemble a mountain range, which is quite a surprise since the rest of the ring-plane is extremely flat. Note also the bright diagonals, one of which is clearly casting a shadow. These streaks might be due to ring material moving radially, perhaps due to avalanches of ring-matter tumbling down the supposed mountainside? Such radial motion would then get dragged along a diagonal due to the ring's faster orbital speed in regions closer to Saturn. But at this stage, this is all just speculation...

This image was acquired on July 26, 2009, and can be found at the Cassini Equinox Mission's raw image archive. A followup comment will describe how to use this archive effectively to search for other interesting Cassini images.

1 comment:

Joe Hahn said...

The Cassini's raw image archive has a *huge* number of images. Consequently, finding an interesting picture from so many can be challenging. The key is to search the archive for images acquired when Cassini is close to Saturn, ie, near periapsis. This is the moment when Cassini can acquire its highest-resolution images of the rings.

Dates for Cassini's periapsis passage can be found in this table provided by the Planetary Society.

Next, go to the archive, and choose a target (such as SATURN-RINGS) and observation dates within a day or so of periapse passage. This search will then return hundreds of images for your inspection. But some of those pictures will provide a unique hi-res view of your target, revealing things that no-one has ever seen before.

And for those of you who do go explore in this image archive, if you do spot something interesting, please post a description here!