Friday, May 20, 2005

New Enceladus Image: Bright Ice, Dirty Ice

This image is a color view released by CICLOPS showing Saturn's A, B, and F rings as well as Enceladus. This color view highlights the slight compositional differences between Enceladus and the rings. In both cases, water ice is the main "surface" constituent. However, the rings here appear slightly pale yellow, indicating contamination from dust and organics. Enceladus' surface, in contrast, is a very bright white with patches of blue. This indicates that it has been able to maintain a more prestine surface. From higher resolution images, this is likely due to a combination of cryovolcanism and tectonic resurfacing.

New Dione Image: F Ring Edges

CICLOPS has released this view of Dione, eclipsed, from this perspective, by Saturn's rings. Cassini was orbiting near the orbital plane of the rings, causing them to look edge on. The bright lines in this view are the F ring, which dominates the ring brightness when the rings are viewed edge-on. The dark space in between the two bright lines are the A and B ring.

New Mimas Image: Near the Ringplane

CICLOPS has released this view of Saturn's moon Mimas along with a nearly edge-on ring system. The geometry of this view of the ring system maybe strange for Earth-based observers, seeing the rings as a thin filament as well as seeing the finger-like intrusion of Saturn's shadow coming in from top center. Mimas here looks beaten and battered, as it always does. Mimas north is up and the resolution (on Mimas) is 9 km/pixel.

Lack of Updates

I'm sorry for not keeping up with updates lately. LPL had a local conference on Tuesday and Wednesday keeping me away from updating on those days. Then yesterday, well, Star Wars happened. I am going to post a bunch of updates over the next few hours to cover the last few days.

I apologize to all the "regulars" who may have wondered what happened to me.

Monday, May 16, 2005

Did Iapetus Consume One of Saturn's Rings?

One of the stories making the rounds lately has been this one on the formation of Iapetus' equatorial ridge. This theory, posited by Paulo C.C. Freire of Arecibo Observatory suggests that the ring formed as the result of Iapetus skimming the outer edge of Saturn's rings earlier in its history. No doubt, Iapetus is one battered and bruised body. It has no less than SEVEN impact basins larger than 400 km!! One, announced at the EGU conference in Vienna, is over 850 km wide and has a 400 km wide basin lying within it!! The shape of Iapetus is lumpy, with bulges 10-20 km above the reference ellipsoid, not to mention the ridge that is 10-20 km in places. The elllisoid itself is unusual. The shape suggest that Iapetus "froze" as a body that rotated with a period of 17 hours, compared to its current 79 day rotation.

Given all these unusual features related to this moon, what does this suggest and is this idea of the ridge being formed by the rings even possible? Somehow, I don't buy this. First, the author makes a big deal about the feature being on the equator. However, a ridge of that size need not FORM along the equator but the pole can shift so that the ridge (a rather large mass) could be on it. Secondly, if Iapetus did make short excursions into the inner Saturnian system, it would have seriously played havok on the inner moons.

Definitely, some thing seriously wrong happened to Iapetus. Maybe a satellite became disrupted and Iapetus bore the brunt of the onslaught of satellite debris?

Cassini Significant Events for 05/05/05 - 05/11/05

JPL released the weekly Significant Events Report on Friday. Among the items of note in this edition include the the success of the radio ring occultation and the announcement of S/ 2005 S 1. Definitely a quite week between periapses.

New Tethys Image: Tethys and Rings

CICLOPS has released this view of the anti-Saturnian side of Tethys and Saturn's rings. On Tethys you can see both Odysseus at top and Melanthius at the bottom. This image was taken on April 3 and has a resolution of 11 km/pixel.

First Full Mosaics of Titan's Surface

The DISR team has officially released two of their mosaics, one showing the surface as if through a fish-eye lens and the other a map projected image showing features very close to the Huygens landing site. These mosaics were released earlier on the DISR website, but I guess they have taken a while to show up on the Cassini site. A few items of note about these mosaics. One is the direction of north, it has changed. This change makes it very difficult to reconcile with known features in the region, based on ISS and VIMS data.

The DISR team has also removed three mosaics released a few weeks ago from their website. I have saved them so you should still be able to access them from their post earlier this month.

New Rhea Image: Great White Splat

CICLOPS has released this 1 km/pixel view of Saturn's moon Rhea. This image was taken on April 14 and was previously highlighted here. This image show a relatively fresh crater on its surface. This view, while not the highest resolution view of this ray crater, has the best geometry for seeing both the surface albedo of the bright rays as well as the topography of the crater itself.