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The Planetary Society Blog

By Emily Lakdawalla

Tuesday Morning Sessions: More Enceladus, a Little Ceres

Weblog Archive

by Brad Thomson

Monday Night's Planetary Society Event
I was unable to make it to the Planetary Society public panel discussion Monday night (I live over 30 miles from the conference location, and I need sleep!). This panel discussion was intended for a public audience. Panelists included Buzz Aldrin, Jim Bell, Chris McKay, and Bill Nye and was moderated by Planetary Society Executive Director Louis Friedman. Unfortunately, Ray Bradbury was a no-show due to illness (Ray is over 80 years old, by the way). On his behalf, Bruce Murray accepted a Mars flag that was flown on the space shuttle (STS 121). I only have second-hand information to pass along, so I can't really go into specifics, but from what I hear it was... interesting.

As another aside, many thanks to the readers who sent me ideas of presentations they are interested in. For example, Thursday morning I will definitely be going to oral sessions on Titan's surface. You can still send me suggestions or comments at bradley.thomson@gmail.com.

Tuesday Morning: An Icy "Old Faithful"
Caroline Porco led off the morning's session with a summary of Cassini's results at Enceladus. This ground was covered yesterday at John's Spencer talk, but several new nuggets were discussed here. Caroline noted that one of the interesting aspects of the terrain that contains the"tiger stripes" is that it has boundaries look like thrust faults in places, meaning that one part of the surface is being shoved against and under another part. The old view of the formation of the polar terrain (and here old means about 9 months old) is that is was due to a global-scale processes such as uniaxial compression. The team has mapped out tectonic patterns that appear to be inconsistent with uniaxial compression, and the new view is that this is a regional-scale process. Caroline mentioned the Nimmo and Pappalardo hypothesis about a single diapir (which was mentioned in John Spencer's talk yesterday), and there's another paper by the team on this topic coming out in Nature soon.

Also discussed in this Nature paper (with lead author Paul Helfenstein) is recently recognized evidence that Enceladus may have relict south polar-type terrains. One example in particular is located near the equator and has hints of faint tiger stripe-like cracks. Caroline also showed a fantastic image mosaic of the entire Saturn ring system taken while the Cassini spacecraft was in Saturn's shadow. It's really amazing -- I'm sure it's coming to a screen saver, coffee mug, and tee-shirt near you soon. Word on the street is that is will be publicly available tomorrow, so stay tuned. I'll post it as soon as I can.

Plume Models
The next speakers, Andy Ingersoll and Feng Tian, talked about models of the geysers. Andy's modeling indicated that not all of the jets point exactly normal (perpendicular) to the surface, meaning some of the jets may be spraying material off to the side rather than straight up. He also briefly mentioned an additional continuous source, which I didn't quite understand if it was separate from the plumes or if he meant that the plumes need to be continually active for his model to satisfy the observations. His favored model is a boiling liquid with bubbles driving the plumes. Feng Tian's modeling suggests that particle velocities are initially in the range of 300-500 m/s. This is an important result that points to active venting rather than simple sublimation.

I missed a talk by trying to run over to the Deep Impact session, but timing differences between the two sessions prevented me from catching much of the talk I was trying to see. Grrr. But back to Enceladus, a subsequent talk by John Cooper stressed the possible contribution of energetic particles on surface ice chemistry. Peroxide (H₂O₂) and free oxygen O₂ may be common on all icy surfaces. This has biological implications since these may provide sources of chemical energy.

Don't Forget Poland Ceres!
Also, check out this excellent BBC article by Molly Bentley on newly revised near infrared maps of the asteroid Ceres.