Enceladus-3 (March 12, 2008) |
Enceladus-3 (March 12, 2008) |
Guest_AlexBlackwell_* |
Feb 24 2006, 09:12 PM
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Guests |
Excerpt from Cassini Significant Events for 02/16/06 - 02/22/06:
"As mentioned in previous weeks, the project has been working on adopting a new reference trajectory in order to raise the minimum Titan flyby altitude for various encounters. Today the project reached a decision to proceed with the 'optocc2' trajectory. Additional work is still to be performed before delivery of the final files. This will include minor tweaks that have been analyzed in other trajectories, adjusting orbit 68 timing, and capture of an Enceladus plume occultation on orbit 28." For the record, the new reference trajectory will result in an even more spectacular Enceladus-3 flyby [61EN (t) E3] on March 12, 2008. |
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Guest_BruceMoomaw_* |
Mar 12 2006, 11:30 PM
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why is that a pity? There are other instruments you know. And it seems like plume science is better done with in situ measurements than remote sensing. Remote sensing would be better for looking at the vents more closely... but E3's geometry doesn't allow that, so imaging on E3 would be a big waste INMNSHO. Oh, I'm most emphatically not saying that such very low-altitude flybys aren't very much worth doing for Cassini -- probably several times. Besides mass spectrometric analysis of the denser plume cloud and better gravity data, the CIRS could probably nail down with great accuracy both how wide the tiger-stripe vents really are and how warm the fluid coming out of them really is -- and, if it was warm enough, the NIMS could also provide more data on the composition of the erupting fluid when it first emerges. It's just a pity that we couldn't also get really high-res photos of the vent sites as well -- especially since, according to Scalbers in the "Stardust Mission to Saturn" thread below, the region will soon be in seasonal shadow until 2030. In that connection, I was puzzled by the failure of Porco's "Science" article to mention at all one thing that positively jumps out at the viewer even in Cassini's first Enceladus close-ups: the moon's "freckles". Quoting Helfenstein ( http://www.aas.org/publications/baas/v37n3/dps2005/450.htm ): "Among the most mysterious newly-discovered features are small, sub-kilometer-sized dark spots and circular pits that sometimes cluster in a honeycomb like patterns near faults and scarps. Their origin is unknown, but perhaps the pits and dark spots identify sites of explosive venting of subsurface volatiles through fractures or volcanic conduits." But there's not a peep about these in Porco's otherwise very detailed "Science" article. The fact that they're dark makes it likely that we're looking at the dark products of methane and the other organics expelled from the vents and then radiation-processed by solar UV and Saturn's own radiation belts -- although it's possible that they might also contain some bits of rocky debris from Enceladus' interior, or salts dissolved from that rock into the water and then redrying on the surface after expulsion. Maybe they're mentioned in some of the other "Science" articles, since I only have Porco's and Spencer's? |
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Mar 13 2006, 02:46 AM
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#3
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Senior Member Group: Moderator Posts: 3242 Joined: 11-February 04 From: Tucson, AZ Member No.: 23 |
In that connection, I was puzzled by the failure of Porco's "Science" article to mention at all one thing that positively jumps out at the viewer even in Cassini's first Enceladus close-ups: the moon's "freckles". Quoting Helfenstein ( http://www.aas.org/publications/baas/v37n3/dps2005/450.htm ): "Among the most mysterious newly-discovered features are small, sub-kilometer-sized dark spots and circular pits that sometimes cluster in a honeycomb like patterns near faults and scarps. Their origin is unknown, but perhaps the pits and dark spots identify sites of explosive venting of subsurface volatiles through fractures or volcanic conduits." But there's not a peep about these in Porco's otherwise very detailed "Science" article. The fact that they're dark makes it likely that we're looking at the dark products of methane and the other organics expelled from the vents and then radiation-processed by solar UV and Saturn's own radiation belts -- although it's possible that they might also contain some bits of rocky debris from Enceladus' interior, or salts dissolved from that rock into the water and then redrying on the surface after expulsion. Maybe they're mentioned in some of the other "Science" articles, since I only have Porco's and Spencer's? No, they are not mentioned. The dark leopard spots are found in Samarkand Sulci in the equatorial sub-Saturnian hemisphere. to keep the Science article manageable, it was limited to South Polar geology and plume analysis. -------------------- &@^^!% Jim! I'm a geologist, not a physicist!
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