[X] My Assistant

[djellison]

Cool eh?

I'm afraid my IcySats knowledge is terrible - and I just go from what the raw images website tells me..and it says Tethys....if anyone can fill me in on the 'other' one

Hands up if you thought the darker moon was going to go infront of the brighter moon !

Doug

[Phil Stooke]

It's Dione!

Phil

[djellison]

So Tethys is the 'static' one which was targetted, and Dione moved past.

Just doing the Pandora + Ring movie that's on the raw's as well.

GET OUT THE INTERNET CAFE PHIL, for the only day of the year, it's Sunny in the UK and you're WASTING it



Doug

[djellison]

And Pandora popping out of eclipse while another moon ( Hyperion? ) drifts across and into Eclipse...



Doug

[TheChemist]

Wonderful animations Doug !!

And of course I thought Dione was in front of Tethys too In the darkness of space, the mind assigns the larger to the closer

[mike]

I too thought the lower moon (Dione?) would pass in front of the upper.. is it bigger? I suppose it is, a little.. but even if it were smaller I suspect I would have expected the lower moon to pass in front. The question is - why? I think it's because the lower moon is moving, whereas the upper appears to be stationary. Alternatively, it could be because the upper moon is higher. I'm sure neurologist types have studied this sort of thing exhaustively regardless, and uhh, yeah, cool animation.

[ilbasso]

I think it's because we're used to seeing eclipses and occultations, where the moving, closer object passes in front of the stationary, distant object.

[ElkGroveDan]

What's up with that bobbing and weaving? I feel like I need some sea-sickness pills.

[hendric]

I think it's because we're used to seeing eclipses and occultations, where the moving, closer  object passes in front of the stationary, distant object.

More likely because our visual system puts lower things closer, ie look at a landscape and everything "lower" in your minds' eye the brain interprets as "closer".

[Decepticon]

Can the animations be colored?

[djellison]

Nope - it's just clear filtered stuff

I mean - you could fake some, but there's no colour to be had from the data.
Doug

[Guest_BruceMoomaw_*]

That moon occulting Pandora could well be Janus rather than Hyperion -- I've already seen some views of Janus from a side that gave it that general shape.

[volcanopele]

It is Janus.

[djellison]

Ah...fame....

http://planetary.org/blog/20050912.html



Doug

[SigurRosFan]

What's next?

[jmknapp]

Is the upcoming flyby of Tethys quite a bit closer than originally planned? According to the countdown applet on the Cassini website http://saturn.jpl.nasa.gov/home/index.cfm in 4 days or so there will be a Tethys flyby at 1,500 km. However, the itinerary at http://saturn.jpl.nasa.gov/operations/satu...ur-dates-05.cfm has the flyby distance at 29,773 km. What happened? Or am I reading it wrong?

[djellison]

Dione + 1 + rings at end

Doug

[Guest_BruceMoomaw_*]

The Tethys flyby is indeed radically closer than originally planned. In fact, originally there were no "planned flybys" of Tethys in the 4-year primary mission at all (as there still aren't of Mimas) -- that 29,000-km flyby was one of the numerous "unplanned" ones in which Cassini simply happens to fly reasonably close to a moon as a side effect of getting to its actually aimed-for goal. (The very first of its close flybys of Enceladus -- 1500 km in February -- was, remarkably, another unplanned flyby, as a side effect of the recent changes in its first three orbits around Saturn to compensate for the Huygens radio frequency problem. So was its 60,000 km flyby of Iapetus last New Year's. Two very nice side effects.)

From the start, Cassini was supposed to make an unplanned Tethys flyby 6000 km out late in its primary mission -- but the fact that its maneuvers have been so efficient have allowed it to save a bit on maneuvering fuel, and so early this year the mission planners decided that they had a big enough reserve to tweak that "unplanned" Tethys flyby and make into a new "planned" one at only 1500 km distance -- just as they had earlier decided that they had enough spare fuel to tweak their relatively distant Phoebe flyby into a close one during Cassini's initial approach to Saturn. As another benefit of the "Tethys tweak", they will also reduce the distance of their already-planned flyby of Hyperion two days later from 1000 km to only 500 km.

[Bjorn Jonsson]

Is the upcoming flyby of Tethys quite a bit closer than originally planned? According to the countdown applet on the Cassini website http://saturn.jpl.nasa.gov/home/index.cfm in 4 days or so there will be a Tethys flyby at 1,500 km. However, the itinerary at http://saturn.jpl.nasa.gov/operations/satu...ur-dates-05.cfm has the flyby distance at 29,773 km. What happened? Or am I reading it wrong?

Cassini's trajectory was tweaked a bit to achieve a 1500 km flyby of Tethys. This also lowered the Hyperion flyby distance from 1000 km to 500 km.

I will probably be posting an animation of the Tethys flyby tomorrow.

So was its 60,000 km flyby of Iapetus last New Year's.

Actually that flyby later was raised to 120,000 km.

[elakdawalla]

The original JPL commentary on the "Tethys Tweak" can be found in a couple Significant Event reports:
http://saturn.jpl.nasa.gov/news/sig-event-....cfm?newsID=556
http://saturn.jpl.nasa.gov/news/sig-event-....cfm?newsID=558

And some comments from planner Amanda Hendrix in a story I posted on April 15:
http://www.planetary.org/news/2005/cassini..._plan_0415.html

Cassini mission planner Amanda Hendrix explained that there was a Tethys flyby already planned for Cassini on September 24 that would take the spacecraft within 32,000 kilometers of the moon. "But then one of the navigators found that there was an opportunity to get much closer and it wouldn’t require that much delta V." In other words, getting closer to Tethys wouldn't cost much of Cassini's fuel, which is a precious resource that has to be conserved for the benefit of the rest of the four-year primary mission and any extended mission.

"There were a couple of trade-offs, though," Hendrix continued. "The existing timeline had some significant RADAR observations of Saturn, absolutely unique science doing radiometry observations of Saturn that they didn’t have planned out anywhere else in the tour. So one of the requirements [of changing the orbit] was that we not mess up any of that. We managed to make a plan where we could get close to Tethys and preserve the radiometry observations. But the question was, do we want to use up some of the fuel to do this?"

In the end, navigators managed to produce a close Tethys flyby at a cost of only 8 meters per second (18 miles per hour) of change to Cassini's velocity. For the entire primary mission, Cassini has a total of 400 meters per second (900 miles per hour) available for setting up interesting observing opportunities.

The new orbital path has Cassini passing within 1,000 kilometers (600 miles) of Tethys, and "it’s going to be a really cool Tethys encounter because we’ll be right over Ithaca Chasma," Hendrix says. Furthermore, the tweak will also bring Cassini within 500 kilometers (300 miles) of lumpy Hyperion two days later.

--Emily

[Guest_BruceMoomaw_*]

Given the indications from the recent Keck Telescope study of the E Ring that as much as 30% of its particles may be gushing from Tethys rather than Enceladus, it will be very interesting to see if there are any active vents down there at the bottom of Ithaca Chasma.

[Bob Shaw]

Emily (or Bruce):

RADAR observations of Saturn? A gas giant? Do you know what the observations are all about?

Bob Shaw

[jmknapp]

"The new orbital path has Cassini passing within 1,000 kilometers (600 miles) of Tethys, and "it’s going to be a really cool Tethys encounter because we’ll be right over Ithaca Chasma," Hendrix says.

Thanks a lot for those links & your work.

I've been tinkering with an animation of the flyby & was a little concerned that my calcs showed that the closest approach will be very near 0 deg latitude, 0 deg longitude with nearly 100% illumination of the disk. Seemed like maybe a bug. But that indeed would be right over Ithaca Chasma as your link states. Nice targeting at JPL.

[odave]

Nice animation of Dione & the rings, Doug.

I especially like the "scratch & flash" effects added by the raw image noise. Gives it a nice "retro" feel, taking me back to high school science class in the early 80s, when we watched those worn-out 16mm movies made in the early 60s.

[volcanopele]

Emily (or Bruce):

RADAR observations of Saturn? A gas giant? Do you know what the observations are all about?

Bob Shaw

They are radiometry observations of Saturn. Cassini RADAR has three modes: Imaging SAR, which produces an "image" combining roughness, volume scattering, and dielectric constant (only used on Titan), Radiometry, which measures the radiometric temperature of a target, and scatterometry, which measures, IIRC, the roughness of a surface.

[jmknapp]

Here's a movie of the upcoming Tethys flyby--hopefully accurate but a first effort:



http://cboh-t.cboh.org/~jmk/tethys_nac2.mpg

note: 15 MB file

[Bob Shaw]

They are radiometry observations of Saturn.  Cassini RADAR has three modes: Imaging SAR, which produces an "image" combining roughness, volume scattering, and dielectric constant (only used on Titan), Radiometry, which measures the radiometric temperature of a target, and scatterometry, which measures, IIRC, the roughness of a surface.

Thanks! And from the mouth of the horse...

[tfisher]

The CICLOPS imaging team has put up a coverage map for the upcoming Tethys flyby.
The announcement is here.

To quote the announcement:

The new high-resolution coverage will reveal details on the Saturn facing hemisphere of Tethys, including parts of the giant Ithaca Chasma canyon system. Imaging scientists also are hoping to obtain images of an ancient ridge east of Ithaca Chasma, as well as a section of terrain just west of the giant rift that appeared to be unusually smooth in Voyager images.