Rev 126 - Feb 4-22, 2010 - Mimas (main target), Tethys, Iapetus, Calypso and mutual events too Options

[belleraphon1]

All

closest look at Mimas ... 30 minutes after periapsis on 02/13/10 at 17:25 UTC

http://ciclops.org/view/6188/Rev126

"Thirty minutes after periapse, ISS will perform a targeted encounter with Saturn's innermost large icy satellite, Mimas. The altitude for this encounter is 9,510 kilometers (5,910 miles) the closest Cassini has ever gotten to this cratered moon. For this encounter, ISS will acquire three mosaics along with another observation where ISS will be riding along with the Composite Infrared Spectrometer (CIRS). ISS' first mosaic of Mimas, GEOLOG001, will start 30 minutes after closest approach when Cassini is 14,800 kilometers (9,200 miles) away from Mimas. GEOLOG001 is a seven-frame, multi-spectral mosaic of the region surrounding the crater Herschel. Herschel, at 130 kilometers (80 miles) across, is the largest impact basin on Mimas, so large that it caused significant amounts of stress on the lithosphere of the small moon and so distinctive that it helped give the satellite the nickname, "The Death Star Moon." These high-resolution observations of the basin will be used to estimate the age of the crater. Scientists will count the number of smaller craters on the basin floor, compared to other regions on Mimas, to set limits on how old the basin can be. The second mosaic, GEOLOG002, will also be a seven-frame, multi-spectral mosaic, this time covering most of the visible surface of Mimas, shown above left. The best resolutions for these two observations will be 87 meters (285 feet) per pixel for GEOLOG001 and 191 meters (626 feet) per pixel GEOLOG002. Next, Cassini will ride-along with a CIRS FP3 temperature map of Mimas' day side, acquiring six narrow-angle-camera images during the scan. Finally, ISS will acquire a full-frame, multispectral observation (GLOCOL001) of Mimas' anti-Saturn hemisphere from a distance of 70,000 kilometers (44,000 miles). Saturn will provide a backdrop for this observation."

Glorious

Craig

[dilo]

Feb, 14 sequence animation:

Note the curious sudden illumination change on Epimtheus from a body on the right, perhaps from Janus itself (strange geometry, however)

Attached thumbnail(s)

 

[ugordan]

Note the curious sudden illumination change on Epimtheus from a body on the right

Looks like "sunset" to me.

[volcanopele]

Nice catch about the change in illumination on Epimetheus. I doubt it is from Janus since that moon is clearly on the OTHER side of Epimetheus from those craters. I think we are just seeing a slight bit of rotation on Epimetheus, and the Sun is setting on the far rims of three impact craters just beyond the evening terminator.

I have to admit that I started to doubt that explanation since I suddenly thought that north might be up, so the terminator we are seeing would be the dawn one... But nope, south is up in your animation, so my explanation holds...

[belleraphon1]

I do not usually throw in attachments so bare with me...

But in this Mimas image I am not convinced all the low albedo stuff is due to shadow.



It is from NAC image N00151508. Also if you look at dilo's colorized global image you can see a few darkish spots in the high phase region. Kinda like the Rhea ring impactors but more dispersed (not in a line)?

Interesting.

Craig

[Explorer1]

Wow this stuff is truly great. Honestly if it wasn't for the central peak Herschel almost looks like it formed some other way. It's just so irregular and different from other big craters, like on the moon or Callisto.
Mysteries abound!

[Juramike]

Compare it to Rhea. Many of the larger craters on that moon are also irregular.

Mass wasting and slumping the crater walls of Herschel seem evident.

EDIT: Looking at the picture that Craig posted it seems that there is a tendency for the walls to form and slump along parallel lines going from lower left to top right.

[Ian R]

Here are my two 'bouncy' animations of this mutual event:

Epimetheus-centric:



Janus-centric:

[Adam Hurcewicz]

- Full quote deleted. Use the "add reply" button at the bottom of the page. -

Nice work !

Your animations show rotations of this monns

[dilo]

Grat animations, Ian! (original quality is clearly better than mine...)
Gordan, you were right!

[Adam Hurcewicz]

TETHYS in (IR1, G UV3)

ir1 N00151608
g N00151607
uv3 N00151606

Attached thumbnail(s)

 

[Poolio]

What we're seeing here is these two co-orbitals exchanging orbits, correct? It seems natural to think that the switching of orbits would need to cause temporary redirections of the moons from their normal elliptical orbits, and therefore the observed rotations and exposure of hidden surfaces to the sun.

[Floyd]

I'm not exactly sure where they are in the process of exchanging orbits, but I think the relative movement we see here is mainly the changing perspective of Cassini as it rushes by.

[Phil Stooke]

This is not the orbital switch. There are several factors - the moving spacecraft, the moons moving relative to the sun and to each other.

Phil

[Poolio]

But changing the observer's perspective couldn't account for the change in illumination of the subject. We must be seeing physical rotation of the moons themselves relative to the sun.

[Phil Stooke]

"in this Mimas image I am not convinced all the low albedo stuff is due to shadow."

These patches don't look unusually dark in images with more overhead lighting, which you can see further up the thread. - but there are real dark spots in places further east.

Phil